Texas Instruments Differential Passive Signal Switch on Computing (Rev. A) Application Note
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Application Report
SCDA012A – June 2009 – Revised July 2009
Differential Passive Signal Switch on Computing
Samuel Lin ..................................................................................................
Standard Linear and Logic
ABSTRACT
This application report describes multiplexing applications for differential bus signals and how to use Texas Instruments high-speed passive-switch products (TS3DV416,
TS3DV520, TS3DV520E, TS3DV421, and others on the product roadmap such as
TS3DSxxx and TS2DSxxxx) with various bandwidths and data rates. This application report describes the components that make up the system applications, including both the transmitter and receiver sides.
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Contents
................................................................................
Fundamental of Differential Signal Operation
...................................................
Low-Voltage Differential Signaling
...............................................................
......................................................................................
..........................................................................................
References
.........................................................................................
Glossary of Terms
................................................................................
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4
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2
11
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13
14
List of Figures
Driver and Receiver Electrical Characteristics
..................................................
V
OH and V
OL
Changes After AC Coupling
LVDS-TTL Conversion
.......................................................
.............................................................................
Typical Connection Between LVDS Transmitter and Receiver
High-Speed Switch as 1:2 Multiplexer to Two LVDS Receivers
...............................
High-Speed Switch as 2:1 Multiplexer to One LVDS Receiver
...............................
Multiplexing Out to PCIe Slot and HDMI Converter
TMDS Differential Pair Transmitter and Receiver
..........................................
............................................
DVI/HDMI Interconnection by Source and Sink
...............................................
1:2 Switching MUX to DVI and HDMI 1.2
1:2 Switching MUX to DVI and HDMI 1.3
1:2 Switching MUX to DVI and DP
......................................................
......................................................
.............................................................
DisplayPort External Connector (Source)
......................................................
Multiplexing Dual Video Input Source (TS3DV520E)
.........................................
Multiplexing High Bandwidth HDMI 1.3a
.......................................................
Mobile Phone Differential Bus for Panel Display
..............................................
Multiplexing Host_MDDI Transmitter
...........................................................
PCI-Express Link (Transmit and Receive Pairs)
..............................................
PCI Express System Topology
..................................................................
PCI Express Lane Bus Structure
................................................................
TS2PCIE2212 Switching MUX Diagram
.......................................................
PCI Express Port and Multiplexers
.............................................................
Multiplexing SDVO and PCI Express Slot
.....................................................
PCI Express Bus Expansion MUX
V
O vs V
I at 3.3-V V
..............................................................
.............................................................................
Example of Voltage Divider
......................................................................
LVDS Switching MUX for 20-Pin LCD Panel Interface
.......................................
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Differential Passive Signal Switch on Computing 1
General Description
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2
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LVDS Switching MUX for 30-Pin LCD Panel Interface
.......................................
Two LVDS Transmitters to One LVDS Receiver (Dual Link)
................................
Typical Motherboard with High Speed Passive Switch
......................................
Typical Notebook with High-Speed Passive Switch
..........................................
www.ti.com
List of Tables
LVDS Transmitter Electrical Characteristics
....................................................
LVDS Receiver Electrical Characteristics
.......................................................
LCD Panel Signal Interface Connector Pinout
..................................................
SDVO and PCIe Based Graphic Port Signal Mapping
.......................................
Required Operating Conditions
.................................................................
Transmitter DC Characteristics
..................................................................
DisplayPort Panel-Side Internal Connector
....................................................
DisplayPort External Connector (Source) Pins
................................................
MDDI Interface Connector Pinout
...............................................................
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General Description
Differential bus signaling is a new technology that addresses the needs of today’s high-performance data transmission applications, and it is therefore becoming an important I/O bus.
Numerous terms and units are used to quantify the ability of data transmission circuit to move data from one place to another. At the physical layer (electrical and mechanical), data signaling rate, data transfer rate, jitter, and skew are most often specified. The following sections provide the basic definition of differential signaling and demonstrate the use of a high-speed passive switch in several differential bus applications.
Fundamental of Differential Signal Operation
High-speed data-transfer rates are necessary in video, Ethernet, memory, and data communications equipment. In the past, the processors and controllers used TTL/CMOS I/Os from 8-bit width increasing to
16-bit, 32-bit, and 64-bit width with higher clock frequencies and data-transfer rates. These incremental changes have limitations caused by board space, EMI, noise, and design difficulties.
Differential signal I/O is gaining popularity in computing platforms, because it can offer faster data-transfer rates, lower power consumption, and lower voltage. Digital signal I/O is also a relatively well-established standard specification from standard work groups.
The differential signal uses two wires for each electrical path, providing high immunity to noise and crosstalk. The signals transmitted are a positive signal on one wire and a negative signal on the other.
The receiving end derives the signal from the difference between the two wires. The technique can be used for both digital and analog signals, such as the audio and digital signals of RS-422, RS-485,
Ethernet, PCI Express (PCIe), USB, DVI, HDMI, LVDS, and DVI.
The two major signaling systems are high-voltage differential signaling and low-voltage differential signaling.
High-voltage differential signaling is a generic term that describes a variety of systems. In computer electronics, "high voltage" is normally considered 5 V or higher.
Low-voltage differential signaling (LVDS) is an electrical signaling system that can run at very high speeds over inexpensive twisted-pair copper cables. It was introduced in 1994 and has since become very popular in computers, where it forms part of very high-speed networks and other computer buses.
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3 Low-Voltage Differential Signaling
Low-Voltage Differential Signaling
Differential technology allows products to provide high data rates that range from hundreds of megabits per second to 2 Gbps, 5 Gbps, or even faster. With the various data rates required in different equipment and applications, a number of products and devices are defined by standard work groups.
One of the differential signaling technologies is known as LVDS-EIA/TIA644, and it is a signaling method used for high-speed transmission of binary data over copper wires. The benefits of balanced data transmission begin to outweigh the costs over single-ended techniques when signal transition times approach 10 ns.
The LVDS working group defines driver and receiver electrical characteristics to ensure that LVDS becomes a multipurpose interface standard. It does not define protocol, interconnect, or connector details, because these details are application specific. Therefore, each application that uses LVDS should also reference the appropriate protocol and interconnect standards.
The LVDS driver produces a differential voltage across a 100-
Ω load in the range of 247 mV to 454 mV with typical offset voltage of 1.2 V relative to ground (see
).The recommended voltage applied to the receiver is between ground and 2.4 V with a common mode range of 0.5 V to 2.35 V. The receiver has a sensitivity level of
±
100 mV. The LVDS interconnecting media must be matched with the 100-
Ω termination resistor located at the inputs of the receiver.
Because the standard does not specify power-supply voltage, and the driver output characteristics are independent of power supply, the supply voltage may be 5 V, 3.3 V, or even lower.
2.4 V
Common-Mode
Voltage
2.2 V
100 mV
Receiver
Sensitivity Levels
–100 mV
2 V
247 – 454 mV
Common-Mode
Voltage
1.2 V
± 1 V Ground Noise
0.4 V
DRIVER OUTPUT LEVELS
Common-Mode
Voltage
0.2 V
0 V
RECEIVER INPUT LEVELS
Figure 1. Driver and Receiver Electrical Characteristics
100 mV
Receiver
Sensitivity Levels
–100 mV
The I/O buses described below use differential signaling technology with defined data rates and required channels. Each new standard bus structure has its own protocols, interconnections, connectors, and voltage swing.
LVDS bus structure can be ac-coupled or dc-coupled. AC coupling adds capacitance on the transmission line and allows both transmitter and receiver to operate at dc voltage levels that are optimal. AC coupling shifts the common voltage
±
200 mV. Most ac coupling is done on the transmitter side, and placing the capacitor close to the transmitter side is recommended.
