ADC121S021

IN

V

+

LM4140A

6

2

1,4,7,8

3

V

+

1 PF

+

-

0.1 PF

10 PF

VA

V

+

+

-

+

-

-

+

12 k:

10 k:

40 k:

½

LMP2232

R+'R

R+'R

R

R

V

+

V

+

V

+

12 k:

10 k:

40 k:

1 k:

½

LMP2232

GND

½

LMP2232

½

LMP2232

EXCITATION

SOURCE

R1

R2

R3

R4

VOUT

(a)

VOUT

1 +

R3

R1

¨

¨

©

§

1 +

R4

R2

¨

¨

©

§

R3

R1

-

R4

R2

x VSOURCE

=

EXCITATION

SOURCE

R + 'R

R - 'R

R - 'R

R + 'R

VOUT

(b)

VOUT =

'R

R

x VSOURCE

LMP2232

www.ti.com

SNOSB02C – JANUARY 2008 – REVISED MARCH 2013

Figure 50(a) shows a typical bridge sensor and Figure 50(b) shows the bridge with four sensors. R in

Figure 50(b) is the nominal value of the sense resistor and the deviations from R are proportional to the quantity

being measured.

Figure 50. Bridge Sensor

Instrumentation amplifiers are great for interfacing with bridge sensors. Bridge sensors often sense a very small

differential signal in the presence of a larger common mode voltage. Instrumentation amplifiers reject this

common mode signal.

Figure 51 shows a strain gauge bridge amplifier. In this application one of the LMP2232 amplifiers is used to

buffer the LM4140A's precision output voltage. The LM4140A is a precision voltage reference. The other three

amplifiers in the LMP2232 are used to form an instrumentation amplifier. This instrumentation amplifier uses the

LMP2232's high CMRR and low VOS and TCVOS to accurately amplify the small differential signal generated by

the output of the bridge sensor. This amplified signal is then fed into the ADC121S021 which is a 12-bit analog to

digital converter. This circuit works on a single supply voltage of 5V.

Figure 51. Strain Gage Bridge Amplifier

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