AN-1618 LMH1980 Evaluation Board Instruction Manual User's Guide 1 General Description

AN-1618 LMH1980 Evaluation Board Instruction Manual User's Guide 1 General Description
User's Guide
SNLA096B – July 2007 – Revised April 2013
AN-1618 LMH1980 Evaluation Board Instruction Manual
1
General Description
The LMH1980 evaluation board can be used to test the LMH1980 auto-detecting SD/HD/PC video sync
separator and as a reference for printed circuit board (PCB) layout design.
2
Power Supply
The board can be powered using a clean supply voltage, between 3.3 V and 5.0 V, connected to VCC (J1)
and GND (J2) via banana jacks. The LMH1980 supply voltage should be regulated within ±10% variation
of the voltage range and should not be shared directly with other digital circuitry.
3
Video Input
A clean, 75 Ω video source can be connected to the board via the video input BNC (J3), which is
terminated with a 75 Ω load resistor on the board. Because the input can accept either SD or HD video
inputs, a switch-controlled chroma filter, consisting of R9 and C2, is provided on the board. If a PC video
input is used, C2 should be removed to disable the chroma filter.
4
Input Filtering
When an HD tri-level sync input signal is applied, the HD flag (pin 5) will output logic low (following a brief
delay for auto format detection) and Q1 will turn off, disabling the SD video chroma filter. When an SD bilevel sync input signal (NTSC/PAL) is applied, HD will output logic high and Q1 will turn on, enabling the
chroma filter. When enabled, this low-pass filter will attenuate any chroma subcarrier amplitude extending
near the sync pulse so it does not interfere with sync separation. The filter will also improve the input
signal-to-noise ratio. The filter cutoff frequency (fCO), set by R9 and C2, can be changed depending on the
attenuation needed for the SD video signal. Keep in mind that as fCO decreases, the LMH1980 output
propagation delays increase, which will affect the timing relationship between the sync and video signals.
Important: If fCO is set too low and HD video is applied, the filter can severely roll off and attenuate the
input's high-bandwidth tri-level sync pulses such that the LMH1980 cannot detect a valid HD input signal.
If the LMH1980 cannot detect a valid HD input, then the HD flag will never change from logic high to low
and the switch-controlled filter will never be disabled via Q1. In other words, fCO should not be set so low
that the filter impairs the LMH1980's ability to detect a valid HD input. The values of R9 and C2 shown in
Figure 1 give fCO = 2.79 MHz (about -4 dB at 3.58 MHz NTSC subcarrier frequency) and does not impair
auto format detection.
If a PC video input is to be used, C2 should be removed to disable chroma filtering. This is necessary
because HD will output logic high (as in the SD video input case) and enable the filter. A chroma filter
could severely band-limit a high-bandwidth PC video signal, which could roll-off and attenuate the sync
pulses such that the LMH1980 cannot detect a valid input signal.
If some high-frequency noise filtering is needed for all video signal inputs, a small capacitor may be
optionally placed at C1. The RC filter formed by R9 and C1 is always connected regardless of Q1’s switch
state. When Q1 is turned on, C1 and C2 will be connected in parallel (C1+C2).
5
Test Points
Test points and ground points are provided to measure the input and output signals using 10 MΩ
oscilloscope probes with 10 pF load capacitance.
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SNLA096B – July 2007 – Revised April 2013
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AN-1618 LMH1980 Evaluation Board Instruction Manual
Copyright © 2007–2013, Texas Instruments Incorporated
1
Board Schematic
6
www.ti.com
Board Schematic
J1
VCC
TP8
VCC
J2
GND
REXT
1
1
1
10 k:
1%
1
1
U2
R2
TP7
GND
C4
10 PF
2
GND
C3
0.1 PF 3
+
R9
100:
C5
0.1 PF
4
VIN
R1
75:
C1
*OPT
C2
560 pF
Q1
MMBT3904
R3
10 k:
5
BPOUT
LMH1980
VCC
BNC
J3
OEOUT
HD
CSOUT
VSOUT
HSOUT
10
R4
100:
9
R5
100:
8
R6
100:
7
R7
100:
6
R8
100:
2
2
TP3
Burst/Back
Porch Output
2
TP4
Composite
Sync Output
2
TP5
Vertical Sync
Output
2
TP6
Horizontal
Sync Output
1
1
1
1
R10
100:
1
2
TP2
Odd/Even
Field Output
1
TP1
HD Detect Flag Output
Figure 1. LMH1980 Eval Board 870013153–200 Rev A
7
Board Layout
Figure 2. Top Side
2
AN-1618 LMH1980 Evaluation Board Instruction Manual
Copyright © 2007–2013, Texas Instruments Incorporated
SNLA096B – July 2007 – Revised April 2013
Submit Documentation Feedback
Bill of Materials
www.ti.com
Figure 3. Bottom Side
8
Bill of Materials
Item
Part Number
1
LMH1980
2
MMBT3904
3
Part Description
Qty
Ref Designator
1
U2
NPN Transistor, SOT-23
1
Q1
Digi-key PCC1762CTND
Capacitor Ceramic 0.1 μF, X7R, 0603, 16V
1
C3
4
Digi-key PCC1828CTND
Capacitor Ceramic 0.1 μF, X7R, 0805, 25V
1
C5
5
Digi-key PCC561BNCTND
Capacitor Ceramic 560 pF, NPO, 0805, 50V
1
C2
6
Digi-key PCC561BNCTND
Capacitor Ceramic 560 pF, NPO, 0805, 50V
1
C4
7
Digi-key P10.0KHCT-ND Resistor, 10 kΩ, 1%, 1/10W 0603
1
R2
8
Digi-key P10.0KCCT-ND Resistor, 10 kΩ, 1%, 1/8W 0805
1
R3
9
Digi-key P75.0CCT-ND
Resistor, 75Ω, 1%, 1/8W 0805
1
R1
10
Digi-key P100CCT-ND
Resistor, 100Ω, 1%, 1/8W 0805
7
R4, R5, R6, R7, R8,
R9, R10
11
MOUSER 16BJ381
Banana Jack, Red
1
J1
12
12 MOUSER 16BJ382
Banana Jack, Black
1
J2
13
Newark 22C4690
EDGE-MOUNT BNC
1
J3
14
Digi-key 5001K-ND
Test Point, Black
1
TP7
15
Digi-key 5000K-ND
Test Point, Red
1
TP8
16
Digi-key 5001K-ND,
5004-ND
Test Points, Black and Yellow
6
TP1, TP2, TP3,
TP4, TP5, TP6
SNLA096B – July 2007 – Revised April 2013
Submit Documentation Feedback
Remark
Must be 1% or
better
Trompeter
UCBJE20-1
Use black for
GND points
AN-1618 LMH1980 Evaluation Board Instruction Manual
Copyright © 2007–2013, Texas Instruments Incorporated
3
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