Bio Medical Engineering Solutions @ SL: Comparator using AD741, Operational Amplifier

Fundamentals of Op-Amp

An op-amp operates on analog input. It can be used to amplify or attenuate this input, and to carry out mathematical operations such as addition, subtraction, integration, and differentiation. Because of their wide range of uses, op-amps are encountered in most electronic circuits.

Vin (+) ==> non-inverting input

Vin (−) ==> inverting input

Vout ==> output ()

voltage supply terminals are not shown in figure.

The fundamental function of an op-amp is to greatly amplify the differential between the two inputs, and output the result. If input at V(+) is greater than at V(−), the op-amp will amplify and output a positive signal; if V(−) is greater, the op-amp will output an amplified negative signal.

Two other features of a typical op-amp are:

(a) the input impedance is extremely high,

(b) the output impedance is extremely low.
Because the op-amp's gain is so high, even small differences in the inputs will rapidly drive the output voltage to its maximum or minimum value. For this reason, op-amps are usually connected to a negative feedback.

Comparator

A comparator circuit compares two voltages and outputs either a 1 (the voltage at the plus side; VDD in the illustration) or a 0 (the voltage at the negative side) to indicate which is larger. Comparators are often used, for example, to check whether an input has reached some predetermined value. In most cases a comparator is implemented using a dedicated comparator IC, but op-amps may be used as an alternative. Comparator diagrams and op-amp diagrams use the same symbols. Figure 4: Comparator Circuit

Note first that the circuit does not use feedback. The circuit amplifies the voltage difference between Vin and VREF, and outputs the result at Vout. If Vin is greater than VREF, then voltage at Vout will rise to its positive saturation level; that is, to the voltage at the positive side. If Vin is lower than VREF, then Vout, will fall to its negative saturation level, equal to the voltage at the negative side.
In practice, this circuit can be improved by incorporating a hysteresis voltage range to reduce its sensitivity to noise. The circuit shown in below, for example, will provide stable operation even when the Vin signal is somewhat noisy.

Download Schematic, Component Top View, and PCB as PDF.

https://app.box.com/s/dknrl3wm52rgt54e44fg

One of the application of comparator circuits

This is a circuit which make sound when light is fallen in to the LDR. In the same manner I am going to use above five comparator circuits to recognize black line of a Line Follower.