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Frequency mixer

 
Frequency Mixer

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Frequency mixer



 
 
In telecommunication
Telecommunication

Telecommunication is the assisted Transmission of Signal over a distance for the purpose of communication. In earlier times, this may have involved the use of smoke signals, Drum , Semaphore line, flag signals or heliograph....
s, a mixer is a nonlinear or time-varying circuit
Electrical network

An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, and switches....
 or device that accepts as its input
Input

Input is the term denote either an entrance or changes which are inserted into a system and which activate/modify a process. It is an abstract concept, used in the model ing, system design and system exploitation....
 two different frequencies and presents at its output
Output

Output is the term denote either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the model ing, system design and system exploitation....
 a mixture of signals at several frequencies
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....
:
  1. the sum of the frequencies of the input signals
  2. the difference between the frequencies of the input signals
  3. both original input frequencies — these are often considered parasitic and are filtered
    Electronic filter

    Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal and/or to enhance wanted ones....
     out in subsequent filter stages.
  4. unwanted intermodulation products from the inputs.


This nonlinear effect can be created by using a nonlinear electrical component, such as a diode
Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
.






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Encyclopedia


In telecommunication
Telecommunication

Telecommunication is the assisted Transmission of Signal over a distance for the purpose of communication. In earlier times, this may have involved the use of smoke signals, Drum , Semaphore line, flag signals or heliograph....
s, a mixer is a nonlinear or time-varying circuit
Electrical network

An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, and switches....
 or device that accepts as its input
Input

Input is the term denote either an entrance or changes which are inserted into a system and which activate/modify a process. It is an abstract concept, used in the model ing, system design and system exploitation....
 two different frequencies and presents at its output
Output

Output is the term denote either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the model ing, system design and system exploitation....
 a mixture of signals at several frequencies
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....
:
  1. the sum of the frequencies of the input signals
  2. the difference between the frequencies of the input signals
  3. both original input frequencies — these are often considered parasitic and are filtered
    Electronic filter

    Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal and/or to enhance wanted ones....
     out in subsequent filter stages.
    • a balanced mixer passes only a small leakage of the original signal to the output, often implemented as a double balanced mixer which has high isolation of both inputs.
  4. unwanted intermodulation products from the inputs.


This nonlinear effect can be created by using a nonlinear electrical component, such as a diode
Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
. The time-varying effect can be created using a multiplier circuit such as a Gilbert Cell
Gilbert cell

In electronics, the Gilbert cell is an Electronic mixer first described by Barrie Gilbert in 1968. The output current of the circuit is an accurate multiplication of the base currents of both inputs....
 or passive switches.

The manipulations of frequency performed by a mixer can be used to move signals between band
Channel (communications)

Channel, in communications , refers to the :wikt:medium used to information transfer information from a sender to a receiver ....
s, or to encode and decode them. One other application of a mixer is as a product detector
Product detector

A product detector is a type of demodulator used for amplitude modulation and Single-sideband modulation signals. Rather than converting the envelope of the signal into the decoded waveform like an envelope detector, the product detector takes the product of the modulated signal and a local oscillator, hence the name....
.

Mathematical description

The input signals are, in the simplest case, sinusoidal voltage waves, representable as where each A is an amplitude
Amplitude

Amplitude is the magnitude of change in the oscillating variable, with each oscillation, within an oscillating system. For instance, sound waves are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation....
, each f is a frequency, and t represents time. (In reality even such simple waves can have various phase
Phase (waves)

The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0....
s, but that does not enter here.) One common approach for adding and subtracting the frequencies is to multiply the two signals; using the trigonometric identity we have where the sum and difference frequencies appear. This is the inverse of the production of acoustic beat
Beat (acoustics)

In acoustics, a beat is an interference between two sounds of slightly different frequency, perceived as periodic variations in volume whose rate is the difference between the two frequencies....
s.

