High Speed Amplifiers – Video Tips and Tricks

High Speed Amplifiers – Video Tips and Tricks

Randy Stephens – Member Group Technical Staff

Agenda

• Video Overview– Analog Video – But Everything is Digital, Right?– Standards– Video Signal – What Does it Look Like?– Why Use a Filter?– Test Equipment

• Solving Common Video Issues– Measurement Discrepancies– Input Coupling – AC or DC– Output Coupling – AC or DC– Output Coupling – Frequency Tweaks– A Few Solutions – Think Outside the Box– Comparison to Passive Filters

• Questions

Analog Video is Everywhere

DVI/HDMI

Receiver

Tuner

VCR/DVDR

DDR SDRAM

Antenna/CableConnection

DTV, HDTV, CRT

AudioDAC Amp

AV Receiver

Digital AudioOutput Jack

CVBS

S-Video

ComponentYPbPr

1394Link &Phy

Media Interface Card

AudioA/D

TMDS341

Decoder / Video ADC

XDRMemory

Video Processor

High Performance Clocking

Encoder / Video DAC

DVD Player

DSC

PVR Set Top Box

ProjectorDigi-Cam

PC

PMP

Camera Phone

MediaInterface

Logic

A/V

In

pu

ts

A/V

Ou

tpu

ts

CVBS

S-Video

ComponentYPbPr

Overview – Resolution & Format

3DCombFilter

Tuner

Video Decoder(TVP5160)

Close Caption

V Chip

Tele Text

Micro-Processor

EEPROM

or Flash

Audio Processor

De-Interlacer

Class D Audio Amp

(TPA3100D2)

Scaler

A/D Converter

DVI/RxHDCP/HDMI LVDS Tx

TTL Output

OSDSDRAM

DVIPC-VGA

YPbPr

S Video

CVBS (Composite)

RF In

Audio

LVDS Rx

LCD Gate Driver

LCD Panel

Lamp

Back LightConverter

SDTVCVBS SDTVCVBS

SDTV/EDTV/

HDTV

Component SDTV/EDTV/

HDTV

ComponentSDTVS-Video SDTVS-Video

SD/ED/HDTVYCbCr

Digital RGB

SD/ED/HDTVYCbCr

Digital RGB

VGA/SVGA/XGA

SXGA/UXGA/QXGA

Analog RGB

VGA/SVGA/XGA

SXGA/UXGA/QXGA

Analog RGB

VGA/SVGAXGA

SXGA/UXGA/QXGA

Digital RGB

VGA/SVGAXGA

SXGA/UXGA/QXGA

Digital RGB

HDMIComponent New : Display Port

Common Video StandardsSDTV – Standard Definition Television:

– CVBS (Composite Video Baseband Signal) - SMPTE 170M– S-Video– 480i (NTSC) or 576i (PAL) – Interlaced

EDTV – Enhanced Definition Television:– 480p (NTSC) or 576p (PAL) – Progressive - SMPTE 293M

HDTV – High Definition Television:– 720p – Progressive - SMPTE 296M– 1080i – Interlaced - SMPTE 274M / ITU-R BT.709– 1080p – Progressive - SMPTE 274M / ITU-R BT.709

SMPTE = Society of Motion Picture and Television EngineersITU-R = International Telecommunication Union – Radiocommunication

ITU-R BT.1358

ITU-R BT.601 (Formerly CCIR)

Color Signal Flow

R

G

B

Gamma

R’

G’

B’

Y’NTSC/PAL/480ip/576ip = 0.299R’ + 0.587G’ + 0.114B’Y’720p/1080ip = 0.2126R’ + 0.7152G’ + 0.0722B’

P’B 480ip/576ip = 0.5 (B’ - Y’) / (1 – 0.114)

P’B 720p/1080ip = 0.5 (B’ - Y’) / (1 – 0.0722)

Luma (Y’)

Blue Color Difference (P’B)

P’R 480ip/576ip = 0.5 (R’ - Y’) / (1 – 0.299)

P’R 720p/1080ip = 0.5 (R’ - Y’) / (1 – 0.2126)

Red Color Difference (P’R)

