Electronic mixer

Multiplicative mixers multiply together two time-varying input signals instantaneously (instant-by-instant).

Any nonlinear electronic block driven by two signals with frequencies f1 and f2 would generate intermodulation (mixing) products.

Therefore, normal nonlinear amplifiers or just single diodes have been used as mixers, instead of a more complex multiplier.

A multiplier usually has the advantage of rejecting – at least partly – undesired higher-order intermodulations and larger conversion gain.

The simplest additive mixers are resistor networks, and thus purely passive, while more complex matrix mixers employ active components such as buffer amplifiers for impedance matching and better isolation.

In communications, a multiplicative mixer is often used together with an oscillator to modulate signal frequencies.

A multiplicative mixer can be coupled with a filter to either up-convert or down-convert an input signal frequency, but they are more commonly used to down-convert to a lower frequency to allow for simpler filter designs, as done in superheterodyne receivers.

The output signal may be obtained by removing the other signal components with a filter.í The received signal can be represented as and that of the local oscillator can be represented as For simplicity, assume that the output I of the detector is proportional to the square of the amplitude: The output has high frequency (

then the beat component is a recovered version of the original signal, with the amplitude equal to the product of

; that is, the received signal is amplified by mixing with the local oscillator[clarification needed].

They are very inefficient as most of the power output is in other unwanted terms which need filtering out.

They are designed for a wide variety of frequency ranges, and they are mass-produced to tight tolerances by the hundreds of thousands, making them relatively cheap.

Gilbert cell mixers are an arrangement of transistors that multiplies the two signals.