PIN DESIGNATION
1
+V
S
positvive supply voltage
2
C
HOLD
clamp holding capacitor
3
COMP
output freq'y comp'n R-C
4
C
OS1
control input offset adjust
5
C
OS2
control input offset adjust
6
S1
span adjust
7
V
REF
0.5 volt reference input
8
S2
span adjust
9
V
CONT
control signal input
10
GND
ground
11
STROBE
strobe input
12
R
EXT
current setting resistor
13
+IN A
A video + signal input
14
-IN A
A video - signal input
15
CLAMP SIG clamp signal
16
CLAMP REF clamp reference
17
+IN B
B video + signal input
18
-IN B
B video - signal input
19
OUTPUT
video output
20
-V
S
negative supply voltage
Document No. 520 - 59 - 2
DATA SHEET
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
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
GT4124 Video Multiplier
with Strobed DC Restore
Device Function: V
OUT
= A
OL
[V
A
(0.5+V
K
) + V
B
(0.5 - V
K
)] where A
OL
~ 2000, V
K
=V
CONT
- V
REF,
AK
0.85
R
EXT
R
SPAN
FUNCTIONAL BLOCK DIAGRAM
R
EXT
V
REF
CONTROL
VOLTAGE
(VCONT)
+
-
-
V
S
GND
+
IN A
-
IN A
-
IN B
V
CA
=0.5 + V
K
+
IN B
+
V
S
BIAS
AMP 3
COMP.
OUTPUT
V
NOM
AMP 1
AMP 2
+
-
+
-
XA
V
CB
=0.5 - V
K
XB
+
+
AMP 4
-
+
A
K
C
OS1
C
OS2
S1
S2
0.5V
2
3
+
-
+
-
+
+
V
K
-
V
K
4
+
+
STROBE
C
HOLD
CLAMP REF.
CLAMP SIG.
1
CLAMP
V
NOM
+
+
VIDEO
INPUT A
VIDEO
INPUT B
0.5V
ORDERING INFORMATION
Part Number
Package Type Temperature Range
GT4124-CDF
20 pin PDIP
0 to 70
GT4124-CKF
20 pin SOIC
0 to 70
Revision Date: February 1994
A
B
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
C
+ V
IN
(1 - V
C
)
where V
C
is the control input voltage, which may be varied
over the control range, and V
IN
A
and V
IN
B
are the video
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.
An application note entitled "Using the GT4122 and GT4124
Video Mixer ICs" (Document 520-44) is available from
Gennum Corporation.
2
520 - 59 - 2
PARAMETER VALUE/UNITS
Supply Voltage (V
S
)
13.5 V
Operating Temperature Range
0
C
T
A
70
C
Storage Temperature Range
-65
C
T
S
150
C
Lead Temperature
(Soldering, 10 Sec)
260
C
Differential Video Input Voltage
5 V
Strobe Input Voltage
V
EE
V
CLAMP
V
CC
ABSOLUTE MAXIMUM RATINGS
TOP VIEW
20
PIN 1
10
11
+IN B
-IN A
+IN A
GND
C
OS1
+V
S
C
OS2
-V
S
C
HOLD
R
EXT
PIN CONNECTIONS
V
CONT
V
REF
-IN B
OUTPUT
CLAMP
REF
CLAMP
SIG
Supply Voltage
V
S
Operating Range
9
10
12
volts
POWER
Supply Current (pos)
I
+
R
EXT
= 1 k
-
24
28
mA
SUPPLIES
Supply Current (neg)
I
-
R
EXT
= 1 k
-
18
20
mA
Small Signal Bandwidth
BW at
0.1 dB V
SIG
= 150 mVp-p
25
30
-
MHz
Full Power Bandwidth
BW at -3.0 dB V
SIG
= 1 V p-p
20
25
-
MHz
Frequency Response
DC - 10 MHz
-
0.05
-
dB
Differential Gain
g
V
IN
= 40 IRE at 3.58 MHz
-
0.01
0.03
%
Differential Phase
p
V
IN
= 40 IRE at 3.58 MHz
-
0.01
0.03
degrees
SIGNAL
Signal to Noise
S/N
V
SIG
= 1 volt, BW = 5 MHz
64
70
-
dB
CHANNEL
Gain - open loop
A
OL
100 kHz ( = 0%)
54
60
66
dB
Gain - closed loop
A
CL
100 kHz ( = 100%)
-0.01
-0.005
-
dB
Phase Delay
td
SIG
-
-
10
ns
Off Isolation & Crosstalk
V
A or B
/V
O
SIG
= 5 MHz (see note 1)
80
85
-
dB
V
C
/V
A or B
SIG
= 5 MHz (see note 2)
90
95
-
dB
Bandwidth
BW
at
0.1 dB V
SIG
= 150 mVp-p
25
30
-
MHz
CONTROL
Phase Delay
t
d CONT
-
-
10
ns
CHANNEL
Linearity
-
1
-
%
Control Breakthrough
V
CONT
= 0-1 V = 1-10 MHz
-
-55
-50
dB
Crossfade Balance
V
CONT
= 0-1 V = 3.58 MHz
-
3
5
mVpp
Control Range
V
CONT
-5
-
+5
V
Strobe Pulse Width
500
1000
-
ns
Strobe Level
V
INHI
2.0
-
-
V
V
INLO
-
-
0.8
V
Clamp Accuracy
-
1
2
mV
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ELECTRICAL CHARACTERISTICS
+V
S
= -V
S
=10V, 0
C
T
A
70
C unless otherwise shown
STROBE
20 PIN DIP / SOIC
COMP
S-1
S-2
Notes:
1. V
A or B
= 1 Vp-p output taken from OUTPUT
2. V
CONT
= 1 Vp-p output taken from V
A
or
V
B
3
520 - 59 - 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 (V
CA
)
or (V
CB
). The controlling voltage V
CA
is the sum of a nominal
0.5V source (V
NOM
) and a variable source V
K
while V
CB
is
made up of the sum of the nominal voltage V
NOM
and -V
K
.