U = 0.492 (B’ - Y’)V = 0.877 (R’ - Y’)

NTSC/PAL

NTSC = 3.58MHzPAL = 4.43MHz

SubcarrierModulator

P’B

P’R

ComponentOutput

Y’

S

I = Vcos 33° - Usin 33°Q = Vsin 33° + Ucos 33°

S-VideoOutput

CVBS

++

Chroma (C’)

Simplified Color Flow in Consumer Video System

Sou

rce

Video Signal Summary

SRMIN = 2 Pi Vpk (1Vpk) x 0.707 (-3dB) x 2 (to ensure no problems)

Format Standard / Display

Resolution Signal

Element

Analog Bandwidth

(MHz)

Ideal Min. SR

(V/us)

H. Sync Width (us)

Max. Video Amplitude

(Vpp) CVBS CVBS 4.2* ; <6 53 4.7 1.221

Y’/G’/B’/R’ 4.2* ; <6 53 4.7 1 S-Video

C’ 2.2 to 4.2 37 None 0.836 Y’/G’/B’/R’ 6*, <6.75 60 4.7 1

480i/525i (SD) P’B/P’R 3*, <3.375 30 None* (9.4) 0.7

Y’/G’/B’/R’ 12 106 2.33 1

NTSC

480p/525p (ED) P’B/P’R 6 53 None* (4.67) 0.7

CVBS CVBS 5*; <6 53 4.7 1.2335 Y’/G’/B’/R’ 5*; <6 53 4.7 1

S-Video C’ 3.2 to 5 44 None 0.885

Y’/G’/B’/R’ 6*, <6.75 60 4.7 1 576i/625i (SD)

P’B/P’R 3*, <3.375 30 None* (9.4) 0.7 Y’/G’/B’/R’ 12 106 2.33 1

PAL

576p/625p (ED) P’B/P’R 6 53 None* (4.67) 0.7

Y’/G’/B’/R’ 30 266 0.54/0.59 1 720p/1080i @ 60Hz

P’B/P’R 15 133 1.08/1.18 0.7 Y’/G’/B’/R’ 60 532 0.296 1

HDTV 1080p @ 60Hz

P’B/P’R 30 266 0.592 0.7 VGA 640 X 480 @ 60Hz R’G’B’ 12.6 112 3.8 1 or 0.7

SVGA 800 X 600 @ 60Hz R’G’B’ 20 178 3.2 1 or 0.7 XGA 1024 X 768 @ 60Hz R’G’B’ 32.5 289 2.092 1 or 0.7

SXGA 1280 X 1024 @ 60Hz R’G’B’ 54 480 1.037 1 or 0.7 UXGA 1600 X 1200 @ 60Hz R’G’B’ 81 719 1.185 1 or 0.7

UWXGA 1920 X 1200 @ 60Hz R’G’B’ 96.6 858 1.035 1 or 0.7

*Generally Used Limit, but not Required

CVBS Video Signal = S-Video Y’ + C’

NTSC 100 IRE = 714mV

40 IRE = 286mVGR

RD

BL

Wh Yel Cy Gr Mg Rd BL BLK

100

89

70

59

41

30

11

0

S-Video Y’100% Saturation

IRE Units

+0.714V

-0.286V

-40

-20

0

2010

100

80

60

40

+0.700V

-0.300V

NTSC PAL

82.8

NTSC S-Video C'100% Saturation

IRE Units

20

60

40

-60

0

-20

-40

117 117109.2 109.282.8

167.1°

0

283.5° 240.7° 60.7° 103.5°

347.1°

40

0°

0

0.7V

0.62V

0.49V

0.41V

0.29V

0.21V

0.08V0V

PAL 100 IRE = 700mV

40 IRE = 300mV

100% Saturation Color Bars Screen Shots

Screen Shots – NTSC & PAL

NTSC: S-Video Y’ C’CVBS

PAL: S-Video Y’ C’CVBS

Note : 100% Color Saturation causes CVBS Signal to be about 1.25Vpp75% Color Saturation causes CVBS Signal to be 1Vpp

10uS / Div10uS / Div

Screen Shots – 480i Component

480i Y’P’BP’R 480i G’B’R’10uS / Div 10uS / Div

Notes : 1) Maximum Voltage Swing is 1Vpp on Channels with Sync 2) HSync can also be found on Color Difference Signals

Screen Shots – 480p / 576p Component

480p Y’P’BP’R 576p Y’P’BP’R

4uS / Div 4uS / Div

Notes : 1) Maximum Voltage Swing is 1Vpp on Channels with Sync 2) HSync can also be found on Color Difference Signals

Screen Shots – 720p Component

720p @ 60Hz Y’P’BP’R

720p @ 60Hz G’B’R’

4uS / Div 4uS / Div

Note : Maximum Voltage Swing is 1Vpp on Channels with Sync

Screen Shots – 1080i / 1080p Component

4uS / Div 2uS / Div1080i @ 60Hz

Y’P’BP’R

1080p @ 60Hz Y’P’BP’R

Note : Maximum Voltage Swing is 1Vpp on Channels with Sync

Screen Shot – Computer Video (VGA)

1280 X 1024 @ 60Hz R’G’SB’ 1920 X 1440 @ 75Hz R’G’SB’2uS / Div 1uS / Div

Notes : 1) Maximum Voltage Swing is 1Vpp on Channels with Sync 2) HSync can also be found on All or None of these Signals

SDTV Video DAC

Every video DAC shows aliasing artifacts.

Vertical or diagonal lines appear throughout picture.

Remember this Signal Feeds into an ADC in modern designs -> Aliasing.

Why Filter DAC Output?Actual DVD Player Encoder (DAC) Output

-90

-80

-70

-60

-50

-40

-30

-20

000E+0 20E+6 40E+6 60E+6 80E+6 100E+6 120E+6Frequency

Ou

tpu

t -

dB

-90

-80

-70

-60

-50

-40

-30

-20

000E+0 50E+6 100E+6 150E+6 200E+6 250E+6 300E+6 350E+6 400E+6

Frequency

Ou

tpu

t -

dB

Baseband Baseband SignalSignal

Nyquist Nyquist Zone 2 & 3Zone 2 & 3

2Fs2Fs3Fs3Fs

4Fs4Fs 5Fs5Fs 6Fs 6Fs 7Fs7Fs 8Fs 8Fs 9Fs 9Fs 10Fs 10Fs 11Fs11Fs 12Fs12Fs 13Fs13Fs 14Fs14Fs

Nyquist Nyquist Zone 4 & 5Zone 4 & 5

Nyquist Nyquist Zone 6 & 7Zone 6 & 7 Nyquist Nyquist

Zone 8 & 9Zone 8 & 9

FsFs

FsFs 2Fs2Fs3Fs3Fs

4Fs4Fs

No DAC Filter Gives Poor Video

Buffer amp without filter: Video

display shows DAC image interference

Standard Video Test Patterns

Using DAC Filter Gives Good Video

THS7303 Buffer amp with filter: Video

display clean

Standard Video Test Patterns

Low Pass Filters : Part 1 - Amplitude

•VERY Hard to Achieve in Any System

•SYSTEM Level Response – Not just the Amplifier or Filter Alone

•Targeted for Broadcast Quality Systems (Many Systems in Series and the effects are additive)

•Consumer Video is More Relaxed !!!

•Most Standards Show Requirements

Example

ITU-R BT.601 (SDTV)

Standard Shows:

5th-Order Filter Responses - Amplitude

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

100E+3 1E+6 10E+6 100E+6Frequency - Hz

Ou

tpu

t -

dB

0.5dB 10MHz Chebyshev

8.5MHz Modified Butterworth

Ex: Low Pass Filters - Amplitude

5th-Order Filter Responses - Amplitude

-50

-40

-30

-20

-10

0

10

100E+3 1E+6 10E+6 100E+6Frequency - Hz

Ou

tpu

t -

dB



Look at a 5th-Order Filter Comparison:•Modified Butterworth at 8.5MHz•0.5-dB Chebyshev at 10MHz

Attenuation at 27-MHz :•Chebyshev = 57dB•Butterworth = 46dB

0.5dB Flatness Bandwidth :•Chebyshev = 10-MHz•Butterworth = 6-MHz

Low Pass Filters : Part 2 - Group Delay

ITU-R BT.601 (SDTV)

Standard Shows:

Do NOT Forget About Group Delay !!!

