Operational amplifier or Op-Amp is an analog component, this component was used in old analog computers for performing operations such as addition/multiplication by constant, integration and differentiation etc.. Because of its versatility and reliability, it is very much being used in large number of circuits and devices. Here I won't be discussing about various application of Op-Amp, but rather try to explain Op-Amp a component and the concept which makes this component so special. I hope this article will give you enough food for thought and will enable you to think various applications where the op-amp can be used.
First lets see how OpAmp looks like...
I called op-amp as a component, but it comes as an ICs, so doesn't have its own look like transistors and resistors..
![opamp_ic](/images/opamp_ic.jpg)
Opamp in circuits are represented by much simpler symbol shown below..
![opamp](/images/opamp.jpg)
Opamp is generally represented a three pin device, two input and one output. The power pins +Vcc and -Vcc are normally ignored in diagrams. Now lets see some properties of this Opamp..
- Opamp has got two input pins (as shown), One with +ve sign is called non-inverting input, while other one with -ve sign is called inverting input.
- Inputs are called differential input, because difference in voltage levels on these input causes output voltage.
- What is amplifier in Operational amplifier ? Yes! the output is not just difference between voltage on both input, but it is the voltage difference multiplied by gain.
- Gain of an OpAmp is generally in range of 106 (very high)
-
Does this means that 1V differential voltage will cause 1000000 Volts at output ? theoretically yes, but practically NO!
Voltage swing of an opamp is limited by its supply voltage (-Vcc to +Vcc only). - This high gain is actual strength of opamp which is tamed and used in many applications.
-
If voltage on -ve pin is more than +ve pin, opamp will swing toward -Vcc. And if voltage on +ve pin is more than voltage on -ve pin, the opamp will swing toward +Vcc. e.g if +1v is applied on +ve pin and +2 volts is applied on -ve pin, the opamp will swing toward -Vcc (difference x gain concept).
Again, if +2V is applied on +ve pin and +1V is applied on -ve pin, the opamp will swing toward +Vcc (same, difference x gain concept)
Here we can derive one equation, output_voltage =
[voltage_on_+ve_pin - voltage_on_-ve_pin] * gainRemember that the output voltage is limited by supply voltage (+Vcc and -Vcc). This means that even though due to high gain opamp may try to shoot at very high output voltage (106), but it will be limited by supply voltage +Vcc and -Vcc.
- Input Impedance of Opamp is also very high, in range of MegaOhms. This high impedance make it a pure voltage toy, voltage at input, voltage at output simple!
In the next section we will put opamp in various scenarios and will try to analyze its behavior.