OPAMP APPLICATIONS – ADDER, SUBTRACTOR & COMPARATOR CIRCUITS
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Adder circuit is a Summing Amplifier. Op-amp can be used to design a circuit whose output is the sum of several input signals. Such a circuit is called a summing amplifier or a summer. Summing amplifier can be classified as inverting & non-inverting summer depending on the input applied to inverting & non-inverting terminals respectively. Fig shows an inverting summer with two inputs. Here the output will be the linear summation of input voltages. Here the feedback forces a virtual ground to exist at the inverting input . The output is equal to the negative weighted sum of the input voltages. The summing operation depends exclusively on the sum of the resistor ratios. Fig . shows the inverting configuration with three inputs Va, Vb, Vc depending on the relationship between the feedback resistor RF and the input resistors Ra ,Rb and Rc , the circuit can be used as either a summing amplifier, scaling amplifier, or averaging amplifier. By connecting more than one input voltages to the inverting input, the resulting circuit is the Adder.
A Comparator is a 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 a reference voltage at the other input. Here the Op-amp is operated in open loop mode and hence the input is ± Vsat. It is basically classified as inverting and non-inverting comparator. In a non inverting comparator Vin is given to +ve terminal and Vref to –ve terminal. When Vin < Vref, the output is –Vsat and when Vin > Vref, the output is + Vsat. In an inverting comparator input is given to the inverting terminal and referenceis given to the non inverting terminal. The comparator can be used as a zero crossing detector , window detector, time marker, phase meter.
1. Connect the subtractor circuit as shown in fig. by connecting the appropriate resistors to 741 IC.
2. Switch on the trainer.
3. Apply dc voltages at each input terminals for V1 and V2 from the dc supply and check the output voltage Vo at the output terminal.
4. Tabulate the readings.
5. Compare the practical Vo with the theoretical output voltage Vo=(-Rf/R1)(V2-V1) value.
1. connect the comparator circuit as shown in fig.
2. Apply 1 KHz sine wave with 5 Vp-p at the inverting input terminal of 741 IC using a function generator.
3. Apply 3V dc voltage as reference voltage at the non-inverting terminal of 741 IC.
3. Connect channel -1 of CRO at the input terminals and channel-2 of CRO at the output terminals.
4. Observe the input sinusoidal signal in ch-1 and the corresponding output square wave in ch-2 of CRO.
5. Note the amplitude and timeperiods of Vin and Vo.