Why common collector is called emitter follower

Common emitter is the most basic configuration for amplifier circuits. It also provide the maximum transconductance or voltage gain for a given load. CE is most widely used because it provides the voltage gain required for most of the day to day applications of preamp and power amps.. In a common-collector amplifier circuit, the output voltage at the emitter terminal "follows" the applied input signal at the base terminal.

The input impedance of an electrical network is the measure of the opposition to current flow impedance , both static resistance and dynamic reactance , into the load network being that is external to the electrical source. Characteristics of Common Emitter Amplifier.

The voltage gain of common emitter amplifier is medium. The power gain is high in the common emitter amplifier. There is a phase relationship of degrees in input and output.

In the common emitter amplifier, the input and output resistors are medium. The field-effect transistor FET is a transistor that uses an electric field to control the electrical behaviour of the device. FETs are also known as unipolar transistors since they involve single-carrier-type operation. Field effect transistors generally display very high input impedance at low frequencies. The current gain of a common - base amplifier is always less than 1. The voltage gain is a function of input and output resistances, and also the internal resistance of the emitter- base junction, which is subject to change with variations in DC bias voltage.

The Early effect , named after its discoverer James M. Early , is the variation in the effective width of the base in a bipolar junction transistor BJT due to a variation in the applied base-to-collector voltage.

In electronics, a common - base also known as grounded- base amplifier is one of three basic single-stage bipolar junction transistor BJT amplifier topologies, typically used as a current buffer or voltage amplifier.

The emitter follower transistor amplifier has a very straightforward circuit. It is not always possible to directly couple the emitter follower, common collector buffer. When this is the case, it is necessary to add coupling capacitors and bias resistors to the circuit.

The emitter follower can be designed using the design flow below as a basis:. As it is normally used as a buffer amplifier, this is the key parameter. The current gain is defined as the ratio of the load current to the input current. The current gain is dependent only on the BJT characteristics and independent of any other circuit element values.

Its value is given by. This result is identical to that for a common emitter amplifier with an emitter resistor. The input resistance to a common collector amplifier is large for typical values of the load resistance Re.

The voltage gain is the ratio of output voltage to input voltage. If the input voltage is again taken to be the voltage at the input to the transistor, Vb. The above equation is somewhat less than unity. The approximation equation of voltage gain is given by. This ratio can be directly derived from the voltage gain Av, and a voltage division between the source resistance Rs and the amplifier input resistance Ri.

After substitutions of appropriate equations, the overall voltage gain is given by. The output resistance is defined as the Thevenin resistance at the output of the amplifier looking back into the amplifier.

The circuit is shown below, the AC equivalent circuit to calculate the output resistance. If a voltage v is applied to the output terminals, the base current is found to be.

The output resistance for a common collector transistor amplifier is typically small.