ECE 201L Circuit Analysis Laboratory
Lab 7

This lab explores the AC behavior of capacitors and inductors, reviews some elements of diodes, and introduces operational amplifiers.

Do the following exercises. Report your results by writing a Word document and submitting it in Isidore. Submit one report per group.

  1. Pick and inductor from 1-10 mH and a capacitor of 1-100 nF. Measure the inductance and capacitance and calculate the resonant frequency fo from

    Adjust your choice of components so that the frequency is between 5 kHz and 30 kHz.

    ComponentMeasuredCalculated
    L
    n/a
    C
    n/a
    fo n/a

    In each of the following exercises you will need to record the following measurements from the oscilloscope.

  2. Construct the following circuit

    This is a resonant circuit. Adjust the frequency to give maximum output signal. Record the AC response (voltage and phase). Change the frequency higher and lower until the gain (ratio of output to input amplitude) has dropped to 0.707 of the peak gain. The phase shift at this point should be ±45°. Repeat the measurement using a different resistance. Start with a resistance of about 1 kΩ and then about 20 kΩ.

    Case 1 (R =            )

    FrequencyVin VoutRatio (gain)Phase















    Case 2 (R =            )

    FrequencyVin VoutRatio (gain)Phase















  3. Calculate the resonant frequency, bandwidth and Q values for the two sets of measurements above. Bandwidth is the difference between the higher and lower frequencies where the gain drops by 0.707 of its peak value. Compare with the theoretical expressions for the resonant frequency and Q value:

           

    CaseMeasuredCalculated
    Resonant frequencyBandwidthQResonant frequencyBandwidthQ
    1





    2





  4. Repeat the above analysis using the circuit below. Use the same inductor and capacitor, but use resistor values of 50 - 300 Ω. Note that a different formula applies for the bandwidth. Plot bandwidth vs. resistance for 3 or 4 values and try to determine the dependence of bandwidth on resistance.

  5. Construct the full-wave bridge rectifier shown in below. Use a 1 kΩ resistor for the load. Use 1N4000 series diodes (1N4004, for example).


    Measure source voltage on oscilloscope with probes between A and B. Measure load voltage with probes between C and D. Do not attempt to measure both signals on the oscilloscope at the same time, the oscilloscope channels share a common ground and trying to make simultaneous measurements will introduce ground loop problems.

    Set the frequency of the source to 50 Hz and the amplitude to 10 volts peak-to-peak. Attach oscilloscope images of the source voltage and the load voltage to the report, showing the frequency, maximum voltage, and minimum voltage in each signal. Take several pictures with the input varying from 10 volts to 1 volt peak-to-peak. Determine the input amplitude at which the output signal vanishes.

  6. Put a capacitor (try about 10 μF) in parallel with the load resistor and measure the maximum and minimum voltage for an input voltage of about 10 V peak-to-peak. This adds a smoothing filter to the output, making the circuit a simple AC - DC converter.

  7. This exercise exlores the use of the LM348 operational amplifier, which you should find in your parts kit. You will use the triple-output DC supply on the lab bench to provide the ±12-volt power to the op-amp. Figure 1 at the end of this document shows recommended power connections. Connect the +12-volt supply to Va and the −12-volt supply to Vb. Connect the COM output to ground. The pin diagram for the LM348 is reproduced below.


    Pin Diagram of LM348 IC

    Construct the inverting amplifier circuit shown below, with resistances Rf = 470 kΩ, Rs = 47 kΩ, and RC = 10 kΩ. Calculate the ideal gain and phase shift from the nominal resistance values.

    1. Measure the gain and phase shift at the following frequencies.

      Frequency 400 Hz700 Hz1 kHz5 kHz10 kHz50 kHz

    2. Find the frequency and gain at which the phase has shifted by 20° and shifted by 45°


    Inverting amplifier


Connecting prototype board to the triple-output power supply


Figure 1. Connecting prototype board to the triple-output power supply.


Maintained by John Loomis, last updated 2 July 2014