1. Instrumentation Amplifier
There are 2 types of instrumentation amplifiers
2 op-amp (e.g. INA122)
3 op-amp (e.g. INA333)

2. Instrumentation Amplifier
Notice both have gain equations so you can vary the gain
Notice the input impedance is that of the non-inverting terminal of a non-inverting amplifier
High-Z Nodes
Difference Amp
High-Z Nodes
Variable Gain

3. Instrumentation Amplifier
Recall the 0V-0A input properties of an ideal amplifier
Let’s analyze the INA333

4. Instrumentation Amplifier
From the 0V criteria we can determine that the voltage across Rg=Vin1-Vin2
V=0V +
VRg=Vin1-Vin2 -
V=0V

5. Instrumentation Amplifier
We can now solve for VRg in terms of Vcm and Vd.
Notice the common-mode voltage cancels!

6. Instrumentation Amplifier
From the 0A criteria we know that the current through the R3 resistors must be the same as the current through Rg. 0A I I 0A

7. Instrumentation Amplifier
Current through Rg
From Ohm’s law we therefore know that
Substituting for Vin1-Vin2 and re-arranging we get
Differential Gain

8. Instrumentation Amplifier-INA333
From previous slide:

9. Instrumentation Amplifier
Input stage also known as:
Diff-in, diff-out stage
Gain stage
The difference amplifier stage is also known as:
Output stage
Diff-in, single-ended output stage
From our difference amplifier discussion we know the differential gain of the output stage is 1. Therefore,
Same as PDS