Using the GT4122 & GT4124 Video Mixer ICs APPLICATION NOTE by Ian Ridpath, Senior Applications Engineer, Video & Broadcast Group INTRODUCTION and DEVICE TOPOLOGY The GT4122 and GT4124 are broadcast quality monolithic integrated circuits specifically designed to linearly mix two video signals under the control of a third channel. Figures 1 and 2 show the functional block diagrams of the GT4122 and the GT4124 respectively. The corresponding external connections are shown in Figures 3 and 6. +IN A + - IN A - XA AMP 1 COMP VCA=0.5 + VK A OS1 + Σ1 A OS2 OUT AMP 4 + + +IN B REXT XB AMP 2 - IN B BIAS + - VK Σ2 + B OS1 VCB=0.5 - VK B OS2 + VK Σ3 VNOM + +V S 0.5V - - VREF + VC S1 S2 GND COS2 COS1 Fig. 1 Functional Block Diagram of the GT4122 CHOLD STROBE +IN A + - IN A - CLAMP XA AMP 1 CLREF CLSIG COMP VCA=0.5 + VK + + Σ1 + Σ4 AMP 4 OUT + +IN B + REXT AMP 2 - IN B XB BIAS + VCB=0.5 - VK Σ2 Σ3 + VK + - VS +VS + - VK VNOM + - 0.5V + VK and -V K are themselves proportional to the difference between an externally applied reference voltage (VREF) and an externally applied CONTROL voltage (VC ). The voltages VK and -VK are produced by a differential amplifier (AMP3) whose gain is AK. This gain can be altered by two external resistors, REXT and RSPAN according to the following formula: 0.85 • REXT AK ≈ ————— RSPAN AK VNOM + Following each input amplifier, the signals are applied to linear multiplier circuits (XA and XB) whose outputs are the product of the incoming signals and controlling voltages (VCA) or (VCB). The controlling voltage VCA is the sum of a nominal 0.5V source (VNOM) and a variable source VK while VCB is made up of the sum of the nominal voltage VNOM and -VK. AMP 3 + - VS For both devices, the input signals are applied to conventional differential amplifiers (AMP1 and AMP2). In the case of the GT4122, each amplifier has provisions for individually adjusting the DC offset (OFFSET). For the GT4124, these offsets are trimmed by on-chip resistors. AMP 3 - VREF + VC AK VNOM S1 - [1kΩ < REXT < 3kΩ] Note that REXT is connected between the REXT pin and ground and RSPAN is connected between the pins S1 and S2. Each of the voltages (+VK and -VK) is applied to summing circuits (Σ2 and Σ3) whose second inputs are DC voltage sources that can also be slightly varied. The nominal value of these voltage sources is 0.5 volts. When they are exactly 0.5V and when VC = VREF then the gain of each signal channel of the mixer is 0.5 (50%). By connecting the ends of an external potentiometer (CONTROL OFFSET) between the offset pins COS1 and COS2, the voltage sources can be altered differentially. If a second potentiometer (50% GAIN) is connected between the wiper of the CONTROL OFFSET potentiometer and the supply voltage, the voltage sources can be varied in a common mode fashion. In this way not only can the control range of the mixer be varied but also the point at which 50% of each input signal appears at the output. The outputs from the multiplier circuits (XA and XB) are then applied to a summing circuit (Σ1) whose output feeds a wideband amplifier (AMP4) and presents the mixed signals to the outside world. S2 GND COS2 COS1 Although there are two separate differential inputs, the usual operational amplifier gain-setting methods can be applied to determine the closed loop gain of the mixer. Usually the mixer Fig. 2 Functional Block Diagram of the GT4124 520 - 44 - 00 will be configured for unity gain by connecting both inverting inputs (-IN A , -IN B) to the common output (OUT). In this case, the general transfer function is: The