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.
+10V
C5
47
-10V
+5V
GT4122
1 -V
S
2
R1
+V
S
OUT
20
IC2
CLC110
4
ROUT
10k or
OPEN
5
1
8
VIDEO OUT
C7 0.1
C6 0.1
C5
47
+
-10V
C1
0.1
+
C2 0.1
0.1
or LINK
COUT
RV4
500
B BLACK
LEVEL
ADJUST
B
OS2
19
-IN B
+IN B
B
OS1
A
OS2
-IN A
+IN A
A
OS1
R
EXT
12
11
R2
1k
18
17
16
15
14
13
RV5
500
RV1
200
3 COMP
4 C
OS1
5 C
OS2
6 S1
7
1K
8
9
V
REF
S2
V
C
GND
5 - 25pF
CCOMP
50%
GAIN
CONTROL
OFFSET
560
RV2
100
-5V
B VIDEO INPUT
75
if required
A VIDEO INPUT
75
if required
CONTROL INPUT
75
if required
R3
1k
RV3
SPAN
C3 ADJUST
0.1
A BLACK
LEVEL
ADJUST
R4
5.6k
RV6
1k
(0.5V)
C5
0.1
VREF
ADJUST
10
Z1
6.2V
NOTE: C5 is used when the CONTROL VOLTAGE (V
C
) is derived from a power supply.
All resistors in ohms, all capacitors in
µF
unless otherwise stated.
Fig. 1 Test Circuit
520 - 25 - 4
4
GENNUM [ GENNUM CORPORATION ]