In higher-speed applications, ac coupling is recommended only for dc-balanced signals. AC coupling generates baseline wander in high-speed serial data transmissions that are not dc balanced.
shows an example of V
OH and V
OL changes after ac coupling.
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Differential Passive Signal Switch on Computing 3
Low-Voltage Differential Signaling
V = 1.4 V
OH
V = 1 V
OL
V = Vterm + 0.2 V
OH
V =
OL
Vterm – 0.2 V www.ti.com
Vterm
Figure 2. V
OH and V
OL
Changes After AC Coupling
The following are some LVDS protocols that are defined for convenient development of related components and programming at fixed high-speed data transmission rates.
•
HyperTransport (since 2001)
•
FireWire (IEE1394-1995)
•
Serial ATA (since 2004)
•
RapidIO (since 2004)
•
PCI Express known as PCI-E or PCI-e (2004 by Intel)
•
Flat Panel Display Interface (since 1996 by VESA)
•
OpenLDI (since 1999 by National)
•
Gigabit Ethernet (IEEE 802.3-2005)
3.1
Flat Panel Display Interface
The panel industry is rapidly accelerating to higher resolution and a greater number of color bits per pixel.
Breakthroughs in better color resolution are possible only by increasing the overall data rate from the host to the panel.
Digital image processing enhances the overall viewing by using LVDS signaling to transmit and receive the high-speed video data stream.
With the growth of digital displays, many IP cores have been created to support LVDS buses, and they have been embedded in applications such as graphic video controllers, application processors, and display devices for notebooks, motherboards, set top boxes, DVD players, and other audio/video equipment.
VESA (Video Electronics Standards Association) defines the standardization of selected electrical interface requirements for LCD panels intended for notebook computers, LCD display monitors, and other video interfaces, which allows the designers of the IP cores, LVDS transmitters, and receivers to follow the defined electrical specifications.
The LVDS transmitter is a device that converts LVCMOS/LVTTL data into LVDS channels at transmit clock speeds. LVDS transmission data rate can be calculated by number of bits and clock frequency. For example 6 bits
×
65 MHz = 390 Mbps per pair.
The LVDS receiver is a device that converts the LVDS signal to LVCMOS/LVTTL. Both LVDS transmitters and receivers must comply with the same LVDS specification to communicate.
The specified electrical characteristics of LVDS transmitters and receivers are shown in
and
with key related parameter of I/O behaviors.
The LVDS transmitter in notebooks, set-top boxes, ultra-mobile PCs, mobile processors, and portable media player processors is used as an internal video output for panel connection. The LVDS receiver in
LCD monitors and TV displays is used as a video input for scalar IC and TFT LCD panel display.
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Low-Voltage Differential Signaling
V
OD
ΔV
OD
V
OS
ΔV
OS
I
OS
I
OZ
V
ID
Table 1. LVDS Transmitter Electrical Characteristics
Parameter
Normal differential output voltage
Reduced differential output voltage
Changes in V
OD between complimentary output states
Offset voltage
Changes in V
OS between complimentary output states
Output short-circuit current
High-impedance output current
Differential input voltage
Test Conditions
R
L
= 100
Ω
Min Typ Max Unit
250
100
450
300 mV
1.125
0.1
35 mV
1.2
1.375
V
35 mV
24 mA
10
µ
A
0.5
V
V
TH
V
TL
I
IN
V
ID
V
CM
Table 2. LVDS Receiver Electrical Characteristics
Parameter
Differential input high threshold
Differential input low threshold
Input current
Differential input voltage
Common-mode input voltage
Test Conditions
V
CM
= 1.2 V
V
CM
= 1.2 V
V
DD
= 3.3 V
V
DD
= 2.5 V
Min Max Unit
100 mV
–100 mV
±
10
µ
A mV 100
V
ID
/ 2 2.4 – V
ID
/ 2
V
ID
/ 2 V
DD
– 0.4 – V
ID
/ 2
V
LVDS is a standard interface between the host and the LCD panel module, which would be either
FPD-Link or LDI interface. The LVDS receiver function is typically integrated into the panel timing controller and three or four data pairs per primary color (red, green, and blue) and clock, depending on depth color supported (6-bit or 8-bit color) .
The Standard Panel Working Group (SPWG) and VESA established a set of panels with dimensions and interface characteristics that allow both notebook and LCD supplier industries to manage design more easily.
Today the main standard buses for LCD panel module connections use 20 pins, 30 pins, 40 pins, or 50 pins, with varying numbers of channels and sideband control signals.
shows the detailed interface connection pin assignments.
The 20-pin panel interface is intended for 12.1", 12.1"W, and 13.3"W display interfaces with four main
LVDS channels and a pair for the I
2
C display data channel (DDC). The 30-pin panel interface is intended
I for 13.3", 14.1", 14.1"W, 15", 15.4"W, and 17"W panel sizes with eight LVDS channels and a pair for the
2
C DDC.
The 30-pin and 40-pin interfaces are intended to achieve higher resolution and require 10 LVDS channels and a pair for I
2
C DDC.
6-bit and 8-bit links are a feature of each LVDS channel (two wires), and the transmitter converts the 6 bits of TTL/CMOS data to each LVDS pair for transmission, and the receiver converts the LVDS signals back into the 6 bits of TTL/CMOS data at the receiver side (see
TTL Interface LVDS TTL Interface
RED
6 6
RED
Figure 3. LVDS-TTL Conversion
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Differential Passive Signal Switch on Computing 5
30
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40
Channels
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20
21
22
23
24
15
16
17
18
19
10
11
12
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6
7
8
9
Pin No.
1
2
3
4
Low-Voltage Differential Signaling
Table 3. LCD Panel Signal Interface Connector Pinout
6-Bit Single Link
GND
3.3V
3.3V
3.3V
NC
SCL
SDA
RinX0-
RinX0+
GND
RinX1-
RinX1+
GND
RinX2-
RinX2+
GND
CLK-
CLK+
GND
GND
6-Bit Dual Link
GND
3.3V
3.3V
3.3V
NC
SCL
SDA
RinXO0-
RinXO0+
GND
RinXO1-
RinXO1+
GND
RinXO2-
RinXO2+
GND
CLKO-
CLKO+
GND
RinE0-
RinE0+
GND
RinE1-
RinE1+
GND
RinE2-
RinE2+
GND
CLKE-
CLKE+
RinXO1-
RinXO1+
RinXO2-
RinXO2+
CLKO-
CLKO+
GND
RinXO3-
RinXO3+
RinE0-
8-Bit Link
GND
GND
3.3V
3.3V
3.3V
SCL
SDA
RinXO0-
RinXO0+
RinE0+
RinE1-
RinE1+
RinE2-
RinE2+
CLKE-
CLKE+
GND
RinE3-
RinE3+
NC
4 Pairs 8 Pairs 10 Pairs www.ti.com
GND
RinE2-
RinE2+
GND
CLKE-
CLKE+
GND
RinE3-
RinE3+
GND
NC
10 Pairs
CLKO+
GND
RinO3-
RinO3+
GND
RinE0-
RinE0+
GND
RinE1-
RinE1+
RinXO0-
RinXO0+
GND
RinXO1-
RinXO1+
GND
RinXO2-
RinXO2+
GND
CLKO-
8-Bit Link
GND
GND
3.3V
3.3V
3.3V
3.3V
3.3V
SCL
SDA
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Low-Voltage Differential Signaling
3.2
Embedded Video Controller With LVDS Output
To allow the system to send the display data to the panel module faster, the LVDS transmitter converts the TTL/CMOS (R, G, B) parallel data to serial LVDS signaling. A phase-locked transmit clock is transmitted in parallel with the data stream over another LVDS link. The RGB data can be 6-, 7-, or 8-bit parallel data input to each LVDS pair depending on the specific LVDS transmitter specification and transmitted clock frequency.
shows the connection between the host (LVDS transmitter) and the peripheral (LVDS receiver).
