The common-base circuit
Schematic of the common-base circuit with NPN- and PNP-BJT
The picture on the left shows the schematic of the common-base circuit with an NPN transistor. The picture on the right shows the schematic of the common-base circuit with a PNP transistor.
Fields of application for the common-base circuit
The common-base circuit is a basic transistor amplifier with voltage gain. It has a low input impedance and a medium output impedance, which is significantly determined by the collector resistor R2. The current gain is slightly lower than one.
Because of its low input impedance, the common-base circuit is eligible as a current output follower circuit, i.e. a current voltage converter (I-U-converter). In such an application, the output voltage is almost the input current multiplied by the collector resistor R2.
How to design a transistor amplifier in common-base configuration
Transistor amplifiers in common-base configuration can be designed with TransistorAmp 1.1 software. Open TransistorAmp software and click on New Amplifier - Common-Base circuit:
Now, the dialog Common-base circuit appears. Here you must input all parameters of your amplifier circuit:
To select the transistor type for your circuit, you must click the button Select transistor type from list and choose the transistor type within the next dialog:
TransistorAmp software contains almost every usual type of bipolar transistor (thousands of types). So, you will certainly find there the transistor type you need. After having chosen a transistor type, you must click on OK and you will get back to the previous dialog (where you specify your amplifier). Now, that dialog contains the transistor type which you have selected and you can click on OK. Then, the dialog closes and you will see immediately the design result of your new transistor amplifier:
Here, you can see your input parameters, the circuit and the values of all components. Furthermore, you can see the most important parameters of the operation point, i.e. collector current, collector emitter voltage and power consumption.
If you want to change any parameter of the circuit, simply click again on New Amplifier - Common-Base circuit and you will see, that the input dialog remembers all of your inputs, so it is easy for you to make changes.
If you want to save your result, click on Result - Save:
Then, input a file name and save the file.
Here, you can see the result file from our example: Amplifier in common-base configuration