AD8328 - Analog Devices
5 V Upstream
Cable Line Driver
AD8328
FUNCTIONAL BLOCK DIAGRAM
FEATURES
VIN–
VOUT+
The AD8328 is a low cost amplifier designed for coaxial line
driving. The features and specifications make the AD8328
ideally suited for MCNS-DOCSIS and EuroDOCSIS applications.
The gain of the AD8328 is digitally controlled. An 8-bit serial
word determines the desired output gain over a 59 dB range,
resulting in gain changes of 1 dB/LSB.
The AD8328 accepts a differential or single-ended input signal.
The output is specified for driving a 75 Ω load through a 2:1
transformer.
O
Distortion performance of −53 dBc is achieved with an output
level up to 60 dBmV at 65 MHz bandwidth over a wide
temperature range.
This device has a sleep mode function that reduces the quiescent
current to 2.6 mA and a full power-down function that reduces
power-down current to 20 μA.
ATTENUATION
CORE
VERNIER
POWER
AMP
ZOUT DIFF =
300Ω
8
ZIN (SINGLE) = 800Ω
ZIN (DIFF) = 1.6kΩ
VOUT–
DECODE
8
DATA LATCH
POWER-DOWN
LOGIC
RAMP
GND
DATEN SDATA CLK
TXEN
03158-001
8
SHIFT
REGISTER
SLEEP
Figure 1.
–50
–52
VOUT = 60dBmV
@ MAX GAIN,
THIRD HARMONIC
–54
–56
–58
–60
–62
VOUT = 60dBmV
@ MAX GAIN,
SECOND HARMONIC
–64
–66
03158-002
B
SO
GENERAL DESCRIPTION
DIFF
OR
SINGLE
INPUT
AMP
VIN+
DISTORTION (dBc)
DOCSIS and EuroDOCSIS cable modems
CATV set-top boxes
CATV telephony modems
Coaxial and twisted pair line drivers
AD8328
LE
APPLICATIONS
BYP
TE
Supports DOCSIS and EuroDOCSIS standards for reverse
path transmission systems
Gain programmable in 1 dB steps over a 59 dB range
Low distortion at 60 dBmV output
−57.5 dBc SFDR at 21 MHz
−54 dBc SFDR at 65 MHz
Output noise level @ minimum gain 1.2 nV/√Hz
Maintains 300 Ω output impedance Tx-enable and
Tx-disable condition
Upper bandwidth: 107 MHz (full gain range)
5 V supply operation
Supports SPI interfaces
–68
–70
5
15
25
35
45
FREQUENCY (MHz)
55
65
Figure 2. Worst Harmonic Distortion vs. Frequency
The AD8328 is packaged in a low cost 20-lead LFCSP and
a 20-lead QSOP. The AD8328 operates from a single 5 V supply
and has an operational temperature range of −40°C to +85°C.
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
© 2005 Analog Devices, Inc. All rights reserved.
AD8328
TABLE OF CONTENTS
Signal Integrity Layout Considerations................................... 11
Applications....................................................................................... 1
Initial Power-Up ......................................................................... 12
Functional Block Diagram .............................................................. 1
RAMP Pin and BYP Pin Features ............................................ 12
General Description ......................................................................... 1
Transmit Enable (TXEN) and SLEEP ...................................... 12
Revision History ............................................................................... 2
Distortion, Adjacent Channel Power, and DOCSIS .............. 12
Specifications..................................................................................... 3
Noise and DOCSIS..................................................................... 12
Logic Inputs (TTL-/CMOS-Compatible Logic)....................... 4
Evaluation Board Features and Operation.............................. 12
Timing Requirements .................................................................. 4
Differential Signal Source ......................................................... 13
Absolute Maximum Ratings............................................................ 6
Differential Signal from Single-Ended Source ....................... 13
ESD Caution.................................................................................. 6
Single-Ended Source.................................................................. 13
Pin Configurations and Function Descriptions ........................... 7
Overshoot on PC Printer Ports ................................................ 13
LE
TE
Features .............................................................................................. 1
Installing Visual Basic Control Software................................. 13
Applications..................................................................................... 10
Running AD8328 Software ....................................................... 14
General Applications.................................................................. 10
Controlling Gain/Attenuation of the AD8328 ....................... 14
Circuit Description..................................................................... 10
Transmit Enable and Sleep Mode............................................. 14
B
SO
Typical Performance Characteristics ............................................. 8
SPI Programming and Gain Adjustment ................................ 10
Memory Functions..................................................................... 14
Input Bias, Impedance, and Termination................................ 10
Outline Dimensions ....................................................................... 17
Output Bias, Impedance, and Termination............................. 10
Ordering Guide............................................................................... 18
Power Supply............................................................................... 11
REVISION HISTORY
O
10/05—Rev. 0 to Rev. A
Updated Format..................................................................Universal
Changes to Table 4............................................................................ 6
Updated Outline Dimensions ....................................................... 17
Changes to Ordering Guide .......................................................... 18
11/02—Revision 0: Initial Version
Rev. A | Page 2 of 20
AD8328
SPECIFICATIONS
TA = 25°C, VS = 5 V, RL = RIN = 75 Ω, VIN (differential) = 29 dBmV. The AD8328 is characterized using a 2:1 transformer 1 at the device output.
Table 1.
