Op Amp Asgmt Or

UNIVERSITI KUALA LUMPUR MALAYSIA FRANCE INSTITUTE

(FLB: 20102)

OP-AMP & NON LINEAR CIRCUIT Assignment 1 Prepared by: Mohd Shaffuan B. Mat Yatim (50207108079)

Comparator In electronics, a comparator is a device which compares two voltages or currents and switches its output to indicate which is larger. A dedicated voltage comparator will generally be faster than a general-purpose op-amp pressed into service as a comparator. A dedicated voltage comparator may also contain additional features such as an accurate, internal voltage reference, an adjustable hysteresis and a clock gated input. A comparator is non-linear signal processor. It is an open loop mode application of op-amp operated in saturation mode. Comparator compares a signal voltage at one input with reference voltage at the other input. Here the op-amp is operated in the open loop mode and hence the input is ±Vsat. It is basically classified as inverting comparator and non-inverting comparator and non-inverting comparator, Vi is given to the positive terminal and Vref to the negative terminal. When Vi Vref the output is +Vsat. In a inverting comparator, input is given to the inverting terminal and reference is given to non-inverting terminal. The comparator can be use as a : • Zero crossing detector • Window detector • Time marker • Phase detector

Non-inverting Comparator

When Vi is positive, ton = toff and ton < toff

If Vr is beyond the swing of the input, there won’t be any comparison

Window comparator

It is obtained by connecting an inverting type comparator and non-inverting type comparator as shown in the figure below. The comparators in the window circuit have different reference voltages.

The output V0 is zero when Vi lies between Vhigh and Vlow, and output is +Vcc otherwise the circuit checks if the input V1 between Vhigh and Vlow or not and hence the name sense amplifier.

Zero Crossing Detector It is a non-inverting signal processor. It is an open loop/saturation mode operation of opamp. It is basically a comparator with zero reference voltage. Types 1. Inverting type. 2. non-inverting type. Inverting Type Zero Crossing Detector

When the input crosses zero voltage axis, the output changes abruptly and hence the name zero crossing detector. Since the input is given to inverting terminal, output signal is out of phase (180°) with respect to the input signal. Hence the name. Non-inverting Type Zero Crossing Detector

Here the input signal is given to non-inverting terminal. So output signal is maintaining same phase(0°) as that of the input signal.

Schmitt Trigger It is a regenerative comparator or it is comparator with hysteresis. The circuit is a closed loop mode application of op-amp employing only positive feedback and hence it is equivalent to an open loop mode application operated in saturation.

The output takes two values, either +Vcc or –VEE. Let the volatage at the non-inverting tterminal be Vb with respect to Vi is the time varying signal. Vr is the fixed reference volatages source. Corresponding to the two values at the output, we can define two values for Vb and they are known as threshold voltages or trip points. One is known as UTP (upper trip point) and the other is known as LTP ( lower trip point).

Hysteresis Curve The difference between Vb1 and Vb2 is known as hysteresis. This hysteresis is due to positive feedback. The hysteresis avoids false triggering of the circuit by noise. If the peak to peak noise voltage is less than the hysteresis, then there is no way the noise can provide false triggering.

Let us take an example : Vb1 = 2V and Vb2 = 3V then, (Vb1 – Vb2) = 1.7V. If the peak to peak voltage of the noise is less than 1.7, then false triggering is impossible by the noise. When the input signal Vi cross Vb1 in the positive direction (increasing), then the output makes transition from +Vcc to – VEE. Similarly, when the input Vi crosses Vb2 in the negative direction (decreasing), then the output makes transition from –VEE to +Vcc. Figure below show the hysteresis curve.