Consider a BJT serving as an amplifier. No suppose I need to subtract the output obtained from two such BJT amplifiers A1 and A2.
Then I can simply connect the output from A1 to one of the input terminals of another transistor amplifier A3 and connect the other terminal to the output obtained from A2. In this way I can obtain the output from A3 as the difference of two signals.
Now similarly suppose I need A non inverting amplifier. Then I can measure the output of a CE transistor amplifier in a reverse way so as to get the output in phase with the input.
Now consider an integrator circuit. When an ac source is connected in series with a resistor and capacitor then if the function to be integrated is taken as the current then obviously the voltage gives the integrand of the function (although multiplied by the capacitance).
In all the above situations I have sen opamps being used. When the circuit arrangement is as simple as mentioned above why do we use opamps(which have complicated internal circuit arrangements)? I don't intend to be a critic but rather I want to know the actual purpose for which opamps are used at the expense of simplicity?
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