AD830

REV. A

–15–

AC COUPLED LINE RECEIVER

The 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

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. The 10 k

Ω re-

impedance to keep the input coupling corner frequency low, but

not too large so that residual bias current induced offset voltage

becomes troublesome. For dual supply operation, the 10 k

Ω

resistors may go directly to ground. The 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. The 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. This level of performance is almost

impossible to achieve with discrete solutions.

4

5

3

6

AD830

1

2

8

7

A=1

+12V

0.1µF

75

Ω

75

Ω

1000µF

75

Ω

COAX

CABLE

+12V

4.7k

Ω

6.8V

1N4736

10k

Ω

10k

Ω

10µF

10µF

10k

Ω

10k

Ω

2k

Ω*

*OPTIONAL TUNING FOR

IMPROVING VERY LOW

FREQUENCY CMR.

C

INPUT

SIGNAL

Figure 42. AC Coupled Line Receiver

120

100

20

10

100

100M

10M

1M

100k

10k

1k

80

60

40

FREQUENCY – Hz

WITH CIRCUIT TRIMMED

USING EXTERNAL 2k

Ω

POTENTIOMETER

WITHOUT EXTERNAL

2k

Ω POTENTIOMETER

Figure 43. Common-Mode Rejection vs. Frequency for

Line Receiver

1

–0.4

–0.9

10

100

10M

1M

100k

10k

1k

–0.3

–0.2

–0.1

0

–0.8

–0.7

–0.6

–0.5

FREQUENCY – Hz

Figure 44. Amplitude Response vs. Frequency for Line

Receiver