Group Delay is Defined as:

Change in Phase (Degrees)

360 X Change in Frequency (Hz)

5th-Order Filter Responses - Group Delay

20

40

60

80

100

120

140

160

180

100E+3 1E+6 10E+6 100E+6Frequency

Gro

up

De

lay

- n

s

0.5dB 10MHzChebyshev


Ex: Low Pass Filters – Group Delay

5th-Order Filter Responses - Phase

-405

-360

-315

-270

-225

-180

-135

-90

-45

0

45

100E+3 1E+6 10E+6 100E+6Frequency

Ph

ase

- D

egre

es

0.5dB 10MHzChebyshev

8.5MHz ModifiedButterworth

•Typically only Concerned with Group Delay Variation at a Specific Frequency (Relative to 100kHz typ)

•Absolute Value of Group Delay is Generally not a Concern - Except for Channel to Channel Timing Matching

Why is this Important ??? …...

Low Pass Filters – Pulse Response

Remember:Video Signal Amplitude = Amount of Color, Brightness, etc. to Display on the Screen

If the Signal Goes from say Black to White to Black (0V to 0.7V to 0V) in successive pixels, then overshoot and ringing must be avoided.

Otherwise smearing and other artifacts will be seen on the display.

5th-Order Filter Responses - Pulse Response

0.951

0.965

0.979

0.993

1.007

1.021

1.035

1.049

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time - us

Ou

tpu

t V

olt

ag

e



Input

Low Pass Filters – Pulse Response

5th-Order Filter Responses - Pulse Response

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time - us

Ou

tpu

t V

olt

ag

e 0.5dB 10MHz Chebyshev

8.5MHz Modified ButterworthInput

Rule of Thumb : The more variation in Group Delay, The more Overshoot and Ringing will Occur

1 IRE (~7mV) Settling Time: Chebyshev = 482nS Butterworth = 217nS

Current Consumer Integrated Filter ProductsAll Utilize Butterworth Filters

VideoVideoStandardStandard

Fix

ed

Fil

ter

SDTV :CVBS

S-Video480i / 576i

Sel

ecta

ble

LP

F

HDTV :1080p501080p60

HDTV : 720p1080i

1080p24/30

EDTV :480p576p

THS7303 / THS73533-Channels

9/16/35MHz FiltersI2C Control

THS73143-Channels

8.5MHz Filters

THS73133-Channels

8.5MHz FiltersI2C Control

THS73153-Channels

8.5MHz FiltersGain = 5.2V/V

Bypass Mode ≥150MHz

THS73183-Channels

20MHz Filters3.5mA Total

WCSP

THS73163-Channels

36MHz Filters

OPA360 / 611-Ch / 9MHz Filter

2V/V / 5.2V/V

THS73744-Channels

9.5MHz Filters

Test Equipment for Video - Standard Definition

• VM700T – “THE” SD Video Analyzer– NTSC and PAL– CVBS, S-Video, Component

Differential Gain and Phase

CVBS Video – Differential Gain and Phase

Differential Phase: dP• Change in Phase (Hue) of the color modulation

(Chroma) due to a change in brightness (Luma) amplitude

• Affects the actual color

• Consumer Products > 0.5%

• Professional Products target < 0.05%

Differential Gain: dG• Change in Amplitude (Saturation) of the color

modulation (Chroma) due to a change in brightness (Luma) amplitude

• Affects color Saturation

• Consumer Products > 0.5°

• Professional Products target < 0.05°

VM700T Tests

Signal to Noise Ratio MeasurementK2T Pulse Test

Measures Potential Issues Before and After a Pulse

VM700T Tests

Short Time Distortion TestMeasures Potential Overshoot and Settling

Time Issues

Horizontal Sync + Color Burst TimingMeasures H-Sync Amplitude, Time, rise/fall

times, color burst amplitude and duration

VM700T Tests

Chroma and Luma Gain DelayMeasures Both Luma and Chroma Signals

for Gain Errors and Relative Timing

Note – Frequency Responses Can also be done, but a Network Analyzer is Significantly Better than Video Analyzers