Output = 60 dBmV, max gain
Single-ended input
Differential input
Gain code = 60 decimal codes
Gain code = 1 decimal code
TA = −40°C to +85°C
Third-Order Harmonic Distortion4, 5
O
ACPR2, 6
Isolation (Tx Disable)2
POWER CONTROL
Tx Enable Settling Time
Tx Disable Settling Time
Output Switching Transients2
Output Settling
Due to Gain Change
Due to Input Step Change
POWER SUPPLY
Operating Range
Quiescent Current
Typ
All gain codes (1 to 60 decimal codes)
f = 65 MHz
Maximum gain, f = 10 MHz, output referred
Minimum gain, f = 10 MHz, input referred
Max
29
800
1600
2
58
30.5
−28.5
0.6
17.9
2.2
59.0
31.5
−27.5
1.0
±0.0005
Unit
dBmV
Ω
Ω
pF
60
32.5
−26.5
1.4
107
1.2
18.4
3.3
dB
dB
dB
dB/LSB
dB/°C
MHz
dB
dBm
dBm
f = 10 MHz
f = 10 MHz
f = 10 MHz
135
1.2
1.1
151
1.3
1.2
nV/√Hz
nV/√Hz
nV/√Hz
f = 10 MHz
Tx enable and Tx disable
16.7
75 ± 30% 3
17.7
dB
Ω
f = 33 MHz, VOUT = 60 dBmV @ maximum gain
f = 65 MHz, VOUT = 60 dBmV @ maximum gain
f = 21 MHz, VOUT = 60 dBmV @ maximum gain
f = 65 MHz, VOUT = 60 dBmV @ maximum gain
Maximum gain, f = 65 MHz
−67
−61
−57.5
−54
−58
−85
−56
−55
−56
−52.5
−56
−81
dBc
dBc
dBc
dBc
dBc
dB
Maximum gain, VIN = 0
Maximum gain, VIN = 0
Equivalent output = 31 dBmV
Equivalent output = 61 dBmV
2.5
3.8
2.5
16
6
54
μs
μs
mV p-p
mV p-p
Minimum to maximum gain
Maximum gain, VIN = 29 dBmV
60
30
B
SO
Output Noise2
Maximum Gain
Minimum Gain
Tx Disable
Noise Figure2
Maximum Gain
Differential Output Impedance
OVERALL PERFORMANCE
Second-Order Harmonic Distortion 4, 5
Min
TE
Input Capacitance
GAIN CONTROL INTERFACE
Voltage Gain Range
Maximum Gain
Minimum Gain
Output Step Size
Output Step Size Temperature Coefficient
OUTPUT CHARACTERISTICS
Bandwidth (−3 dB)
Bandwidth Roll-Off
1 dB Compression Point 2
Conditions
LE
Parameter
INPUT CHARACTERISTICS
Specified AC Voltage
Input Resistance
Maximum gain
Minimum gain
Tx disable (TXEN = 0)
SLEEP mode (power-down)
OPERATING TEMPERATURE RANGE
4.75
98
18
1
1
−40
Rev. A | Page 3 of 20
5
120
26
2.6
20
ns
ns
5.25
140
34
3.5
100
V
mA
mA
mA
μA
+85
°C
AD8328
1
TOKO 458 PT-1087 used for above specifications. Typical insertion loss of 0.3 dB @ 10 MHz.
Guaranteed by design and characterization to ±4 sigma for TA = 25°C.
3
Measured through a 2:1 transformer.
4
Specification is worst case over all gain codes.
5
Guaranteed by design and characterization to ±3 sigma for TA = 25°C.
6
VIN = 29 dBmV, QPSK modulation, 160 kSPS symbol rate.
2
LOGIC INPUTS (TTL-/CMOS-COMPATIBLE LOGIC)
DATEN, CLK, SDATA, TXEN, SLEEP, VCC = 5 V; full temperature range.
Table 2.
Typ
LE
TIMING REQUIREMENTS
Min
2.1
0
0
–600
50
−250
50
−250
Max
5.0
0.8
20
–100
190
−30
190
−30
TE
Parameter
Logic 1 Voltage
Logic 0 Voltage
Logic 1 Current (VINH = 5 V) CLK, SDATA, DATEN
Logic 0 Current (VINL = 0 V) CLK, SDATA, DATEN
Logic 1 Current (VINH = 5 V) TXEN
Logic 0 Current (VINL = 0 V) TXEN
Logic 1 Current (VINH = 5 V) SLEEP
Logic 0 Current (VINL = 0 V) SLEEP
Unit
V
V
nA
nA
μA
μA
μA
μA
Full temperature range, VCC = 5 V, tR = tF = 4 ns, fCLK = 8 MHz, unless otherwise noted.
Table 3.
