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Common Base Amplifier

Description

Theory: It is called the common base configuration because (DC power source aside), the signal source and the loadshare the base of the transistor as a common connection point shown in Figure by bold lines

Perhaps the most striking characteristic of this configuration is that the input signal source must carry thefull emitter current of the transistor, as indicated by the heavy arrows in the first illustration.

As we know, the emitter current is greater than any other current in the transistor, being the sum of baseand collector currents. Because the input current exceeds all other currents in the circuit, including theoutput current, the current gain of this amplifier is actually less than. In other words, it attenuates currentrather than amplifying it. With common-emitter and common-collector amplifier configurations, the transistor parameter mostclosely associated with gain was β. In the common-base circuit, we follow another basic transistor parameter:the ratio between collector current and emitter current, which is a fraction always less than 1. Thisfractional value for any transistor is called the alpha ratio. Since it obviously can't boost signal current, it only seems reasonable to expect it to boost signal voltage. Letus now analyze the circuit under AC analysis by giving small AC signal and DC Bias to the circuit. 1. Drag and Drop a function generator and one more AC Voltmeter.2. Connect the circuit as shown.3. Provide in Function generator – 0.12V, 2KHz sine wave.

COMMON BASE BJT AMPLIFIER

AimAim is to 1. Construct a common base amplifier2. Perform AC and DC signal analysis on it.

Related Experiments

3. Provide in Function generator – 0.12V, 2KHz sine wave.4. Provide a bias of 0.95 V(DC Source0) to the emitter.5. Now since the voltage gain would be expectedly high, let us put an equation to measure the input voltage.6. Run the Time domain analysis for 2 ms.

Conclusion

This will be the result that is obtained: