2 Stage RC Coupled Amplifier for PA

This is most popular type of coupling as it provides excellent audio fidelity. A coupling capacitor is used to connect output of first stage to input of second stage. Resistances R5, R2, R3 form biasing and stabilization network for Q1 and R7, R8 and R9 for Q2. Emitter bypass capacitor offers low reactance paths to signal. coupling Capacitor transmits AC signal, blocks DC. Cascaded stages amplify the signal, the overall gain is increased. Thus, coupling is done for more gain and overall gain of two stages equals to A=A1*A2 A1=voltage gain of first stage=V01/Vi A2=voltage gain of second stage= V02/V01 A= V02/Vi When ac signal is applied to the base of the transistor, its amplified output appears across the collector resistor Rc. It is given to the second stage for further amplification and signal appears with more strength. Frequency response curve is obtained by plotting a graph between frequency and gain in dB. The gain is constant in mid frequency range and gain decreases on both sides of the mid frequency range. The gain decreases in the low frequency range due to coupling capacitor Cc and at high frequencies due to junction capacitance Cbe. Resistance-capacitance (RC) coupling in amplifiers are most widely used to connect the output of first stage to the input (base) of the second stage and so on. This type of coupling is most popular because it is cheap and provides a constant amplification over a wide range of frequencies. Applications of RC Coupled Amplifier: Optical Fiber Communications. Public address systems as pre-amplifiers. Controllers. Radio or TV Receivers as small signal amplifiers.