topology is designed so that once the control voltage reaches either end of its range, the channel which is ON remains fully ON and the OFF channel remains fully OFF. VO = VA •[VNOM + AK•(VC - V REF)] + V B•[VNOM - A K•(VC - V REF)] This is critical for good off-isolation performance. (Unity gain configuration) Most of the internal circuitry of the GT4124 is identical to that of the GT4122. The unique feature of the GT4124 is the addition of an accurate and stable strobed clamp. Where VA and VB are the input analog signals applied to +IN A and +IN B respectively, and VC is the CONTROL voltage. Note that VNOM ranges between 0.45V < VNOM < 0.55. Figure 2, shows the topology of the GT4124 and includes the strobed clamp block. This circuit samples the OUTPUT signal when CL SIG is connected to the OUTPUT, and compares it to a CLAMP REFERENCE voltage which normally is set to 0V. For normal video mixer operation, the control range (SPAN) is usually 0 to 1V and will occur when AK=1, VREF= 0.5V and VNOM=0.5 volts. A change in VC from 0 to 1V will then produce an effect such that the output signal contains 100% of Channel B when VC is 0V and 100% of Channel A when VC is 1 volt. For the above conditions, the general unity gain transfer function reduces to: During the strobe period, which is usually the back porch period of the video signal, DC feedback is applied to the summing circuit Σ4 located between the output of the mixers and the input of the output amplifier such that the DC offset is held to within one or two millivolts of the clamp REFERENCE. V O = VA•VC + VB•(1-VC ) Since the operation of the mixer is limited to one quadrant, no signal inversions occur if the control voltage exceeds the range zero to one volt in either direction. A holding capacitor CHOLD is used to assure effective clamp operation and filter residual noise. GT4122 CIRCUIT APPLICATIONS Video applications for the GT4122, and GT4124 range from simple two input mixers using a single device to a multifunctional production switcher performing many video effects including fading, wiping and keying, by cascading several devices. included. Using this circuit, many of the critical circuit parameters can be measured including Crossfade Balance, Linearity, Bandwidth and Differential Gain and Phase. An output amplifier is shown but is only necessary when driving low impedance loads such as co-axial cables. The load on the GT4122 output itself should be kept above 5kΩ. Figure 3 shows the GT4122 used as a two input video mixer. An evaluation PC board has been made and the artwork is +10V -10V +5V C5 47 -10V 50% GAIN + C5 47 + C1 0.1 GT4122 C2 1 -V S 0.1 2 R1 RV1 200 RV2 100 CONTROL OFFSET R3 1k C3 0.1 5 C OS2 B OS1 7 1k 8 RV6 1k Z1 6.2V NOTE: 10 (0.5V) -IN B 18 +IN B 9 R4 5.6k +VS 4 C OS1 6 RV3 SPAN ADJUST S1 0.1 or LINK 20 A OS2 VREF -IN A S2 +IN A VC AOS1 GND REXT 17 RV4 500 B BLACK LEVEL ADJUST 16 VIDEO OUT 8 ROUT 10k or OPEN 5 C7 0.1 -5V B VIDEO INPUT 15 14 13 RV5 500 A BLACK LEVEL ADJUST 75 if required A VIDEO INPUT 12 75 if required 11 R2 1k C5 0.1 1 4 COUT B OS2 19 3 COMP 560 5 - 25pF CCOMP OUT C6 0.1 IC2 CLC110 VREF ADJUST CONTROL INPUT 75 if required 1.C5 is used when the CONTROL VOLTAGE (VC) is derived from a power supply. 