O
B
SO
Parameter
Clock Pulse Width (tWH)
Clock Period (tC)
Setup Time SDATA vs. Clock (tDS)
Setup Time DATEN vs. Clock (tES)
Hold Time SDATA vs. Clock (tDH)
Hold Time DATEN vs. Clock (tEH)
Input Rise and Fall Times, SDATA, DATEN, Clock (tR, tF)
Rev. A | Page 4 of 20
Min
16.0
32.0
5.0
15.0
5.0
3.0
Typ
Max
10
Unit
ns
ns
ns
ns
ns
ns
ns
AD8328
t DS
VALID DATA-WORD G1
MSB. . . .LSB
SDATA
VALID DATA-WORD G2
tC
t WH
CLK
t EH
t ES
8 CLOCK CYCLES
DATEN
GAIN TRANSFER (G1)
GAIN TRANSFER (G2)
t GS
TE
t OFF
TXEN
t ON
03158-003
ANALOG
OUTPUT
SIGNAL AMPLITUDE (p-p)
LE
Figure 3. Serial Interface Timing
VALID DATA BIT
MSB-1
t DS
MSB-2
t DH
CLK
O
Figure 4. SDATA Timing
Rev. A | Page 5 of 20
03158-004
MSB
B
SO
SDATA
AD8328
ABSOLUTE MAXIMUM RATINGS
Parameter
Supply Voltage VCC
Input Voltage
VIN+, VIN−
DATEN, SDATA, CLK, SLEEP, TXEN
Internal Power Dissipation
QSOP (θJA = 83.2°C/W) 1
LFCSP (θJA = 30.4°C/W) 2
Operating Temperature Range
Storage Temperature Range
Lead Temperature, Soldering 60 sec
2
1.5 V p-p
−0.8 V to +5.5 V
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
700 mW
700 mW
−40°C to +85°C
−65°C to +150°C
300°C
Thermal resistance measured on SEMI standard 4-layer board.
Thermal resistance measured on SEMI standard 4-layer board, paddle
soldered to board.
LE
1
Rating
6V
TE
Table 4.
ESD CAUTION
O
B
SO
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. A | Page 6 of 20
AD8328
TXEN
GND
20
GND
VCC
2
19
VCC
20 19 18 17 16
GND 3
18
TXEN
17
RAMP
NC
SDATA
9
12
SLEEP
CLK 10
11
GND
12 BYP
6
7
8
9
10
Figure 5. 20-Lead QSOP Pin Configuration
03158-006
13
03158-005
8
13 VOUT–
11 NC
GND 5
DATEN
NC = NO CONNECT
VIN– 4
SLEEP
BYP
TOP VIEW
(Not to Scale)
GND
14
AD8328
VIN+ 3
CLK
GND 7
14 VOUT+
GND 2
SDATA
VIN–
16 VOUT+
TOP VIEW
6 (Not to Scale) 15 V
OUT–
5
15 RAMP
GND 1
TE
VIN+
AD8328
DATEN
GND 4
VCC
GND 1
VCC
GND
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
Figure 6. 20-Lead LFCSP Pin Configuration
Table 5. 20-Lead QSOP and 20-Lead LFCSP Pin Function Descriptions
Pin No.
20-Lead
LFCSP
1, 2, 5, 9,
18, 19
17, 20
3
4
6
Mnemonic
GND
Description
Common External Ground Reference.
VCC
VIN+
VIN−
DATEN
9
7
SDATA
10
8
12
10
Common Positive External Supply Voltage. A 0.1 μF capacitor must decouple each pin.
Noninverting Input. DC-biased to approximately VCC/2. Should be ac-coupled with a 0.1 μF capacitor.
Inverting Input. DC-biased to approximately VCC/2. Should be ac-coupled with a 0.1 μF capacitor.
Data Enable Low Input. This port controls the 8-bit parallel data latch and shift register.
A Logic 0-to-Logic 1 transition transfers the latched data to the attenuator core (updates the gain)
and simultaneously inhibits serial data transfer into the register.
A Logic 1-to-Logic 0 transition inhibits the data latch (holds the previous gain state) and
simultaneously enables the register for serial data load.
Serial Data Input. This digital input allows an 8-bit serial (gain) word to be loaded into the
internal register with the most significant bit (MSB) first.
Clock Input. The clock port controls the serial attenuator data transfer rate to the 8-bit
master-slave register.
A Logic 0-to-Logic 1 transition latches the data bit, and a Logic 1-to-Logic 0 transfers the data bit
to the slave. This requires the input serial data-word to be valid at or before this clock transition.
Low Power Sleep Mode. In the sleep mode, the AD8328’s supply current is reduced to 20 μA.
A Logic 0 powers down the part (high ZOUT state), and a Logic 1 powers up the part.
No Connect.
Internal Bypass. This pin must be externally ac-coupled (0.1 μF capacitor).
Negative Output Signal
Positive Output Signal
External RAMP Capacitor (Optional)
Logic 0 Disables Forward Transmission. Logic 1 enables forward transmission.
B
SO
CLK
SLEEP
O
13
14
15
16
17
18
LE
Pin No.
20-Lead
QSOP
1, 3, 4, 7,
11, 20
2, 19
5
6
8
11
12
13
14
15
16
NC
BYP
VOUT−
VOUT+
RAMP
TXEN
Rev. A | Page 7 of 20
AD8328
TYPICAL PERFORMANCE CHARACTERISTICS
–55
–50
VOUT = 61dBmV
@ MAX GAIN
–55
VOUT = 60dBmV
@ MAX GAIN
–65
–60
–70
03158-007
–75
15
25
35
45
FREQUENCY (MHz)
TE
–65
VOUT = 59dBmV
@ MAX GAIN
5
55
–70
65
Figure 7. Second-Order Harmonic Distortion vs.
