# Operational Amplifier Building Blocks

We have seen that we can connect resistors to a basic operational amplifier to produce various inverting and non-inverting outputs and configurations along with their respective gains.

So to make things a little bit easier for all, here is a list of some of the “Basic Operational Amplifier Building Blocks” we can use to create different electronic circuits and filters.

## The Voltage Follower

The Voltage Follower, also called a buffer dose not amplify or invert the input signal but instead provides isolation between two circuits. The input impedance is very high while the output impedance is low avoiding any loading effects within the circuit. As the output is connected back directly to one of the inputs, the overall gain of the buffer is +1 and Vout = Vin.

## The Op-amp Inverter

The Inverter, also called an inverting buffer is the opposite to that of the previous voltage follower. The inverter does not amplify if both resistances are equal but does invert the input signal. The input impedance is equal to R and the gain is -1 giving Vout = -Vin.

## The Non-inverting Amplifier

The Non-inverting Amplifier does not invert the input signal or produce an inverting signal but instead amplifies it by the ratio of: (RA + RB)/RB or commonly 1+(RA/RB). The input signal is connected to the non-inverting (+) input.

## The Inverting Amplifier

The Inverting Amplifier both inverts and amplifies the input signal by the ratio of -RA/RB. The gain of the amplifier is controlled by negative feedback using the feedback resistor RA and the input signal is fed to the inverting () input.

## The Bridge Amplifier

The inverting and non-inverting amplifier circuits from above can be connected together to form a bridge amplifier configuration. The input signal is common to both op-amps with the output voltage signal taken across the load resistor, RL. If the magnitudes of the two gains, A1 and A2 are equal to each other then the output signal will be doubled as it is effectively the combination of the two individual amplifier gains.

### The Bridge Op-amp Circuit

The Adder, also called a summing amplifier, produces an inverted output voltage which is proportional to the sum of the input voltages V1 and V2. More inputs can be summed. If the input resistors are equal in value (R1 = R2 = R) then the summed output voltage is as given and the gain is +1. If the input resistors are unequal then the output voltage is a weighted sum and becomes:

Vout = -(V1(RA/R1) + V2(RA/R2) + etc.)

## The Voltage Subtractor

The Subtractor also called a differential amplifier, uses both the inverting and non-inverting inputs to produce an output signal which is the difference between the two input voltages V1 and V2 allowing one signal to be subtracted from another. More inputs can be added to be subtracted if required.

If resistances are equal (R = R3 and RA = R4) then the output voltage is as given and the voltage gain is +1. If the input resistance are unequal the circuit becomes a differential amplifier producing a negative output when V1 is higher than V2 and a positive output when V1 is lower than V2.

## The Op-amp Comparator

The Comparator has many uses but the most common is to compare the input voltage to a reference voltage and switch the output if the input voltage is above the reference voltage. If the input goes more positive than the reference voltage set by the voltage divider, Vin > Vref, the output changes state. When the input voltage drops below the preset reference voltage and Vin < Vref, the output switches back. By using positive feedback the basic comparator circuit can easily be converted into a Schmitt Trigger to reduce oscillations around the switching point.

### The Comparator Op-amp Circuit

Here are just some of the more common and basic operational amplifier building block configurations discussed in this section that we can use in electronic circuits. All the above circuits can be constructed using a variety of different op-amps including the famous 741 op-amp. I hope that this short tutorial about basic op-amp building blocks will help you to understand the different basic op-amp circuit configurations.

• S
Steve Darrow

In your OP-AMP COMPARITOR section, you meant to add POSITIVE FEEDBACK to give it hysteresis and make it a Schmidt Trigger.

• T
Thallam karthik

Can anyone suggest to use op amp in detecting earthquake or tsunamis

• T
Ted

The comparator will suffer from saturation as shown, and will not respond quickly to any change that crosses the threshold, unless some more complexity is added to the circuit to avoid driving the op-amp into saturation. Warning FYI.

• V
VIMAR

IT HELPS A LOT ..THANK YOU SO MUCH I HAVE LEARN FROM IT…..

• j
jingyi

For the Voltage Subtractor Op-amp circuit, I doubt why the sign is negative before RA/R(V2-V1). I deduct it myself and is Vout=RA/R(V2-V1), positive sign. Could you check it please?

• Wayne Storr

The subtractor (differential amplifier) has a gain equal to RA/R around the inverting input, so the gain is negative.

• M
Moulika

i just want the comparator with input given at negative terminal of opamp , circuit and the output equation too

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Feroz Hossen

I don’t understand the the operation of Bridge Op-amp Circuit. How will the voltage be doubled? According to the circuit, the output of the inverting and non-inverting op-amp are opposite phase, so how the voltage will be twice at the load.

• Wayne Storr

The outputs of the two op-amps are complements of each other, because when Vo1 is heading in a positive direction, Vo2 is heading in a negative direction and vice versa. So if for example, Vo1 = +3v and Vo2 = -3v, then the voltage across RL will be: +3v – (-3) = 6v or double Vout.

• S
Shreedevi.B.R

I want to design a current amplifier circuit, please let me know how to go about, Rsh is around 1k ohm – 1M ohm.

• A
ABC

Hi,
I want to confirm that are the output waveforms of A1 and A2 opamp are correct or not in bridge opamp amplifier ckt. As per the fig. A1 is inverting amplifier and A2 is non inverting amplifier but the output waveforms are opposite.. so please confirm.

• Wayne Storr

The direction of the input waveform is not given, the outputs from the inverting and non-inverting configurations are complementary to each other and are therefore correct.

• A
ABC