Precision Rectifier

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 VOA also becomes positive. Then the closed loop condition is achieved for the op-amp and the output voltage V0 = Vi.
• When Vi < 0, the voltage V0A becomes negative and the diode is reverse biased. The loop is then broken and the output V0 = 0.

Half wave rectifier

• The below circuit is non-saturating half wave precision rectifier.
• When Vi > 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 Vi > 0, the op-amp output VOA 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 Rf = Ri. Half Wave Rectifier

The circuit operation can mathematically be expressed as The voltage VoA 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 Vi > 0V and assuming that RF =Ri = R, the output voltage VOA = Vi. 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 Vi also appears as an input to the summing amplifier. Then, the net output is
• V0 = -Vi -2V0= -Vi -2(-Vi) = Vi.

• Since Vi > 0V, V0 will be positive, with its input output characteristics in first quadrant. For negative input Vi < 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, Vi 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 = -Vi. Since Vi 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

• 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