VM5000 Testing

•VM5000 – Just About Everything Else–NTSC and PAL Component Video (SD/ED/HD)–RGB, GBR–Recently Replaced by VM6000

–Test Results are Not Graphical (like VM700T)–Test Results are Numbers Only–Examples:

•SNR = 70.1dB•Y to Pb, Y to Pr, Pb to Pr Timing Error = 1.1ns, 1.1ns, 0.5ns•Color Bar Amplitude : White = 698mV, Yellow = 647mV, Cyan = 549mV, Green = 498mV….. •Etc…

VM5000 Test

Ex: Short Time Distortion Test

Osc

illosc

ope

Porti

on

of th

e D

ispl

ay

Vide

o M

easu

rem

ent

Porti

on o

f the

Dis

play

Measurement Issues• Key Issue – Differences Between Bench Testing and

Customer Product Testing– Bench Measurements

• Uses Video Signal Generators (Ex: Tektronix TG700, Quantum Data 802R, etc…)

• Many VM700T / VM5000 Tests can Calibrate Out the Video Generator + Cables + …

• VM700T / VM5000 Measurement Results with Amplifier in the Signal Chain shows “Only” Amplifier Impact on the Video Signal

Calibrate Path MeasurementVideo Generator

DUT / EVM

Measurement Issues• Key Issue – Differences Between Bench Testing and

Customer Product Testing– Customer System Measurements

• Uses Video Encoder/DAC/SOC as Signal Source

– Uses SOC/Encoder/DAC On-Chip Signals, or

– DVD/Sat/Cable/Ext. Input/etc. Signal Source (+ Decoding + Processing + Encoder)

• Little or No Calibration done

– Customer Shows Test Results of the System which Shows Possible Performance Issues

Measurement

Source(Cable/Sat/DVD/Gen)

System

Measurement Issues

• How to Resolve Issue:– Measure the Signal Before the Amplifier and then

After the Amplifier– Possible Solutions:

• Many SOC/Encoders/DAC have some capability to tweak the processing. Usually a Register Setting.

• If a Front-End Decoder is being used, maybe a tweak to a Register on the Decoder can help.

• If all else fails, Maybe some Tweaks to the Amplifier Can Help the Customer….

Resolving Issues – Common Solutions

1) Modify the Interface Between the DAC output and the Amplifier.

2) Modify the Output Interface to the Line

5

8

7

6

VS+ GND

CH.2 IN

CH.3 IN

CH.1 IN

CH.3 OUT

CH.2 OUT

CH.1 OUT

DAC / Encoder

+3.3V

1

2

3

4

CVBS

Y’

C’

CVBSOut

75

Y’Out

75

C’Out75+3.3V

75

75

SDTV CVBS

S-Video Y’S-Video C’480i/576iY’P’BP’RG’B’R’ 75

S-Video

R

R

R

THS7314

Video Amplifier Signal Biasing – Single Supply

DC Modes

AC Modes

DC

DC+SHIFT

ACSTC

ACBIAS

1.65V3.3V

AC BIAS

AC Sync Tip Clamp

250mV0V

DC + Level Shift

250mV0V

DC

0V

Make Sure Input Signal is >50mV or Output Clipping May Occur

Allows Input Signal to go to 0V without Output Clipping Problems

3.3V

• Input Tweaks:– Sometimes the Interface is Wrong

• Current Sinking DAC is DC coupled to the Amplifier– Problem is DC Level is Typically too High for DC Coupling to Occur

Resulting in Saturation of the Amplifier– Solution – AC Couple between the DAC and Amplifier

» Utilize Sync Tip Clamp Function of the Amplifier for Video Signals with Bottom-Level Sync (ex: CVBS, S-Video Y, Comp. Y)

» Utilize Bias for all other signals (ex: S-Video C, Comp. Pb and Pr)