2. All resistors in ohms, all capacitors in µF unless otherwise stated. Fig. 3 GT4122 Test Circuit 520 - 44 - 00 The reference voltage VREF is derived from a simple Zener diode regulator from the +10V supply. It is important to maintain a constant reference voltage for repeatable performance. The circuit shown, or any other stabilized voltage source can be used. A 0.1µF capacitor (C3) is used to decouple any noise from the reference supply. All adjustments are made using small trimmer potentiometers and it is critical that they be carbon or carbon film types. Ten turn potentiometers have too much inductance and will adversely affect the operation of the mixer. The set up of the circuit is straightforward and is outlined below. TEST SET-UP FOR GT4122 VIDEO MIXER BOARD NOTE: Initially set all trim pots to mid-position 1) 0.5V Reference Adjustment 3) A-B Null Adjustment RV6 GND 1V P-P TRIANGLE WAVE AT 400Hz (V = 0 to 1V) CONTROL OUT B - IN A - IN GND GND RV5 METHOD: Adjust RV6 for 0.5V ± 0.005V at pin 11 of the GT4122 device. [DO NOT touch this adjustment again.] 2) Span, Crossfade & Control Offset Adjustments RV4 B - IN A - IN GND GND OUT TO SCOPE NOTE: VA and VB must be set to 0 volts. METHOD: Adjust RV4 and RV5 to produce the best null of the triangle wave at the output. 4) Frequency Compensation Adjustment RV1 RV3 1V P-P TRIANGLE WAVE AT 400Hz (V = 0 to 1V) CONTROL CONTROL RV2 OUT B - IN A - IN 1.0V GND SET TO 0V FOR A - IN AND 1.0V FOR B - IN TESTS TO SCOPE CONTROL OUT B - IN METHOD: Adjust RV1, RV2 and RV3 to produce the best 0 to 1V (1V peak to peak) triangle waveform at the output. These adjustments interact and so should be repeated until the best waveform is obtained. (See Photographs 1 through 6). METHOD: CCOMP TO NETWOK ANALYSER A - IN FROM NETWORK ANALYSER VSIG = 0dBm Connect either the A-IN or B-IN pins to the Network Analyser Output Port. Terminate these in p u t s w i t h 5 0Ω r e s i s t o r s . C o n n e c t t h e OUTPUT to the Input Port of the Network Analyser. Set the voltage on the CONTROL to 1V in order to measure the frequency response of the A-INPUT. Conversely, set the CONTROL voltage to 0V for the B-INPUT measurement. A d j u s t t h e c o m p e n s a t i n g c a p a c i t o r C COMP f o r t h e f l a t t e s t fr e q u e n c y r e s p o n s e o n b o t h channels. 520 - 44 - 00 Photographs showing the effects of varying the SPAN, CONTROL OFFSET and 50% GAIN potentiometers. VOUT VIN VIN 200mV / div 200mV / div VOUT 5µs / div 5µs / div Photograph 1. SPAN ADJUST (RV3) - fully c.w. (min) Photograph 2. SPAN ADJUST (RV3) - fully c.c.w.(max) VOUT VIN 200mV / div 200mV / div VIN 5µs / div VOUT 5µs / div Photograph 3. CONTROL OFFSET (RV2) fully c.w. Photograph 4. CONTROL OFFSET (RV2) - fully c.c.w. VOUT VIN VOUT 200mV / div 200mV / div VIN 5µs / div 5µs / div Photograph 5. 50% GAIN (RV1) - fully c.c.w. (min) Photograph 6. 50% GAIN (RV1) - fully c.w. (max) 520 - 44 - 00 Once the board has been set up using the above procedures, other tests such as Linearity and Differential Gain and Phase can be performed. Tracking of the control characteristics from one device to another indicates approximately 1 IRE variation is possible making the GT4122 suitable for R-G-B and multi-signal mixing systems. 200mV / div 200mV / div Photograph 7 shows the input and output triangle waveforms slightly offset from each other. This clearly shows the excellent linearity of the GT4122 control characteristics. The CONTROL signal itself is a 1V peak to peak triangle wave. The output signal (top trace, Photo 7) indicates less than 1% non-linearity over the control range. Photograph 8 shows a closer view of the output signal with a vertical scale of 20 mV/ div. 5µs / div 5µs / div Photograph 8. Close Up View of Output Triangle Wave Photograph 7. Comparison of Input and Output Triangle Wave DIFFERENTIAL GAIN AND PHASE MEASUREMENTS Figure 4 shows a typical plot