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| GT4124 Video Multiplier with Strobed DC Restore DATA SHEET FEATURES * 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.) * adjustable DC offset and span on the control input * adjustable clamp reference level * active low STROBE input * 20 pin PDIP and SOIC packaging. APPLICATIONS * Production switcher video mixers * Linear Keyers ORDERING INFORMATION Part Number GT4124-CDF GT4124-CKF Package Type Temperature Range 20 pin PDIP 20 pin SOIC 0 to 70 0 to 70 An application note entitled "Using the GT4122 and GT4124 Video Mixer ICs" (Document 520-44) is available from Gennum Corporation. DESCRIPTION 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: V OUT = V IN * V A C + V IN (1 - V ) B C 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. 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. PIN DESIGNATION 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 +V S CHOLD COMP COS1 COS2 S1 VREF S2 VCONT GND STROBE REXT +IN A -IN A positvive supply voltage clamp holding capacitor output freq'y comp'n R-C control input offset adjust control input offset adjust span adjust 0.5 volt reference input span adjust control signal input ground strobe input current setting resistor A video + signal input A video - signal input - VS +VS GND VNOM 0.5V CHOLD +IN A - IN A + AMP 1 STROBE XA CLAMP CLAMP REF. CLAMP SIG. - VIDEO INPUT A +IN B - IN B + AMP 2 + VCA=0.5 + VK + + 4 AMP 4 COMP. OUTPUT 1 + XB REXT BIAS - VIDEO INPUT B VCB=0.5 - VK + 2 3 + - VK AMP 3 VK AK + CONTROL VOLTAGE (VCONT) S1 S2 COS2 COS1 - + VREF + + 0.5V + - - VNOM CLAMP SIG clamp signal CLAMP REF clamp reference +IN B -IN B OUTPUT -VS B video + signal input B video - signal input video output negative supply voltage 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 Document No. 520 - 59 - 2 Revision Date: February 1994 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 ABSOLUTE MAXIMUM RATINGS PARAMETER Supply Voltage (VS) Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering, 10 Sec) Differential Video Input Voltage Strobe Input Voltage VALUE/UNITS 13.5 V 0 C T A 70 C -65 C TS 150 C 260 C 5 V VEE VCLAMP VCC +V S C HOLD PIN CONNECTIONS TOP VIEW PIN 1 20 -V S OUTPUT -IN B +IN B CLAMP REF CLAMP SIG -IN A +IN A R EXT 10 11 STROBE COMP C OS1 C OS2 S-1 V REF S-2 VCONT GND 20 PIN DIP / SOIC ELECTRICAL CHARACTERISTICS PARAMETER Supply Voltage POWER SUPPLIES +VS = -V S =10V, 0C TA 70C unless otherwise shown SYMBOL VS I I + CONDITIONS Operating Range REXT = 1 k REXT = 1 k at 0.1 dB V SIG = 150 mVp-p at -3.0 dB VSIG = 1 V p-p DC - 10 MHz VIN = 40 IRE at 3.58 MHz VIN = 40 IRE at 3.58 MHz VSIG = 1 volt, BW = 5 MHz 100 kHz ( = 0%) 100 kHz ( = 100%) MIN 9 25 20 64 54 -0.01 - TYP 10 24 18 30 25 0.05 0.01 0.01 70 60 -0.005 85 95 30 1 -55 3 1000 1 MAX 12 28 20 0.03 0.03 66 10 10 -50 5 +5 0.8 2 UNITS volts mA mA MHz MHz dB % degrees dB dB dB ns dB dB MHz ns % dB mVpp V ns V V mV Supply Current (pos) Supply Current (neg) Small Signal Bandwidth Full Power Bandwidth Frequency Response Differential Gain Differential Phase - BW BW g p S/N A OL A CL td SIG V A or B/VO V C/VA or B BW t d CONT SIGNAL CHANNEL Signal to Noise Gain - open loop Gain - closed loop Phase Delay Off Isolation & Crosstalk SIG = 5 MHz (see note 1) SIG = 5 MHz (see note 2) at 0.1 dB V SIG = 150 mVp-p 80 90 25 - Bandwidth CONTROL CHANNEL Phase Delay Linearity Control Breakthrough Crossfade Balance Control Range Strobe Pulse Width Strobe Level V CONT = 0-1 V = 1-10 MHz VCONT = 0-1 V = 3.58 MHz V CONT V INHI V INLO -5 500 2.0 - Clamp Accuracy Notes: 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 2 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. 