Intermodulation Distortion of a BipolarCommon-Emitter Amplifier With Arbitrary EmitterImpedance and Input Matching Network

Intermodulation distortion (IMD) is a type of distortion that occurs in electronic systems when two or more signals with different frequencies are amplified or processed. In a bipolar common-emitter amplifier, IMD can arise due to the non-linearity of the transistor and the intermodulation of the input signals. This distortion can be minimized by designing the amplifier with appropriate input matching network and emitter impedance.

The input matching network is used to match the impedance of the input signal source with the input impedance of the amplifier. This helps to maximize the power transfer and minimize the reflections. The emitter impedance affects the gain, stability, and linearity of the amplifier. An arbitrary emitter impedance can be used to optimize the amplifier performance for a specific application.

To calculate the IMD of a bipolar common-emitter amplifier, we need to consider the intermodulation products generated due to the non-linearity of the transistor. The third-order IMD (IMD3) is the most important and is given by:

IMD3 = 2V1^2V2 - 3V1V2^2

where V1 and V2 are the amplitudes of the input signals at frequencies f1 and f2, respectively. The IMD3 is a function of the input power levels and the transistor parameters such as the gain, bias voltage, and emitter resistance.

To minimize the IMD, we can use techniques such as feedback, biasing, and impedance matching. Feedback reduces the non-linearity of the transistor by reducing the gain at high frequencies. Biasing the transistor in the linear region also helps to reduce the IMD. Impedance matching ensures maximum power transfer and reduces reflections, thereby minimizing the IMD.

In summary, the intermodulation distortion of a bipolar common-emitter amplifier can be minimized by designing the amplifier with appropriate input matching network and emitter impedance, and using techniques such as feedback, biasing, and impedance matching