ECE 2212

Experiment 3: Additional Operational Amplifier Circuits

Fall 2003

PURPOSE

To implement the designs of a:

Ø Low-Pass Filter and Integrator

Ø High-Pass Filter and Differentiator

Ø Comparator With Hysteresis and examine the performance by observing transfer and output characteristics.

PRELAB

Design the circuits to meet the indicated specifications. You should come to the lab with a list of the components you will need to meet the specifications. For the Low-Pass Filter and Integrator, the corner frequency is computed from and the low frequency voltage gain is given by and for the High-Pass Filter and Differentiator, and the high frequency voltage gain is given by . The derivation of the corner frequencies follows that of the passive RC circuits from Experiment 1. Include the derivations in your notebook.

PROCEDURE

Refer to the mA741 data sheet. Observe, you are using the 8-pin DIP. You do not need to include the 10 kW offset voltage potentiometer. All resistors must be > 2 kW. Use ± 12 volts for the power supplies. Your designs should be supported analytically and by SPICE simulation results. Use the operational amplifier model in Text Figure 1.12b and information from the mA741 data sheet. You may also use the .LIB model for the mA741 included in ORCAD PSPICE 9.1, as well as other versions, if you want to. Always look at your output waveforms, experimentally insure you are not clipping. Explain why you will not observe clipping when you use the linear op amp model and perform a .TRAN simulation. Also be able to explain why the comparator with hysteresis will not model using the linear model from Figure 1.12b.

Design and test an integrator/low-pass filter with a low-frequency voltage gain of 20 dB and a 3 dB corner frequency of approximately 3 kHz.

Ø Experimentally verify your design and simulation results.

Ø For verifying low-pass filter operation, measure 20 log|A(jf)| and q(jf) and compare your results with the PSPICE .AC simulation over a similar range.

Ø For verifying integrator operation, let Vs be a 5 kHz, square wave, triangular wave, and sine wave. Predict the output and verify. Compare with a .TRAN simulation.

Design and test a differentiator /high-pass filter with a high-frequency voltage gain of 20 dB and a 3 dB corner frequency approximately 3 kHz.

Ø Experimentally verify your design and simulation results.

Ø For verifying high-pass filter operation, measure 20 log|A(jf)| and q(jf) and compare your results with the PSPICE .AC simulation over a similar range.

Ø For verifying differentiator operation, let Vs be a 100 Hz, square wave, triangular wave, and sine wave. Predict the output and verify. Compare with a .TRAN simulation.

The following circuit is called a COMPARATOR with hysteresis.

Ø Verify the operation with a 100 Hz triangular wave and R = 100 kW and then with R = 22 kW. You will have to carefully adjust the input amplitude to verify switching operation.

Ø To do this, you will need to use the oscilloscope to plot Vo versus Vs, that is the transfer characteristic.

Ø Explain why a .TRAN operation will not work to simulate your results using Text Figure 1.12(b) for a model but would work if you used the .LIB model for the mA741 included in ORCAD PSPICE 9.1

Ø Explain your results analytically. Note this is a positive feedback circuit so that the summing point constraint approach will not be valid when you do the analysis.