AN57 - Video Circuit Collection - Analog Devices

1 Application Note 57AN57-1an57faJanuary 1994, LT, LTC and LTM are registered trademarks of linear Technology Corporation. All other trademarks are the property of their respective Circuit CollectionJon Munson and Frank CoxINTRODUCTIONEven in a time of rapidly advancing digital image process-ing, Analog Video signal processing still remains eminently viable. The Video A/D converters need a supply of properly amplifi ed, limited, DC restored, clamped, clipped, con-toured, multiplexed, faded and fi ltered Analog Video before they can accomplish anything. After the digital magic is performed, there is usually more amplifying and fi ltering to do as an adjunct to the D/A conversion process, not to mention all those pesky cables to drive. The Analog way is often the most expedient and effi cient, and you don t have to write all that foregoing is only partly in jest. The experienced engineer will use whatever method will properly get the job done; Analog , digital or magic (more realistically, a combination of all three).

2 Presented here is a Collection of Analog Video circuits that have proven themselves INDEXI. Video Amplifi er Selection Guide .. 2II. Video Cable Drivers .. 3 AC-Coupled Video Drivers .. 3 DC-Coupled Video Drivers .. 4 Clamped AC-Input Video Cable Driver .. 5 Twisted-Pair Video Driver and Receiver .. 5 III. Video Processing Circuits .. 6 ADC Driver .. 6 Video Fader .. 7 Color Matrix Conversion .. 7 Video Inversion .. 10 Graphics Overlay Adder .. 10 Variable Gain Amplifi er .. 12 Black Clamp .. 12 Video Limiter .. 13 Circuit for Gamma Correction.

3 14 LT1228 Sync Summer .. 16IV. Multiplexer Circuits .. 17 Integrated Three-Channel Output Multiplexer .. 17 Integrated Three-Channel Input Multiplexer .. 18 Forming RGB Multiplexers from Triple Amplifi ers .. 20 Stepped Gain Amplifi er Using the LT1204 .. 21 LT1204 Amplifi er/Multiplexer Sends Video Over Long Twisted Pair .. 21 Fast Differential Multiplexer .. 22 Application Note 57AN57-2an57faVideo Amplifi er Selection GuidePARTGBW (MHz)CONFIGURATIONCOMMENTSLT65531200 (A = 2)TA = 2 (Fixed), 6ns Settling TimeLT65551200 (A = 2)T2:1 MUX, A = 2 (Fixed)LT12261000 (AV 25) S400V/ s SR, Good DC SpecsLT65571000 (A = 2)TA = 2 (Fixed), Automatic Bias for Single SupplyLT6554650 (A = 1)TA = 1 (Fixed), 6ns Settling TimeLT6556650 (A = 1)T2:1 MUX, A = 1 (Fixed)LT1222500 (AV 10)S12-Bit AccurateLT1395/LT1396/LT1397400S, D, QCFA, DG = , DP = , Flat to 100 MHzLT1818/LT1819400S, D900V/ s SR, DG = , DP = (AV 5)SLow Voltage, 50mA OutputLT1194350 (AV = 10)SDifferential Input, Low Voltage, Fixed Gain of 10LT6559300 TCFA, Independant Enable Controls, Low CostLT1398/LT1399300D, TCFA, Independant Enable ControlsLT1675-1/LT1675250 (A = 2)S, T2.