TTL Interface LVDS
TTL Interface
RED
6
6
GREEN
6
BLUE
FPLINE
FPFRAME
DRDY
TX Clock PLL PLL
6
RED
6
GREEN
6
BLUE
FPLINE
FPFRAME
DRDY
RX Clock
FlatLink Transmitter
(Notebook Computer PC)
FlatLink Receiver
(Notebook Computer Display)
Figure 4. Typical Connection Between LVDS Transmitter and Receiver
3.2.1
Connecting a Single LVDS Source to a Dual LVDS Expansion Multiplexer
The application in
shows how to use a passive switch to expand the LVDS transmitter to two
LVDS receivers in two different LCD panel modules without a second LVDS transmitter. One example of equipment that might require this system is a PC notebook with two displays—the main display and a second LCD panel located on the front cover for media movie display, checking email, tasks, schedule, weathers, internet, and GPS map viewing without opening the notebook. In this design, the notebook would need a simple high-speed passive switch to expand the LVDS source and select the LCD panel that is currently being used as the display.
The correct differential switch must be selected based on the LCD panel type, the number of LVDS channels, the data rate, and the V
IO range.
shows the typical switching route between one LVDS transmitter and two receivers connected to
LCD panel modules.
The figure shows how the high-speed passive switch can switch any LVDS signals within its specified data rate and V
IO range. Other key characteristics of the switch related to signal integrity and are also important. These high-speed passive switches can be used not only for LCD panel buses and but also for non-LCD panel LVDS bus signaling.
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Differential Passive Signal Switch on Computing 7
Low-Voltage Differential Signaling
LVDS Transmitter Serializer
RED
GRN
BLUE
Hsync
Vsync
Command
LVDS
Receiver
Deserializer 1 www.ti.com
LVDS
Receiver
Deserializer 2
High-Speed Passive Switch
Figure 5. High-Speed Switch as 1:2 Multiplexer to Two LVDS Receivers
3.2.2
Connecting from Two LVDS Sources to a Single Panel Display
Some systems have two video sources (that is, two LVDS transmitters) with a single LCD panel module
(the LVDS receiver). Often, the first LVDS transmitter is embedded into the graphic video controller or
FPGA, and the second LVDS transmitter is from a second processor or expansion bus (SDVO, PCIe bus) used for high-performance graphics.
The intention of adding two LVDS sources is that the first (embedded) LVDS is a default display for power saving during battery mode, and the second LVDS transmitter is higher performance and, therefore, consumes more power and is used when the notebook is powered by ac.
shows a typical example of switching for two different LVDS transmitters to a single LVDS receiver. All high-speed passive switches allow bidirectional signaling and feature a select control pin that can be set high or low by a system-monitoring circuit to connect the desired LVDS transmitter to the receiver.
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LVDS Transmitter Serializer
Red
Green
Blue
H Sync
V Sync
Command
Low-Voltage Differential Signaling
LVDS
Receiver
Deserializer 1
LVDS Transmitter Serializer
Red
Green
Blue
H Sync
V Sync
Command
High-Speed Passive Switch
Figure 6. High-Speed Switch as 2:1 Multiplexer to One LVDS Receiver
3.2.3
Multiplexing SDVO and PCI Express (PCIe) Signals
Some integrated video controllers such as Intel GMCH chip support Serial Digital Video Output (SDVO) and multiplex PCIe signals on the same pins for dual functions. SDVO is a proprietary Intel technology introduced with their 9xx-series of motherboard chipsets. SDVO makes it possible to use a 16-lane PCIe slot to add additional video signaling interfaces such as VGA and DVI monitor outputs or SDTV and HDTV television outputs.
shows SDVO and PCIe signaling names on the same pin.
shows an example of how to use differential switches for 1:2 connection of an SDVO bus and PCIe slot.
The SDVO port is an optional bus for converting to LVDS, DVI, HDMI, or other video type. The PCIe bus is a standard high-speed expansion bus slot that can be used in any peripheral function including video.
The passive switch in this application makes two connections from the source for easy implementation of
SDVO or PCIe bus.
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Differential Passive Signal Switch on Computing 9
Low-Voltage Differential Signaling
Table 4. SDVO and PCIe Based Graphic Port Signal
Mapping
SDVO Mode
SDVOB_RED
SDVOB_RED#
SDVOB_GREEN
SDVOB_GREEN#
SDVOB_BLUE
SDVOB_BLUE#
SDVOB_CLK
SDVOB_CLK#
SDVOC_RED
SDVOC_RED#
SDVOC_GREEN
SDVOC_GREEN#
SDVOC_BLUE
SDVOC_BLUE#
SDVOC_CLK
SDVOC_CLK#
SDVO_TV_CLKIN
SDVO_TV_CLKIN#
SDVO_INT
SDVO_INT#
SDVO_FLD_STALL
SDVO_FLD_STALL#
PCIe Mode
PEG_TXP0
PEG_TXN0
PEG_TXP1
PEG_TXN1
PEG_TXP2
PEG_TXN2
PEG_TXP3
PEG_TXN3
PEG_TXP4
PEG_TXN4
PEG_TXP5
PEG_TXN5
PEG_TXP6
PEG_TXN6
PEG_TXP7
PEG_TXN7
PEG_RXP0
PEG_RXN0
PEG_RXP1
PEG_RXN1
PEG_RXP2
PEG_RXN2 www.ti.com
Third
Party
Video
(HDMI,
LVDS,
DP,
DVI,
VGA)
TS2DS30812
VDD = 1.8 V
VSS = 0 V
PCIe x16 Slot
Figure 7. Multiplexing Out to PCIe Slot and HDMI Converter
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Low-Voltage Differential Signaling
PCIe Gen I data rate is higher than SDVO at is 2.5 Gbps/pair. TS3DV421 and TS2DS38012 can be used in this application as they support 3.8 Gbps. V
IO can be set from 0 V to 1.8 V by connecting the
V
DD
= 1.8 V and V
SS
= 0 V. Both devices have four channels, and the system may need more devices to multiplex based on the number of PCIe lanes and SDVO channels.
The PCIe Gen II data rate is higher, up to 5 Gbps, and it may require a different high-speed differential switch that is specified for this higher data rate.
3.3
External Video Output Multiplexing
PC monitor applications sometimes use VGA as external video interface, but VGA is limited in its ability to scale to support higher resolutions and color depths. Differential signaling can be used for not only internal
LCD panel module interfaces but also for external video interfaces, and can overcome these limitations.
There are many standard digital video output types such as Digital Video Port (DVP) (defined by
InfiniteReality), DFP, SGI Open LDI, DVI, HDMI, and DisplayPort, which all use differential signaling with different video encoding and decoding protocols, interconnections, clock or embedded clock, and number of channels, as well as different types of connectors.
A digital display interface is desired by the PC industry and other home audio/video electronics. A digital interface reduces the design complexity when connecting to digital display technologies such as Digital
Visual Interface (DVI), High Definition Multimedia Interface (HDMI), and DisplayPort (DP).
The data format used in DVI is based on a panel serial format that uses transition minimized differential signaling (TMDS). Each DVI single link consists of four pairs of differentials (one for each color code of red, blue, and green, and one for a clock signal). DVI Dual Link consists of seven differential pairs to transmit 24 bits per pixel. The clock signal is nearly the same as that of the analog video signal.
