CLIPPING AND CLAMPING DIODE CIRCUITS

OBJECTIVES:

  • To understand the theory of operation of the clipping and clamping diode circuits.
  • To design wave shapes that meet different circuits needs.

INTRODUCTION:

By definition, clipping circuits clip signals above a selected voltage level, whereas clamping circuits shift the DC voltage of a waveform. Many wave shapes can be produced with the proper application of these two important diode functions.

PRE-LAB WORK:

  1. Theoretical Output Voltages
    Predict the expected output waveform of each circuit shown in Figures 1 through 6. Assume that the diodes used in the circuit are ideal. For all the cases use a 1kHz triangle wave with a 10-volt peak-to-peak magnitude and zero DC offset unless instructed otherwise.
  2. Clipping Circuit Design
    Design a circuit to obtain an output waveform as shown in Figure 7.

LAB WORK:

  1. Clipping Circuit
    Form the circuit of Figure 1 on the breadboard. Display both input and output on two separate DC coupled oscilloscope channels. Observe and make scaled sketches of both input and output waveforms. Use a 10 Volt peak-to-peak triangle wave with zero DC offset at 1kHz as the input signal in this as well as all other measurements of this experiment.
    Clipping Circuit
    Figure 1 Clipping Circuit used in experiment. The diode is a 1N914 silicon diode.

    Replace the DC supply shown in Fig. 1 with a Zener diode as shown in Figure 2. Measure the DC characteristic for the circuit.
    • How will this characteristic change if both diodes reverse polarity?
    • Apply a 10V peak-to-peak triangular waveform to the input and monitor both input and output waveforms simultaneously. Capture the oscilloscope display.
    • Measure the clipping level of the waveform and compare it with the measured DC characteristic. Comment on your finding!

    Clipping Circuit used in experiment. The diode is a 1N914 silicon diode. The Zener diode is 1N4614.
    Figure 2 - Clipping Circuit used in experiment. The diode is a 1N914 silicon diode. The Zener diode is 1N4614.

    Compare the waveforms obtained from the circuit in Figure 1 with those obtained from the circuit in Figure 2. Comment on the similarities and dissimilarities in the performance.
  2. Inverse Clipping Circuit Form the circuit of Figure 3 on the breadboard. Repeat the measurement by reversing the polarity of the diode used in the circuit of Figure 1. Note that the white stripe on the black plastic diode corresponds to the cathode (black line on the right hand side of the diode symbol). Display both input and output waveforms on two separate (dual channels) DC coupled oscilloscope channels. Capture both input and output waveforms on the same screen. Scale the drawing.
    Inverse Clipping Circuit
    Figure 3 - Inverse Clipping Circuit
  3. Clipping with Zener diodes
    Measure the DC characteristic for the circuit shown in Figure 4.
    • Apply a 10V peak-to-peak triangular waveform and capture both input and output waveforms on the same trace.
    • Measure the clipping levels for the output waveforms and compare it with the measured DC characteristic and the ratings of the Zener diodes. Comment on your finding!
    Clipping with two Zener diodes
    Figure 4 - Clipping with two Zener diodes

  4. Clamping Circuit 1
    Form the circuit of Figure 5 by replacing the 1kΩ resistor used in the circuit of Figure 1 with an l µF capacitor. Display both input and output on two separate (dual channel oscilloscope) DC coupled oscilloscope channels. Observe and make scaled sketches of both input and output waveforms on the same graph.
    Clamping Circuit 1
    Figure 5 - Clamping Circuit 1
  5. Clamping Circuit 2
    Form the circuit of Figure 6 by removing the 1.8-Volt DC power supply from the circuit of Figure 5. Observe and capture both input and output waveforms on the same graph.
    Clamping Circuit 2
    Figure 6 - Clamping Circuit 2
  6. Square Wave Input
    Apply a square wave to the circuit of Figure 6. The square wave should be 10 Volts peak-to-peak, 1000Hz with zero DC offset. Observe and record the scaled sketches of the output waveforms for two values of RL (22kΩ and 1kΩ)
  7. Circuit Design and Testing
    Build the circuit designed in the second item of the Prelab work. Observe and sketch the output waveform. Again, the input is a triangle wave, 1kHz and 10 Volts peak to peak to peak to peak with zero DC offset.
Output waveform of circuit designed in Prelab Section 2
Figure 7 - Output Waveform of Circuit Designed in Prelab Part 2

RESULTS:

  1. Error Analysis
    Perform an error analysis on the scaled sketches of the preceding section. Compare the theoretical waveforms of the Prelab with all of the experimentally measured waveforms. Calculate a percent error for each of the key points of the output waveforms. The key points of the output waveforms are the clip voltage levels, clamp offset levels and voltage magnitudes.
  2. Discussion
    Discuss the significance of the change in the output waveform observed in Measurement # 7of the lab work for the two values of RL used. Compare the theoretical output waveform to the measured output waveform.