AD828
A
IN
510
2
510
510
536
100FT
RG59A/U
R
Z
= 75
510
510
536
3
1/2
AD828
R
Z
1
R
Z
1
3
B
IN
510
1/2
AD828
2
6
B
OUT
7
6
1/2
AD828
5
5
1/2
AD828
7
A
OUT
Figure 6. Bidirectional Transmission CKT
Full-Duplex Transmission
Superior load handling capability (50 mA min/amp), high
bandwidth, wide supply voltage range, and excellent crosstalk
rejection makes the AD828 an ideal choice for even 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 7 and 8. These pictures
clearly show that each input signal appears undisturbed at its out-
put, 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 7. A Transmission/B Reception
Figure 8. B Transmission/A Reception
A High Performance Video Line Driver
+15V
0.1 F
V
IN
R
T
75
3
8
1.0 F
75
1
R
BT
75
R
T
75
The buffer circuit shown in Figure 9 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 requirements for
high definition video displays and test equipment, is achieved
using only 7 mA quiescent current/amplifier.
1/2
AD828
2
4
–15V
1k
1k
0.1 F
1.0 F
Figure 9. Video Line Driver
REV. C
–11–
AD [ ANALOG DEVICES ]
