EE 321 Lab
Prelab for Lab 7: DIFFERENTIAL AND INSTRUMENTATION AMPLIFIERS
Read the lab before answering these questions.
1) Consider the difference amplifier shown in Figure 1 and in example 2.6 in Sedra and Smith.
Design the amplifier with a differential gain of about 30 with R_{1} between 4 and 6 k.
2) Consider the instrumentation amplifier shown in Figure 3 and in example 2.7 in Sedra and Smith.
Design the amplifier with a total differential gain of about 600, that is V_{0} = 600(V_{1}V_{2})
(the differential gain of 30 is part of this).
3) Consider Wheatstone bridge in Figure 4 (ignore R_{1} and R_{2} initially).
This simple 4 resistor circuit has been used for many years to convert a change in small resistance
to a proportional change in output voltage.

Assume that the resistance of the strain gauge is equal to R. Show that V_{0} is 0.0 V.
Hint: each side of the bridge is a simple voltage divider.

Find V_{0} if the resistance of the strain gauge increased by 0.1 %.

Find V_{0} if the resistance of the strain gauge decreased by 0.1 %.

How close are these values to the approximation, V_{0} = ( Delta R /R ) V^{+} / 4 ?

The resistance of the strain gauge is close to 120 ohms. The other resistors, R are about 121 ohms.
R_{1} and R_{2} are used to balance the bridge (set V_{0} to 0.00 V).
If R_{1} and R_{2} are both 10 K, what is the minimum and maximum of the parallel resistance
of that section of the bridge?
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