[tronla1]experiment 4

8/4/2019 [Tronla1]Experiment 4

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I. Objective

A. To evaluate and design a clipping circuit

B. To evaluate and design a clamping circuit

II. Conceptual Framework

As you know, diodes can be used as switches depending on the biasing

type, reverse of forward. The clipping circuit, also referred to as clipper, clips off

some of the portions of the input signal and uses the clipped signal as the output

signal. The

clamping

circuit orclamper keeps the

amplitude of the output signal same as that of the input signal except that the

D.C. level (offset) has been changed. The clamper through which the input

waveform shifts to positive direction is called positive clamper, otherwise, is

called negative clamper

Fig. 2.1 – Ideal Diode – Switch Terminalogy

a. Clipper Circuits There are two types of clipper circuits, the series and parallel diode clipping

circuits.

1 Series Diode Clipping Circuit



In these type of circuits, the diode is connected between the input andoutput

voltage terminals (Fig 2.2)

Fig. 2.2

As Fig.2.2 reveals, the negative cycle of the input voltage can be clipped of by this

type of series clippers. Reverse of the diode pins yields to a positive cycle clippingcircuit as shown in Fig. 2.3.

Fig. 2.3

Previous circuits clip the values larger or smaller than zero voltage. Thisvoltage, technically called “threshold voltage” and can be changed to a desiredvalue by inserting a D.C. voltage source. This is achieved in two different ways.

In the first type, the voltage source of Em ( positive or negative) is connectedthrough output terminals as in Fig. 2.4. Depending on the diode connection (normalor reverse), the values smaller (Fig.2.4.a) or greater (Fig.2.4.b) than Em is clippedand assigned as Em.

a



bFig. 2.4.

Note that if Em is negative, ( where the voltage source is reverselyconnected) again the values smaller or larger than this negative value is clipped, donot get confused.

In the second type of thresholded series clipping, the voltage source isapplied between the input and output terminals, series with the diode. This time,the clipped values areassigned to zero andthe net output voltageequals to the differencebetween the input and

threshold values.(If Em is negative, then E0 =E – Em = E + | Em|)

a



bFig. 2.5

2.2.a.2 Parallel Diode Clipping Circuit

In this type of clippers, the diode is connected between output terminals. The on/off

state of diode directly affects the output voltage. These type of clippers may also

have a non-zero threshold voltage by addition of a voltage series with diode.

Following figures

illustrate the

clipping process.

a

b



Fig 2.8Being different from clippers, clamping circuits uses a capacitor and a diode

connection. When diode is in its on state, the output voltage equals to diode drop

voltage (ideally zero) plus the voltage source, if any. Now let us examine the

clamping process for the circuit in Fig. 2.9.

Fig 2.9 - Typical Clamping Circuit

As you know, this circuit, in fact, is a series R-C circuit. The resistance of diode( several ohms above its drop voltage) and the small capacitance yield to a smalltime-constant for this circuit. This means that the capacitor will rapidly be charged if any

input voltage, that is enough to swtich on the diode, is applied. The diode will conductduring the positive cycle of the input signal (Fig. 2.10) and output voltage will be ideallyzero ( in practice this voltage equals ~0.6 V).



Fig 2.10. Diode conducts during positive cycle

Note that during positive cycle the capacitor is rapidly charged in inversepolarity with the input voltage. After transition to negative cycle, the diode becomes to its off state. In this case, the output voltage equals to the sum of the input voltage and thevoltage across the terminals of the capacitor which have the same polarity with each

other.(Fig 2.11)

E0 = - ( |Ei |+ |Ec | )

The resulting signal after a complete cycle is shown below.



By this process, the input signal is shifted to negative D.C. value (its

maximum value is ideally zero) without any change in its amplitude ideally.



There

exist again

modified

versions

of this circuit in

which athreshold

value is inserted

for clamping.

Following

figures illustrate

these

modifications and resulting outputs.



III.Materials

- Silicon Diodes – 2pcs- 1K ohm Resistor- 10K ohm Resistor- 10µF Capacitor- DC Supply- 12-0-12 transformer- Signal Generator- Digital Multi Meter- Alligator Clips

IV.Procedure

1.) Design a biased negative parallel clipper with clipping voltage equal toyour group no. Let V1= 12Vrms



2.) Design a biased clamper that will clamp down the square wave input to aspecified clamping level CL=(0.25*Group No.)+1



V. Data

The data that have been gathered during the experiment was the outputwaveform from the circuit produced in the oscilloscope

A.)Clipping Circuit

Output Waveform

B.)Clamping CircuitOutput Waveform



VI.AnalysisVII. Conclusions

[tronla1]experiment 4

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