per Clam & er Clipp 1

Topics t o b e discu ssed • What is a Clipper Circuit ? • General characteristic of a double clipper. • Series negative clipper. • Processing by series negative clipper. • Series Biased Clippers. • Guidelines to Solve. • Numerical Examples. 2014-12-24 Oscillators By S.M.Mehzabeen 2

Clippers • A circuit that clips off or removes a portion of the input signal. • A clipper can process any type of signal. 2014-12-24 Oscillators By S.M.Mehzabeen 3

SINGLE CLIPPERS – Positive Negative There can be single clippers : – – Two Positive Negative categories : Series – Diode and load in series. Parallel – Diode and load in parallel. 2014-12-24 Oscillators By S.M.Mehzabeen 4

SINGLE CLIPPERS The circuit The transfer characteristics 5 2014-12-24 Oscillators By S.M.Mehzabeen 5

P rocessin g b y series n egat iv e clipper Square wave Triangular • This clipper is like a half-wave rectifier. 2014-12-24 Oscillators By S.M.Mehzabeen 6

R ect an gu lar w av e or Squ are w av e ? • Ans. Both are same. Usually, we call it a square wave. 2014-12-24 Oscillators By S.M.Mehzabeen 7

What happens if the diode in a half-wave rectifier is reversed ? Ans. It still remains a half-wave rectifier, but it now works as a positive clipper. 2014-12-24 Oscillators By S.M.Mehzabeen 8

Series Biased Clippers • Bias means applying a circuit. dc voltage to change the dc level of a 2014-12-24 Oscillators By S.M.Mehzabeen 9

Plot the waveshape of vo for given input. Guidelines to Solve • Determine the transition level at which the diode turns ON. With diode ON, find relation between vo and vi. • • Draw the transfer characteristic of the clipper. • Plot the waveshape of vo for given input. 2014-12-24 Oscillators By S.M.Mehzabeen 10

• When diode is ON, vo = vi – VB. We find • Diode is ON for vi > VB. that • Therefore, vi(tr) = VB. • When diode is ON, vo = vi – • When diode is OFF, vo = 0. VB. • Plot the transfer characteristic of the clipper. 2014-12-24 Oscillators By S.M.Mehzabeen 11

Output... 12 Now, draw the output. 2014-12-24 Oscillators By S.M.Mehzabeen 12

Example 1 • Determine the output waveform for the clipper circuit, if input is a sinusoidal wave of peak value 15 V. 2014-12-24 Oscillators By S.M.Mehzabeen 13

vd  0 V id  0 A; vo  vi ( tr ) id RL  0 vi ( tr ) Solution and • The direction of the diode suggests that it will be ON for positive values of vi. • At transition level, vd  0 V and id  0 A; so that  0  vo  vi ( tr ) id RL  0  3 V Writing KVL, vi ( tr )  3 2014-12-24 Oscillators By S.M.Mehzabeen 14

vo  vi  3 Solution • After diode is ON, 15 2014-12-24 Oscillators By S.M.Mehzabeen 15

Output... Draw the output. Transfer characteristic 16 2014-12-24 Oscillators By S.M.Mehzabeen 16

Example 2 • Determine the output waveform for the clipper circuit of 1, if its input is as follows 2014-12-24 Oscillators By S.M.Mehzabeen 17

vi vi = Solution Problem is simpler. Only two levels : = +15 V and -5 2014-12-24 Oscillators By S.M.Mehzabeen 18

Solution output. Now, you can draw the 19 2014-12-24 Oscillators By S.M.Mehzabeen 19

swing of vi is 2. Total swing of vo is 18 – 0 SINGLE CLIPPERS Note that 1. Total 15 – swing of vi is (-5) = 20 V. 2. Total swing of vo is 18 – 0 = 18 V. 3. Clipper circuit clipped off 2 V, and raised the dc level by 3 V. 2014-12-24 Oscillators By S.M.Mehzabeen 20

Clamper • A circuit that places either the positive or negative peak of a signal at a desired D.C level is known as a clamping circuit. • A clamping circuit introduces (or restores) a D.C level to an A.C signal. Thus a clamping as D.C restorer, or D.C reinserted stabilizer. circuit is also or a baseline known 2014-12-24 Oscillators By S.M.Mehzabeen 21

• Negative clamping occurs when positive peaks raised or General types of clamping • Positive clamping occurs when negative peaks raised or clamped to ground or on the zero level In other words, it pushes the signal upwards so that negative peaks fall on zero level. • Negative clamping occurs when positive peaks raised or the clamped to pushes the on the zero ground or on the zero level In signal downwards so that the level other words, it positive peaks fall 2014-12-24 Oscillators By S.M.Mehzabeen 22

Clamping Waveform 2014-12-24 Oscillators By S.M.Mehzabeen 23

POSITIVE CLAMPER • Consists of a diode and a capacitor the clamper output is taken across the load resistance R. 2014-12-24 Oscillators By S.M.Mehzabeen 24

POSITIVE CLAMPER • During the negative half cycle of the input voltage, the diode conducts heavily and behaves as a closed switch At the negative peak, the capacitor is charged to maximum voltage V slightly beyond the negative peak, the diode is shunt off and the capacitor charged to Vm behaves as a battery during the positive half cycle of the input signal. 2014-12-24 Oscillators By S.M.Mehzabeen 25

POSITIVE CLAMPER • During the negative half cycle of the input voltage, the diode conducts heavily and behaves as a closed switch At the negative peak, the capacitor is charged to maximum voltage V slightly beyond the negative peak, the diode is shunt off and the capacitor charged to Vm behaves as a battery during the positive half cycle of the input signal. 2014-12-24 Oscillators By S.M.Mehzabeen 26

POSITIVE CLAMPER • The diode is reversed biased and the output voltage will be equal to Vm + V this gives positive clamped voltage and is called positive clamper circuit. 2014-12-24 Oscillators By S.M.Mehzabeen 27

Positive clamper with bias 2014-12-24 Oscillators By S.M.Mehzabeen 28

Positive clamper with bias • Biased clamper circuit operates in exactly the same manner as unbiased clampers. • The different is only that a dc bias voltage is add in series with the diode and resistor. • A biased clamper means that the clamping can be done at any voltage level other than zero. 2014-12-24 Oscillators By S.M.Mehzabeen 29

Negative CLAMPER • Negative clamper during the positive half cycle of the input signal, the capacitor is charged to Vm, with the polarity R. shown in Fig . is taken across the load resistance 2014-12-24 Oscillators By S.M.Mehzabeen 30

Negative CLAMPER 2014-12-24 Oscillators By S.M.Mehzabeen 31

Negative Clampers • Voltage across the capacitor is opposing the input voltage V. This gives negative clamped voltage and is called negative clamper circuit. 2014-12-24 Oscillators By S.M.Mehzabeen 32