# Precision Rectifier

## Applications of Operational Amplifiers in Tamil

## Precision Rectifier

- The ordinary diodes cannot rectify voltages below the cut-in-voltage of the diode.
- A circuit which can act as an ideal diode or precision signal–processing rectifier circuit for rectifying voltages which are below the level of cut-in voltage of the diode can be designed by placing the diode in the feedback loop of an op-amp.

## Precision Diodes

Precision Diodes

- It is a single diode arrangement and functions as a non-inverting precision half– wave rectifier circuit.
- If V
_{1}in the circuit is positive, the op-amp output V_{OA}also becomes positive. Then the closed loop condition is achieved for the op-amp and the output voltage V_{0}= V_{i}. - When V
_{i}< 0, the voltage V_{0A}becomes negative and the diode is reverse biased. The loop is then broken and the output V_{0}= 0.

## Precision Diodes Applications

- The precision diodes are used in
- Half wave rectifier
- Full-wave rectifier
- Peak value detector
- Clipper and clamper circuits

## Half wave rectifier

- The below circuit is non-saturating half wave precision rectifier.
- When V
_{i}> 0V, the voltage at the inverting input becomes positive, forcing the output VOA to go negative. - This results in forward biasing the diode D
_{1}and the op-amp output drops only by ≈ 0.7V below the inverting input voltage. - Diode D
_{2}becomes reverse biased. The output voltage V_{0}is zero when the input is positive. - When V
_{i}> 0, the op-amp output V_{OA}becomes positive, forward biasing the diode D_{2}and reverse biasing the diode D_{1}. The circuit then acts like an inverting amplifier circuit with a non- linear diode in the forward path. The gain of the circuit is unity when R_{f}= R_{i}.

Half Wave Rectifier

The circuit operation can mathematically be expressed as

The voltage V_{oA} at the op amp output is

The advantages of half wave rectifier is a precision half wave rectifier and it is a non saturating.

## Full wave Rectifier

The first part of the Full wave circuit is a half wave rectifier circuit. The second part of the circuit is an inverting amplifier.

Full Wave Rectifier

- For positive input voltage V
_{i}> 0V and assuming that R_{F}=R_{i}= R, the output voltage V_{OA}= V_{i}. The voltage V_{0}appears as (-) input to the summing op-amp circuit formed by A_{2}, The gain for the input V‘_{0}is R/(R/2) - The input V
_{i}also appears as an input to the summing amplifier. Then, the net output is

**V _{0}
= -V_{i} -2V_{0}= -V_{i} -2(-V_{i}) = V_{i}.**

- Since V
_{i}> 0V, V_{0}will be positive, with its input output characteristics in first quadrant. For negative input V_{i}< 0V, the output V‘0 of the first part of rectifier circuit is zero. Thus, one input of the summing circuit has a value of zero. However, V_{i}is also applied as an input to the summer circuit formed by the op-amp A_{2}. - The gain for this input id (-R/R) = -1, and hence the output is V
_{0}= -V_{i}. Since V_{i}is negative, V_{0}will be inverted and will thus be positive. This corresponds to the second quadrant of the circuit.

To summarize the operation of the circuit,

## Peak Detector

- Peak detector detects and holds the most positive value of attained by the input signal prior to the time when the switch is closed.

## Clipping Circuit

- Clipping circuit is a wave-shaping circuit, and is used to either remove or clip a portion of the applied wave in order to control the shape of the output waveform.
- One of the most basic clipping circuit is the half-wave rectifier.
- A half-wave rectifier clips either the negative half cycle or the positive half cycle of an alternating waveform, and allows to pass only one half cycle.
- Clipping circuits are also referred to as voltage limiters, amplitude selectors, or slicers.
- Clippers are used to eliminate amplitude noise or to fabricate new waveforms from an existing signal.

Clipping Circuit

## Clamping Circuit

- A clamping circuit is used to place either the positive or negative peak of a signal at a desired level.
- The dc component is simply added or subtracted to/from the input signal.
- The clamper is also referred to as an IC restorer and ac signal level shifter.

Clamping Circuit

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