of Differential Gain and Differential Phase versus Frequency using the Network Analyser method. Under software control, an input carrier is stepped from a zero volt DC level to a 0.714V DC level and back again many times. The resulting changes in gain and phase at the output are averaged over a long time period by taking several hundred samples. The results of this test method, with accuracies of better than 0.001% and 0.001 degree, form the basis of all differential gain and phase tests at GENNUM. Appendix A is a program listing used in the HP-4195 Network Analyser to measure differential gain and differential Phase. This method is now becoming a standard with component manufacturers. An earlier methodology is fully described in Information Note No. 510 - 14 which forms part of the GENNUM IC Data Book. 520 - 44 - 00 0.03 0.02 dg (%) / dp (deg) Differential gain and differential phase can be accurately measured using a Network Analyser and S-parameter test set. Vectorscopes do not provide enough accuracy at the component level. 0.01 dg 0.00 dp -0.01 -0.02 -0.03 11 3 5 FREQUENCY (MHz) Fig. 4 Typical dg / dp Plot 1010 THREE LEVEL VIDEO MIXER - GT4122 Figure 5 shows an implementation of the GT4122 as a 3-level mixer incorporating external clamping circuits made up of GB4551 high performance, back-porch clamps. These devices are available from GENNUM Corporation. In this circuit, three video signals are combined by cascading two GT4122 devices. The input signals could be BORDER video, BACKGROUND video or even a PREVIOUS video signal. In any case, full control is achieved with a high degree of accuracy by providing the appropriate KEY signals to the CONTROL inputs of the two GT4122 devices. The control signal circuitry is not included in this circuit and would depend on each individual requirement. 10 VIDEO SOURCE No. 1 GB4551 1 IN 3 GT4122 OUT 5 8 17 +IN B 6 S1 7 GB4551 OUT -IN B Back Porch Pulse 8 SPAN 0.5V VIDEO SOURCE No. 2 10 7 18 IN OUT 5 3 1 IN 8 OUT 5 3 VIDEO 1 & 2 OUTPUT 7 14 S2 -IN A VREF REXT 11 GB4551 1 10 20 Back Porch Pulse 1k 8 7 13 +IN A VC G 10 17 GT4122 +IN B 6 S1 9 GB4551 OUT 20 10 1 IN SPAN Back Porch Pulse No. 18, No. 2 MIX CONTROL -IN B 8 GB4551 VIDEO SOURCE No. 3 10 1 IN 3 (1+2) & No. 3 MIX CONTROL OUT 5 8 0.5V 0.1 7 18 3 14 S2 -IN A VREF REXT 11 Back Porch Pulse 1k 13 7 +IN A VC 9 G 10 Back Porch Pulse NOTES: 1. All non-marked capacitors connected to GROUND are 470pF. 2. All resistors are in ohms, all capacitors in µF unless otherwise shown. 3. For clarity, power supply and offset adjustments are not shown. Fig. 5 Three Level Mixer using Two GT4122 Devices 520 - 44 - 00 OUT 5 7 8 VIDEO 1, 2 & 3 OUTPUT GT4124 CIRCUIT APPLICATIONS The test set up shown, uses a low frequency triangle waveform for the signal sources, and derives a triggered negative going pulse from the same generator to act as the STROBE input. Figure 6 shows a test circuit for the GT4124. It is very similar to the GT4122 circuit shown in Figure 3. In this circuit, there are no DC offset adjustments required for the two video input channels. The 0.5V REFERENCE adjustment as well as the SPAN, 50% GAIN and CONTROL OFFSET adjustments are identical to those used on the GT4122 board. If actual video is used, the STROBE pulse can be obtained from the output of a sync separator circuit. In either case, the performance of the clamp can be evaluated using this test board. The major difference in this circuit is the need for an active low STROBE pulse in order to activate the on-board clamp. As well, parameters such as Frequency Response, Linearity