CE Amplifier

COMMON - EMITTER AMPLIFIER

 The single stage common emitter amplifier circuit shown 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.

 This method of biasing the transistor greatly reduces the effects of varying Beta, ( β ) by holding the Base bias at a constant steady voltage level

allowing for best stability. The quiescent Base voltage is determined by the potential divider network formed by the two resistors, and the power

supply voltage as shown with the current flowing through both resistors.

 Then the total resistance will be equal to sum giving the current. The voltage level generated at the junction of two resistors holds the Base voltage

constant at a value below the supply voltage.

Output Voltage Input Voltage

 Common-Emitter amplifier with voltage-divider bias and coupling capacitors on the input and output and a bypass capacitor, from emitter to ground.

The input signal, Vin, is capacitive coupled to the base terminal, the output signal, Vout, is capacitive coupled from the collector to the load. The

amplified output is 180° out of phase with the input. Because the ac signal is applied to the base terminal as the input and taken from the collector

terminal as the output, the emitter is common to both the input and output signals. There is no signal at the emitter because the bypass capacitor

effectively shorts the emitter to ground at the signal frequency. All amplifiers have a combination of both AC and DC operation, which must be

considered, but keep in mind that the common-emitter designation refers to the AC operation.

 The Voltage Gain of the common emitter amplifier is equal to the ratio of the change in the input voltage to the change in the amplifiers output

voltage. Then ΔVL is Vout and ΔVB is Vin. But voltage gain is also equal to the ratio of the signal resistance in the Collector to the signal resistance

in the Emitter.

 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

 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.

 Thus the Common Emitter model is implemented using the Activate tool.

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