What is Operational Amplifier (OP-AMP) ?

                         

                           OPERATIONAL AMPLIFIER

Schematic symbol for OP-AMP

Operational amplifiers are some of the most basic active components in analogue systems. For instance, by connecting two external resistors, we can adjust the voltage gain and bandwidth of an OP-AMP to our exact requirements. Furthermore, with other external components, we can build waveform converters, oscillator, active filter and other interesting circuit.

Characteristics of an ideal Operational amplifier(OP-AMP)

      1.      Open loop voltage gain is infinite.

      2.       Input impedance is infinite.                                     

      3.       Output impedance is zero.

      4.       Bandwidth is infinite.

      5.       Perfect balance i.e output is zero when two input voltages are equal.

      6.       Characteristics dos not drift with temperature.

Equivalent circuit of OP-AMP

      7.       Common mode Rejection Ratio is finite.

      8.       Slew rate is finite.

However, a practical OP-AMP deviates from these 
ideal Characteristics                                                                                                      In practical OP-AMP

      1.       d.c or low frequency voltage gain is finite but very high.                        

      2.       The voltage gain varies from 10³ to 10⁶.                                                                                           

      3.       The bandwidth is also finite.

Pin diagram of an 741 OP-AMP 

      4.       The gain also is constant upto a few hundred kilo Hz and then       decreases monotonically with increase in frequency.

      5.       Input impedance lies in the range of 150 kilo-ohms to
          a few hundred mega-ohms.

      6.    Output impedance of OP-AMP varies between 0.75 to 100 ohms.