AD746
A HIGH SPEED 3 OR AMP INSTRUMENTATION
AMPLIFIER CIRCUIT
Table I. Performance Summary for the 3 Op 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).
Gain
2
10
100
R
G
20 kΩ
4.04 kΩ
404
Ω
Bandwidth
2.5 MHz
1 MHz
290 kHz
T
SETTLE
(0.01%)
1.0
µs
2.0
µs
5.0
µs
Figure 25. Settling Time of the 3 Op
Amp Instrumentation Amplifier.
Gain = 10, Horizontal Scale: 0.5
µ
s/Div,
Vertical Scale: 5 V/Div.
Error Signal Scale: 0.01%/Div.
THD Performance Considerations
Figure 23. A High Performance, 3 Op Amp, Instrumenta-
tion Amplifier Circuit
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 24. Pulse Response of the 3
Op Amp Instrumentation Amplifier.
Gain = 10, Horizontal Scale:
0.5
µ
s/Div, Vertical Scale: 5 V/Div.
Figure 27. THD Measurement, Follower Circuit
REV. B
–7–
AD [ ANALOG DEVICES ]