Frequency for Various Output Powers
TA = –40°C
–60
TA = +25°C
B
SO
–65
VOUT = 60dBmV
@ MAX GAIN
TA = +85°C
TA = +25°C
TA = –40°C
15
25
35
45
55
–65
65
03158-011
03158-008
5
Figure 8. Second-Order Harmonic Distortion vs. Frequency vs. Temperature
10
CH PWR
ACP
0
5
15
25
35
45
FREQUENCY (MHz)
55
65
Figure 11. Third-Order Harmonic Distortion vs. Frequency vs. Temperature
60
60dBmV
–58.2dB
O
–10
50
30
VOUT (dBmV)
–30
–40
–50
VOUT = 57dBmV/TONE
@ MAX GAIN
40
–20
20
10
0
–10
–60
–20
–70
C0
C0
c11
cu1
75kHz/DIV
cu1
03158-012
c11
–30
03158-009
POUT (dBm)
65
–60
FREQUENCY (MHz)
–90
55
TA = +85°C
–70
–80
25
35
45
FREQUENCY (MHz)
–55
DISTORTION (dBc)
–55
15
LE
–50
VOUT = 60dBmV
@ MAX GAIN
DISTORTION (dBc)
5
Figure 10. Third-Order Harmonic Distortion vs.
Frequency for Various Output Powers
–50
–75
VOUT = 59dBmV
@ MAX GAIN
03158-010
VOUT = 61dBmV
@ MAX GAIN
DISTORTION (dBc)
DISTORTION (dBc)
–60
VOUT = 60dBmV
@ MAX GAIN
–40
41.6
SPAN 750kHz
Figure 9. Adjacent Channel Power
41.7
41.8
41.9 42.0 42.1 42.2
FREQUENCY (MHz)
42.3
42.4
Figure 12. Two-Tone Intermodulation Distortion
Rev. A | Page 8 of 20
42.5
AD8328
0
40
–20
DEC60
–30
DEC48
DEC42
0
DEC36
–10 DEC30
DEC24
–20
–60
–80
03158-013
DEC12
DEC 1 TO DEC 6
1
10
100
FREQUENCY (MHz)
MAX GAIN
–90
–100
1000
MIN GAIN
1
100
1000
FREQUENCY (MHz)
Figure 13. AC Response
Figure 16. Isolation in Transmit Disable Mode vs. Frequency
1.4
1.6
f = 10MHz
1.2
1.2
0.4
f = 10MHz
0
f = 5MHz
LE
GAIN ERROR (dB)
0.8
1.0
0.8
–0.4
f = 42MHz
–0.8
0
B
SO
03158-014
–1.2
6
12
18
24
30
36
42
48
54
–1.6
60
GAIN CONTROL (Decimal Code)
0
100
80
f = 10MHz
130
TXEN = 1
120
O
60
40
03158-015
20
0
0
6
12
18
24
30
36
42
48
GAIN CONTROL (Decimal Code)
54
18
24
30
36
42
48
54
60
110
100
90
80
70
60
50
40
03158-018
120
12
Figure 17. Gain Error vs. Gain Control
QUIESCENT SUPPLY CURRENT (mA)
140
6
f = 65MHz
GAIN CONTROL (Decimal Code)
Figure 14. Output Step Size vs. Gain Control
OUTPUT REFERRED VOLTAGE NOISE (nV/√Hz)
10
TE
–40
0.1
OUTPUT STEP SIZE (dB)
–50
–70
DEC18
–30
–40
03158-017
GAIN (dB)
ISOLATION (dB)
DEC54
10
03158-016
20
0.6
TXEN = 0
VIN = 29dBmV
–10
30
30
20
60
0
Figure 15. Output Referred Voltage Noise vs. Gain Control
10
20
30
40
GAIN CONTROL (Decimal Code)
50
Figure 18. Supply Current vs. Gain Control
Rev. A | Page 9 of 20
60
AD8328
APPLICATIONS
SPI PROGRAMMING AND GAIN ADJUSTMENT
The AD8328 is primarily intended for use as the power
amplifier (PA) in Data Over Cable Service Interface Specification
(DOCSIS)-certified cable modems and CATV set-top boxes.
The upstream signal is either a QPSK or QAM signal generated
by a DSP, a dedicated QPSK/QAM modulator, or a DAC. In all
cases, the signal must be low-pass filtered before being applied
to the PA to filter out-of-band noise and higher order
harmonics from the amplified signal.
The AD8328 is controlled through a serial peripheral interface
(SPI) of three digital data lines: CLK, DATEN, and SDATA.
Changing the gain requires eight bits of data to be streamed into
the SDATA port. The sequence of loading the SDATA register
begins on the falling edge of the DATEN pin, which activates
the CLK line. With the CLK line activated, data on the SDATA
line is clocked into the serial shift register on the rising edge of
the CLK pulses, MSB first. The 8-bit data-word is latched into
the attenuator core on the rising edge of the DATEN line. This
provides control over the changes in the output signal level. The
serial interface timing for the AD8328 is shown in Figure 3 and
Figure 4. The programmable gain range of the AD8328 is
−28 dB to +31 dB with steps of 1 dB per least significant bit
(LSB). This provides a total gain range of 59 dB. The AD8328
was characterized with a differential signal on the input and a
TOKO 458PT-1087 2:1 transformer on the output. The AD8328
incorporates supply current scaling with gain code, as shown in
Figure 18. This allows reduced power consumption when
operating in lower gain codes.
