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Up: Lab 6: Design and
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The circuit in Figure 6.2 is a differential amplifier. The only difference
between this circuit and the one you designed
is that the RC's have been replace by an active load. The active
load is actually a current source that provides a very large
effective load effective resistance for RC.
- 1.
- Build the
circuit. By adjusting the 1K potentiometer, set the DC level between
Q2 and Q4 at approx. volts.
This eliminates offset voltages due
to transistor mismatches.
- 2.
- Using a very small input (approx. 1mV) determine the
gain at 100Hz, 1KHz, 10KHz and 50kHz.
(You may have to use an inverting op-amp circuit to get the
required small signal.)
- 3.
- What happens if the magnitude of the input is too big?
- 4.
- Try to determine a method to measure the input resistance of the
diff-amp.
- 5.
- By AC coupling 50K, 100K and 200K loads to your circuit,
try to measure its output resistance. (Use a cap.
for AC coupling the load).
Figure 6.2:
Differential Amplifier
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Next: Experiment: Realistic Op-Amp
Up: Lab 6: Design and
Previous: Current Mirror Current Source
Neil Goldsman
10/23/1998