Clippers -- Overview
Lab Overview
After performing this lab exercise, learner will be able to:
• Design positive and negative shunt clipper
• Design positive and negative series clipper
• Build the clipper circuit and observe the output
Equipment
To carry out this experiment, you will need:
• TBS 1000B-EDUOscilloscope from Tektronix.
• Voltage probe (provided with oscilloscope) / BNC cables
• Breadboard and connecting wires
• Circuit components - Resistor 1K, 0.25W, Diode 1N4002
/IN4148/equ, Regulated DC supply 0-30V DC, Signal /Function
generator 10Hz to 1 Mhz
Theory
• Clipping circuits are used to select and transmit a part of the given
waveform. The other parts of the waveform are clipped or removed
by the diode clipper circuit.
• These circuits are also known as voltage or current limiters,
amplitude selectors or slicers.
• The piecewise linear model of diode characteristic exhibits a
discontinuity in slope at the cut off voltage Vk. and this point of
slope discontinuity is called a break point.
• For silicon diode the break point occurs at VK ~ 0.7V. This concept
can be used to explain the transfer characteristics of a clipper
circuit, which is a plot of output voltage against the input voltage.
Design
• The limiting resistor R in the circuit can be designed in the
following manner.
• From the diode forward and reverse characteristics, the resistance
in either direction can be determined, respectively, as Rf and Rr. It
can be shown that limiting resistor R =
.
• The ratio Rr/Rf can be called the figure of merit of the diode. From
V-I characteristics of diode, we have Rf= 20 Ω and Rr = 1 MΩ. From
these values, limiting resistor required is R = 3.3 KΩ (std), ½ watt
and we can use 1KΩ to 5K Ω.
Circuit Diagram
Biased Clipping Circuits
Clippers -- Procedures
Step 1
Study the circuit, expected waveform and transfer characteristic.
Step 2
Place the components on bread board or connection board and
connect them as per given circuit diagram. Use patch cords/ wires
for connection as required.
Step 3
Switch on the signal generator and set voltage to 10V P-P and
frequency to 1kHz
Step 4
Set DC voltage to 2 V in case of biased circuits
Step 5
Connect the input and output of the circuit to the two channels of
the CRO. Observe the input and output ( in DC mode only)
waveforms and ensures that it matches with expected wave form.
Step 6
Measure the voltage amplitude, clipping voltage using CRO. Keep
CRO setting in XY mode and observe the transfer characteristic.
Step 7
Draw the waveform on graph sheet.
Step 8
Repeat this for all clipping circuits.
Step 9
Expected Input and Output waveforms
Step 10
Result
Clipper circuits have been tested and out put wave forms match with
the expected waveforms.