HDMI is another interface standard used for audiovisual equipment such as television and home theater as well as LCD PC monitor video interface. HDMI supports standard video formats, enhanced video, and high-definition. It is also backward compatible with DVI. HDMI Type A uses four differential pairs, and
Type B uses seven differential pairs.
DisplayPort is an open industrial standard digital display interface under the VESA display system committee. It supports both video and audio digital signaling for the notebook PC video interface. It has five differential pairs—four main link differential pairs carrying the audio/video data and one AUX differential pair that is bidirectional and used for realizing robust plug-n-play for ease of use.
Notebooks, DVD players, portable A/V players, LCD display monitors, and televisions are required to support many types of video interfaces. These systems often require high-speed differential signal multiplexing to switch between video ports, such as from a single video source output to two video output sources using 1:2 multiplexing. The passive switch is an inexpensive solution that can switch the source to two different video output at a high data rate.
DVI and HDMI 1.2a use the same data rate (up to 1.65 Gbps per channel) and compatible TMDS signaling levels. HDMI 1.3 standard increases the link's data rate from 165 MHz to an expected 275 MHz and the data rate up to 3.4 Gbps per channel.
DisplayPort is a royalty-free option that aims to surpass both DVI and HDMI on several fronts. DisplayPort uses the electrical layer of 2.5-Gbps channels, and the bandwidth is up to 10.8 Gbps over four channels. It supports cable lengths of up to 15 m while using lower voltage levels than DVI.
Because HDMI and DP use different signaling levels, an additional component is required for signal translation of DP to TMDS when using both HDMI and DP on the same system.
3.3.1
DVI/HDMI Electrical Characteristic
An illustration of DVI/HDMI using a TMDS differential pair is shown in
Figure 8 . TMDS technology uses
current drive to develop a low-voltage differential signal at the receiver side of the dc-coupled transmission line. The link reference voltage AV
CC sets the high voltage level of the differential signals, while the low voltage level is set by the current source of the transmitter and termination resistance at the receiver.
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Differential Passive Signal Switch on Computing 11
Low-Voltage Differential Signaling www.ti.com
Transmitter
R
T
R
T
AV
CC
Z
0
D D
Current
Source
Receiver
Figure 8. TMDS Differential Pair Transmitter and Receiver
The operating conditions of TMDS interface are specified at 3.3 V
±
5% (see
electrical specifications are dc-coupled TMDS link and single-ended high-level output voltage, V
H
±
10 mV and low level output voltage, V
L is (AV
CC
– 600 mV) < V
L
< (AV
CC is AV
– 400 mV) (see
CC
Combining the single-ended swing voltage (V swing
) specified with the overshoot and undershoots requirements; it is possible to calculate the minimum and maximum high-level voltage (V
H
) and low-level voltage (V
L
) that allowable on the interface (see
).
As DVI and HDMI TMDS is based on 3.3-V condition, any high-speed passive switch can be used in multiplexing with the feature signal path can pass through within 2.7 V to 3.6 V at defined data rate.
AV
CC
R
T
T
OP
Table 5. Required Operating Conditions
Parameter
Termination supply voltage
Termination resistance
Operating temperature
Value
3.3 V
±
5%
50
Ω ±
10%
0
°
C to 70
°
C
V
H
V
L
V swing
V
OFF
Table 6. Transmitter DC Characteristics
Parameter
Single-ended high-level output voltage
Single-ended low-level output voltage
Single-ended output swing voltage
Single-ended standby (off) output voltage
Calculation of Minimum Opening at Transmitter
V high
(max) = V swing
(max) + 15%
×
2
×
(V swing
(max)) = 600 + 180 = 780 mV
V high
(min) = V swing
(min) – 25%
×
2
×
(V swing
(min)) = 400 – 200 = 200 mV
V low
(max) = V swing
(max) – 15%
×
2
×
(V swing
(max)) = –600 – 180 = –780 mV
V low
(min) = V swing
(min) + 25%
×
2
×
(V swing
(min)) = –400 + 200 = –200 mV
Minimum opening at transmitter = V high
(min) – V low
(min) = 400 mV
Value
(AV
CC
AV
CC
±
10 mV
– 600 mV)
≤
V
L
≤
(AV
CC
– 400 mV)
400 mV
≤
V
AV
CC
SWING
≤
600 mV
±
10 mV
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Low-Voltage Differential Signaling
3.3.2
Supporting Both DVI and HDMI with a Single Video Source
HDMI builds on the DVI specification. DVI only handles video data and is widely used in LCD monitor displays. HDMI includes audio as well as video data with increased piracy protection in the form of a digital encryption protocol called HDCP and used in both LCD monitor display and LCD TV display.
The DVI 1.0 specification was released by the Digital Display Working Group (DDWG). DVI defines a single link (four pairs) and dual link (seven pairs) transferring only a video digital data. The HDMI transfer both video and audio and there are four versions developed over the years—HDMI 1.0, 1.1, 1.2, and 1.3.
Both DVI 1.0 and HDMI 1.2 support the same 1.65-Gbps data rate, and HDMI 1.3 supports up to 3.4 Gbps by increasing the clock frequency.
DVI and HDMI have the same electrical characteristics and the same dc coupling. Both use four pairs of channels transmitting the data and clock.
shows the switching route without passive switch.
DVI and HDMI 1.2 are often still used in portable equipment, because it usually does not need high data rates. HDMI 1.3 supports increased data rates, and its requirements must be used to select a higher data rate passive switch if the system is going to support both lower data rate DVI and higher data rate HDMI
1.3.
Red
Transmitter Chip
R
Computer
Graphics
Controller
Green
Blue
Clock
Control
Parallel to
Serial
Encoder
G
B
Clk
Display
Data
Channel
(DDC)
PLL
DDC Data
DDC Clock
TMDS
Single Link
G
B
Clk
R
Receiver Chip
Serial to
Parallel
Encoder
Image
Data
Clock
Control
Display
Controller
PLL
DDC Data
DDC Clock
Figure 9. DVI/HDMI Interconnection by Source and Sink
To support both DVI and HDMI 1.2 or HDMI 1.3 video outputs, TS3DV520E is suitable for DVI and
HDMI 1.2, and TS3DV421 is recommended for HDMI 1.3.
Supporting the HDMI 1.2 and DVI video outputs, TS3DV520E is recommended as it supports higher than
2 Gbps per pair and is a five-pair switching multiplexer. Four pairs can be used in multiplexing the source of TMDS to both DVI and HDMI 1.2 video connector, and the additional pair can be used for DDC (data and clock). TS3DV520E has 14-kV Human-Body Model ESD protection level, which can save some cost by not requiring an external ESD chip (see
).
Supporting DVI and HDMI 1.3 (2.25 Gbps or 3.4 Gbps), TS3DV421 is recommended as it can switch signals at 3.8 Gbps/pair. TS3DV421 is high-speed using 1.8-V technology. To meet the HDMI/DVI signaling, it is recommended to connect V
SS
3.6 V.
= 1.5 V and V
DD
= 3.3 V to allow a signal path from 1.5 V to
Both DVI and HDMI have four sideband control signals (DDC data and clock, CEC, and HPD), and the solution may need another 4-bit multiplexer (CBT3257C is recommended).
shows the complete solution of HDMI 1.3 and DVI video output with a single video source. The CBT3257C is n-channel FET and I/Os can be pulled up to 5 V for DDC and CEC.
DVI dual link (DVI-DL) and HDMI Type B need an additional three pairs to achieve high definition video with higher total data rate. In this application, the main link becomes seven pairs and the DDC channel becomes one pair. TS3DV416 (four pairs) and TS3DV520E (five pairs) are recommended for easy combination using two devices.
