Study the characteristics of the operational amplifier
Design and test an operational amplifier circuit
Preparation:
Determine the value of Rf for which the gain, Vo/Vi, is -5 in the inverting amplifier circuit given above.
Determine the maximum and minimum values of Vi for which the op-amp will not saturate if the supply voltages are ±15 V.
Use PSpice to simulate the circuit. Do a DC sweep analysis to create a plot of Vo verses Vi over the range of -15 V to 15 V with 0.5 V increments. (Read about DC Sweep in the
PSpice Appendex starting on page A-29.) Set the supply voltages for the op-amp to ±15 V. Use Probe
under the Analysis menu to create a plot of Vo and determine the gain from the plot. (If you can't figure this out, move on!)
Equipment and Parts:
Power Supply
Digital Multimeter(s)
Resistors: 800 Ω , 1 kΩ , & ? kΩ
An LM741C op-amp or equivalent
Procedure:
Create the inverting amplifier circuit from the preparation on a proto board with
supply voltages of ± 15 V. Record actual values.
Measure Vo for various values of Vi. Use 0.5 V increments starting just below the calculated lower limit in step 2 of
the preparation to just above the upper limit.
Calculate the voltage gain of the circuit in its linear region (non-saturated region)
for all appropriate sets of voltages.
Determine the input resistance of the inverting amplifier circuit as seen by the voltage
source. The input resistance is Ri = Vi/Ii. Ii is deteremined by measuring the current through the 1 kΩ series resistor.
Determine the output resistance of the inverting amplifier circuit. To find the output
resistance, the inverting amplifier circuit can be thought of as a Thevenin equivalent
circuit consisting of a voltage source with a series resistor (the output resistance).
With no load attached, the output voltage will be equal to the source voltage. By
attaching a known load resistance, the output voltage is based on a voltage divider
between the output resistance and the load resistor. Attach several load resistors
and determine the output resistance of the circuit.
Conclusions:
Compare the predicted values from the preparation with the measured values from the
procedure. Indicate how closely the measurements matched the predictions.
Discuss how well op-amp approaches the ideal op-amp characteristics.
