Question

Problem Statement:
Amplifier is the generic term used to describe a circuit which produces and increased version of
its input signal. However, not all amplifier circuits are the same as they are classified according to
their circuit configurations and modes of operation.
A two stage audio amplifier has two stages with the audio signal being given as the input of first
stage and the amplified voltage signal is the output of the second stage amplifier) which drives the
load (8 ohm speaker). The block diagram of a two stage amplifier is given by:

First Stage: The first stage is a common emitter amplifier configuration. The common emitter
amplifier is used as a voltage amplifier. The input of this amplifier is taken from the base terminal,
the output is collected from the collector terminal and the emitter terminal is common for both the
terminals.
It is commonly used in the following applications:
 The common emitter amplifiers are used in the low-frequency voltage amplifiers.
 These amplifiers are used typically in the RF circuits.
 In general, the amplifiers are used in the Low noise amplifiers
It has the following advantages:
 The common emitter amplifier has a low input impedance and it is an inverting amplifier
 The output impedance of this amplifier is high
 This amplifier has highest power gain when combined with medium voltage and current
gain
 The current gain of the common emitter amplifier is high
Second Stage: The second stage is a common collector amplifier configuration. Input signal is
applied to the base terminal and the output signal taken from the emitter terminal. Thus the
collector terminal is common to both the input and output circuits. This type of configuration is
called Common Collector, (CC) because the collector terminal is effectively “grounded” or
“earthed” through the power supply

*TASK*:

To solve the Complex Engineering Problem refer to the above circuit diagram and follow these
steps :
Step 1. It is required to design the first amplifier stage with the following specifications for Q1:
IE= 1.5mA β=100 Vcc=15V

Step 2: Using the results obtained in step 1, perform the complete DC analysis of the above circuit.
Assume that β=100 for Q2
Step 3: Select the appropriate small signal model to carry out the ac analysis of the circuit. Assume
that the input signal from the mic vsig=10mVpeak sinusoidal waveform with f=20 kHz. Also find
the peak value of the amplified output signal.

Answer 1