EXPERIMENT 6

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.

2. Clipping Circuit Design

Design a circuit to obtain an output waveform as shown in Figure 7. Use a 1 kHz triangle wave with

a 10-volt peak-to-peak magnitude (zero DC offset) as the input signal. 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

1000 Hz as the input signal in this as well as all other measurements of this experiment

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 Fig. 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!

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 Fig. 1 with those obtained from the circuit in Fig. 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.

Figure 3 Inverse Clipping Circuit. 3. Clipping with Zener diodes Measure the DC characteristic for the circuit shown in Fig. 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!

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.

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.

Figure 4 Clipping with two Zener diodes.

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.

Figure 7 Output waveform of circuit designed in Prelab Section 3.2.1

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.

REQUIRED PARTS Item Description Qty

1 1µF capacitor 1

2 1kΩ resistor 1

3 22kΩ resistor 1

4 1N914 Diodes 2