and Differential Gain and Phase can be measured. An artwork for this board is included in this application note. -10V +10V -10V 50% GAIN 1 C1 0.1 10nF R1 RV1 200 560 5 - 25pF CCOMP RV2 100 C3 0.1 RV3 SPAN ADJUST 2 CHOLD BOS2 3 COMP -IN B CLREF 6 S1 CLSIG 8 9 R4 5.6k Z1 6.2V 1k 10 (0.5V) RV4 VREF ADJUST +IN B 5 C OS2 7 1k -VS 20 +VS 4 C OS1 CONTROL OFFSET R3 1k + GT4124 C5 47 + VREF -IN A S2 +IN A VC GND +5V 0.1 REXT STROBE C6 0.1 IC2 CLC110 47 1 4 19 8 ROUT 10k 18 5 VIDEO OUT C7 0.1 17 -5V 16 B VIDEO INPUT 15 75 if required 14 13 A VIDEO INPUT 12 75 if required 11 R2 1k C5 0.1 CONTROL INPUT 75 if required STROBE NOTE: 1. All resistors in ohms, all capacitors in µF unless otherwise stated. 2. C5 is used when the CONTROL VOLTAGE (VC) is derived from a power supply. Fig. 6 GT4124 Test Circuit 520 - 44 - 00 TEST SET-UP FOR GT4124 MIXER BOARD NOTE: Initially set all trim pots to mid-position. 1) 0.5V Reference Adjustment (RV4) 3) Crossfade Balance (No adjustments) METHOD: RV4 GND The crossfade balance (control breakthrough) is measured over frequency by using a Network Analyser or Waveform Generator. Both INPUT-A and INPUT-B are terminated with their 75Ω resistors. The control voltage of 0-1V p-p with a 0.5V DC offset is swept over the frequency range desired. CONTROL INPUT OUT STROBE O/C A - IN B - IN GND GND 4) Frequency compensation (CCOMP ) METHOD: Adjust RV4 for 0.5V ± 0.005V at pin 7 of the GT4124 device. [DO NOT touch this adjustment again.] SET TO 1V FOR A - IN AND 0V FOR B - IN TESTS 2) Span, 50% Gain & Control Offset (RV1, RV2 & RV3) CONTROL OUT STROBE O/C CONTROL INPUT RV2 CHOLD OUT STROBE A - IN TO NETWORK ANALYSER B - IN RV1 RV3 1V P-P TRIANGLE WAVE AT15 kHz (V = 0 to 1V) DC OFFSET = 0.5V CCOMP A - IN FROM NETWORK ANALYSER VSIG = 0 dBm TO SCOPE B - IN METHOD: O/C 1.0V Connect either the A-IN or B-IN pins to the Network Analyser Output Port. Terminate these inputs with 50Ω resistors. Connect the OUTPUT to the Input Port of the Network Analyser. GND METHOD: Temporarily put a short circuit across the CHOLD capacitor on pin 2 of the device. This will disable the clamping action. Set the voltage on the CONTROL to 1V in order to measure the frequency response of the A-INPUT. Apply 1.0V DC to A-INPUT and 0V to INPUT-B (this may be done by leaving INPUT-B open with the 75Ω resistor connected to ground). Adjust RV1, RV2 and RV3 to produce the best 0 to 1V (1V peak to peak) triangle waveform at the output. These adjustments interact and so should be repeated until the best waveform is obtained. Remove the short across CHOLD. 520 - 44 - 00 Conversely, set the CONTROL voltage to 0V for t h e B - I N P U T m e a s u r e m e n t . A d j u s t t h e compensating capacitor C COMP for the flattest frequency response on both channels. 5) Clamp Operation (No adjustments) SET TO 1V FOR A - IN & 0V FOR B - IN TESTS METHOD: Connect either the A-IN or B-IN pins t o the W a v e f o r m Generator or video source. Terminate these inputs with 50Ω resistors. Connect t h e OUTPUT to the Input of the Oscilloscope. Set t h e v o l t a g e o n t h e C O N T R O L t o 1 V i n order to observe the clamping accuracy of the A-INPUT. CONTROL OUT STROBE CLAMP PULSE TO SCOPE Conversely, set the INPUT voltage to 0V for the B-INPUT measurement. Apply a 1µs, 15kHz negative pulse triggered by the Waveform Generator (or a burst pulse from a sync separator i f a v i d e o s i g n a l i s u s e d ) t o t h e S T R O B E INPUT and observe that the output is clamped to within 1mV of 0V DC. B - IN A - IN 1V P-P TRIANGLE AT 15 kHz OR VIDEO SIGNAL THREE