Design of a mixer using diodes

Design of a mixer using diodes

A frequency mixer is a three port device that implements the technology of generating new frequencies from two frequencies, also known as a frequency conversion.

In order to achieve frequency conversion, mixers often use nonlinear or time-varying components. The output of an ideal mixer consists of the sum and difference frequencies of two input signals.

The operation of actual RF and microwave mixers is usually based on the nonlinearity provided by diodes or transistors. Nonlinear components can generate many harmonics or other products of the input frequency, so the desired frequency components must be selected through filtering.

Modern microwave systems often use several mixers and filters to achieve up conversion and down conversion between the baseband signal frequency and the RF carrier frequency.

Mixers can be used for both transmitting and receiving devices. Especially in superheterodyne receivers, the mixer is an important component. The signal type remains unchanged after mixing, for example, an amplitude modulated signal remains an amplitude modulated signal after mixing, with only the carrier frequency changing.

High quality communication receivers widely use high-performance multiplier circuits, such as diode double balanced mixers or double differential balanced modulators.

However, general receivers (such as broadcast and television receivers) may use simple transistors or field-effect transistor mixers to simplify circuits and reduce costs.