LE
Due to the varying distances between the cable modem and the
head-end, the upstream PA must be capable of varying the
output power by applying gain or attenuation. The ability to
vary the output power of the AD8328 ensures that the signal
from the cable modem has the proper level once it arrives at the
head-end. The upstream signal path commonly includes a
diplexer and cable splitters. The AD8328 has been designed to
overcome losses associated with these passive components in
the upstream cable path.
TE
GENERAL APPLICATIONS
CIRCUIT DESCRIPTION
INPUT BIAS, IMPEDANCE, AND TERMINATION
The VIN+ and VIN− inputs have a dc bias level of VCC/2; therefore,
the input signal should be ac-coupled as shown in Figure 20.
The differential input impedance of the AD8328 is approximately
1.6 kΩ, while the single-ended input is 800 Ω. The high input
impedance of the AD8328 allows flexibility in termination and
properly matching filter networks. The AD8328 exhibits
optimum performance when driven with a pure differential
signal.
B
SO
The AD8328 is composed of three analog functions in the
power-up or forward mode. The input amplifier (preamp) can
be used single-ended or differentially. If the input is used in the
differential configuration, it is imperative that the input signals
be 180° out of phase and of equal amplitude. A vernier is used
in the input stage for controlling the fine 1 dB gain steps. This
stage then drives a DAC, which provides the bulk of the
AD8328’s attenuation. The signals in the preamp and DAC gain
blocks are differential to improve the PSRR and linearity. A
differential current is fed from the DAC into the output stage.
The output stage maintains 300 Ω differential output impedance,
which maintains proper match to 75 Ω when used with a 2:1
balun transformer.
O
5V
OUTPUT BIAS, IMPEDANCE, AND TERMINATION
The output stage of the AD8328 requires a bias of 5 V. The 5 V
power supply should be connected to the center tap of the
output transformer. In addition, the VCC applied to the center
tap of the transformer should be decoupled as seen in Figure 20.
VCC
VIN+
VOUT+
AD8328
1V
2 IN
VIN–
BYP
GND
03158-019
1V
2 IN
RL
VOUT–
Figure 19. Characterization Circuit
Rev. A | Page 10 of 20
AD8328
VCC
10µF
1
0.1µF
VIN+
165Ω
0.1µF
VIN–
SDATA
CLK
TXEN
SLEEP
1kΩ
20
GND
19
VCC
18
TXEN
17
RAMP
16
VOUT+
15
VOUT–
14
BYP
13
NC
0.1μF
12
SLEEP
11
GND
0.1μF
TO DIPLEXER
ZIN = 75Ω
TOKO 458PT-1087
0.1μF
1kΩ
1kΩ
1kΩ
1kΩ
03158-020
DATEN
QSOP
TE
ZIN = 150Ω
AD8328
GND
2
VCC
3
GND
4
GND
5
VIN+
6
VIN–
7
GND
8
DATEN
9
SDATA
10
CLK
Figure 20. Typical Application Circuit
Table 6. Adjacent Channel Power
LE
Adjacent Channel Symbol Rate (kSym/s)
160
320
640
1280
−58
−60
−63
−66
−58
−59
−60
−64
−60
−58
−59
−61
−62
−60
−59
−60
−64
−62
−60
−59
−66
−65
−62
−61
B
SO
Channel Symbol Rate (kSym/s)
160
320
640
1280
2560
5120
O
The output impedance of the AD8328 is 300 Ω, regardless
of whether the amplifier is in transmit enable or transmit
disable mode. This, when combined with a 2:1 voltage ratio
(4:1 impedance ratio) transformer, eliminates the need for
external back termination resistors. If the output signal is being
evaluated using standard 50 Ω test equipment, a minimum loss
75 Ω to 50 Ω pad must be used to provide the test circuit with
the proper impedance match. The AD8328 evaluation board
provides a convenient means to implement a matching attenuator.
Soldering a 43.3 Ω resistor in the R15 placeholder and an 86.6 Ω
resistor in the R16 placeholder allows testing on a 50 Ω system.
When using a matching attenuator, it should be noted that there
is a 5.7 dB of power loss (7.5 dB voltage) through the network.
POWER SUPPLY
The 5 V supply should be delivered to each of the VCC pins via a
low impedance power bus to ensure that each pin is at the same
potential. The power bus should be decoupled to ground using
a 10 μF tantalum capacitor located close to the AD8328. In
addition to the 10 μF capacitor, each VCC pin should be individually
decoupled to ground with ceramic chip capacitors located close
to the pins. The bypass pin, BYP, should also be decoupled. The
PCB should have a low impedance ground plane covering all
unused portions of the board, except in areas of the board
where input and output traces are in close proximity to the
2560
−66
−66
−64
−61
−60
−59
5120
−64
−65
−65
−63
−61
−60
AD8328 and the output transformer. All AD8328 ground pins
must be connected to the ground plane to ensure proper
grounding of all internal nodes.
SIGNAL INTEGRITY LAYOUT CONSIDERATIONS
Careful attention to printed circuit board layout details will
prevent problems due to board parasitics. Proper RF design
techniques are mandatory. The differential input and output
traces should be kept as short as possible. Keeping the traces
short minimizes parasitic capacitance and inductance. This is
most critical between the outputs of the AD8328 and the 2:1
output transformer. It is also critical that all differential signal
paths be symmetrical in length and width. In addition, the
input and output traces should be adequately spaced to
minimize coupling (crosstalk) through the board. Following
these guidelines optimizes the overall performance of the
AD8328 in all applications.
