Datasheet

Two Operational Amplifier Instrumentation Amplifier
4-8
Example Circuits
4.6 Two Operational Amplifier Instrumentation Amplifier
Figure 4–5 shows area 200 equipped with a dual operational amplifier config-
ured 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
1
2 R 206
R 210
R 206
R 221
VREF 2
Where
R206 = R202 and R221 = R204
To cancel the effects of input bias current, set R208 = R206 || R210 and set
R211 = R202 ||R204, or use a 0-Ω jumper for R208 and R211 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 R216 and R217 for the desired
VREF2 voltage. The formula for calculating VREF2 is:
VREF 2 1.24 V
R 216 R 217
R 217