LEVEL VIDEO MIXER - GT4124 Figure 7 shows an implementation of the GT4124 as a three-level video mixer incorporating two mixers and three back porch clamps. In this case, the GB4551 clamps are only used at the video inputs. Since the GT4124 devices have on-board clamps themselves, subsequent circuit clamps are not needed. As with the GT4122 three-level mixer circuit (Figure 5), control, power and offset circuitry are not included for clarity. The control channels are identical for both the GT4122 and GT4124 in terms of SPAN range and frequency response. Since the STROBE inputs to the GT4124 and the GB4551 are both active low, these inputs can be paralleled and driven from any conventional sync separator circuit. 1k 8 6 S1 SPAN S2 15 17 +IN B CLSIG 19 11 STRB OUT GB4551 10 1 VIDEO SOURCE No. 1 IN 3 OUT 5 8 7 -IN B 18 Back Porch GT4124 -IN A 14 Pulse REXT 12 7 V 0.5V REF CLREF 16 0.1 Back Porch Pulse GB4551 10 1 VIDEO SOURCE No. 2 IN OUT 5 3 8 7 13 +IN A 2 C-HD VC 9 0.01 (1+2) & No. 3 MIX CONTROL GB4551 1 IN 3 OUT 5 6 8 S1 SPAN S2 15 17 +IN B CLSIG 11 19 STRB OUT -IN B Back Porch GT4124 -IN A Pulse REXT 7 VREF 0.5V CL 0.1 REF No. 1 & No. 2 MIX CONTROL 10 1k 1k GND 10 Back Porch Pulse VIDEO SOURCE No. 3 VIDEO 1 & 2 OUTPUT 8 7 0.01 Back Porch Pulse Fig. 7 Three Level Mixer Using Two GT4124 Devices 520 - 44 - 00 18 14 12 16 GND 10 13 +IN A 2 C-HD VC 9 NOTE: 1. All non marked capacitors connected to GROUND are 470 pF. 2. All resistors in ohms, all capacitors in µF unless otherwise shown. 3. For clarity, power supply and offset adjustments are not shown. VIDEO 1, 2 & 3 OUTPUT 1k NON - VIDEO APPLICATIONS The previous applications use the GT4122 as an overall unity gain, non-inverting system. With this same configuration it is possible to make a simple Amplitude Modulator. It is also possible to configure either input stage as an inverting amplifier and produce anti-phase signals which are then applied to the internal summing circuits. This allows the device to be used as a Double Sideband Balanced Modulator. Both of these applications are described below. AMPLITUDE MODULATOR An Amplitude Modulator circuit is shown in Figure 8 and produces an output spectrum as shown in Figure 9. The resulting envelope waveform is shown in Photograph 9. For this application, a 1V peak to peak, 1 MHz carrier is applied to the non-inverting B-INPUT. A 3kHz, 1V peak to peak audio signal is applied to the CONTROL input superimposed on a +0.5V DC bias. The bias centres the CONTROL signal with respect to the 0.5V DC REFERENCE voltage. Modulation is achieved by varying the CONTROL signal at the audio rate which in turn allows more or less of the carrier, appearing on B-INPUT, through to the OUTPUT. Post mixing of this signal would place the carrier on any desired RF channel. 0 RV1 CONTROL INPUT RV2 -20 CHOLD OUT STROBE A - IN GAIN (dB) RV3 1V P-P TRIANGLE WAVE AT15 kHz (V = 0 to 1V) DC OFFSET = 0.5V TO SCOPE -40 -60 B - IN -80 O/C 1.0V -100 GND -9k -6k -3k 1M 3k 6k FREQUENCY (Hz) Fig. 9 Spectrum of A.M. Signal Fig. 8 Amplitude Modulator Circuit Photograph 9. Envelope Waveform of A.M. Signal 520 - 44 - 00 9k DOUBLE SIDEBAND SUPPRESSED CARRIER MODULATOR In order to produce a suppressed carrier signal, mixing must occur between in-phase and anti-phase signals. To achieve this, the A-INPUT is configured as an inverting amplifier with unity gain by using two 2.2kΩ resistors in the feedback loop. This is illustrated in Figure 10. The audio signal is now applied to both the A-INPUT and the B-INPUT. The signals reach the summing circuits within the device 