Resolving Issues – Input Tweak

5

8

7

6

VS+ GND

CH.2 IN

CH.3 IN

CH.1 IN

CH.3 OUT

CH.2 OUT

CH.1 OUT

DAC / Encoder

+3.3V

1

2

3

4

Y’

P’B

P’R

+3.3V

SDTV480i/576iY’P’BP’RG’B’R’

THS7314

0.1uF

22uF

+

R

+3.3V

R

+3.3V

R

+3.3V

0.1uF

0.1uF

0.1uF

3.01M

+3.3V

3.01M

+3.3V

Bias

STC

Resolving Issues – Input Tweak• Input Tweaks:

– DC Coupling is Generally Best• Used with Current Source DAC’s with Output Voltage of Sync Signal

Approaching 0V (Most Common)– Ideal for Amplifiers with Internal Level Shift to Prevent Output Sat.

• AC Coupling can also Work, but DC Coupling is Generally Better– No AC Coupled Tilt / Droop– No “Abberations” due to Sync Tip Clamp Function (Never Perfect)

• Even if DC Coupling is Utilized, Tweaking the DAC Termination Resistor (and/or DAC Bias Setting Resistor) may Improve Performance

5

8

7

6

VS+ GND

CH.2 IN

CH.3 IN

CH.1 IN

CH.3 OUT

CH.2 OUT

CH.1 OUT

DAC / Encoder

+3.3V

1

2

3

4

CVBS

Y’

C’

+3.3V

SDTV CVBS

S-Video Y’S-Video C’480i/576iY’P’BP’RG’B’R’

R

R

R

THS7314

DC Coupling

Output Coupling – AC or DC ???• AC Coupled

– Legacy Way of Output Coupling– Universally Acceptable– Meets All Specifications for DC levels on Output– Possible Issues:

• Line Tilt or Droop • Large Capacitor (330uF to 470uF typ) = Increased Cost and

PCB Size

330uF

0.1uF

+

5

8

7

6

VS+ GND

CH.2 IN

CH.3 IN

CH.1 IN

CH.3 OUT

CH.2 OUT

CH.1 OUT

DAC / Encoder

+3.3V

1

2

3

4

CVBS

Y’

C’

CVBSOut

75

Y’Out

75

C’Out75

+3V to 5V

75

75

SDTV CVBS


S-Video

R

R

R

THS7314

330uF+

0.1uF

22uF

+

Output Coupling – AC or DC ???• DC Coupled

– “New” Way of Coupling– No Capacitor = Lower Cost and Smaller PCB Area– No Line Tilt or Droop– Possible Issues:

• Amplifier Offsets Cause a Current Flow.

• EIA-770 Specification Requires Backporch Voltage = 0V +/- 1V at Receiver (0V +/- 2V at Amplifier Output).

• Japan Specification EIAJ CP-1203 Requires Output Voltage = 0V +/- 0.1V with No Video Signal.

5

8

7

6

VS+ GND

CH.2 IN

CH.3 IN

CH.1 IN

CH.3 OUT

CH.2 OUT

CH.1 OUT

DAC / Encoder

+3.3V

1

2

3

4

CVBS

Y’

C’

CVBSOut

75

Y’Out

75

C’Out75+3.3V

75

75

SDTV CVBS


S-Video

R

R

R

THS7314

0V ± 1V

0.7V ± 1V

-0.3V ± 1V

Output Coupling - AC with SAG Correction

To See How it Works, Break it up into Low-Frequency and High-Frequency Operation:

DC : Zc = infinity Amp Gain = 1 + [(R1 + RF) / RG]

High Freq: Zc = 0 Amp Gain = 1+[((R1||R2) + RF) / RG) = 2 V/V (6 dB)

Choosing Proper Component Values will result in the Amplifier Gain Increasing as the Capacitors’ Impedance Increases (which would normally result in Video Output amplitude reduction).

Thus the effects cancel each other out resulting in Low-Frequency Extension while using Much Smaller Capacitors.

