AD830
AC CO UP LED LINE RECEIVER
becomes troublesome. For dual supply operation, the 10 kΩ
resistors may go directly to ground. T he output common is con-
veniently set by a Zener diode for a low impedance reference to
preserve the high frequency CMR. However, a simple resistive
divider will work fine and good high frequency CMR can be
maintained by placing a compensating resistor in series with the
+Y input. T he excellent CMRR response of the circuit is shown
in Figure 43. A plot of the 0.1 dB flatness from 10 Hz is also
shown. With the use of 10 µF capacitors, the CMR is >90 dB
down to a few tens of hertz. T his level of performance is almost
impossible to achieve with discrete solutions.
T he AD830 is configurable as an ac coupled differential ampli-
fier on a single or bipolar supply voltages. All that is needed is
inclusion of a few noncritical passive components as illustrated
below in Figure 42. A simple resistive network at the X GM
input establishes a common-mode bias. Here, the common
mode is centered at 6 volts, but in principle can be any voltage
within the common-mode limits of the AD830. T he 10 kΩ re-
sistors to each input bias the X GM stage with sufficiently high
impedance to keep the input coupling corner frequency low, but
not too large so that residual bias current induced offset voltage
+12V
INPUT
10µF
0.1µF
AD830
SIGNAL
8
1
75Ω
COAX
G
M
R
T
V
CABLE
75Ω
OUT
2
3
4
7
6
5
Z
CM
A=1
10µF
1000µF
10kΩ
10kΩ
2kΩ*
75Ω
+V
S
G
M
C
10kΩ
+12V
4.7kΩ
10kΩ
*OPTIONAL TUNING FOR
IMPROVING VERY LOW
FREQUENCY CMR.
6.8V
1N4736
Figure 42. AC Coupled Line Receiver
120
100
80
1
0
WITH CIRCUIT TRIMMED
USING EXTERNAL 2kΩ
POTENTIOMETER
–0.1
–0.2
–0.3
–0.4
–0.5
WITHOUT EXTERNAL
2kΩ POTENTIOMETER
60
–0.6
–0.7
–0.8
40
–0.9
10
20
100
1k
10k
100k
1M
10M
10
100
1k
10k
100k
1M
10M
100M
FREQUENCY – Hz
FREQUENCY – Hz
Figure 44. Am plitude Response vs. Frequency for Line
Receiver
Figure 43. Com m on-Mode Rejection vs. Frequency for
Line Receiver
REV. A
–15–
ADI [ ADI ]
