CLIPPING AND CLAMPING DIODE CIRCUITS

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					                                          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 1k 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 4 Clipping with two Zener diodes.




                                  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 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 (22k and 1k )

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      1k resistor                                                 1
3      22k resistor                                                1
4      1N914 Diodes                                                2