Rev. A | Page 11 of 20
AD8328
When the supply voltage is first applied to the AD8328, the gain
of the amplifier is initially set to Gain Code 1. Since power is
first applied to the amplifier, the TXEN pin should be held low
(Logic 0) to prevent forward signal transmission. After power is
applied to the amplifier, the gain can be set to the desired level
by following the procedure provided in the SPI Programming
and Gain Adjustment section. The TXEN pin can then be
brought from Logic 0 to Logic 1, enabling forward signal
transmission at the desired gain level.
RAMP PIN AND BYP PIN FEATURES
Another measure of signal integrity is adjacent channel power,
commonly referred to as ACP. DOCSIS 2.0, Section 6.2.21.1.1
states, “Spurious emissions from a transmitted carrier may
occur in an adjacent channel that could be occupied by a carrier
of the same or different symbol rates.” Figure 9 shows the
measured ACP for a 60 dBmV QPSK signal taken at the output
of the AD8328 evaluation board. The transmit channel width
and adjacent channel width in Figure 9 correspond to the
symbol rates of 160 kSym/s. Table 6 shows the ACP results for
the AD8328 driving a QPSK 60 dBmV signal for all conditions
in DOCSIS Table 6-9, Adjacent Channel Spurious Emissions.
NOISE AND DOCSIS
At minimum gain, the AD8328 output noise spectral density is
1.2 nV/√Hz measured at 10 MHz. DOCSIS Table 6-10, Spurious
Emissions in 5 MHz to 42 MHz, specifies the output noise for
various symbol rates. The calculated noise power in dBmV for
160 kSym/s is
LE
The RAMP pin is used to control the length of the burst on and
off transients. By default, leaving the RAMP pin unconnected
results in a transient that is fully compliant with DOCSIS 2.0
Section 6.2.21.2, Spurious Emissions During Burst On/Off
Transients. DOCSIS requires that all between-burst transients
must be dissipated no faster than 2 μs; and adding capacitance
to the RAMP pin adds more time to the transient.
various output power levels. These figures are useful for
determining the in-band harmonic levels from 5 MHz to
65 MHz. Harmonics higher in frequency (above 42 MHz for
DOCSIS and above 65 MHz for EuroDOCSIS) are sharply
attenuated by the low-pass filter function of the diplexer.
TE
INITIAL POWER-UP
B
SO
The BYP pin is used to decouple the output stage at midsupply.
Typically, for normal DOCSIS operation, the BYP pin should be
decoupled to ground with a 0.1 μF capacitor. However, in
applications that require transient on/off times faster than 2 μs,
smaller capacitors can be used, but it should be noted that the
BYP pin should always be decoupled to ground.
TRANSMIT ENABLE (TXEN) AND SLEEP
O
The asynchronous TXEN pin is used to place the AD8328 into
between-burst mode. In this reduced current state, the output
impedance of 75 Ω is maintained. Applying Logic 0 to the
TXEN pin deactivates the on-chip amplifier, providing a 97.8%
reduction in consumed power. For 5 V operation, the supply
current is typically reduced from 120 mA to 2.6 mA. In this
mode of operation, between-burst noise is minimized and high
input to output isolation is achieved. In addition to the TXEN
pin, the AD8328 also incorporates an asynchronous SLEEP pin,
which can be used to further reduce the supply current to
approximately 20 μA. Applying Logic 0 to the SLEEP pin places
the amplifier into SLEEP mode. Transitioning into or out of
SLEEP mode can result in a transient voltage at the output of
the amplifier.
DISTORTION, ADJACENT CHANNEL POWER, AND
DOCSIS
To deliver the DOCSIS required 58 dBmV of QPSK signal and
55 dBmV of 16 QAM signal, the PA is required to deliver up to
60 dBmV. This added power is required to compensate for
losses associated with the diplex filter or other passive components
that may be included in the upstream path of cable modems
or set-top boxes. It should be noted that the AD8328 was
characterized with a differential input signal. Figure 7 and
Figure 10 show the AD8328 second and third harmonic
distortion performance vs. the fundamental frequency for
2
⎡
⎛
⎞⎤
⎢20 × log⎜ ⎛⎜ 1.2 nV ⎞⎟ × 160 kHz ⎟⎥ + 60 = −66.4 dBmV
⎜⎜ ⎝ Hz ⎠
⎟⎟⎥
⎢
⎝
⎠⎦
⎣
(1)
Comparing the computed noise power of −66.4 dBmV to the
+8 dBmV signal yields −74.4 dBc, which meets the required
level set forth in DOCSIS Table 6-10. As the AD8328 gain is
increased above this minimum value, the output signal
increases at a faster rate than the noise, resulting in a signalto-noise ratio that improves with gain. In transmit disable
mode, the output noise spectral density is 1.1 nV/√Hz, which
results in −67 dBmV when computed over 160 kSym/s. The
noise power was measured directly at the output of the
AD8328AR-EVAL board.