180° out of phase. The carrier applied to the CONTROL input modulates these signals and produces a suppressed carrier output. The spectrum is shown in Figure 11 and indicates a carrier null of at least 50dB. The carrier is a 1V peak to peak, 1MHz signal superimposed on a +0.5V bias. The audio level is varied to control the amount of modulation. Photograph 10 shows the resulting envelope waveform. Again, this signal may be prescaled to place it on any desired channel. One sideband may also be filtered in order to produce a Single Sideband Suppressed Carrier signal. 0 14 -INA 13 +INA 2200 + GND AUDIO 1.0µF CARRIER RF CHOKE or 1-5k RESISTOR -20 OUT 20 18 -INB 10µF GT4122 17 +INB 9 VC 7 REF + GAIN (dB) 2200 DSB OUTPUT + -40 -60 -80 0.5V REF -100 -6k Fig. 10 Double Sideband Modulator Circuit -3k 1M 3k 6k FREQUENCY (Hz) Fig. 11 Spectrum of Double Sideband Signal Photograph 10. Envelope Waveform of Double Sideband Signal CONCLUSION The GT4122 and GT4124 are available in both 20 pin PDIP and 20 pin SOIC packaging. They each represent a dedicated video mixer function in one package and offer professional video mixing with very few external parts. These devices are specifically designed for the professional broadcast market and are used in Production Switchers (Vision Mixers) and Multilayer Keyers. Full data is available from the device data sheets in the GENNUM Data Book. Applications engineers at GENNUM will be pleased to answer technical questions about any of the wide range of Video & Broadcast products made by GENNUM Corporation. 520 - 44 - 00 APPENDIX A Program Listing for Differential Gain and Phase Measurements using the HP-4195 Network Analyser. 10 15 20 30 40 50 60 65 67 70 80 90 100 110 120 130 140 150 160 170 175 180 190 200 210 220 230 240 250 260 265 270 280 290 300 330 340 !GDP - VS FREQUENCY RST !RESET !NETWORK; PORTS T2/R1; T/R()-(DEG) FNC1;PORT2;GPP2 !LOG SCALE SWT2 !DEFINE SWEEP TABLE CPL0 RBW=1KHZ !BANDWIDTH PTSET PTN=1 PTCLR PTSWP=1 POINT=1.000 MHZ POINT=1.295 MHZ POINT=1.585 MHZ POINT=1.995 MHZ POINT=2.215 MHZ POINT=3.162 MHZ POINT=3.580 MHZ POINT=3.981 MHZ POINT=4.430 MHZ POINT=5.012 MHZ POINT=6.310 MHZ POINT=7.943 MHZ POINT=10.00 MHZ PTEND ! SET UP GRAPHICS CMT “DG & DP VS. FREQUENCY” !COMMENT LINE ON SCREEN SCL1 !SCALE 1 REF=0.05 BTM=-0.05 SCL2!SCALE2 REF=0.05 BTM=-0.05 !SET SWEEP PARAMETERS VFTR1 350 352 354 356 360 370 380 382 384 390 400 410 420 422 425 430 440 445 450 460 1000 1010 1050 1060 1065 1070 1080 1090 1100 1105 1110 1120 1130 1140 1150 1200 520 - 44 - 00 PPM1 !SET MARKERS MCF2;MKCR1;MKACT1;MKCR2;MKACT0 MKR=3.58M;SMKR=3.58M !DEFINE MATH MTHA1;DMA=I MTHB1;DMB=J PRMA”DG”;UNIT”%” PRMB”DP”;UNITB”” !CLEAR REGISTERS A=0;B=0;E=0;F=0;G=0;H=0 I=0;J=0;RA=0;RB=0 !SET SIGNAL LEVEL OSC1=0.4 V;ATR1=0;ATT2=10 DISP “PRESS CONT(INUE) WHEN READY” BEEP PAUSE GOSUB 1000 MKR=3.58M;SMKR=3.58M END !MEASUREMENT FOR R0=1 TO 1000 BIAS=0 !EDIT FOR BLANKING LEVEL WAIT 200 SWTRG E=MA F=MB BIAS=0.75 !EDIT FOR LUMINANCE LEVEL WAIT SWTRG G=G+100 *(E-MA)/E H=H+F-MB I=G/R0 J=H/R0 NEXT R0 RETURN TEST BOARD ARTWORKS Fig. 12 Component Side Artwork for GT4122 Test Board Fig. 13 Copper Side Artwork for GT4122 Test Board 520 - 44 - 00 Fig. 14 Component Silkscreen for GT4122 Test Board Fig. 15 Component Side Artwork for GT4124 Test Board 520 - 44 - 00 Fig. 16 Copper Side Artwork for GT4124 Test Board Fig. 17 Component Silkscreen for GT4124 Test Board Gennum Corporation assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement. © Copyright June 1992 Gennum Corporation. All rights reserved. 520 - 44 - 00 Printed in Canada.