V
K
and -V
K
are themselves proportional to the difference
between an externally applied reference voltage (V
REF
) and
an externally applied CONTROL voltage (V
C
). The voltages V
K
and -V
K
are produced by a differential amplifier (AMP3) whose
gain is A
K
. This gain can be altered by two external resistors,
R
EXT
and R
SPAN
according to the following formula:
Note that R
EXT
is connected between the R
EXT
pin and ground
and R
SPAN
is connected between the pins S1 and S2.
Each of the voltages (+V
K
and -V
K
) 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 V
C
= V
REF
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.
0.85 R
EXT
A
K
---------- [1k
< R
EXT
< 3k
]
R
SPAN
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 C
HOLD
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:
V
O
= V
A
[V
NOM
+ A
K
(V
C
- V
REF
)] + V
B
[V
NOM
- A
K
(V
C
- V
REF
)]
(Unity gain configuration)
Where V
A
and V
B
are the input analog signals applied to +IN A
and +IN B respectively, and V
C
is the CONTROL voltage.
Note that V
NOM
ranges between 0.45V < V
NOM
< 0.55.
For normal video mixer operation, the control range (SPAN) is
usually 0 to 1V and will occur when A
K
=1, V
REF
= 0.5V and
V
NOM
=0.5 volts. A change in V
C
from 0 to 1V will then produce
an effect such that the output signal contains 100% of Channel
B when V
C
is 0V and 100% of Channel A when V
C
is 1 volt. For
the above conditions, the general unity gain transfer function
reduces to:
V
O
= V
A
V
C
+ V
B
(1-V
C
)
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.
4
520 - 59 - 2
*
Capacitor C5 required if the
control voltage is from a power
supply.
All resistors in ohms, all capacitors
in F unless otherwise stated.
Fig. 1 Test Circuit
-5V
+5V
GT4124
CONTROL
OFFSET
RV2
100
C3
0.1
Z1
6.2V
R3
1k
RV1
200
R2
1k
10nF
R1
560
(0.5V)
R4
5.6k
50%
GAIN
1
4
3
17
18
19
20
+10V
-10V
-V
S
GND
COMP
C
OS1
B
OS2
6
5
7
15
16
14
+IN B
S1
-IN B
-IN A
9
8
10
12
13
S 2
V
REF
+IN A
11
-10V
C5
47
C1
0.1
5 - 25pF
C
COMP
1k
RV4
VREF
ADJUST
RV3
SPAN
ADJUST
C5
0.1
+V
S
C
OS2
V
C
R
EXT
C
LREF
+
C
LSIG
STROBE
2
C
HOLD
C6
0.1
B VIDEO INPUT
CONTROL INPUT
75
if required
C7
0.1
A VIDEO INPUT
75
if required
75
if required
IC2
CLC110
1
4
5
8
VIDEO OUT
STROBE
0.1
1k
47
+
*
Fig. 2 Gain vs Frequency
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
2.5
3.0
GAIN (dB)
GAIN (dB)
1
100
1
50
1
10
100
FREQUENCY (MHz)
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
1
10
50
FREQUENCY (MHz)
TYPICAL PERFORMANCE CURVES
(unless otherwise shown V
S
=
10V)
CH - B
V
IN
= 1 V p-p
CH - A
Fig. 3 Full Power Bandwidth
V
IN
= 150 mVp-p
5
520 - 59 - 2
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.
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
-20
-25
-30
-35
-40
-45
-50
-55
-60
PHASE (deg)
1
3
5
10
FREQUENCY (MHz)
1
10
1
10
GAIN (dB)
0 .1
1
10
FREQUENCY (MHz)
Fig. 4 Crossfade Balance vs Frequency
Fig. 5 Phase Delay vs Frequency
1
3
5
10
FREQUENCY (MHz)
0.03
0.02
0.01
0.00
-0.01
-0.02
-0.03
Fig. 6 Differential Gain and Phase
vs Frequency
dg (%) dp (deg)
C
COMP
= 5pF
C
COMP
= 25pF
C
COMP
= 18 pF
dg
dp
V
CONT
= 1 V p-p +0.5 VDC
REF = 1 V p-p (0dB)
2
0
-2
-4
-6
-8
-10
-12
-14
-16
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