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Low-Voltage Differential Signaling
Red
Transmitter Chip
R
Computer
Graphics
Controller
Green
Blue
Clock
Control
Parallel to
Serial
Encoder
G
B
Clk
Display
Data
Channel
(DDC)
PLL
DDC Data
DDC Clock
DVI
TS3DV520E
5-Pair Differential-Channel MUX/DEMUX
Figure 10. 1:2 Switching MUX to DVI and HDMI 1.2
HDMI 1.2
Red
Transmitter Chip
R
Computer
Graphics
Controller
Green
Blue
Clock
Control
Parallel to
Serial
Encoder
G
B
Clk
Display
Data
Channel
(DDC)
PLL
DDC Data
DDC Clock
TS2DV421
High-Speed
MUX
VDD = 3.3 V
VSS = 1.5 V
DVI
CBT3257C
CEC
HPD
Figure 11. 1:2 Switching MUX to DVI and HDMI 1.3
HDMI 1.3
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Low-Voltage Differential Signaling
3.3.3
Supporting DisplayPort and HDMI 1.3 With One Video Source
DisplayPort is defined by VESA, and the standard specifies an open digital communication interface. It is defined in both internal connection for panel bus and external video port for PC, monitor, projector, DVD player, and TV.
The DisplayPort physical layer is similar to the PCIe physical layer, with an ac-coupled voltage-differential interface supporting five channels at 2.7 Gbps per pair. Four pairs are used for data transfer with embedded clock and one pair for the auxiliary channel.
shows detailed pin assignment of an external DisplayPort.
DisplayPort is also designed to be used as an internal LCD panel bus by increasing the data rate and configurable channels to support the required data rates of different LCD panels. The initial data rate per pair is defined at 1.6 Gbps or 2.7 Gbps.
shows DisplayPort Panel Bus pin assignment. Based on the total data rate requirements, it could be a pair, dual pairs or triple pairs.
A notebook with an embedded DisplayPort system needs a TMDS output translator (such as the TI
SN75DP129) for HDMI 1.3 signaling. Because the limited DisplayPort Source, it requires a high-speed passive switch to expand DisplayPort outputs into two DisplayPort sources.
TS3DV421 is a 3.8-Gbps data rate four-differential-pairs multiplexer and can expand the DisplayPort source to two DisplayPort sources. One connects to DisplayPort video output connector, and the other connects to SN75DP129, which translates DisplayPort to TMDS output for HDMI video output.
shows an example of supporting both DisplayPort and HDMI 1.3 on a PC.
Because DisplayPort is lower voltage signaling from 0 V to 1.8 V, TS3DV421 is recommended by connecting V
DD
= 1.8 V and V
SS
= 0 V.
DisplayPort has another auxiliary channel that requires 1-MHz bandwidth, and TS5A23157 can be used in multiplexing this AUX channel. TS5A23157 is a 200-MHz bandwidth analog switch dual SPDT.
The SN75DP129 is a dual-mode DisplayPort input to TMDS output. The TMDS output has a built-in level translator, compliant with DVI 1.0 and HDMI 1.3 standards. The SN75DP129 is specified up to a maximum data rate of 2.5 Gbps, supporting resolutions greater than 1920x1200 or HDTV 12-bit color depth at 1080p.
TS3DV421
Display Port
Embedded
Graphic
Controller
0
1
2
3
Aux
High-Speed
MUX
Display Port
VDD = 1.8 V
VSS = 0 V
SN75DP129
TS5A23157
HDMI 1.3
Figure 12. 1:2 Switching MUX to DVI and DP
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Differential Passive Signal Switch on Computing 15
Low-Voltage Differential Signaling
Panel Standard Pin No.
Frame
1
2
3
4
5
6
7
8
14
15
16
17
18
9
10
11
12
13
24
25
26
27
28
19
20
21
22
23
29
30
Frame
Table 7. DisplayPort Panel-Side Internal Connector
Pin Name Pin Definition
Outer shell
Reserved
LCDVCC
LCDVCC
LCDVCC
LCDVCC
Ground
Ground
Ground
Ground
Hot Plug Detect
Reserved
Reserved
H_GND
ML_Lane 3(n)
ML_Lane 3(p)
H_GND
ML_Lane 3(n)
ML_Lane 2(p)
H_GND
ML_Lane 1(n)
ML_Lane 1(p)
H_GND
ML_Lane 0(n)
ML_Lane 0(p)
H_GND
AUX_CH (p)
AUX_CH (n)
H_GND
AUX_PWR
Reserved
Power to LCD panel
Power return (ground)
Hot plug detect, optional
High-speed (main link) ground
'True' signal - main link
'Complement' signal - main link
High-speed (main link) ground
'True' signal - main link
'Complement' signal - main link
High-speed (main link) ground
'True' signal - main link
'Complement' signal - main link
High-speed (main link) ground
'True' signal - main link
'Complement' signal - main link
High-speed (main link) ground
'True' signal - auxiliary channel
'Complement' signal - auxiliary channel
High-speed (main link) ground
3.3-V trickle power
Outer shell
DisplayPort
Transmitter
Main Link Lane (0-3) / 4 Pairs
AUX Channel
Hot Plug Detect
DisplayPort
Receiver
Figure 13. DisplayPort External Connector (Source)
Table 8. DisplayPort External Connector (Source)
Pins
Pin No.
1
Signal Type
Out
Pin Name
ML_Lane 0+
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Low-Voltage Differential Signaling
Table 8. DisplayPort External Connector (Source)
Pins (continued)
16
17
18
19
20
11
12
13
14
15
6
7
8
9
10
Pin No.
2
3
4
5
Signal Type
GND
Out
Out
GND
Out
Out
GND
Out
Out
GND
Out
GND
GND
I/O
GND
I/O
In
Power Return
Power Out
Pin Name
Ground
ML_Lane 0–
ML_Lane 1+
Ground
ML_Lane 1–
ML_Lane 2+
Ground
ML_Lane 2–
ML_Lane 3+
Ground
ML_Lane 3–
Ground
Ground
AUX_CH+
GND
AUX_CH–
HPD
Return DP_PWR
DP_PWR
3.4
External Video Inputs Multiplexing on Sink Link
All differential passive switches have bidirectional signal bypass capability and can be used for 2:1 multiplexing. In LCD monitor/TV applications, the differential switch is used as a video input multiplexer to connect the selected video input channel to connect to internal graphic processing unit.
is a typical design example using TS3DV520E switching between DVI and HDMI 1.2 inputs connected to a TMDS receiver. Because TS3DV520E offers high ESD protection on the connector sides
(up to 14-kV HBM), it may not require an external ESD protection chip.
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HDMI 1.2
Video
Image
Processing
TFT Panel
LCD Display
DVI
VDD = 3.3 V
VSS = 0 V
Figure 14. Multiplexing Dual Video Input Source (TS3DV520E)
If the system uses HDMI 1.3 input, TS3DV421 and CBT3257C are recommended—the TS3DV421 to switch the high-speed main links and the SN74CBT3257C to switch the other four signals of DDC data and clock, CEC, and HPD. The SN74CBT3257C I/O can be pulled up to 5 V to meet the HDMI requirements.
is an example of using both TS3DV421/TS2DS30812 and SN74CBT3257C to multiplex the two types of DVI video input and HDMI inputs to a video controller TMDS receiver.
