The performance obtainable from a single-stage amplifier is often insufficient for many applications, hence several stages may be combined forming a multistage amplifier. These stages are connected in cascade, i.e. output of the first stage is connected to form input of second stage, whose output becomes input of third stage, and so on.
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Overall gain
The overall gain of a multistage amplifier is the product of the gains of the individual stages (ignoring potential loading effects):
Gain (A) = A1* A2*A3 *A4 *... *An.Alternately, if the gain of each amplifier stage is expressed in decibels (dB), the total gain is the sum of the gains of the individual stages:
Gain in dB (A) = A1 + A2 + A3 + A4 + ... AnInter-stage coupling
Depending on the manner in which the different amplifier stages are connected, one of the following amplifiers may result:
References
Multistage amplifier Wikipedia(Text) CC BY-SA