Amplifier Group Members: Shrivastav Mehul S. Katara Sandeep. Amiraj Collage of Engineering & Technology

An Introduction to the Amplifier Not all amplifiers are the same and are therefore classified according to their circuit configurations and methods of operation. In “Electronics”, small signal amplifiers are commonly used devices as they have the ability to amplify a relatively small input signal, for example from a Sensor such as a photo-device, into a much larger output signal to drive a relay, lamp or loudspeaker for example. An Introduction to the Amplifier

Classification of Amplifiers

1)Common Emitter Amplifier Circuit

Common Emitter Amplifier Circuit The single stage common emitter amplifier circuit shown above uses what is commonly called “Voltage Divider Biasing”. This type of biasing arrangement uses two resistors as a potential divider network across the supply with their center point supplying the required Base bias voltage to the transistor. Voltage divider biasing is commonly used in the design of bipolar transistor amplifier circuits. Common Emitter Amplifier Circuit

2) Common base amplifiers:

Common base amplifiers: Fig. shows the circuit of a single-stage CB amplifier using NPN transistor. As seen, input ac signal is injected into the emitter-base circuit and output is taken from the collector-base circuit. The E/B junction is forward-biased by VEE where as C/B junction is reverse-biased by VCC. The Q-point or dc working conditions are determined by dc batteries along with resistors RE and RC. In other words, values of IE, IB and VCB are decided by VCC, VEE, RE and RC. The voltage VCB is given by the equation VCB= VCC – ICRC. When no signal is applied to the input circuit, the output just sits at the Q-point so that there is no output signal. Let us now see what happens when we apply an ac signal to the E/B junction via a coupling capacitor C1 (which is assumed to offer no reactance to the signal). Common base amplifiers:

3) Common Collector Amplifier

Common Collector Amplifier In common collector amplifier as the collector resistance is made to zero, the collector is at AC ground that is the reason for which the circuit is also called as grounded-collector amplifier or this configuration has voltage gain close to unity and hence a change in base voltage appears as an equal change across the load at the emitter, hence the name emitter follower is given to this circuit. In other words emitter follows the input signal.  Common Collector Amplifier

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