AD828
A
IN
510
2
510
510
536
100FT
RG59A/U
R
Z
= 75
510
510
536
3
R
Z
1
R
Z
1
3
B
IN
510
2
1/2
AD828
1/2
AD828
6
B
OUT
7
6
1/2
AD828
5
5
1/2
AD828
7
A
OUT
Figure 42. Bidirectional Transmission CKT
Full-Duplex Transmission
Superior load handling capability (50 mA min/amp), high band-
width, wide supply voltage range and excellent crosstalk
rejection makes the AD828 an ideal choice even for the most
demanding high speed transmission applications.
The schematic below shows a pair of AD828s configured to
drive 100 feet of coaxial cable in a full-duplex fashion.
Two different NTSC video signals are simultaneously applied at
A
IN
and B
IN
and are recovered at A
OUT
and B
OUT
, respectively.
This situation is illustrated in Figures 43 and 44. These pictures
clearly show that each input signal appears undisturbed at its
output, while the unwanted signal is eliminated at either receiver.
The transmitters operate as followers, while the receivers’ gain is
chosen to take full advantage of the AD828’s unparalleled CMRR.
(In practice this gain is adjusted slightly from its theoretical
value to compensate for cable nonidealities and losses.) R
Z
is
chosen to match the characteristic impedance of the cable
employed.
Finally, although a coaxial cable was used, the same topology
applies unmodified to a variety of cables (such, as twisted pairs
often used in telephony).
500mV
100
500mV
100
A
IN
90
B
IN
90
B
OUT
10
0%
A
OUT
10
0%
500mV
10µs
500mV
10µs
Figure 43. A Transmission/B Reception
Figure 44. B Transmission/A Reception
+15V
A High Performance Video Line Driver
The buffer circuit shown in Figure 45 will drive a back-
terminated 75
Ω
video line to standard video levels (1 V p-p)
with 0.1 dB gain flatness to 40 MHz with only 0.05° and 0.01%
differential phase and gain at the 3.58 MHz NTSC subcarrier
frequency. This level of performance, which meets the require-
ments for high-definition video displays and test equipment, is
achieved using only 7 mA quiescent current/amplifier.
0.1 F
V
IN
R
T
75
2
8
1.0 F
75
1/2
AD828
3
4
1
R
BT
75
R
T
75
–15V
1k
1k
0.1 F
1.0 F
Figure 45. Video Line Driver
REV. B
–11–
AD [ ANALOG DEVICES ]