Out

SAG

47uF

33uF75

75

VideoOut

+

-

RG RF

R1

R2

Input

-20

-15

-10

-5

0

5

10

15

20

1 10 100Frequency - Hz

Gai

n -

dB

47uF Only

Amp Gain

330uF

-20

-15

-10

-5

0

5

10

15

20


Gai

n -

dB

Amp Gain + 47uF = Same as 330uF + 6dB

AC-Bypass Video Output Responses

-18

-15

-12

-9

-6

-3

0

3


Ou

tpu

t - d

B

47uF

100uF

330uF

47uF + 33uF SAG

Out

SAG

47uF

33uF75

75

VideoOut

+

-

RG RF

R1

R2

Input

Measurement Point

AC-Bypass Amplifer Responses

0

3

6

9

12

15


Ou

tpu

t - d

B

AmplifierOutput

with SAG

SAG FeedbackPoint

Traditional AmplifierOutput (330uF)

SAG = 47uF + 33UF

Amp Output Measurement Point

SA

G F

eedb

ack

Mea

sure

men

t Poi

nt

SAG Correction – Real Data

Resolving Issues – Output Tweak

• Modify the Source Termination Resistor

5

8

7

6

VS+ GND

CH.2 IN

CH.3 IN

CH.1 IN

CH.3 OUT

CH.2 OUT

CH.1 OUT1

2

3

4

CVBSOut

75

Y’Out

75

C’Out75+3.3V

75

75 75

S-Video

THS7314

5.07575

75

IN

OUT

V

V

SOURCENTERMINATIO

NTERMINATIO

IN

OUT

RR

R

V

V

Traditional :

Ex: If Gain Needs to be Increased, Reducing Source Resistor Increases System Gain.

While not an Ideal Solution, Testing (K2T Pulse) Shows that Reflections are not an Issue and all Other Tests Pass


• Frequency Compensation

75

75+

-

R C

VOUT

VIN )275(2

)75(1

RsC

RsC

V

V

IN

OUT

Should Not Let R be less than 25-ohms as this can cause Instability to the Amplifier

• Capacitive Load of Cable will Appear Directly on the Amplifier Output with no R.


75

75+

-

R C

VOUT

VIN

C = 180pF

R = Variable


75

75+

-

R C

VOUT

VIN

C = Variable

R = 75

Resolving Issues – Output Tweak• THS7314 Bench Testing

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

1E+6 10E+6Frequency

Ou

tpu

t -

dB

No Compensation

120pF

R = 75-Ohms

180pF

220pF

270pF

75

75+

-

R C

VOUT

VIN

Drawback – An Increase in Group Delay Variation

Configuration Tweak – CVBS From S-Video

Scenario: DAC only has S-Video Y’ and C’ Outputs. Need CVBS Output.Solution: THS7314 – Low Cost 3-Channel SDTV Amplifier

330uF

0.1uF

+

5

8

7

6

VS+ GND

CH.2 IN

CH.3 IN

CH.1 IN

CH.3 OUT

CH.2 OUT

CH.1 OUT

DA

C /

En

cod

er

+VD

1

2

3

4

Y’

C’

CVBSOut

75

Y’Out

75

C’Out75

+VA

75

75 75

S-VideoOPTIONAL - 1

RDAC

THS7314

330uF+

0.1uF

10uF

+

0.1uF

0.1uF

+VA

RPRDAC

OPTIONAL - 2

150

150

0.1uF

R C

Optional - 3

• Optional – 1 : Not Required. Only needed if DAC voltages are above 1.4V Max– Note : RP is not critical. Allowable value is from 3.1Mohm to 5.6Mohm – Sets DC input

Bias operating point and ultimately output DC operating point.• Optional – 2 : Not Required for SMPTE/IEC/EIA standards. Can be used if

desired or to meet EIAJ CP1203 Specification• Optional – 3 : Not Required. Use to get a boost in the upper frequency area due

to 2 X filters for CVBS signal. Good starting point is R = 150 and C = 68 pF

Configuration Tweak - SCARTScenario: System Needs to Support SCART output – Cost IssuesSolution: THS7374 + Low Cost Switches

11

14

13

12

CH.4 IN CH.4 OUT

CH.2 IN

CH.3 IN

CH.1 IN

CH.3 OUT

CH.2 OUT

CH.1 OUT1

2

3

4

R’

