Gennum GT4124-CKF Gt4124 video multiplier with strobed dc restore Datasheet

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
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