Op-Amp comparator – working, waveforms and analysis

Op-Amp Comparator:

In this section we are going to learn a basic op-amp application as a comparator. Comparator is a circuit used for comparing two voltages (either DC or both AC or one DC & one AC) and indicating the relationship between those voltages.

Generally comparators are used to compare either:

a)      Two changing voltages to each other, example: two different sinusoidal waveforms.

b)      A changing voltage to a set DC reference voltage.

The circuit diagram of op-amp comparator is sown below. There is no feedback path present in the circuit. To understand the working of op-amp comparator let us consider a sinusoidal input voltage is applied to the non-inverting terminal where as a fixed DC voltage (V reference) is applied to the inverting terminal.

Circuit diagram:

op amp comparator
op amp comparator

In this example we are going to compare sinusoidal voltage with fixed dc voltage using op-amp comparator. The working of this comparator is explained as follows.

Working:

As long as the input voltage is below the reference voltage (which is connected to the non-inverting terminal) , the comparator output is approximately “-Vmax” volts. When input voltage equals to reference voltage or exceeds, the output voltage of the comparator becomes “+Vmax” volts. Thus op-amp comparator shows the relationship between the magnitudes of two voltages applied to its input. Following figure shows the polarity (or magnitude) relationship between two voltages.

op amp comparator waveforms
op amp comparator waveforms

Now let us discuss one special case of op-amp comparator. If we apply reference voltage (Vref) to the inverting terminal and made it ground so that V ref =0V. Now in this case the output of the comparator will be “- V max” volts as long as the input voltage is below 0V. When input voltage exceeds 0V the output of the comparator switches to “+V max” volts.

Such special case op-amp comparator is called as zero-level detector. This zero-level detector circuit can be used to obtain square waveform from a sinusoidal waveform.

You may also like:

If you like this article, please share it with your friends and like or facebook page for future updates. Subscribe to our newsletter to get notifications about our updates via email. If you have any queries, feel free to ask in the comments section below. Have a nice day!

Differential, Inverting And Non-inverting Operational Amplifier

Open loop OP-AMP Configurations:

In the case of amplifiers, the term open loop indicates that there is no connection, either direct or via another network, exists between the output and input terminals. That is the output signal is not fed back in any form as part of the input signal, and the loop that has would be formed with feedback is open.

When op-amp is connected in open loop configuration, it acts as high gain amplifier. There exist three open loop op-amp configurations as follows:

  • 1)   Differential amplifier
  • 2)   Inverting amplifier
  • 3)   Noninverting amplifier

These three configurations are classed according to the number of inputs used and the terminal to which the input is applied when a single input is used.

The differential amplifier:

The following figure shows the differential amplifier in which input signals Vin1 and Vin2 are applied to the positive and negative terminal of the op-amp respectively. As the op-amp amplifies the difference between the two input signals, this configuration is called ‘differential amplifier’.

Differential amplifier
Differential amplifier

The op-amp is called versatile device because it amplifies both AC as well as DC input signals. The voltage drop across Rin1 and Rin2 can be neglected since they are very small as compared to input resistance of op-amp. Which then implies that V1=Vin1 and V2=Vin2.

Thus from the equation Vo=A(Vid)=A(V1-V2)

We get

Vo=A(Vin1-Vin2)

Thus the output voltage is equal to the voltage gain A times the difference between input voltages. The polarity of the output voltage depends upon the difference (Vin1-Vin2). In open loop configurations, the gain A is commonly referred as open-loop gain.

The Inverting Amplifier:

Inverting Amplifier
Inverting Amplifier

In inverting amplifier there is only one input which is applied to the inverting input terminal (which is negative). The Noninverting terminal is grounded.

Since V1=0V and V2=Vin

From the equation Vo=A(Vid)=A(Vin1-Vin2)

We get  Vo=-AVin

The negative sign shows that the output voltage is out of phase with respect to input by 180 degrees or is of opposite polarity.

The Noninverting Amplifier:

The following figure shows the Noninverting amplifier. In this configuration, input is applied to the Noninverting input terminal, and the inverting terminal is connected to the ground.

Noninverting Amplifier
Noninverting Amplifier

Here we have V1=Vin  and V2=0V.

Therefore according to the equation Vo=A(Vid)=A(Vin1-Vin2)

We get Vo=AVin

It implies that the output voltage is voltage gain A times the applied voltage.

You may also like:

If you like this article, please share it with your friends and like or facebook page for future updates. Subscribe to our newsletter to get notifications about our updates via email. If you have any queries, feel free to ask in the comments section below. Have a nice day!