The op-amp is linear, active device that consists of a complex array of resistors, transistors, diodes, capacitors etc. Integrated on a tiny silicon chip. It can perform mathematical operations like addition subtraction multiplication division integration etc. It can serve as an amplifier, filter or even used in making analog computer.
Op-amps are mostly preferred by the electronics industry these days and in fact it is used for a variety of applications, including scientific, military, industrial and consumer electronics. Normally standard ICs with op-amps configuration have a low cost production value, but some op-amps are packed with a lot more in them like a hybrid or integrated designs that have specific applications could swell over $100 USD even in minimal production. Op-amps can be used as an integral part of IC circuits that have a lot more complex operations than regular transistors.
NOTATION: It is a five terminal device
A-Non inverting input
B-Inverting input
C-Output pins
D-Positive power supply
E-Negative power supply
EXPLANATION: The two input pins (A,B) are where the voltage to be amplified is supplied. No current flows through them i.e. they are of infinite impedance.
The D and E are the power pins through which the power is supplied to the op-amp. Usually these are not shown in the circuit. The value of power supplied at these pins determines the upper and lower limits on the op-amp voltage terminals.
The C terminal is the output pin where we get the amplified output.
Figure 1:
Writing the KCL equation we have,
Io=ic+ + ic-+ ip + iN
Io=ip + iN
Figure 2:
Hence Vo =A(Vp - VN)
As seen from figure the output voltage is A (gain) multiplied by the difference of non-inverting and inverting inputs. The slope of the graph is equal to gain of A. The voltage saturates at +Vcc and -Vcc.The op-amp can be operated in two modes-linear mode where the graph is a straight line passing through origin where a corresponding increase in the difference between Vp and Vnresults in corresponding increase in Vout. The second mode is the saturation mode where the Vout is saturated or fixed at + or -Vcc.
THE IDEAL OP-AMP
Op-amp has infinite input impedance i.e. no current flows into the inputs of op-amp. When two input voltages V1 and V2 is applied, the op-amp produces an output, Vout =A(V1- V2) where A is the gain of the amplifier. The output voltage is zero when input voltage difference is zero.
APPLICATIONS:
It is used to perform various mathematical operations like addition, subtraction, multiplication, differentiation, integration etc. It is specifically used as a device which amplifies voltage input and also sometimes changes the polarity. It finds it uses in oscillators, filter circuits and other instrumentation amplifier. Some of the application circuits of op-amp are listed below:
- Comparator
- Switchable inverter/non inverter circuits
- Inverter with adjustable gain
- Sign/polarity changer
- Jfet controlled switchable inverter
- Phase shifter
- Instrumentation amplifier
- Oscillators
- Analog to digital and digital to analog converters
- Gyrators
- Analog computer
- Charge amplifier
- Voltage and current regulator
- Schmitt trigger
- Capacitance multiplier
- Voltage clamps