GT4124 Video Multiplier with Strobed DC Restore DATA SHEET FEATURES DESCRIPTION • broadcast quality video multiplier with a very accurate back porch clamp, (less than 2mV DC offset) • 30 MHz at -1.0dB video and control channel bandwidth • one external frequency compensation adjustment • ultra low differential gain and differential phase, (typically 0.01% and 0.01 deg.) The GT4124 multiplier is a monolithic dual-channel video multiplier for use in the professional broadcast field. It incorporates a very fast and accurate strobed clamp to insure black level accuracy. Featuring two wideband video inputs and a single control input, the GT4124 achieves high quality video mixing of the two synchronized video input signals to a single output by implementing the transfer function: • adjustable DC offset and span on the control input • adjustable clamp reference level • active low STROBE input V • 20 pin PDIP and SOIC packaging. = V IN • V A C + V IN (1 - V ) C B where VC is the control input voltage, which may be varied over the control range, and VIN and VIN are the video A B input signals. APPLICATIONS • Production switcher video mixers The GT4124 operates with power supply voltages of ± 9 to ± 12 volts. At a nominal supply of ± 10 volts, it draws an average of 20 mA of current. The GT4124 is available in 20 pin PDIP and 20 pin SOIC packages. • Linear Keyers ORDERING INFORMATION Part Number OUT Package Type Temperature Range GT4124-CDF 20 pin PDIP 0 to 70˚ GT4124-CKF 20 pin SOIC 0 to 70˚ An application note entitled "Using the GT4122 and GT4124 Video Mixer ICs" (Document 520-44) is available from Gennum Corporation. PIN DESIGNATION 1 +V S positvive supply voltage 2 CHOLD clamp holding capacitor 3 COMP output freq'y comp'n R-C 4 COS1 control input offset adjust 5 COS2 control input offset adjust 6 S1 span adjust 7 VREF 0.5 volt reference input 8 S2 span adjust 9 VCONT control signal input 10 GND ground 11 STROBE strobe input CHOLD +IN A AMP 1 - IN A STROBE + CLAMP XA CLAMP REF. CLAMP SIG. - VIDEO INPUT A +IN B + - IN B - AMP 2 + VCA=0.5 + VK COMP. + Σ1 + Σ4 AMP 4 OUTPUT + XB REXT VIDEO INPUT B BIAS VCB=0.5 - VK + + - VK Σ2 Σ3 12 REXT current setting resistor 13 +IN A A video + signal input - VS 14 -IN A A video - signal input +V S 15 CLAMP SIG clamp signal 16 CLAMP REF clamp reference 17 +IN B 18 -IN B B video - signal input 19 OUTPUT video output 20 -VS negative supply voltage + AMP 3 VK + 0.5V VNOM 0.5V + + - - - VREF + CONTROL VOLTAGE (VCONT) AK VNOM S1 S2 GND COS2 B video + signal input COS1 Device Function: V OUT = A OL [VA (0.5+V K) + VB (0.5 - VK)] where AOL ~ 2000, VK=VCONT - VREF, AK ≈ 0.85 REXT RSPAN FUNCTIONAL BLOCK DIAGRAM Revision Date: February 1994 Document No. 520 - 59 - 2 GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3 tel. (905) 632-2996 fax: (905) 632-5946 Japan Branch: A-302 Miyamae Village, 2-10-42 Miyamae, Suginami-ku, Tokyo 168, Japan tel. (03) 3334-7700 fax: (03) 3247-8839 PIN CONNECTIONS ABSOLUTE MAXIMUM RATINGS PARAMETER TOP VIEW VALUE/UNITS ± 13.5 V Supply Voltage (VS) C 0° C ≤ T A ≤ 70° C Operating Temperature Range -65° C ≤ TS ≤ 150° C Storage Temperature Range Lead Temperature (Soldering, 10 Sec) 260° C ±5 V Differential Video Input Voltage Strobe Input Voltage +V S -V 20 PIN 1 OUTPUT COMP -IN B C OS1 C OS2 +IN B CLAMP REF CLAMP SIG S-1 VEE ¯≤ VCLAMP ≤ VCC S HOLD V REF -IN A S-2 +IN A VCONT R EXT GND 11 10 STROBE 20 PIN DIP / SOIC ELECTRICAL CHARACTERISTICS PARAMETER Supply Voltage POWER SUPPLIES Supply Current (pos) +VS = -V S =10V, 0°C ≤ TA ≤ 70°C unless otherwise shown SYMBOL ± VS I + - Supply Current (neg) I Small Signal Bandwidth BW Full Power Bandwidth BW Frequency Response SIGNAL CHANNEL CONDITIONS Operating Range REXT = 1 kΩ REXT = 1 kΩ MAX UNITS ±9 ± 10 ± 12 volts - 24 28 mA - 18 20 mA 25 30 - MHz 20 25 - MHz DC - 10 MHz - ± 0.05 - dB at ± 0.1 dB V SIG = 150 mVp-p at -3.0 dB VSIG = 1 V p-p ∂g VIN = 40 IRE at 3.58 MHz - 0.01 0.03 % Differential Phase ∂p VIN = 40 IRE at 3.58 MHz - 0.01 0.03 degrees Signal to Noise S/N VSIG = 1 volt, BW = 5 MHz 64 70 - dB Gain - open loop A OL 100 kHz (ß = 0%) 54 60 66 dB Gain - closed loop A CL 100 kHz (ß = 100%) -0.01 -0.005 - dB Phase Delay td SIG V A or B/VO - - 10 ns ƒSIG = 5 MHz (see note 1) 80 85 - dB V C/VA or B ƒSIG = 5 MHz (see note 2) 90 95 - dB at ± 0.1 dB 25 30 - MHz - - 10 ns - 1 - % - -55 -50 dB Bandwidth BW CONTROL Phase Delay t d CONT CHANNEL Linearity Control Breakthrough Control Range VCONT = 0-1 V ƒ = 3.58 MHz V CONT Strobe Pulse Width Strobe Level V SIG = 150 mVp-p V CONT = 0-1 V ƒ = 1-10 MHz Crossfade Balance V INHI V INLO Clamp Accuracy 1. V A or B = 1 Vp-p output taken from OUTPUT 2. V CONT = 1 Vp-p output taken from VA or V B 520 - 59 - 2 TYP Differential Gain Off Isolation & Crosstalk Notes: MIN 2 - 3 5 mVpp -5 - +5 V 500 1000 - ns 2.0 - - V - - 0.8 V - ±1 ±2 mV DETAILED DESCRIPTION The GT4124 is a broadcast quality monolithic integrated circuit specifically designed to linearly mix two video signals under the control of a third channel. The GT4124 includes the strobed clamp block. This circuit samples the output signal when CLAMP SIG. is connected to the OUTPUT, and compares it to a CLAMP REFERENCE voltage which normally is set to 0V. Referring to the Functional Block Diagram, the input signals are applied to conventional differential amplifiers (AMP1 and AMP2) whose offsets are trimmed by on-chip resistors. During the strobe period, which is usually the back porch period of the video signal, DC feedback is applied to the summing circuit Σ4 such that the DC offset is held to within one or two millivolts of the clamp REFERENCE. 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 V K while V CB is made up of the sum of the nominal voltage VNOM and -VK. A holding capacitor CHOLD is used to assure effective clamp operation and filter residual noise. 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 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: VK and -VK are themselves proportional to the difference between an externally applied reference voltage (VREF) and an externally applied CONTROL voltage (VC). The voltages VK and -V K 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 VO = VA •[VNOM + AK•(VC - V REF)] + VB•[VNOM - A K•(VC - V REF)] (Unity gain configuration) [1kΩ < REXT < 3kΩ] 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 R EXT is connected between the REXT pin and ground and RSPAN is connected between the pins S1 and S2. Note that VNOM ranges between 0.45V < VNOM < 0.55. 