OPERATIONAL AMPLIFIER (OP-AMP)

                                        Introduction             

Fig a. Shows ic-741 op-amp

Operational amplifier is also known as op-amp. It is invented by karl D Swartzel in 1967. An Op-amp is a direct coupled, differential input, high gain electronic voltage amplifier with the different input , usually packaged in the form of a small Integrated circuit or single ended output. Op-amp work on both the AC and DC voltage. Op-amp are components that can be connected with other electrical components in circuits to amplify voltage, isolate circuits, count signals, or performed arithmetical and mathematical operations (addition, integration, multiplication, differentiation etc).

The symbol of an op-amp which is shown in fig, indicates it's main feature of having two input ports (a positive one and a negative one) and therefore differential input voltages are usually measured with respect to the ground ( which has zero voltage).

Pin configuration

Fig b. Shows symbolic form of ic

History

Brief history:
Operational amplifiers began in the days of vacuum tubes and analog computers. They consisted of relatively complex differential amplifiers with feedback. The circuit was constructed such that the characteristics of the overall amplifier were largely determined by the type and amount of feedback. Thus the complex differential amplifier itself had become a building block that could function in different “operations” by altering the feedback. Some of the operations that were used included adding, multiplying, and logarithmic operations.

The operational amplifier continued to evolve through the transistor era and continued to decrease in size and increase in performance.

1967: Release of the μA741. The popularity of monolithic op-amps was further improved upon the release of the LM101 in 1967, which solved a variety of issues, and the subsequent release of the μA741 in 1968. The μA741 was extremely similar to the LM101 except that Fairchild's facilities allowed them to include a 30 pF compensation capacitor inside the chip instead of requiring external compensation. This simple difference has made the 741 the canonical op-amp and many modern amps base their pinout on the 741s. The μA741 is still in production, and has become ubiquitous in electronics—many manufacturers produce a version of this classic chip, recognizable by part numbers containing 741. The same part is manufactured by several companies.

In spite of all the improvements, however, the high-performance, integrated operational amplifier of today is still based on the fundamental differential amplifier. Although the individual components in the amplifier are not accessible to you, it will enhance your understanding of the op amp if you have some appreciation for the internal circuitry.


Ideal characteristics:

An ideal op-amp is usually considered to have the following characteristics;

• The open loop voltage gain A  is very high . Typically Ao > 10^5 and in most simple analysis, you can assume Ao = infinity.
• The input impedence R1 is very high and can be assumed to be infinite. This means there is no current in the opamp at input port V+ and V-.
• zero output resistance (Ro = 0)
• zero input offset voltage (Voff = 0)
• infinite band width zero phase shift 
• infinite common mode rejection ratio (CMRR) (CMRR = infinity)
• Infinity slow rate (S = infinity)
• Zero power supply rejection ratio (PSRR = 0)  these ideals can be summarized by the two golden rules.
• In a closed loop the output attempts to do whatever is neccesary to make the voltage difference between the inputs zero.
• The inputs draw no current.  

Inverting and non inverting amplifier

Inverting and the non-inverting amplifiers are the basic types that arouse from the terminals involvement in the Op-amps.

Inverting amplifier

This is a basic Op-Amp where the terminal with minus sign is provided with minus sign is provided with the feedback from the output of it. Therefore the feedback is provided for this terminal of the amplifier it is known as inverting amplifier.

In this case the non-inverting terminal is connected to the ground. The gain for this kind of amplifiers is high.

The relation between the input and the output signal generated is  180 degree phase shift.

The ratio in between the resistors gives the amplifier gain for these amplifiers.

In this type of amplifiers the slew rate and CMRR is high.

Non-inverting amplifier

The basic op-amp where the output of it and the input are in phase with each other this type of amplifiers are known as non-inverting amplifiers. The gain for this type of amplifiers is easy to determine.

 In this amplifier the output generated is the same as that of the applied input.

In this case one plus the ratio of the resistors determines the non-inverting gain for these amplifiers.

In this type the amplifier functionality is dependent on the non-inverting terminal.

The inverting input terminal is connected to the ground in these types of amplifiers.

Inverting and the non-inverting amplifiers are the basic types that arouse from the terminals involvement in the Op-amps.

Applications

Below are the applications of IC 741 Op Amp across different use cases:-

1) Computational: Many electronic circuits that perform mathematical operations like integration, differentiation, summers etc. use 741 Op-Amp.

2) Comparators: The 741 IC can be used to compare voltage signals and determine if they are almost of the same voltage. This can be used in voltage regulators and signal comparators.

3) Amplifiers: 741 IC is mostly used to amplify signals of varying frequencies ranging from DC to higher radio frequencies. It is also used in frequency selective amplifiers which filter out signals of unwanted frequencies, E.g. tone control systems in stereo and Hi Fi systems.