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HDMI 1.3
HDMI 1.3/DVI
VDD = 3.3 V
TS2DS30812
VSS = 1.5 V
VCC = 5 V
Low-Voltage Differential Signaling
Receiver Chip
R
G
B
Clk
Serial to
Parallel
Encoder
Image
Data
Clock
Control
Display
Controller
PLL
DDC Data
DDC Clock
CEC
HPD
CBT3257C
GND
Figure 15. Multiplexing High Bandwidth HDMI 1.3a
3.4.1
Selecting the Right High-Speed Differential Switch
LCD displays such as monitors and TVs support multiple video input types for user convenience. Most of the LCD display controllers support a single video decoder to achieve the effective cost. Differential passive switches are inexpensive solution for video input multiplexing to support an LCD display with more video input types.
Both DVI 1.0 and HDMI 1.2a support a data rate of 1.65 Gbps, and the TS3DV520E, TS3DS20812 or
TS3DV416 are recommended for their low cost and ease of design.
If the video input is a dual link, it needs a 10-pair differential signal switch and it may require two devices of TS3DV520E or TS3DS31012E.
LCD TV requires the higher bandwidth HDMI 1.3a and more HDMI video inputs to connect a DVD player, notebook PC, digital camera, or other audio/video equipment. TS2DV421 data rate is up to 3.8 Gbps, and it can be used for higher-bandwidth video multiplexing applications.
3.5
LCD Display Trend in Portable Equipment
Mobile phones have become multifunctional and are no longer simple communication appliances. An advanced mobile phone may be an MP3 player, digital camera, PDA, media player, GPS receiver, portable TV, and computer. The mobile phone’s display screen plays an important role in supporting those functions.
One area where the display devices need to upgrade panel response and display performance is to
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Differential Passive Signal Switch on Computing 19
Low-Voltage Differential Signaling www.ti.com
support video streaming. To achieve faster video streaming, mobile processors and their peripherals are moving away from a parallel TTL/CMOS interface to support a differential serial bus interface. A new mobile video interface uses LVDS signaling, and the initial data rate is about 200 Mbps per channel in both directions with maximum 20-cm cable length. Faster data transfer can be implemented by increasing number of channels (see
).
MDDI and MIPI are differential signaling interfaces for a mobile display bus with lower power consumption and lower voltage operation, compared to a TTL/CMOS display bus.
shows a differential bus between the display controller and the display driver. This system can be simplified by a portable processor with an embedded differential bus for the display controller, and a display driver with an embedded differential receiver.
Host Client
Display
Controller
DISPC_DATA_LCD[23:0]
DISPC_PCLK
DISPC_VSYNC
DISPC_HSYNC
DISPC_ACBIAS
RFBI
Display
Driver
LCD
Display
Mobile Display System
Differential Bus Link
Figure 16. Mobile Phone Differential Bus for Panel Display
13
14
15
16
17
18
19
20
6
7
8
9
10
11
12
Pin No.
1
2
3
4
5
Table 9. MDDI Interface Connector Pinout
Signal Type
Host_Pwr
Host_Gnd
MDDI_Stb+
MDDI_Stb-
MDDI_Data0+
MDDI_Data0-
MDDI_Data1+
MDDI_Data1-
MDDI_Data2+
MDDI_Data2-
MDDI_Data3+
MDDI_Data3-
MDDI_DataPwr4+
MDDI_DataPwr4-
MDDI_DataPwr5+
MDDI_DataPwr5-
MDDI_DataPwr6+
MDDI_DataPwr6-
MDDI_DataPwr7+
MDDI_DataPwr7-
Description
200 mA (3.2 V to 4.3 V)
Ground
Differential signal
Differential signal
Differential signal
Differential signal
Differential signal
Differential signal
Differential signal
Differential signal
Differential signal
Differential signal
Power
Power
Power
Power
Power
Power
Power
Power
3.5.1
Mobile Phone Display
The new LVDS panel bus interface was implemented on the mobile phone for high-performance display for TV, game, and movie player. Some phones also support cradle docking with an external display and may need a passive switch to select between the internal display bus and the cradle I/O connector.
The current defined data rate is 200 Mbps per channel maximum, and TS3V340 is a 500-MHz high-speed
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Low-Voltage Differential Signaling digital switch supporting a data rate up to 1 Gbps per pair. It may be used on a lower data rate differential bus. TS3V340 can operate at 2.5 V or 3.3 V, and the V
IO range is from 0 V to 3.6 V (2.5-V V
CC
) or 0 V to
5 V (3.3-V V
CC
). The signal output voltage (V
OUT
) is equal to the voltage on the signal inputs (V
IN
).
TS3V340 I/O rail-to-rail feature enables switching any type of LVDS signaling within the defined data rate specified in the data sheet.
is a potential application of mobile connecting to internal display bus and cradle docking for external display.
Primary
LCD Panel
MDDI
Host
MDDI_Data 0+
MDDI_Data 0–
MDDI_Stb+
MDDI_ Stb –
500-MHz
MUX
MDDI_Data 0+
MDDI_Data 0–
MDDI
LCD Controller
TS3V340
External
LCD Display
MDDI
LCD Controller
Power
Management
Figure 17. Multiplexing Host_MDDI Transmitter
3.6
PCI Express (PCIe) Signaling
PCIe is a standard local I/O bus for a wide variety of computing platforms including desktop, server and communication, workstation, and embedded devices. PCIe is a multi-drop parallel bus topology containing a hot bridge and several end points (the I/O devices) (see
).
The fundamental PCIe link consists of two low-voltage differential driven pairs of signals: a transmit pair and a receive pair as shown in
Figure 18 . A data clock is embedded using the 8b/10b encoding scheme to
achieve a very high data rate—PCIe Gen 1 supports a 2.5-Gbps transfer rate, and PCIe Gen 2 supports a
5-Gbps transfer rate.
TX RX
PCIe
Device
A
Link (x1, x2, x4, x8, x12, x16, or x32
PCIe
Device
B
RX TX
Figure 18. PCI-Express Link (Transmit and Receive Pairs)
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Low-Voltage Differential Signaling www.ti.com
CPU
Root Complex Memory
Switch
PCI Express
End Point
PCI Express
End Point
PCI Express
End Point
PCI Express
End Point
Figure 19. PCI Express System Topology
A PCIe bus can be configured as lanes of x1, x4, x8, and x16. Each PCIe lane contains two pairs of wires—one to send and one to receive, as shown in
Figure 20 . TI offers several product types of PCIe
bridge, end points, physical layers, packet switches, and PCIe signal switches. A PCIe signal switch is a high-speed passive switch that supports both transmit and receive.
0.1 µF x1 2.5 Gbit/sec
0.1 µF
Lane 1
Lanes x1 x4 x8 x16
Single
Direction
2.5 Gbps
10 Gbps
20 Gbps
40 Gbps
Dual
Direction
5 Gbps
20 Gbps
40 Gbps
80 Gbps
No. of
Wires
4
16
32
64 x4 x8 x16
Figure 20. PCI Express Lane Bus Structure
TS2PCIE2212 and TS2PCIE412 are PCIe Gen I high-speed passive switch multiplexers/demultiplexers
(MUX/DEMUX) supporting 2.5-Gbps bandwidth and allowing expansion of the PCIe lanes from the root complex to end points dynamically using the select control pin to assign the active PCIe slot.
TS2PCIE2212 is a four PCIe differential signal MUX/DEMUX with bypass switch (see
be used for either single direction (on transmitter or receiver side) or dual direction.