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. 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. 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 [1k < REXT < 3k] 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. During the strobe period, which is usually the back porch period of the video signal, DC feedback is applied to the summing circuit 4 such that the DC offset is held to within one or two millivolts of the clamp REFERENCE. 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: VO = VA *[VNOM + AK*(VC - V REF)] + VB*[VNOM - A K*(VC - V REF)] (Unity gain configuration) 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. 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: V O = VA*VC + VB*(1-VC ) Note that R EXT 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 (2 and 3) 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 (1) whose output feeds a wideband amplifier (AMP4) via a second summing circuit (4) and presents the mixed signals to the outside world. 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. 3 520 - 59 - 2 +10V -10V 0.1 +5V C6 0.1 IC2 CLC110 1 4 5 C7 0.1 -5V B VIDEO INPUT 75 if required A VIDEO INPUT 75 if required R2 1k CONTROL INPUT 75 if required 8 VIDEO OUT C5 47 + -10V 50% GAIN RV1 200 C1 0.1 R1 5 - 25pF CCOMP CONTROL OFFSET RV3 SPAN C3 ADJUST 0.1 1k 560 RV2 100 10nF GT4124 1 2 +VS CHOLD -VS 20 BOS2 19 -IN B +IN B CLREF CLSIG -IN A +IN A REXT STROBE 12 11 18 17 16 15 14 13 S2 VC GND 47 + 3 COMP 4C OS1 5C OS2 6 7 8 9 S1 VREF R3 1k R4 5.6k Z1 6.2V (0.5V) C5 0.1 10 1k RV4 VREF ADJUST * * Capacitor C5 required if the control voltage is from a power supply. All resistors in ohms, all capacitors in F unless otherwise stated. STROBE Fig. 1 Test Circuit TYPICAL PERFORMANCE CURVES (unless otherwise shown VS = 10V) 1.0 0.5 0.0 1.0 CH - A 0.5 0.0 -0.5 GAIN (dB) -0.5 -1.0 -1.5 -2.0 2.5 -3.5 3.0 1 1 GAIN (dB) CH - B -1.0 -1.5 -2.0 -2.5 -3.0 V IN = 150 mVp-p VIN = 1 V p-p 10 100 100 -4.0 1 1 10 50 50 FREQUENCY (MHz) FREQUENCY (MHz) Fig. 2 Gain vs Frequency Fig. 3 Full Power Bandwidth 520 - 59 - 2 4 -20 -25 -30 -35 2 0 CCOMP = 5pF VCONT = 1 V p-p +0.5 VDC REF = 1 V p-p (0dB) PHASE (deg) -2 -4 -6 -8 -10 -12 -14 -16 GAIN (dB) -40 -45 -50 -55 -60 0 .1 1 10 CCOMP = 25pF CCOMP = 18 pF 1 1 3 5 10 10 FREQUENCY (MHz) FREQUENCY (MHz) Fig. 4 Crossfade Balance vs Frequency Fig. 5 Phase Delay vs Frequency 0.03 0.02 dg (%) dp (deg) 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. PRELIMINARY DATA SHEET The product is in a development phase and specifications are subject to change without notice. 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. CAUTION ELECTROSTATIC SENSITIVE DEVICES DO NOT OPEN PACKAGES OR HANDLE EXCEPT AT A STATIC-FREE WORKSTATION Gennum Corporation assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement. (c) Copyright October 1992 Gennum Corporation. . All rights reserved. Printed in Canada. 5 520 - 59 - 2 |
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