G’

TV CVBS / Sync Out

75

75

75

+3Vto 5V

Vid

eo

SO

C /

DA

C R1

R1

THS7374TV R’ Out

TV G’ Out

B’

5

6

7

10

9

8NC

BYPASSDISABLE

VS+GND

NC

R1

75

TV B’ Out

To GPIOController Or GND

TVSCART330uF *

+

330uF *

330uF *

330uF *

17

1918

20

13

1514

16

9

1110

12

5

76

8

1

32

4

17

1918

20

13

1514

16

9

1110

12

5

76

8

1

32

4

21*Optional

470

Audio Left Out 47uF

470

Audio Right Out 47uF

N/C

N/C

N/C

N/C

N/C

75VCR CVBS /

Sync Out330uF *+

VCR SCART

N/C

N/C

N/C

N/C

N/C

75N/C

+12V

ABC

INHVEEVSS CD4053

CVBS /Sync

R1

Au

dio

Left

R2

Right

R2

22k

22k100

47uF

100

47uF

100k

100k

470

Audio Left Out 47uF

470

Audio Right Out 47uF

AmpLPFBias

0.1uF

220

75

10k

Fast BlankRGB / CVBS(From GPIO)

470

10k

1.5k

+12V

1.8k

Stby/TV(From GPIO)

10k16:9 / 4:3

(From GPIO)

22k

Audio Left In

Audio Right In

VCR Mode

VCR CVBS In

+Vbias

AmpLPFBias

21

NE5532DRV600DRV601

SOCPCM17xx

Note:

This Example Does Not Provide ALL SCART features, but can work for many systems

Other circuit configurations available that include more functions.

Passive vs. Active FiltersActive Filter Passive Filter

Cost Very Low to High Very Low

Tolerance Good due to Element Matching

Inductor ±15% to ±20%

Capacitor ±10% to ±15%

Corner Frequency +/- 10% typ+/-15% to +/-25%

(Depends on Component Tolerances)

Temperature Tolerance

Good due to Matching and Low Coefficient Elements Poor

PCB Area Low to Mid Low to High

Impedance Variations

Small Input and Output Impedance Variations

Significant Input and Output Variations

Misc. Info Can Save System PowerInductors are Magnetic

Components

Active Filters Save Power ??? Yes they Can

Video DAC / Encoder

75

3V

VIDEO OUT

75

26.6 mA

Active Current ≈ Quiescent Current ≈ 26.6 mA

1V

1V

26.6 mA

No Buffer

With Buffer

DAC Quiescent Current = 2mA/Ch → 6.6 mW/Ch

DAC Quiescent Current = 26.6mA/Ch → 88 mW/Ch

3.3V 3.3V

3.3V

Video DAC / Encoder

499

VIDEO OUT

75

75

x2

2 mA

2 mA

1.5 mA

2V1V

13.3 mA

1V

Active Current ≈ 14.5mA (48mW)

Real Video Signals Result in Buffer current of about

7mA RMS → System Savings of ≥60mW/Ch

DAC Quiescent Current with ~1.24Vpp (100% CVBS) = 33mA/Ch → 109 mW/Ch

DAC Quiescent Current with ~1.24Vpp = 2.5mA/Ch → 8.3mW/Ch

Passive Filter Monte Carlo Analysis

DAC

75 150pF

2.2uH 2.2uH

75150pF470pF

Example: 5-Pole 8.5MHz Butterworth Passive Filter

Monte Carlo Anaylsis

Inductors +/-15%

Capacitors +/-10%

Resistors +/-1%

Amplitude Variations

Group Delay Variations

Passive Filter Monte Carlo Analysis

DAC

75 150pF

2.2uH 2.2uH

75150pF470pF

Example: 5-Pole 8.5MHz Butterworth Passive Filter

Monte Carlo Anaylsis

Inductors +/-15%

Capacitors +/-10%

Resistors +/-1%

Input and Output Impedance Variations

Unit Step Response Variations

Questions?

Documents

High Speed Amplifiers – Video Tips and Tricks