4 1 MUX, A = 2 (Fixed)LT1815/LT1816/LT1817220S, D, Q750V/ s SR, DG = , DP = , DCFA, Adjustable Speed and PowerLT1809/LT1810180S, DLow Voltage, Rail-to-Rail Input and OutputLT1203/LT1205170D, QMUX, 25ns Switching, DG = , DP = LT1193160 (AV 2)SLow Voltage, Differential Input, Adjustable Gain, 50mA OutputLT1221150 (AV 4)S250V/ s SR, 12-Bit AccurateLT1227140 SCFA, 1100V/ s SR, DG = , DP = , ShutdownLT1259/LT1260130D, TRGB CFA, Flat to 30 MHz, DG = , DP = , ShutdownLT6550/LT6551110 (A = 2)T, QLow Voltage, Single Supply, A = 2 (Fixed)LT1223100 SCFA, 12-Bit Accurate, Shutdown, 1300V/ s SR, Good DC Specs, DG = , DP = LT1229/LT1230100D, QCFA, 1000V/ s SR, DG = , DP = LT1252100 SCFA, DG = , DP = , Low CostLT1812100 SLow Power, 200V/ s SRLT6205/LT6206/LT6207100S, D, Q3V Single SupplyLT119190 SLow Voltage, 50mA OutputLT1253/LT125490D, QCFA, DG = , DP = , Flat to 30 MHz, , QLow Power, 200V/ s SRLT122880 (gm = ) STransconductance Amp + CFA, Extremely VersatileLT655275 (AV 2)SDifferential Input, Low Power, Low VoltageLT120470 SCFA, 4-Input Video MUX Amp, 1000V/ s SR, Superior IsolationV.

5 Misapplications of CFAs .. 23VI. Appendices Video Circuits from linear Technology Magazine .. 24 A. Temperature-Compensated, Voltage-Controlled Gain Amplifi er Using the LT1228 .. 24 B. Optimizing a Video Gain-Control Stage Using the LT1228 .. 26 C. Using a Fast Analog Multiplexer to Switch Video Signals for NTSC Picture-in-Picture Displays .. 30 Application Note 57AN57-3an57fa10kM4M2M1P1P2P48910123 VOUTf 3dB = 27 MHzRL = 75 220 F47 F47 FVIN5V645AN57 F017LT1995+++75 Figure 1. Single Supply Video Line DriverKey to Abbreviations:CFA = Current Feedback Amplifi erDG = Differential GainDP = Differential PhaseMUX = MultiplexerSR = Slew RateNote:Differential gain and phase is measured with a 150 load, except for the LT1203/LT1205 in which case the load is 1000 .S = SingleD = DualQ = QuadT = TriplePARTGBW (MHz)CONFIGURATIONCOMMENTSLT1363/LT1364/ LT136570S, D, Q1000V/ s SR, IS = per Amp, Good DC SpecsLT120660S250mA Output Current CFA, 600V/ s SR, ShutdownLT118750 (AV 2)SDifferential Input, Low PowerLT119050 SLow VoltageLT1360/LT1361/LT136250S, D, Q600V/ s SR, IS = 5mA per Amp, Good DC SpecsLT1208/LT120945D, Q400V/ s SRLT122045S250V/ s, Good DC Specs, 12-Bit AccurateLT122445S400V/ s SRLT118935 (AV 10)SDifferential Input, Low Power, DecompensatedLT199532 (A = 1)

6 SInternal Resistor ArrayLT1213/LT121428D, QSingle Supply, Excellent DC SpecsLT1358/LT135925D, Q600V/ s SR, IS = per Amp, Good DC SpecsLT1215/LT121623D, QSingle Supply, Excellent DC SpecsLT1211/LT121214D, QSingle Supply, Excellent DC SpecsLT1355/LT135612D, Q400V/ s SR, IS = per Amp, Good DC SpecsLT1200/LT1201/LT120211S, D, QIS = 1mA per Amp, Good DC SpecsLT121710 SCFA, IS = 1mA, ShutdownVIDEO CABLE DRIVERSAC-Coupled Video DriversWhen AC-coupling Video , the waveform dynamics change with respect to the bias point of the amplifi er according to the scene brightness of the Video stream. In the worst case, 1VP-P Video (composite or Luminance + Sync in Y/C or YPBPR format) can exhibit a varying DC content of , with the dynamic requirement being + about the nominal bias level. When this range is ampli-fi ed by two to properly drive a back-terminated cable, the amplifi er output must be able to swing , thus a 5V supply is generally required in such circuits, provided the amplifi er output saturation voltages are suffi ciently small.