EVALUATION BOARD FEATURES AND OPERATION
The AD8328 evaluation board and control software can be used
to control the AD8328 upstream cable driver via the parallel
port of a PC. A standard printer cable connected to the parallel
port of the PC is used to feed all the necessary data to the AD8328
using the Windows®-based control software. This package
provides a means of controlling the gain and the power mode of
the AD8328. With this evaluation kit, the AD8328 can be evaluated
in either a single-ended or differential input configuration. See
Figure 26 for a schematic of the evaluation board.
Rev. A | Page 12 of 20
AD8328
requires the removal of R2 and R3 to be shorted with R4 open,
as well as the addition of 82.5 Ω at R1 and 39.2 Ω at R17 for
75 Ω termination. Table 7 shows the correct values for R11
and R12 for some common input configurations. Other input
impedance configurations can be accommodated using
Equation 4 and Equation 5.
DIFFERENTIAL SIGNAL SOURCE
Typical applications for the AD8328 use a differential input
signal from a modulator or a DAC. See Table 7 for common
values of R4, or calculate other input configurations using
Equation 2. This circuit configuration will give optimal
distortion results due to the symmetric input signals. Note
that this configuration was used to characterize the AD8328.
(2)
1.6 kΩ − Z IN
(4)
Z IN × R1
R1 + Z IN
(5)
R17 =
VIN+
AD8328
VIN+
03158-021
R4
VIN–
AD8328
R1
TE
ZIN
Z IN × 800
800 − Z IN
ZIN
Figure 21. Differential Circuit
R17
DIFFERENTIAL SIGNAL FROM SINGLE-ENDED
SOURCE
03158-023
R4 =
Z IN × 1.6 kΩ
R1 =
Figure 23. Single-Ended Circuit
Table 7. Common Matching Resistors
ZIN (Ω)
50
75
100
150
Differential Input Termination
R2/R3
R4 (Ω)
R1/R17
Open
51.1
Open/Open
Open
78.7
Open/Open
Open
107.0
Open/Open
Open
165.0
Open/Open
Single-Ended Input Termination
R2 (Ω)/R3 (Ω)
R4 (Ω)
R1 (Ω)/R17 (Ω)
0/0
Open
53.6/25.5
0/0
Open
82.5/39.2
B
SO
LE
The default configuration of the evaluation board implements
a differential signal drive from a single-ended signal source.
This configuration uses a 1:1 balun transformer to approximate
a differential signal. Because of the nonideal nature of real
transformers, the differential signal is not purely equal and
opposite in amplitude. Although this circuit slightly sacrifices
even-order harmonic distortion due to asymmetry, it does
provide a convenient way to evaluate the AD8328 with a singleended source.
The AD8328 evaluation board is populated with a TOKO
617DB-A0070 1:1 for this purpose (T1). Table 7 provides
typical R4 values for common input configurations. Other input
impedances can be calculated using Equation 3. See Figure 26
for a schematic of the evaluation board. To use the transformer
for converting a single-ended source into a differential signal,
the input signal must be applied to VIN+.
R4 =
Z IN × 1.6 kΩ
(3)
1.6 kΩ − Z IN
ZIN
R4
AD8328
OVERSHOOT ON PC PRINTER PORTS
The data lines on some PC parallel printer ports have excessive
overshoot that can cause communication problems when
presented to the CLK pin of the AD8328. The evaluation
board was designed to accommodate a series resistor and
shunt capacitor (R2 and C5 in Figure 26) to filter the CLK
signal if required.
INSTALLING VISUAL BASIC CONTROL SOFTWARE
Install the CabDrive_28 software by running the setup.exe file
on Disk One of the AD8328 evaluation software. Follow the onscreen directions and insert Disk Two when prompted. Choose
the installation directory and then select the icon in the upper
left to complete the installation.
03158-022
O
VIN+
ZIN (Ω)
50
75
Figure 22. Single-to-Differential Circuit
SINGLE-ENDED SOURCE
Although the AD8328 was designed to have optimal DOCSIS
performance when used with a differential input signal, the
AD8328 can also be used as a single-ended receiver, or an IF
digitally controlled amplifier. However, as with the singleended-to-differential configuration previously noted, evenorder harmonic distortion is slightly degraded.
When operating the AD8328 in a single-ended input mode,
VIN+ and VIN– should be terminated as shown in Figure 23.
On the AD8328 evaluation boards, this termination method
Rev. A | Page 13 of 20
AD8328
RUNNING AD8328 SOFTWARE
TRANSMIT ENABLE AND SLEEP MODE
To load the control software, go to Start, Programs,
CABDRIVE_28 or select the AD8328.exe file from the
installed directory. Once loaded, select the proper parallel
port to communicate with the AD8328 (see Figure 24).
The Transmit Enable and Transmit Disable buttons select the
mode of operation of the AD8328 by asserting logic levels on
the asynchronous TXEN pin. The Transmit Disable button
applies Logic 0 to the TXEN pin, disabling forward transmission.
The Transmit Enable button applies Logic 1 to the TXEN pin,
enabling the AD8328 for forward transmission. Checking the
Enable SLEEP Mode box applies Logic 0 to the asynchronous
SLEEP pin, setting the AD8328 for SLEEP mode.
MEMORY FUNCTIONS
Figure 24. Parallel Port Selection
TE
LE
03158-024
The Memory section of the software provides a way to alternate
between two gain settings. The X→M1 button stores the current
value of the GAIN SLIDER into memory, while the RM1 button
recalls the stored value, returning the gain SLIDER to the stored
level. The same applies to the X→M2 and RM2 buttons.
