![]() ![]() There is no capacitor used in this method of coupling because the transformer itself conveys the AC component directly to the base of second stage. The coupling method that uses a transformer as the coupling device can be called as Transformer coupling. This method is not so popular and is seldom employed. In this impedance coupling method, the impedance of coupling coil depends on its inductance and signal frequency which is jwL. The coupling network that uses inductance and capacitance as coupling elements can be called as Impedance coupling network. Let us get into the details of this method of coupling in the coming chapters. ![]() While blocking the DC components from DC bias voltages to effect the next stage. The coupling capacitor passes the AC from the output of one stage to the input of its next stage. The capacitor which allows AC and blocks DC is the main coupling element used here. This is the mostly used method of coupling, formed using simple resistor-capacitor combination. There are four basic methods of coupling, using these coupling devices such as resistors, capacitors, transformers etc. Joining one amplifier stage with the other in cascade, using coupling devices form a Multi-stage amplifier circuit. To block the DC to pass from the output of one stage to the input of next stage, which means to isolate the DC conditions. To transfer the AC from the output of one stage to the input of next stage. The basic purposes of a coupling device are If there are n number of stages, the product of voltage gains of those n stages will be the overall gain of that multistage amplifier circuit. Where A V = Overall gain, A V1 = Voltage gain of 1 st stage, and A V2 = Voltage gain of 2 nd stage. The overall gain is the product of voltage gain of individual stages. The following figure shows a two-stage amplifier connected in cascade. This process of joining two amplifier stages using a coupling device can be called as Cascading. These coupling devices can usually be a capacitor or a transformer. In Multi-stage amplifiers, the output of first stage is coupled to the input of next stage using a coupling device. Hence they are replaced by Multi-stage transistor amplifiers. In practical applications, the output of a single state amplifier is usually insufficient, though it is a voltage or power amplifier. Emitter Follower & Darlington Amplifier.Transformer Coupled Class A Power Amplifier.
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