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Low-Voltage Differential Signaling
CTRL0
CTRL1
TxSA:0P
TxSA:0N
TxSB:0P
TxSB:0N
RxSA:0P
RxSA:0N
Control and Configuration
TxDA:0P
TxDA:0N
TxDB:0P
TxDB:0N
RxDA:0P
RxDA:0N
RxSB:0P
RxSB:0N
TxSA:1P
TxSA:1N
TxSB:1P
TxSB:1N
RxSA:1P
RxSA:1N
RxDB:0P
RxDB:0N
TxDA:1P
TxDA:1N
TxDB:1P
TxDB:1N
RxDA:1P
RxDA:1N
RxSB:1P
RxSB:1N
RxDB:1P
RxDB:1N
Figure 21. TS2PCIE2212 Switching MUX Diagram
The typical design example shown in
is multiplexing dual PCIe root complexes to individual slots. This design allows each slot to connect to either the south bridge or the north bridge root complex.
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Differential Passive Signal Switch on Computing 23
Low-Voltage Differential Signaling x2
Lane
North
Bridge x1
(4 wire) x1
(4 wire) www.ti.com
x2
Lane
South
Bridge x2
(8 wire)
TS2PCIE2212
Figure 22. PCI Express Port and Multiplexers
TS2PCIE412 is another differential switch optimized for PCIe signaling. It has four pairs of signal for the
PCIe signal multiplexer and it is used in the PC north bridge with embedded dual functions of SDVO and
PCIe signals on the same pins. In this application, TS2PCIE412 multiplexes the shared input bus out to separate SDVO and PCIe buses connected to other chips or slots.
shows an example of interconnection with TS2PCIE412, with one output connecting SDVO to an HDMI converter and the other output connecting to a PCIe slot for possible external graphic card to upgrade the video output performance. Depending on the number of lanes, it may require up to four
TS2PCIE412 devices to support a PCIe x16 slot.
TX
(4 pairs)
PCIe/
SDVO
HDMI
Translator
North
Bridge
PCIe x4
(PCIe slot)
Figure 23. Multiplexing SDVO and PCI Express Slot
show another interconnection from root PCIe to expand the different type of PCIe Connector by x1, x2, or x4.
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Root
PCIe
Low-Voltage Differential Signaling x1
(4 wire) x1
(4 wire) x2
(8 wire)
Figure 24. PCI Express Bus Expansion MUX
Because TS2PCIE412 is capable of passing high-speed differential signals, it can be used in non-PCIe application (for example, in a DisplayPort application) within the defined data rate and voltage swing range.
3.7
TS3DV416, TS3DV520E, TS3DV20812
The switches of this family are high-speed NMOS with a low and flat r
ON
. The flat r
ON is achieved by an internal charge-pump circuit that generates a voltage up to 7 V at the gate of the N-channel pass transistors. As a result, these switches offer 0-V to 5-V rail-to-rail switching capability, which allows differential signal bypassing freely within the V
IO range of 0 V to 5 V.
In addition to the low and flat r
ON characteristics, this family has low input and output capacitance, making them suitable for differential signaling switching applications. The maximum switching frequency for I/O signals depends on various factors, such as type of load, input-signal magnitude, input-signal edge rates, type of packages, etc.
show the V
O vs V
I characteristics of this switch family at 3.3 V. These switches can be used for switching differential signals ranging from 0 V to 5 V.
TS3DV416 supports four signal pairs for high-speed multiplexing and is used for switching the main four channels.
TS3DV20812 supports three additional side-band bits to manage the DDC (SCL, SDA) and CEC control signals. These three signals are supported by PMOS and NMOS switches, and the I/O of each signal is up to V
CC
.
TS3DV520E supports five signal pairs for high-speed multiplexing and can be used for either high-speed or low-speed signals. All I/Os can accept up to 5-V input even when the chip V
CC is 3.3 V. This 5-V tolerance enables the use of pullup resistors to 5 V to interface the DVI/HDMI defined 5-V DDC and 5-V
CEC control signals.
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Differential Passive Signal Switch on Computing 25
Low-Voltage Differential Signaling
5 www.ti.com
2
1
4
3
0
0 1 2 3
V
I
– V
Figure 25. V
O vs V
I at 3.3-V V
CC
4 5
3.7.1
Multiplexing in DVI and HDMI
These digital video switches are designed for multiplexing high-speed bidirectional differential signals.
They can be used on either the source side to expand the video ports or on the sink side to multiplex the multiple video sources into a single video port that communicates with a display controller that can support only one video port during decoding.
Because these switches support data rates greater than 1.65 Gbps, they can be used in for DVI and
HDMI 1.2a, which are defined at 1.65-Gbps data-rate signaling.
3.8
TS3DV421
TS3DV421 uses a lower-voltage technology to enable up to 3.8-Gbps data rate and is ideal for HDMI 1.3a
and DisplayPort, which need the higher data rate to transfer the video data stream.
TS3DV421 has two different operation mode. One mode, with V from 1.5 V to V
DD
V
IO
= 1.5 V and V
DD
+ 0.7 V to support DVI/HDMI. The second mode, with V
SS
= 3.3 V, allows V
= 0 V and V
DD
IO
= 1.8 V, allows from 0 V to 1.8 V
±
0.7 V to support DisplayPort.
SS
Because select control pin of TS3DV421 is referred to V
SS high or low under the condition of 1.5-V V
SS and 3.3-V V
DD and V
DD
, it needs external voltage divider to set
(see
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V
DD
= 3.3 V
R
V
DD
= 3.3 V
Low-Voltage Differential Signaling
R
SEL
From System GPIO
Figure 26. Example of Voltage Divider
3.9
TS3DS20812, TS3DS21012E
These switches are designed for use as internal LVDS switching, operating as 1:2 or 2:1 MUXes, where they do not need to support higher data rates such as 2.5 Gbps or 3.4 Gbps. They operate at >2-Gbps data rate and can pass any type of differential signaling within a 0-V to 5-V range. They can be used in for
LVDS for panel display and also for other LVDS applications in telecommunication, base stations, and server applications.
r
These switches operate at V
DD
ON
, r
ON flatness, and V
IO range.
= 2.5 V or V
DD
= 3.3 V, and the voltage level changes the characteristics of
A 0-V to 5-V rail-to-rail V
IO can be achieved when V
DD is acceptable.
range can be achieved when V
DD
= 3.3 V. A 0-V to 3.3-V rail-to-rail V
IO range
= 2.5 V. Because the LVDS signal range is 0 V to 2.4 V, either supply voltage
TS3DV20812 switches four pairs of high-speed differential signals and also supports three additional lower-speed signals. The high-speed switches can support LVDS channels, and the low-speed switches can support the DDC channel. Therefore, no additional external analog switch is required to switch the sideband control signals of DDC (SDA, SCL).
shows an example of using TS3DV20812 as a 1:2 MUX switching the LVDS source
(transmitter) to dual LVDS sinks (LVDS receivers) connected to two different LCD panel displays.
CMOS/
TTL
LCD Display1
Graphic
Controller
CMOS/
TTL
High
Speed
MUX
CMOS/
TTL
LCD Display 2
SCL
SDA
Three
Sideband
MUX
Single Link
LCD Panel
TS3DV20812
VDD = 3.3 V
VSS = 0 V
Figure 27. LVDS Switching MUX for 20-Pin LCD Panel Interface
SCDA012A – June 2009 – Revised July 2009
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Differential Passive Signal Switch on Computing 27
Low-Voltage Differential Signaling www.ti.com
According to the LCD standard panel interface (see
Table 3 ), eight pairs or ten pairs are required for the
main links in the 30-pin or 40-pin LCD interfaces, respectively. Therefore, the system requires two
TS3DS21010E devices to get the ten pairs and or two TS3DS20812 devices to get eight pairs as 1:2 or
2:1 MUX/DEMUX application.
TS3DS20812 is a four-pair switching multiplexer for high-speed LVDS signaling, and TS3DS21012E is a five--pair switching multiplexer for LVDS. Both devices are bidirectional and can be used for 2:1 or 1:2 switching.
shows an example of using two TS3DS21012E devices switching the panel LVDS source for
30-pin or 40-pin LCD panel link interfaces to two LCD panel displays.
