Full Form of OP-AMP, Definition, Types, and Characteristics

The full form of OP-AMP is Operational Amplifier. In an integrated circuit, an op-amp is commonly used to amplify the difference in voltages between two inputs. It is also configured to perform arithmetic operations. Hence it was christened an ‘operational’ amplifier.

The most basic function of an op-amp is to amplify differences in voltage (noninverting and inverting amplifiers), but it can also be configured to do a lot more! Many applications and uses of an op-amp depend on additional components. It can quite easily be used as a filter, unity gain buffer and even a voltage follower. 

Usually, the op-amp is equipped with 5 terminals. They are as follows:

• Positive Power Supply
• Negative Power Supply
• Non Inverting Input
• Inverting Input and 
• Output

Types of OP-AMP

On the basis of input/output voltage range, operational amplifiers are classified into three categories. They are dual-supply op-amps, single-supply op-amps and rail-to-rail op-amps.

Let us know a little bit about these operational amplifiers:

Dual Supply OP-AMP

In simple words, in a dual supply operational amplifier, there are two power supplies, a positive supply and the other one negative. 

Since, the op-amps are usually used to amplify small signals (around 0V), in a dual supply op-amp, the VEE must be -1.5V (or less). This is where the negative power supply comes in real handy.  

Single Supply OP-AMP

A single-supply operational amplifier allows you to input signals close to 0V without a negative voltage. 

They are also commonly called ground sense operational amplifiers, as they can operate up to ground-level input signals.

Rail to Rail OP-AMP

Unlike single op-amps, the rail-to-rail operational amplifiers can operate normally even when the input voltage swings from VEE to VCC. For this reason, they are also called input/output full swing op-amps. 

Working of an OP-AMP

Now that we know the basics about op-amp, we can dive deeper into the working principle of the op-amp.

Power Supply of OP-AMP 

Since the operational amplifier has two input terminals (positive and negative), it needs a dual polarity DC supply to run successfully. 

The positive DC supply is connected to the +VCC (positive) terminal, while the negative DC supply is connected to the -VCC (negative) terminal. 

Although, we do find a few exceptions here. For instance, many operational amplifiers can even run on single polarity power supply. 

Working of an OP-AMP in an Open Loop Circuit

As we have noted previously, there are two input terminals and a single output terminal in an op-amp. Thus, if we apply two signals, one at the positive and one at the negative terminal, an ideal op amp will amplify the difference between the two signals. In simpler words, this difference is also called the differential input voltage. We can understand this better with the following equation,

VOUT = AOL (V1-V2) 

In the above equation, VOUT stands for the voltage at the output terminal. 

AOL is the open-loop gain, which ideally remains constant.

(V1 - V2) is the differential input voltage. 

From the equation, it becomes evident that, when V1 & V2 are not equal, the differential input voltage is more than zero. Thus, output is also more than zero. In case, V1 = V2, the output will become zero. 

However, this is an ideal situation. Practically, there are always minor imbalances in an operational amplifier. 

Working of an OP-AMP in a Closed Loop Circuit

It is a fact that op-amp is equally beneficial for open as well as closed-loop circuits. The extra benefit in a closed loop circuit is the addition of a feedback system!

The feedback path feeds the output signal in the input channel. Thus, there are two signals present at the input terminal. One of them is the original input signal, while the other is the feedback signal. The following equation helps show the working of an operational amplifier in a closed-loop circuit, 

VOUT= ACL (V1 - V2) = ACLVD

In the above equation, VOUT is output terminal voltage.  

ACL is the closed-loop gain.

VD = (V1 - V2) is the differential input voltage.

The feedback is said to be positive if the feedback signal feeds part of the output signal back to the non-inverting (positive) terminal. If the same signal is fed to the inverting terminal (negative), the feedback is said to be negative. 

Both negative and positive feedback have their own utilities. For example, positive feedback is used as oscillator, and negative feedback is used as the amplifier. 

Characteristics of an ideal OP-AMP

Following are the ideal characteristics of an operational amplifier:

• Infinite Voltage Gain (to obtain maximum output) 
• Infinite Input Resistance (so that almost any power source can drive it)
• Zero Output Resistance (to avoid change in output due to change in load current)
• Zero Noise
• Infinite Bandwidth 
• Infinite Common Mode Rejection Ratio
• Zero Power Supply Rejection Ratio 

However, keep in mind that these are only the ‘ideal’ conditions. This implies that such characteristics do not exist in reality. Practically, an operational amplifier has some inevitable differences and imperfections. 

For example, the input resistance can’t be infinite. It will surely be very high, but finite. The output resistance cannot be completely zero, it will be a non-zero one. 

Although, the difference in their ideal and practical characteristics is pretty negligible. In fact, even without the ideal characteristics, operational amplifiers have become a crucial part of our daily lives! 

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