An electronic mixer is a device that combines two or more electrical or electronic

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 signals into one or two composite output signals. There are two basic circuits that both use the term mixer, but they are very different types of circuits: additive mixers and multiplying mixers.

Additive mixers add two or more signals together, and this terminology ("mixer") is only used in the realm of audio electronics where audio mixers are used to add together audio frequency

Audio frequency

An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...

 signals such as voice signals, music signals, and sound effect

Sound effect

For the album by The Jam, see Sound Affects.Sound effects or audio effects are artificially created or enhanced sounds, or sound processes used to emphasize artistic or other content of films, television shows, live performance, animation, video games, music, or other media...

s.

Multiplying mixers multiply together two time-varying input signals instantaneously (instant-by-instant). If the two input signals are both sinusoids of specified frequencies f₁ and f₂, then the output of the mixer will contain two new sinsoids that have the sum f₁ + f₂ frequency and the difference frequency absolute value

Absolute value

In mathematics, the absolute value |a| of a real number a is the numerical value of a without regard to its sign. So, for example, the absolute value of 3 is 3, and the absolute value of -3 is also 3...

{f₁ - f₂}.

Note: Any nonlinear electronic block driven by two signals with frequencies f1 and f2 would generate intermodulation (mixing) products. A multiplier (which is a nonlinear device too) will generate ideally only the sum and difference frequencies, whereas an arbitrary nonlinear block would generate also signals at e.g. 2*f1-3*f2, etc. Therefore in the past often more or less normal nonlinear amplifiers or just single diodes have been used as mixers, instead of a more complex multiplier. A multiplier has usually the advantage of rejecting - at least partly - undesired higher-order intermodulations and larger conversion gain.

Additive mixers

Additive mixers add two or more signals

Superposition principle

In physics and systems theory, the superposition principle , also known as superposition property, states that, for all linear systems, the net response at a given place and time caused by two or more stimuli is the sum of the responses which would have been caused by each stimulus individually...

, giving out a composite signal that contains the frequency components of each of the source signals. The simplest additive mixers are simple resistor networks, and thus purely passive

Passivity (engineering)

Passivity is a property of engineering systems, used in a variety of engineering disciplines, but most commonly found in analog electronics and control systems...

, while more complex mixers employ active

Passivity (engineering)

Passivity is a property of engineering systems, used in a variety of engineering disciplines, but most commonly found in analog electronics and control systems...

 components such as buffer amplifiers for impedance matching

Impedance matching

In electronics, impedance matching is the practice of designing the input impedance of an electrical load to maximize the power transfer and/or minimize reflections from the load....

 and better isolation.

Product Mixers

Ideal product mixers act as signal multipliers, producing an output signal equal to the product of the two input signals. Product mixers are often used in conjugation with an oscillator in the communications field to modulate signal frequencies. Product mixers can 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 receiver

Superheterodyne receiver

In electronics, a superheterodyne receiver uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency...

s. In many typical circuits, the single output signal actually contains multiple waveforms, namely those at the sum and difference of the two input frequencies and harmonic waveforms. The output signal may be obtained by removing the other signal components with a filter. (see intermediate frequency

Intermediate frequency

In communications and electronic engineering, an intermediate frequency is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called...

)

Product mixers have been implemented in a wide variety of ways. The most popular are Gilbert cell

Gilbert cell

In electronics, the Gilbert cell is a transistor circuit used as an analog multiplier and frequency mixer, first described by Barrie Gilbert in 1968. The advantage of this circuit is the output current is an accurate multiplication of the base currents of both inputs...

 mixers, diode

Diode

In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...

 mixers, diode ring mixers (ring modulation

Ring modulation

Ring modulation is a signal-processing effect in electronics, an implementation of amplitude modulation or frequency mixing, performed by multiplying two signals, where one is typically a sine-wave or another simple waveform. It is referred to as "ring" modulation because the analog circuit of...

) and switching mixers. Diodes mixers take advantage of the non-linearity of diode devices to produce the desired multiplication in the squared term. It is a very inefficient method as most of the power output is in other unwanted terms which need filtering out. Inexpensive AM radios still use diode mixers.

Electronic mixers are usually made with transistor

Transistor

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s and/or diode

Diode

In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...

s arranged in a balanced circuit

Balanced circuit

A balanced circuit is circuitry for use with a balanced line or the balanced line itself. Balanced lines are a common method of transmitting many types of electrical communication signals between two points on two wires...

 or even a double-balanced circuit. These are readily manufactured by using the technology of either monolithic integrated circuits or hybrid integrated circuits. These are designed for a wide variety of frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 ranges, and they are mass produced to tight toleraces by the hundreds of thousands. These mixers, especially the double-balanced variety, can be bought in large numbers at prices ranging from a dime

Dime

Dime may refer to:Currency* Dime * Dime Media and entertainment* Dime , by Guardian* "Dime" , by Beth* The Dimes, a musical group* Dime novel, a type of popular fictionSports* Dime...

 to a quarter

Quarter

Quarter is one fourth, ¼, or 25%, and may refer to:*Quarter , a section or area, usually of a town*Quarter , valued at one-fourth of a U.S...

 apiece.

These double-balanced mixers are very widely used in microwave communication systems, satellite communication systems, and ultrahigh frequency (UHF) communications transmitter

Transmitter

In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...

s and receiver

Receiver (radio)

A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...

s, and in radar systems transmitters and receivers.

Gilbert cell mixers are just an arrangement of transistors that multiplies the two signals. The switching mixers (below) pass more power and usually insert less distortion.

switching mixers use arrays of field effect transistors or (in older days) vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

s. These are used as electronic switches, to permit the signal to go one direction, then the other. They are controlled by the signal being mixed. They are especially popular with digitally controlled radios.