AD746

REV. B

–7–

Table I. Performance Summary for the 3 Op Amp

Instrumentation Amplifier Circuit

Gain

Bandwidth

(0.01%)

2

20 k

Ω

2.5 MHz

1.0

µs

10

4.04 k

Ω

1 MHz

2.0

µs

100

404

Ω

290 kHz

5.0

µs

Figure 25. Settling Time of the 3 Op

Amp Instrumentation Amplifier.

Gain = 10, Horizontal Scale: 0.5

µs/Div,

Vertical Scale: 5 V/Div.

Error Signal Scale: 0.01%/Div.

THD Performance Considerations

The AD746 was carefully optimized to offer excellent

performance in terms of total harmonic distortion (THD) in

signal processing applications. The THD level when operating

the AD746 in inverting gain applications will show a gradual

rise from the distortion floor of 20 dB/decade (see Figure 28).

In noninverting applications, care should be taken to balance

the source impedances at both the inverting and noninverting

inputs, to avoid distortion caused by the modulation of input

capacitance inherent in all BiFET op amps.

Figure 26. THD Measurement, Inverter Circuit

Figure 27. THD Measurement, Follower Circuit

A HIGH SPEED 3 OR AMP INSTRUMENTATION

AMPLIFIER CIRCUIT

The instrumentation amplifier circuit shown in Figure 23 can

provide a range of gains from 2 up to 1000 and higher. The

circuit bandwidth is 2.5 MHz at a gain of 2 and 750 kHz at a

gain of 10; settling time for the entire circuit is less than 2

µs to

within 0.01% for a 10 volt step, (G = 10).

Figure 23. A High Performance, 3 Op Amp, Instrumenta-

tion Amplifier Circuit

Figure 24. Pulse Response of the 3

Op Amp Instrumentation Amplifier.

Gain = 10, Horizontal Scale:

0.5

µs/Div, Vertical Scale: 5 V/Div.