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 V₁ 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 V₀ = 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 V₀ = 0.

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 D₁ and the op-amp output drops only by ≈ 0.7V below the inverting input voltage.
Diode D₂ becomes reverse biased. The output voltage V₀ is zero when the input is positive.
When V_i > 0, the op-amp output V_OA becomes positive, forward biasing the diode D₂ and reverse biasing the diode D₁. 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.

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 V₀ appears as (-) input to the summing op-amp circuit formed by A₂, 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

V₀ = -V_i -2V₀= -V_i -2(-V_i) = V_i.

Since V_i > 0V, V₀ 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 A₂.
The gain for this input id (-R/R) = -1, and hence the output is V₀ = -V_i. Since V_i is negative, V₀ 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 detects and holds the most positive value of attained by the input signal prior to the time when the switch is closed.

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

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