ELEC 241 Lab

Experiment 3.2

Filters and Transfer Function

Equipment

Standard Instrument Suite
Standard Breadboard Set

Components

Resistor: 2.2 k $\Omega$
Capacitor: .33 $\mu$ F

Part 1: Measuring Transfer Function

Measuring the transfer function of an RC circuit is considerably more involved than measuring the attenuation of a resistive voltage divider. We have to make the measurement at a number of frequencies, and we must measure phase as well as amplitude.

Step 1:

Select a 2.2 k $\Omega$ resistor and a .33 $\mu$ F capacitor from your parts kit.

Note Ceramic capacitors use the same labeling codes as the potentiometers except that the units are picofarads (pF) instead of ohms. So a .33 $\mu$ F capacitor would be a 330,000 pF capacitor which would have the code 334 ( $33 \times 10^4$ ).

Step 2:

Using these components, wire the following circuit: $\includegraphics[scale=0.650000]{ckt3.2.1.ps}$

Step 3:

Connect the function generator to supply $v_{in}$ and the oscilloscope to measure $v_{out}$ .

Step 4:

Using the technique described in the previous section, measure the frequency response of the circuit at the following frequencies: 20 Hz, 50 Hz, 100 Hz, 200 Hz, 500 Hz, 1 kHz, 2 kHz, 5 kHz, 10 kHz, and 20 kHz.

Step 5:

Plot the magnitude of the transfer function vs. frequency on loglog axes and the phase on semilog axes.

Question 4:

Using Matlab, compute and plot the expected transfer function for the circuit you built. How well does this compare with what you measured?

Step 6:

Leave this circuit assembled and connected to the function generator. We will use it in the next experiment.