# Clipper Circuits

A clipper is a device that limits, removes, or prevents some portion of the waveform (input signal voltage) above or below a certain level In other words the circuit which limits positive or negative amplitude, or both is called a clipping circuit. The clipper circuits are of the following types.

1. Series positive clipper
2. Series negative clipper
3. Shunt or parallel clipper
4. Shunt or parallel positive negative
5. Clipper Dual (combination)Diode clipper

## SERIES POSITIVE CLIPPER

In a series positive clipper, a diode is connected in series with the output, as shown in Fig 1(a). During the positive half of the input voltage, terminal A is positive with respect to B. This reverse biases the diode and it acts as an open switch Therefore all the applied voltage drops across the diode and none across the resistor As a result of this there is no output voltage during the positive half cycle of the input voltage.

During the negative half cycle of the input voltage, terminal B is positive with respect to A. Therefore it forward biases the diode and it acts as a closed switch. Thus there is no voltage drop across the diode during the negative half cycle of the input voltage. All the input voltage is dropped across the resistor as shown in the output waveform.

Clippers prevent either or both polarities of a wave from exceeding a specific amplitude level. However, a positive Clipper is that which removes or clips the positive half completely. Hence the circuit of the Fig 2.1 is called a positive Clipper Here it may be noted the diode acts as a series switch between the source and load. Due to this reason, the circuit is called a series positive clipper.

### Merits:

• Clips the positive peaks of the input signal to a preset clipping level
• Produces a clipped output waveform symmetrical around 0 volts
• A simple circuit using just a diode, resistor, and voltage source
• The clipping level is easily adjusted via the DC bias voltage
• Can modify waveform shape and reduce the peak-to-average ratio
• Often used for AM modulation to limit modulation index

### Demerits:

• Distorts the signal by flattening/clipping positive peaks
• May introduce high-frequency harmonics due to clipping
• Clipper output still contains negative peaks of the input signal
• Clipping level very sensitive to diode forward voltage drop
• Power dissipation across the diode if clipping large signals
• Input and output impedance mismatch can distort waveshapes

In summary, series positive clippers provide a simple means to limit positive voltage swings but at the expense of distorting the waveform shape. The merits make them useful for AM radio transmitters. But the non-linear clipping can produce unwanted harmonics and power loss in some applications.

### Applications of series positive clipper circuits

• Used to limit audio modulation index to 100%
• Clips positive audio peaks to prevent over-modulation
• Keeps transmitted signal within the bandwidth

#### Waveform Clamping

• Clips signals to precise voltage levels
• Shifts waveform vertically by controlling clip level
• Creates precise trigger levels for digital circuits

#### Peak Reduction

• Reduces peak-to-average power ratio
• Allows transmitting higher average power in radio systems
• Prevents signal peaks from causing distortions

#### Wave Shaping

• Modifies waveform by flattening tops of peaks
• Changes waveshape to approach square or trapezoid
• Alters harmonics and frequency content

#### Noise Reduction

• Clipping can reduce noise and hum amplitude
• Lower noise peaks result in a higher signal-to-noise ratio

In summary, series positive clippers are commonly used to limit peak amplitudes in transmitters, shape waveforms, set clamping levels, reduce noise, and prevent over-modulation in AM radio broadcasting. The simple diode-based circuit clips positive peaks to achieve these effects.

## SERIES-POSITIVE CLIPPER WITH BIAS

Sometimes it is desired to remove a small portion of the positive or apposite halt cycle of the signal voltage (input signal). For this purpose a biased clipper is used Fig 2 shows the circuit of a biased series positive clipper.

It may be observed that the clipping takes place during the positive cycle only when the input voltage is greater than the battery voltage (i.e. Vi > VB). The chipping level can be shifted up or down by varying the bias voltage (VB)

## SERIES NEGATIVE CLIPPER

In a series negative clipper a diode is connected in a direction appositive to that of a positive clipper Fig 3 shows the circuit of a negative clipper.

During the positive half cycle of the voltage, terminal A is positive with respect to terminal B There for the diode is forward biased and it acts it as a closed switch As a result, all the input voltage appears across the resistor as shown in Fig 3(b). During the negative half cycle of the input voltage, terminal B is positive with respect to the terminal A. Therefore the diode is reverse biased and it acts as an open switch, Thus there is no voltage drop across the resistor during the negative half cycle as shown in the output waveform.

