Clamp diodes used in comparators ______

A comparator is a circuit, which compares a signal voltage on one input of an op-amp with a known reference voltage on the other input.

The above circuit is called a non-inverting comparator circuit as the sinusoidal input signal V_in is applied to the non-inverting terminal. The fixed reference voltage V_ref is connected to the inverting terminal of the op-amp.

Clamp diodes:

• The circuit diagram shows the diodes D₁ and D₂. These two diodes are used to protect the op-amp from damage due to an increase in input voltage.
• These diodes are called clamp diodes as they clamp the differential input voltages to either 0.7V or - 0.7V.
• Most op-amps do not need clamp diodes as most of them already have built-in protection.
• Resistance R₁ is connected in series with the input voltage V_in and R is connected between the inverting input and reference voltage V_ref.
• R₁ limits the current through the clamp diodes and R reduces the offset problem.

Note:

Clamper:

• A clamper is an electronic circuit that fixes either the positive or the negative peak excursions of a signal to a defined value by shifting its DC value.
• The clamper does not restrict the peak-to-peak excursion of the signal, it moves the whole signal up or down so as to place the peaks at the reference level.
• A diode clamp (a simple, common type) consists of a diode, which conducts electric current in only one direction and prevents the signal exceeding the reference value; and a capacitor, which provides a DC offset from the stored charge.
• The capacitor forms a time constant with the resistor load, which determines the range of frequencies over which the clamper will be effective.