Екі сигналдан жаңа жиіліктер құратын тізбек

Circuit that creates new frequencies from two signals
non linear mixing operating in the frequency domain

In electronics, a mixer, or frequency mixer, is an electrical circuit that creates new frequencies from two signals applied to it. In its most common application, two signals are applied to a mixer, and it produces new signals at the sum and difference of the original frequencies. Other frequency components may also be produced in a practical frequency mixer. Mixers are widely used to shift signals from one frequency range to another, a process known as heterodyning, for convenience in transmission or further signal processing. For example, a key component of a superheterodyne receiver is a mixer used to move received signals to a common intermediate frequency. Frequency mixers are also used to modulate a carrier signal in radio transmitters.

Another form of mixer operates by switching, which is equivalent to multiplication of an input signal by a square wave. In a double balanced mixer, the (smaller) input signal is alternately inverted or non inverted according to the phase of the local oscillator (LO). That is, the input signal is effectively multiplied by a square wave that alternates between +1 and 1 at the LO rate. In a single balanced switching mixer, the input signal is alternately passed or blocked. The input signal is thus effectively multiplied by a square wave that alternates between 0 and +1. This results in frequency components of the input signal being present in the output together with the product, since the multiplying signal can be viewed as a square wave with a DC offset (i. e. a zero frequency component). The aim of a switching mixer is to achieve the linear operation by means of hard switching, driven by the local oscillator. In the frequency domain, the switching mixer operation leads to the usual sum and difference frequencies, but also to further terms e. g. ±3fLO, ±5fLO, etc. The advantage of a switching mixer is that it can achieve (with the same effort) a lower noise figure (NF) and larger conversion gain. This is because the switching diodes or transistors act either like a small resistor (switch closed) or large resistor (switch open), and in both cases only a minimal noise is added. From the circuit perspective, many multiplying mixers can be used as switching mixers, just by increasing the LO amplitude. So RF engineers simply talk about mixers, while they mean switching mixers. The mixer circuit can be used not only to shift the frequency of an input signal as in a receiver, but also as a product detector, modulator, phase detector or frequency multiplier. For example, a communications receiver might contain two mixer stages for conversion of the input signal to an intermediate frequency and another mixer employed as a detector for demodulation of the signal.