It may be observed that if it is desired to remove or clip the negative half-cycle of the input, the only thing to be done is to reverse the polarities of the diode in the circuit shown in Fig 1 such a clipper is then called a series negative clipper

### Merits:

• Clips the negative peaks of the input signal to a set clipping level
• Produces a clipped waveform symmetrical around 0 volts
• A simple circuit using a diode, resistor, and DC bias voltage
• The clipping level is easily adjusted via the bias voltage
• Can modify waveform shape and reduce the peak-to-average ratio
• Often used in AM transmitters to limit modulation index

### Demerits:

• Distorts signal by flattening/clipping negative peaks
• May introduce high-frequency harmonics due to clipping
• The output signal retains positive peaks of the input waveform
• Clipping level very sensitive to diode forward voltage drop
• Power dissipation in diode for large input signals
• Impedance mismatch can further distort the clipped shape

In summary, series negative clippers provide a simple method to limit negative voltage swings but distort the waveform. The merits make them useful for AM radio. But the nonlinear clipping can produce unwanted harmonics and power loss in some applications.

## SERIES-NEGATIVE CLIPPER WITH BIAS

Fig 4 shows the circuit of a biased series negative diver. In this circuit, clipping takes place during the negative half cycle only when the input voltage Vi > VB the clipping level can be shifted up or down by varying the bias voltage ( -VB)

## SHUNT OR PARALLEL POSITIVE CLIPPER

A parallel clipper circuit uses the same diode theory and circuit operation a resistor and diode are connected in series with the input signal and the output signal is developed across the diode. The output is in parallel with the diode hence the circuit name is parallel clipper the parallel clipper can limit either the positive or negative alternation of the input signal Fig 5 shows the circuit of a shunt positive clipper In this circuit. The diode acts as a closed switch when the input voltage is positive (i.e. Vi > 0 and as an open switch when the input voltage is negative (i.e. Vi< 0) the output waveform is the same as that of a series positive clipper in the parallel clippers the alp will develop when the diode is cut off.

## SHUNT OR PARALLEL POSITIVE CLIPPER WITH BIAS

As is in Fig 6 (a), the positive terminal of the battery is connected to the cathode of the diode. This causes the diode to be reversed-biased at all times except when the input signal is more positive than the bias voltage(i e Vi > VB). it will be interesting to know that if the polarity of the bias voltage is reversed, the resulting circuits will be as shown in Fig 6(b) Here the input signal lying above the voltage —VB has clipped the waveforms of the output voltage is also shown with figures

## SHUNT OR PARALLEL NEGATIVE CLIPPER

The negative clipper has allowed to pass the positive half cycle of the input voltage and clipped the negative half cycle completely Fig 7 shows the shunt (parallel) negative clipper.

In such a circuit the diode acts as a closed switch for a negative input voltage (i.e. Vi < O) and as an open switch for a positive input voltage (i.e. Vi O) the output waveform of the Circuit is the same as that of the series negative clipper.

## SHUNT OR PARALLEL NEGATIVE CLIPPER WITH BIAS

In such a circuit clipping take place during the negative half cycle only when the input voltage (Vi < VB) the clipping level can be shifted up or down by varying the bias voltage (—VB). It will be interesting to know that if the polarity of the bias voltage is reversed, then the resulting circuits will be as shown in Fig 8 (b) Here the entire signal below the voltage level VII has been clipped off.

## DUAL (COMBINATION) DIODE CLIPPER

The type of clipper combines a parallel negative clipper with a negative bias (D1 and B2) and a parallel positive bias (D1 and B1). Hence the combination of a biased positive clipper and a biased negative clipper is called a combination or dual diode clipper. Such a clipper circuit can clip at both two dependent levels depending upon the bias voltages. Fig 9(a) shows the circuit of a dual (combination) clipper.

Let us suppose a sinusoidal ac voltage is applied at the input terminals of the circuit. Then during the positive half cycle, the diode D1 is forward biased, while diode D2 is reverse. biased. Therefore the diode D1 will conduct and will act as a short circuit. On the other hand, diode D2 will act as an open circuit. However, the value of output voltage cannot exceed the voltage level of VB1 as Shown in Fig 9.

Similarly, during the negative input half-cycle, diode D2 acts as a short circuit while the diode D1 as an open circuit However the value of output voltage cannot exceed the voltage level of VB2 It may be noted that the clipping levels of the circuit be varied by changing the values of VB1 and VB2 If the values of VB1 and VB2 are equal, the circuit will clip both the positive and negative half cycles at the same voltage level. Such a circuit is known as a symmetrical clipper

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