Two Operational Amplifier Instrumentation Amplifier
3-8
Example Circuits
3.7
Two Operational Amplifier Instrumentation Amplifier
Figure 3–6 shows area 200 equipped with a dual operational amplifier
configured as a two-operational-amplifier instrumentation amplifier using a
voltage reference and single power supply.
Basic setup is done by choice of input and feedback resistors. The transfer
function for the circuit as shown is:
V
OUT
+
V
IN
ǒ
1
)
2R212
R220
)
R212
R221
Ǔ
)
VREF2
Where:
R212 = R206 and R221 = R203
To cancel the effects of input bias current, set R217 = R212 || R220 and set
R202 = R206 ||R203, or use a 0-
Ω
jumper for R217 and R202 if the operational
amplifier is a low input bias operational amplifier.
The TLV431 adjustable precision shunt regulator, configured as shown,
provides a low impedance reference for the circuit at about 1/2 V2+ in a 3 V
system. Another option is to adjust resistors R211 and R213 for the desired
VREF2 voltage. The formula for calculating VREF2 is:
VREF2
+
1.24 V
ǒ
R211
)
R213
R213
Ǔ