CONTROLLING GAIN/ATTENUATION OF THE
AD8328
03158-025
O
B
SO
The SLIDER controls the gain/attenuation of the AD8328,
which is displayed in dB and in V/V. The gain scales 1 dB
per LSB. The gain code from the position of the SLIDER is
displayed in decimal, binary, and hexadecimal (see Figure 25).
Figure 25. Control Software Interface
Rev. A | Page 14 of 20
AD8328
VIN+_A
C1A
0.1µF
R2
TP9
TOKO
617DB-A0070
VIN–_A
R4
78.7Ω
C2A
0.1μF
R3
1
2
3
R17
P1 2
TP1
R5
1kΩ
4
R6
0Ω
5
6
C3
7
8
P1 3
TP2
R7
1kΩ
R8
0Ω
P1 5
TP3
10
GND
VCC
VCC
GND
TXEN
RAMP
16
VIN–
VOUT–
15
GND
BYP
SDATA
NC
SLEEP
CLK
GND
QSOP
R10
0Ω
R12
0Ω
R14
0Ω
14
13
C12 0.1µF
VCC1
1
6
2
3
12
CABLE_OA
R16
4
11
B
SO
C7
P1 16
TOKO
R15
458PT-1087 0Ω
C13
0.1µF
TP_AGND1
AGND1
TP5
R13
1kΩ
C11
TP10
C6
P1 7
C10 0.1µF
17
LE
P1 6
TP4
18
VOUT+
DATEN
C9 0.1µF
19
VIN+
C5
R11
1kΩ
20
GND
AD8328
C4
R9
1kΩ
9
GND
VCC
C8
10µF
O
Figure 26. AD8328 Evaluation Board Schematic
Rev. A | Page 15 of 20
TP11
TP12
TP_VCC1
VCC1
P1 19
P1 20
P1 21
P1 22
P1 23
P1 24
P1 25
P1 26
P1 27
P1 28
P1 29
P1 30
P1 33
03158-026
T1
TE
R1
03158-030
03158-027
TE
AD8328
Figure 30. Internal Ground Plane
Figure 31. Secondary Side
03158-029
03158-032
O
Figure 28. Component Side Silkscreen
03158-031
03158-028
B
SO
LE
Figure 27. Primary Side
Figure 32. Secondary Side Silkscreen
Figure 29. Internal Power Plane
Rev. A | Page 16 of 20
AD8328
OUTLINE DIMENSIONS
0.60
MAX
4.00
BSC SQ
0.60
MAX
TOP
VIEW
1.00
0.85
0.80
SEATING
PLANE
0.75
0.55
0.35
11
10
6
2.25
2.10 SQ
1.95
5
0.25 MIN
0.30
0.23
0.18
0.05 MAX
0.02 NOM
0.20
REF
0.50
BSC
20 1
3.75
BCS SQ
0.80 MAX
0.65 TYP
12° MAX
16
15
TE
PIN 1
INDICATOR
PIN 1
INDICATOR
COPLANARITY
0.08
COMPLIANT TO JEDEC STANDARDS MO-220-VGGD-1
LE
Figure 33. 20-Lead Frame Chip Scale Package [LFCSP_VQ]
4 mm × 4 mm Body, Very Thin Quad
(CP-20-1)
Dimensions shown in millimeters
0.345
0.341
0.337
11
B
SO
20
1
0.158
0.154
0.150
10
0.244
0.236
0.228
PIN 1
0.065
0.049
0.010
0.004
0.069
0.053
0.025
BSC
COPLANARITY
0.004
0.012
0.008
SEATING
PLANE
0.010
0.006
8°
0°
O
COMPLIANT TO JEDEC STANDARDS MO-137-AD
Figure 34. 20-Lead Shrink Small Outline Package [QSOP]
(RQ-20)
Dimensions shown in inches
Rev. A | Page 17 of 20
0.050
0.016
AD8328
ORDERING GUIDE
Package Description
20-Lead QSOP
20-Lead QSOP
20-Lead QSOP
20-Lead QSOP
20-Lead LFCSP_VQ
20-Lead LFCSP_VQ
20-Lead LFCSP_VQ
20-Lead LFCSP_VQ
20-Lead LFCSP_VQ
20-Lead LFCSP_VQ
Evaluation Board
Evaluation Board
B
SO
LE
Z = Pb-free part.
O
1
Temperature Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package Option
RQ-20
RQ-20
RQ-20
RQ-20
CP-20-1
CP-20-1
CP-20-1
CP-20-1
CP-20-1
CP-20-1
TE
Model
AD8328ARQ
AD8328ARQ-REEL
AD8328ARQZ 1
AD8328ARQZ-REEL1
AD8328ACP
AD8328ACP-REEL
AD8328ACP-REEL7
AD8328ACPZ1
AD8328ACPZ-REEL1
AD8328ACPZ-REEL71
AD8328ACP-EVAL
AD8328ARQ-EVAL
Rev. A | Page 18 of 20
AD8328
O
B
SO
LE
TE
NOTES
Rev. A | Page 19 of 20
AD8328
O
B
SO
LE
TE
NOTES
© 2005 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
C03158–0–10/05(A)
Rev. A | Page 20 of 20
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement