AD826
SINGLE-ENDED TO DIFFERENTIAL LINE DRIVER
Outstanding CMRR (> 80 dB @ 5 MHz), high bandwidth, wide
supply voltage range, and the ability to drive heavy loads, make
the AD826 an ideal choice for many line driving applications.
In this application, the AD830 high speed video difference
amp serves as the differential line receiver on the end of a back
terminated, 50 ft., twisted-pair transmission line (see Figure 40).
The overall system is configured in a gain of +1 and has a –3 dB
bandwidth of 14 MHz. Figure 39 is the pulse response with a
2 V p-p, 1 MHz signal input.
2V
100
90
200ns
10
0%
2V
Figure 39. Pulse Response
15V
0.01 F
50 FEET TWISTED PAIR
Z = 72
15V
0.01 F
I
N
0.1 F
2.2 F
36
0.1 F
1.05k
BNC
5pF
1.05k
5pF
1/2
AD826
36
V
OUT
1.05k
1.05k
36
36
AD830
1/2
AD826
0.01 F
–15V
–15V
0.1 F
2.2 F
0.01 F
0.1 F
Figure 40. Differential Line Driver
LOW DISTORTION LINE DRIVER
1.1k
V
S
1 F
The AD826 can quickly be turned into a powerful, low distor-
tion line driver (see Figure 41). In this arrangement the AD826
can comfortably drive a 75
Ω
back-terminated cable, with a
5 MHz, 2 V p-p input; all of this while achieving the harmonic
distortion performance outlined in the following table.
Configuration
1. No Load
2. 150
Ω
R
L
Only
3. 150
Ω
R
L
7.5
Ω
R
C
2nd Harmonic
–78.5 dBm
–63.8 dBm
–70.4 dBm
1k
0.1 F
1/2
AD826
1k
R
C
7.5
1k
In this application one half of the AD826 operates at a gain of
2.1 and supplies the current to the load, while the other pro-
vides the overall system gain of 2. This is important for two
reasons: the first is to keep the bandwidth of both amplifiers the
same, and the second is to preserve the AD826’s ability to oper-
ate from low supply voltages. R
C
varies with the load and must
be chosen to satisfy the following equation:
R
C
= MR
L
where
M
is defined by [(M+ 1) G
S
= G
D
] and G
D
= Driver’s Gain,
G
S
= System Gain.
–12–
1/2
AD826
1 F
75
75
R
L
75
0.1 F
Figure 41. Low Distortion Amplifier
REV. B
AD [ ANALOG DEVICES ]
