EE 321 Lab
Prelab for Lab 7: DIFFERENTIAL AND INSTRUMENTATION AMPLIFIERS

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 R1 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 V0 = 600(V1-V2) (the differential gain of 30 is part of this).

3) Consider Wheatstone bridge in Figure 4 (ignore R1 and R2 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 V0 is 0.0 V. Hint: each side of the bridge is a simple voltage divider.
• Find V0 if the resistance of the strain gauge increased by 0.1 %.
• Find V0 if the resistance of the strain gauge decreased by 0.1 %.
• How close are these values to the approximation, V0 = ( Delta R /R ) V+ / 4 ?
• The resistance of the strain gauge is close to 120 ohms. The other resistors, R are about 121 ohms. R1 and R2 are used to balance the bridge (set V0 to 0.00 V). If R1 and R2 are both 10 K, what is the minimum and maximum of the parallel resistance of that section of the bridge?