7 The following circuits show various realizations of AC-coupled Video cable 1 shows the LT1995 as a single-channel driver. All the gain-setting resistors are provided on-chip to minimize part 2 shows an LT6551 quad amplifi er driving two sets of S- Video (Y/C format) output cables from a single Y/C source. Internal gain-setting resistors within the LT6551 reduce 3 shows the LT6553 ultra-high-speed triple Video driver confi gured for single-supply AC-coupled operation. This part is ideal for HD or high-resolution workstation ap-plications that demand high bandwidth and fast settling. The amplifi er gains are factory-set to two by internal Note 57AN57-4an57fa+ OA450 450 + OA450 450 + OA450 450 AN57 F02+ OA450 450 1234510987675 1k4k470 F75 75 1k4k470 FVCC = 5 VVCC = 5 VLUMINANCECHROMA75 75 75 OUT2 OUT1S-VIDEOCONNECTORS-VIDEOCONNECTORLUMI NANCEOUT1 LUMINANCEOUT2 CHROMAOUT1 CHROMAOUT2LT6551+7V TO 75 75 1/3 F*220 F** F03**AVX 12066D226 MATSANYO 6 TPB220 MLAGNDF igure 2.

8 S- Video SplitterFigure 3. Single Supply Confi guration, One Channel ShownDC-Coupled Video DriversThe following circuits show various DC-coupled Video drivers. In DC-coupled systems, the Video swings are fi xed in relation to the supplies used, so back-terminated cable-drivers need only provide 2V of output range when optimally biased. In most cases, this permits operation on lower power supply potential(s) than with AC-coupling (unclamped mode). Generally DC-coupled circuits use split supply potentials since the waveforms often include or pass through zero volts. For single supply operation, the inputs need to have an appropriate offset applied to preserve linear amplifi er operation over the intended signal systems that lack an available negative supply, the LT1983-3 Circuit shown in Figure 5 can be used to easily produce a local-use 3V that can simplify an overall cable-driving solu-tion, eliminating large output electrolytics, for 6 shows a typical 3-channel Video cable driver using an LT6553.

9 This part includes on-chip gain-setting resis-tors and fl ow-through layout that is optimal for HD and RGB wideband Video applications. This Circuit is a good The LT6557 400 MHz triple Video driver is specifi cally de-signed to operate in 5V single supply AC-coupled applications as shown in Figure 4. The input biasing circuitry is contained on-chip for minimal external component count. A single resistor programs the biasing level of all three +VOUTGNDC LTC1983-3 VIN3V TO = 3 VIOUT = UP TO 100mACOUT10 FCIN10 FCFLY1 FOFF ONCFLY: TAIYO YUDEN LMK212BJ105 CIN, COUT: TAIYO YUDEN JMK316BJ106 MLAN57 F051525V161 3V 5V +14370 370 75 + 12370 370 75 + 1095V11 3V13876543370 370 75 RINGINBIN75 75 75 75 75 75 LT6553AN57 F06 Figure 5. 3V at 100mA DC/DC ConverterFigure 6. Triple Video Line Driver+ 500 IN RGNDENIN ROUT RV+V+ RV+ GV+ BBCVLT6557 GND R75 75 412 5V5V5V5 VAN57 F0410 F500 75 220 F+ 500 IN GIN GOUT GGND G75 75 10 F500 75 220 F+ 500 IN BIN BOUT BGND B75 75 10 F500 75 220 FFigure 4.

10 400 MHz, AC-Coupled, 5V Single Supply Video DriverApplication Note 57AN57-5an57facandidate for the LT1983-3 power solution in systems that have only 5V 7 shows the LT6551 driving four cables and op-erating from just The inputs need to have signals centered at for best linearity. This application would be typical of standard-defi nition studio-environment signal distribution equipment (RGBS format).Figure 8 shows a simple Video splitter application using an LT6206. Both amplifi ers are driven by the input signal and each is confi gured for a gain of two, one for driving each output cable. Here again careful input biasing is required (or a negative supply as suggested previously).Figure 9 shows a means of providing a multidrop tap am-plifi er using the differential input LT6552. This Circuit taps the cable (loop-through confi guration) at a high impedance and then amplifi es the signal for transmission to a stan-dard 75 Video load (a display monitor for example).