AD830

REV. A

–13–

Differential Line Receiver

The AD830 was specifically designed to perform as a differen-

tial line receiver. The circuit in Figure 33 shows how simple it is

to configure the AD830 for this function. The signal from sys-

tem “A” is received differentially relative to A’s common, and

that voltage is exactly reproduced relative to the common in sys-

tem B. The common-mode rejection versus frequency, shown in

Figure 1, is excellent, typically 100 dB at low frequencies. The

high input impedance permits the AD830 to operate as a bridg-

ing amplifier across low impedance terminations with negligible

loading. The differential gain and phase specifications are very

good as shown in Figure 7 for 500

Ω and Figure 10 for 150 Ω.

The input and output common should be separated to achieve

the full CMR performance of the AD830 as a differential ampli-

fier. However, a common return path is necessary between sys-

tems A and B.

45

36

AD830

1

2

8

7

A=1

COMMON IN

SYSTEM B

COMMON IN

SYSTEM A

INPUT

SIGNAL

0.1µF

0.1µF

C

Figure 33. Differential Line Receiver

Wide Range Level Shifter

The wide common-mode range and accuracy of the AD830 al-

lows easy level shifting of differential signals referred to an input

common-mode voltage to any new voltage defined at the out-

put. The inputs may be referenced to levels as high as 10 V at

the inputs with a

±2 V swing about 10 V. In the circuit of Fig-

tion shown below. The excellent linearity and low distortion are

preserved over the full input and output common-mode range.

The voltage sources need not be of low impedance, since the

high input resistance and modest input bias current of the

AD830 V-to-I converters permit the use of resistive voltage di-

viders as reference voltages.

45

3

6

AD830

1

2

8

7

A=1

OUTPUT

COMMON

0.1µF

0.1µF

INPUT

COMMON

C

INPUT

SIGNAL

Figure 34. Differential Amplification with Level Shifting

Difference Amplifier with Gain > 1

The AD830 can provide instrumentation amplifier style differ-

ential amplification at gains greater than 1. The input signal is

connected differentially and the gain is set via feedback resistors

can provide either inverting or noninverting differential amplifi-

cation. The polarity of the gain is established by the polarity of

≤ 1 kΩ to maintain closed-loop stability and also keep

bias current induced offsets low. Highest CMRR and lowest dc

offsets are preserved by including a compensating resistor in

series with Pin 3. The gain may be as high as 100.

4

5

36

AD830

1

2

8

7

A=1

0.1µF

0.1µF

R1

R2

INPUT

SIGNAL

C

Figure 35. Gain of G Differential Amplifier, G > 1

Offsetting the Output with Gain

Some applications, such as A/D drivers, require that the signal

be amplified and also offset, typically to accommodate the input

range of the device. The AD830 can offset the output signal

very simply through Pin 3 even with gain > 1. The voltage ap-

plied to Pin 3 must be attenuated by an appropriate factor so

G = desired offset. In Figure 36, a resistive divider

from a voltage reference is used to produce the attenuated offset

voltage.

45

3

6

AD830

1

2

8

7

A=1

INPUT

SIGNAL

0.1µF

0.1µF

C

Figure 36. Offsetting the Output with Differential Gain > 1