  # Simple Diode and Wave shaping Circuits: Clipping, Clamping

By BYJU'S Exam Prep

Updated on: September 25th, 2023 In this study, we explore the fundamental principles behind diodes and their application in wave-shaping circuits, specifically clipping and clamping circuits. Diodes are essential semiconductor devices known for their ability to allow current to flow in one direction while blocking it in the opposite direction. This unique property makes them invaluable components in various electronic circuits, including those used for signal processing and waveform manipulation.

The first part of our study focuses on diode clipping circuits, which play a crucial role in limiting the amplitude of electrical signals. By strategically placing diodes in a circuit, we can “clip” or remove specific portions of a signal that exceed certain voltage thresholds. This allows us to shape the signal’s waveform, removing unwanted distortion and ensuring the signal remains within desired voltage levels. In the second part, we delve into diode clamping circuits, which are used to shift the DC level of an AC signal to a desired reference level. With the combination of diodes and capacitors, clamping circuits modify the waveform’s DC bias, making them invaluable in applications such as data transmission, audio processing, and voltage protection. Join us on this journey to discover the practical applications and the inner workings of these essential diode-based wave-shaping circuits.

Table of content ## Logic Gates

• AND Gate: If one of the inputs A or B is grounded, current flows through the diode and the output node C is at a low voltage. The only way to get a high output is by having both inputs high. This circuit is equivalent to logical AND function.

• OR Gate: If one or both of the inputs A and B are high, current flows through the associated diode and the output node C at a high voltage. It is equivalent to OR Gate.

## Clipper Circuits

A Diode network that has the ability to clip a portion of the input signal without distorting the remaining part of the alternating waveform is known as Clipper.

There are two general categories of clippers

1.  Series clipper
2.  Parallel Clipper

The series configuration is defined as one where the diode is in series with the load, while the parallel configuration has the diode in a branch parallel to the load.

(a) Series Clipper

(i) Unbiased Clipper

The response of the series configuration of Figure 1(a) to a variety of alternating waveforms is provided in Figure 1(b) From figure 1(a), Anode voltage of diode VA = Vi and Cathode voltage VK = 0

Therefore, for positive half cycle VA > VK, which means the diode is forward biased and acts as a short circuit.

For negative half cycle VA < VK, which means the diode is reverse biased and acts as open circuits.

(ii) Biased clipper

The addition of a dc supply that can have a pronounced effect on the output of a clipper is shown in Figure 2.

NOTE: Make a mental sketch of the response of the network based on the direction of the diode and the applied voltage levels. For the given network, the direction of the diode suggests that the signal Vi must be positive to turn it ON. The dc supply further requires that the voltage Vi be greater than V to turn ON the diode. The negative region of the input signal is pressuring the diode into the OFF state, supported further by the dc supply.

NOTE: Determine the applied voltage (transition voltage) that will cause a change in state for the diode.

For the ideal diode, the transition between states will occur on the characteristics, where Vd = 0 V and id = 0A. Applying the condition id = 0 at Vd = 0 to the network of Figure 2 will result in the configuration of Figure 3(a), where it is recognized that the level of Vi that will cause a transition in the state is Vi = V For an input voltage greater than V volts the diode is in the short circuit state, while input voltage less than V volts it is in the open circuit or off state.

NOTE: Be continually aware of the defined terminals and polarity of V0.

When the diode is in the short circuit state, such as shown in Figure 4, the output voltage V0 can be determined by applying KVL in the clockwise direction. Vi – V – V0 = 0

∴ V0 = Vi – V

NOTE: It can be helpful to sketch the input signal above the output and determine the output and determine the output at instantaneous values of the input. For an instantaneous value of Vi, the input can be treated as a dc supply of that value and the corresponding dc value of the output is determined.

For instant at Vi = Vm

For VM > V, diode is short circuit and V0 = Vm – V

When the diode changes state, and Vi = – Vm

Then V0 = 0 V

And now complete the curve for V0 that can be shown in Figure 5.

(b) Parallel Clipper

The network of Figure 6 is the simplest of parallel diode configuration with the output for the same input as discussed earlier. The analysis of parallel configuration is very similar to that applied to series configurations.  ## Clampers

The clamping network is one that will clamp a signal to a different dc level. The network consists of a capacitor, a diode and a resistor element and an independent dc supply to introduce additional shift.

The magnitude of R and C must be chosen such that the time constant τ = RC is large enough to ensure that the voltage across the capacitor does not discharge significantly during the interval the diode is non-conducting.

There are basically two types of clamper: (a) Negative Clamper Figure 8(b): Waveform

When the input is positive, the diode operates in forward bias and the capacitor charges through the diode. If the diode is ideal it behaves as a short circuit and therefore capacitor charges up to the peak input Vm.

When input becomes negative, the capacitor should discharge but the discharge path is not available so capacitor voltage will continue to remain at Vm. Therefore, once the capacitor is fully charged its voltage Vm irrespective of the input being positive or negative.

Applying KVL

–Vi + Vm + V0 = 0

V0 = Vi – Vm

= Vi + (– Vm)

Hence circuit adds a dc voltage of –Vm. So, the output will be a square waveform for given input whose value varies from 0 to – 2Vm.

The positive peak of the output waveform touches the 0V level or the positive peak gets clamped to 0V. Since a negative clamper is clamping a positive peak to 0V so it is called a positive peak clamper.

NOTE: If the diode has a cut in voltage Vγ then it should be replaced with a series connection of the ideal diode and battery Vγ. When the input is +Ve, the capacitor changes through the diode up to a maximum voltage of Vm – Vγ

∴  V0 = Vi = (Vm – Vγ)

V0 = Vi + (–Vm + Vγ)

Hence circuit adds dc voltage equal to – (Vm – Vγ) (b) Positive Clamper

• When the input is negative diode gets forward biased and the capacitor charges through the diode up to peak input Vm
• When input becomes positive capacitor will not be able to discharge as the discharge path is not present. Therefore, the voltage across the capacitor remains Vm irrespective of input being +Vm or –Vm Applying KVL

V0 = Vi + Vm Negative peak output gets clamped to 0 volts therefore positive clamper is also called negative clamper.

NOTE: If the diode has cut in voltage Vγ then the capacitor changes to a voltage (Vm – Vγ)

∴ V0 = Vi + (Vm – Vγ)

Hence added dc voltage is Vm – Vγ Example:

In the circuit shown in the figure the dc value at the output is? Solution:

For the given clamper circuit, make the diode short and calculate the maximum voltage across the capacitor.

– Vi + VC = 0.7V + 0.3 = 0

VC = Vi – 1 = 5 – 1

= 4V

Now, make the diode open circuit

– Vi + VC + V0 = 0

V0 = Vi – VC

= Vi – 4V

Dc value of output = –4V

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