ELE 342 Electronics 1
Lab 3

RC Active Filters

Objective

Apart from amplifying signals, op-amps can also be used to separate signals based on their frequency content. This lab introduces some building blocks frequently encountered in practical filter circuits.

Tasks

  1. For the circuit in Figure 1a select R1=1k and determine R2 and C2 so that you establish a dc gain of 100 and a 3dB corner frequency at fp=100Hz (Assume the op-amp to be ideal).

  2. Verify the frequency response of your design by PSpice and realize the circuit on the breadboard.

  3. Supply the circuit in Figure 1a with a bipolar pulse train of 1V amplitude and a repetition rate of a) 1kHz, b) 10kHz and c) 100kHz. Record the resulting output waveforms and try to explain your observations.

  4. Select R2 in Figure 1b equal to 1k and determine C1 so that the magnitude of the voltage transfer function Vout/Vin becomes unity at fu=10kHz.

  5. Repeat tasks 2 and 3 with this circuit.

  6. Realize the circuit in Figure 2 by selecting R1=R2=R3=1.5k, C1=33nF and C2=3.3nF. Verify the frequency response (magnitude and phase) of the filter by PSpice and use about 20 logarithmically spaced measurement points between 1kHz and 100kH to verify the performance on the board.

  7. Repeat task 3 with the second-order filter circuit and draw your conclusions.

Figure 1   RC-active integrator and differentiator circuits.


Figure 2   Second-order RC-active lowpass filter.