Clipper circuits LET’S REMOVE UNWANTED PART OF SIGNALS

1. What are clipper circuits? 2. Types of clipper circuits. 3. Unbiased positive clipper. 4. Unbiased negative clipper. 5. Biased series positive clipper. 6. Biased series negative clipper.

 Clipper circuits are used to remove the part of a signal that or above or below some defined reference level.  One of the simple example of a clipper is the half-wave rectifier that circuit basically cut off everything at the reference level of zero and let only the positive- going(negative-going) portion of the input waveform through.  Clipping circuits(also known as limiters, amplitude selectors or slicers )

1) Unbiased clipper circuits Unbiased positive clipper Unbiased negative clipper 2) Biased clipper circuits biased positive clipper biased negative clipper

Note: In all the explanations we have considered the diode to be ideal.

 Positive clippers are used to clip positive portions of the input signal and allow the negative portions of the signal to pass through.  Figure below shows the input and output signal along with the positive clipper. The positive cycle is completely clipped off by the clipper.

 Section (b) shows the same clipper configuration as it is shown in (a).but the diodes is replaced with its equivalent circuit model. When the input signal goes positive, the cathode terminal of diode attains a higher potential than anode. This makes the diode reverse biased. The diode in reverse biased configuration can be modeled as an open switch. No current flows through the load and hence no output appears across the load. This is the reason why the positive cycle is completely clipped off.

 Negative clippers are used to clip negative portions of the input signal and allow the positive portions of the signal to pass through.  Figure below shows the input and output signal along with the negative clipper. The negative cycle is completely clipped off by the clipper.

 Section (b) shows the same clipper configuration as it is shown in (a).but the diodes is replaced with its equivalent circuit model. When the input signal goes positive, the anode terminal of diode attains a higher potential than cathode. This makes the diode forward biased. The diode in reverse biased configuration can be modeled as an closed switch. No current flows through the load and hence no output appears across the load. This is the reason why the negative cycle is completely clipped off.

 As shown earlier, we saw the clipping of the signal takes place as soon as input signal goes positive. If we want to change the clipping level of AC voltage, then external biasing voltage must be used. the figure given below shows a biased(series) clipper.

 As shown earlier, we saw the clipping of the signal takes place as soon as input signal goes negative. If we want to change the clipping level of AC voltage, then external biasing voltage must be used. the figure given below shows a biased(series) clipper.

Clamper is a network constructed of a diode, a resister and a capacitor that shifts a waveform to a different level without changing the appearance of the applied signal. A clamper adds a dc voltage to the signal A positive clamper shifts its input waveform in a positive direction, so that it lies above a dc reference voltage. A negative clamper shifts its input waveform in a negative direction, so that it lies below a dc reference voltage.

On the first negative half cycle of the input the diode is turned on. At negative peak capacitor is fully charged to Vp.

Diode is off R L C is made much larger than the time period of the signal. Stiff Clamper R L C > 100T Due to this reason capacitor remains fully Charged During off time of diode

Clampers are used in test equipment radar systems, electronic counter measure systems sonar systems. These are commonly used in analog television receivers to restore the DC component of the video signal.

 In measuring non-sinusoidal signals such as square, saw tooth etc.

VOLTAGE MULTIPLIER

Use clamping action to increase peak rectified voltages without necessary to increase input transformer’s voltage rating. Multiplication factors: two, three or four. Three types of voltage multipliers:

Voltage doubler 1. Half – wave voltage doubler 2. Full – wave voltage doubler  Voltage tripler  Voltage Quadrupler Voltage multipliers are used in high-voltage, low current applications, i.e. TV receivers.

Half-wave voltage Doubler:  Clamping action can be used to increase peak rectified voltage. Once C1 and C2 charges to the peak voltage they act like two batteries in series, effectively doubling the voltage output. The current capacity for voltage multipliers is low.

Full-wave voltage doubler:  Arrangement of diodes and capacitors takes advantage of both positive and negative peaks to charge the capacitors giving it more current capacity.

 Voltage triplers and quadruplers utilize three and four diode capacitor arrangements, respectively.  Voltage tripler and quadrupler gives output 3Vp and 4Vp, respectively.  Tripler output is taken across C1 and C3, thus Vout = 3Vp  Quadrupler output is taken across C2 and C4, thus Vout = 4Vp  PIV for both cases: PIV = 2Vp

Voltage Triple Voltage Quadruple