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: 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%). V O = VA•VC + VB•(1-VC ) 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. Since the operation of the mixer is limited to two quadrants, no signal inversions occur if the control voltage exceeds the range zero to one volt in either direction. 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. 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) via a second summing circuit (Σ4) and presents the mixed signals to the outside world. 3 520 - 59 - 2 -10V +10V 0.1 -10V 50% GAIN 1 C1 0.1 10nF R1 RV1 200 CONTROL OFFSET R3 1k RV3 SPAN C3 ADJUST 0.1 CLREF CLSIG 7 1k Z1 6.2V 1k +IN B 5 C OS2 8 10 (0.5V) -IN B 6 9 R4 5.6k CHOLD 4 C OS1 RV2 100 S1 1 VREF -IN A S2 +IN A 4 18 8 VIDEO OUT 5 17 C7 0.1 16 -5V B VIDEO INPUT 15 75 if required 14 13 REXT VC GND STROBE A VIDEO INPUT 12 75 if required 11 R2 1k C5 0.1 RV4 VREF ADJUST IC2 CLC110 47 BOS2 19 3 COMP 560 5 - 25pF CCOMP 2 -VS 20 +VS C6 0.1 + GT4124 C5 47 + +5V CONTROL INPUT 75 if required * STROBE * Capacitor C5 required if the All resistors in ohms, all capacitors in F unless otherwise stated. control voltage is from a power supply. Fig. 1 Test Circuit TYPICAL PERFORMANCE CURVES (unless otherwise shown VS = ± 10V) 1.0 1.0 0.5 0.5 CH - A 0.0 0.0 CH - B GAIN (dB) GAIN (dB) -0.5 -0.5 -1.0 -1.5 V IN = 150 mVp-p -2.0 -1.0 -1.5 -2.0 -2.5 VIN = 1 V p-p -3.0 2.5 -3.5 3.0 1 1 10 -4.0 100 100 10 FREQUENCY (MHz) Fig. 3 Full Power Bandwidth Fig. 2 Gain vs Frequency 520 - 59 - 2 1 1 FREQUENCY (MHz) 4 50 50 -20 2 -25 0 -2 VCONT = 1 V p-p +0.5 VDC REF = 1 V p-p (0dB) -30 -4 PHASE (deg) GAIN (dB) -35 -40 -45 -6 -8 -10 -50 -12 -55 -14 -60 -16 0 .1 CCOMP = 5pF 1 CCOMP = 25pF CCOMP = 18 pF 1 10 1 FREQUENCY (MHz) 3 5 10 10 FREQUENCY (MHz) Fig. 4 Crossfade Balance vs Frequency Fig. 5 Phase Delay vs Frequency 0.03 dg (%) dp (deg) 0.02 0.01 dg 0.00 -0.01 dp -0.02 -0.03 1 1 3 5 10 10 FREQUENCY (MHz) Fig. 6 Differential Gain and Phase vs Frequency DOCUMENT IDENTIFICATION PRODUCT PROPOSAL This data has been compiled for market investigation purposes only, and does not constitute an offer for sale. ADVANCE INFORMATION NOTE This product is in development phase and specifications are subject to change without notice. Gennum reserves the right to remove the product at any time. Listing the product does not constitute an offer for sale. CAUTION ELECTROSTATIC SENSITIVE DEVICES PRELIMINARY DATA SHEET The product is in a development phase and specifications are subject to change without notice. DO NOT OPEN PACKAGES OR HANDLE EXCEPT AT A STATIC-FREE WORKSTATION DATA SHEET The product is in production. Gennum reserves the right to make changes at any time to improve reliability, function or design, in order to provide the best product possible. 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 October 1992 Gennum Corporation. . All rights reserved. Printed in Canada. 5 520 - 59 - 2