![]() ![]() Note: that the value of Alpha will always be less than unity. A transistors current gain is given the Greek symbol of Beta, ( β ).Īs the emitter current for a common emitter configuration is defined as Ie = Ic + Ib, the ratio of Ic/Ie is called Alpha, given the Greek symbol of α. In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing into the transistor as the emitter current is given as Ie = Ic + Ib.Īs the load resistance ( R L ) is connected in series with the collector, the current gain of the common emitter transistor configuration is quite large as it is the ratio of Ic/Ib. ![]() This is mainly because the input impedance is LOW as it is connected to a forward biased PN-junction, while the output impedance is HIGH as it is taken from a reverse biased PN-junction. The common emitter amplifier configuration produces the highest current and power gain of all the three bipolar transistor configurations. This type of configuration is the most commonly used circuit for transistor based amplifiers and which represents the “normal” method of bipolar transistor connection. In the Common Emitter or grounded emitter configuration, the input signal is applied between the base and the emitter, while the output is taken from between the collector and the emitter as shown. The common base circuit is generally only used in single stage amplifier circuits such as microphone pre-amplifier or radio frequency ( Rƒ ) amplifiers due to its very good high frequency response. Where: Ic/Ie is the current gain, alpha ( α ) and RL/Rin is the resistance gain. The input current flowing into the emitter is quite large as its the sum of both the base current and collector current respectively therefore, the collector current output is less than the emitter current input resulting in a current gain for this type of circuit of “1” (unity) or less, in other words the common base configuration “attenuates” the input signal. The base terminal is grounded or can be connected to some fixed reference voltage point. The input signal is applied between the transistors base and the emitter terminals, while the corresponding output signal is taken from between the base and the collector terminals as shown. Common Collector Configuration – has Current Gain but no Voltage Gain.Īs its name suggests, in the Common Base or grounded base configuration, the BASE connection is common to both the input signal AND the output signal. ![]()
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