Red (upper)
Green (upper)
Blue (upper)
Red (lower)
Green (lower)
Blue (lower)
Horz Sync
Vert Sync
Pixel Clock
Data Enable
LCD Display 1
LCD Display 2
Graphic Controller TS3DS21012E
Open LDI
LCD Panel
Figure 28. LVDS Switching MUX for 30-Pin LCD Panel Interface
shows an example of using TS3DS1012E switching LVDS as a 2:1 MUX from two LVDS transmitters to a single LVDS receiver connected to a TFT LCD panel display.
All of these switches are bidirectional and can also be applied as 2:1 multiplexers. One application for this feature is switching between dual sources of LVDS transmitters to a single receiver on an LCD panel display with the objective of changing the graphic video source for power saving (for example, when connected to ac, the external video controller is used, and when in battery mode, the embedded video is used). Two applications for such a system are PCs and mobile application processors.
28 Differential Passive Signal Switch on Computing SCDA012A – June 2009 – Revised July 2009
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Low-Voltage Differential Signaling
High-Speed
MUX
TS3DS21012E
Graphic
Controller
TFT
LCD Display
High-Speed
MUX
TS3DS21012E
LVDS
Converter
Figure 29. Two LVDS Transmitters to One LVDS Receiver (Dual Link)
The legacy LVDS data rate for LCD panel is from 1 Gbps to 1.65 Gbps. DisplayPort increases this rate to
2.7 Gbps per channel, which can reduce the number of LVDS channels while still achieving higher resolution. Therefore, DisplayPort may become the next standard LVDS signaling for LCD panels.
TS2DS30812 is ideal for this transition, because it supports >3-Gbps data rates and is operated at 1.8-V
V
DD to achieve better dc characteristics and bandwidth switching in the V
IO range from 0 V to 2.4 V. It can be used for the current LVDS signal rates and for the higher-rate DP signaling.
3.10 Summary
The TS3DS, TS2DS, TS3DV, TS2PCIE, and TS3PCIE families are high-speed bidirectional high-performance low-resistance low-r
ON low-voltage switches with controlled channel skew, crosstalk, and insertion loss. These features enable differential signal bypassing with minimum distortion to keep the output signals as close to the input signals as possible, even when multiplexing.
Currently available passive switches support data rates up to 3.8 Gbps, and future devices will support
5 Gbps or even higher to meet future requirements.
There are several key features to consider when selecting the switch to use in particular differential signal application. The V
IO range is a key feature and must be within the differential signal input and output range. The other key feature of high-speed switches is bypassing any type of signal within the specified voltage I/O range and data rate with the least distortion.
SCDA012A – June 2009 – Revised July 2009
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Differential Passive Signal Switch on Computing 29
Motherboards
4 Motherboards
www.ti.com
Motherboards are high-volume applications that require flexibility in providing more standard PCIe bus slots. The high-speed passive switch is an inexpensive component that can switch the PCIe and
DisplayPort signals.
shows an example how a motherboard can use high-speed passive switches to support both
DisplayPort and HDMI. In a similar manner, TS2PCIE412 is shown being used in PCIe bus slot expansion.
CPU
TS3DV421
DisplayPort
DisplayPort
HDMI
TS5A23157
DP to TMDS
Translator
PCIe x8
Root
PCIe
PCIe x16
Figure 30. Typical Motherboard with High Speed Passive Switch
30 Differential Passive Signal Switch on Computing SCDA012A – June 2009 – Revised July 2009
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5 Notebooks
Notebooks
Notebooks designed for gaming, office use, or professional use have different requirements, and notebook designs can be varied using different types of high-speed differential switches.
For example, depending on the GPU that is embedded, the system could require a high-speed passive switch to select between LVDS and DP for the panel interface ,or it might need to select between two different LVDS sources to send to the panel display. To support two different video outputs, the system also needs a passive switch to connect two different video ports. Some embedded GPUs are designed with SDVO and PCIe signaling on the same pin and need passive switching to maximize the function of the notebook.
is a block diagram showing some applications of high-speed passive switches.
CPU
Notebook
Panel
Display
SDVO to LVDS TS3DV520E
HDMI
TS2PCIE412
PCIe to HDMI
Figure 31. Typical Notebook with High-Speed Passive Switch
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Differential Passive Signal Switch on Computing 31
References
6 References
www.ti.com
1. Interface Circuits for TIA/EIA644 (LVDS) ( SLLA038 )
2. FlatLink Data Transmission System Design Overview ( SLLA012 )
3. VESA Notebook Panel Standard Version 1 October 22, 2007
4. Low-Voltage Differential Signaling (LVDS) ( SLLA014 )
5. Mobile Intel ＝ 965 Express Chipset Family data sheet Revision 003, June 2007
6. Digital Visual Interface DVI Revision 1.0, 02 April 1999 by DDWG
7. VESA DisplayPort Standard Version 1, Revision 1a, January 11, 2008
8. High-Definition Multimedia Interface Specification Version 1.3a, November 10, 2006
9. New Series of TFT display driver in mobile phone application by Solomon Systech Limited
10. MIPI Alliance Specification for Display Serial Interface Version 1.01.00-21 February 2008
11. VESA Mobile Display Digital Interface Standard Version 1.2, July 9, 2008
12. Creating a Third Generation I/O Interconnect by Intel Corporation
13. Developer Connection-PCI Product Specific Details developer.apple.com
14. Intel Embedded Graphics Drivers FAQ
15. Intel application note that accompanied the Intel 945G chipset introduction
16. Silicon Image offers an SiI1364 / SiI1362 chipset aimed at board designers who wish to implement
SDVO products
17. Chrontel also provides some chip-level SDVO solutions
18. InfiniteReality Digital Video Port Specification
19. Open LVDS Display Interface (OpenLDI) Specification v0.95 May 13, 1999
20. AC Coupling Between Differential LVPECL, LVDS, HSTL, and CML ( SCAA059 )
32 Differential Passive Signal Switch on Computing SCDA012A – June 2009 – Revised July 2009
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7 Glossary of Terms
Glossary of Terms
Bus LVDS— A parallel transmission system that uses a pair of low-voltage differential signals (LVDS).
Also referred to as BLVDS.
DFP— Digital flat panel
DP— DisplayPort
DP++— Dual-Mode DisplayPort
DVI— Digital visual interface. A standard developed by Intel that defines the digital interface between devices such as projectors, computers, and monitors.
EVC— Enhanced video connector
GPU— Graphic processing unit
HDMI— High-definition multimedia interface
LVDS— Low-voltage differential signaling. The TIA/EIA-644A specification for high-speed transmission.
LVPECL— Low-voltage positive-emitter coupling logic
M-LVDS— Multipoint low-voltage differential signaling. Allows the use of multiple drivers and multiple receivers on a bus. M-LVDS also allows bidirectional half-duplex communication over a single media pair.
MDDI— Mobile Display Digital Interface
MIPI— Mobile Industry Processor Interface
Panel Bus Panel— A digital high-speed (1.65 Gbps) interface used primary for LCDs, digital televisions, and digital CRTs.
PCI Express— PCI Express (PCIe) fits common system architectures, provides greater speed and independence, and increases bandwidth and scalability. PCIe offers 4 Gbps of peak bandwidth per direction and 8 Gbps of concurrent bandwidth. PCIe is referred to as a third-generation input / output (3GIO).
SGI OpenLDI— The connector used on SGI digital flat panel monitors
TMDS— Transmission minimized differential signaling
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Differential Passive Signal Switch on Computing 33
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