C4

0.01

PF

1N4733A

(5.1V)

D1

7

2

6

4

3

-

+

R1

R7, 3.9k

R2

C2

3

2

6

7

4

LMP201X

U1

LM6171

U2

-

+

R5, 1M

(+2.5V)

Output

+15V

R4

3.9k

R3

20k

C3

0.01 PF

+15V

-15V

Input

+

-

+

-

VOUT

5V

R1

R2

R2

R1

10k, 0.1%

2k, 1%

2k, 1%

10k, 0.1%

R3

20:

LMP2012QML

www.ti.com

SNOSAU5H – MARCH 2007 – REVISED APRIL 2013

PRECISION STRAIN-GAUGE AMPLIFIER

This Strain-Gauge amplifier (Figure 5) provides high gain (1006 or ~60 dB) with very low offset and drift. Using

the resistors' tolerances as shown, the worst case CMRR will be greater than 108 dB. The CMRR is directly

related to the resistor mismatch. The rejection of common-mode error, at the output, is independent of the

differential gain, which is set by R3. The CMRR is further improved, if the resistor ratio matching is improved, by

specifying tighter-tolerance resistors, or by trimming.

Figure 5.

Extending Supply Voltages and Output Swing by Using a Composite Amplifier Configuration:

In cases where substantially higher output swing is required with higher supply voltages, arrangements like the

ones shown in Figure 6 and Figure 7 could be used. These configurations utilize the excellent DC performance

of the LMP2012 while at the same time allow the superior voltage and frequency capabilities of the LM6171 to

set the dynamic performance of the overall amplifier. For example, it is possible to achieve ±12V output swing

with 300 MHz of overall GBW (AV = 100) while keeping the worst case output shift due to VOS less than 4 mV.

The LMP2012 output voltage is kept at about mid-point of its overall supply voltage, and its input common mode

voltage range allows the V- terminal to be grounded in one case (Figure 6, inverting operation) and tied to a

small non-critical negative bias in another (Figure 7, non-inverting operation). Higher closed-loop gains are also

possible with a corresponding reduction in realizable bandwidth. Table 2 shows some other closed loop gain

possibilities along with the measured performance in each case.

Figure 6.

Copyright © 2007–2013, Texas Instruments Incorporated

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