Multiplication implementation

There are various ways of multiplying voltages, many of them quite sophisticated. However, as an example, a simple technique involving a diode
Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
 can be described. The importance of the diode is that it is non-linear (or non-Ohmic
Ohm's law

Ohm's law applies to electrical circuits; it states that the electric current through a conductor between two points is directly Proportionality to the potential difference or voltage across the two points, and inversely proportional to the Electrical resistance between them....
), which means its response (current) is not proportional to its input (voltage). The diode therefore does not reproduce the frequencies of its driving voltage in the current through it, which allows the desired frequency manipulation. Certain other non-linear devices could be utilized similarly.

The current I through an ideal diode as a function of the voltage V across it is given by where what is important is that V appears in es exponent. The exponential can be expanded
Taylor series

In mathematics, the Taylor series is a representation of a function as an Series of terms calculated from the values of its derivatives at a single point....
 as and can be approximated for small
x (that is, small voltages) by the first few terms of that series:

Suppose that the sum of the two input signals is applied to a diode, and that an output voltage is generated that is proportional to the current through the diode (perhaps by providing the voltage that is present across a resistor
Resistor

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 in series with the diode). Then, disregarding the constants in the diode equation, the output voltage will have the form The first term on the right is the original two signals, as expected, followed by the square of the sum, which can be rewritten as , where the multiplied signal is obvious. The ellipsis represents all the higher powers of the sum which we assume to be negligible
Negligible

In engineering, mathematics, physics and similar disciplines, the term negligible refers to the quantities so small that they can be ignored when studying the larger effect....
 for small signals.

Output

As every multiplication produces sum and difference frequencies, from the quadratic
Quadratic polynomial

In mathematics, a quadratic polynomial or quadratic is a polynomial of degree of a polynomial two. A quadratic polynomial may involve a single variable x, or multiple variables such as x, y, and z....
 term of the series we expect to find signals at frequencies and from and , and and from the term. Often , so the difference signal has a much lower frequency than the others; extracting this distinct signal is often the principal purpose of using a mixer in such devices as radio receivers.

The other terms of the series give rise to a number of other, weaker signals at various frequencies which act as noise for the desired signal; they may be filtered out downstream to an extent, but sensitive applications will require cleaner output and thus a more complicated design.

Switching

Another form of mixer operates by switching, with the smaller input signal being passed inverted or uninverted according to the phase of the local oscillator. This would be typical of the normal operating mode of a packaged double balanced mixer module such as an SBL-1, with the local oscillator drive considerably higher than the signal amplitude.

The aim of a switching mixer is to achieve linear operation over the signal level, and hard switching driven by the local oscillator.

See also

  • Pentagrid converter
    Pentagrid converter

    The pentagrid converter was a radio receiving valve with five grids used as the frequency mixer stage of a superheterodyne radio receiver.The pentagrid was part of a line of development of valves that were able to take an incoming RF signal and change its frequency to a fixed intermediate frequency which was then amplified, and detected in...
  • Radio transmitter design
    Radio transmitter design

    Radio transmitter design is a complex topic which can be broken down into a series of smaller topics. A radio communication system requires two tuned circuits each at the transmitter and receiver, all four tuned to the same frequency....
  • Receiver (radio)
    Receiver (radio)

    This article is about a radio receiver, for other uses see Radio .A radio receiver is an electronics circuit that receives its input from an antenna , uses electronic filters to separate a wanted radio signal from all other signals picked up by this antenna, electronic amplifier it to a level suitable for further processing, and finally...
  • Satellite dish
    Satellite dish

    A satellite dish is a type of parabolic antenna that receives or transmits electromagnetic signals to and from another location typically a satellite....
  • Spurious emission
    Spurious emission

    A spurious emission is any radio frequency not deliberately created or transmitted, especially in a device which normally does create other frequencies....
  • Transverter
    Transverter

    File:Radioamateur - Xverter ATV 5,7GHz.jpgA transverter is a radio frequency device that consists of an radio frequency upconverter and a radio frequency downconverter in one unit....
  • Tuner (radio)
    Tuner (radio)

    A tuner is an adjustable device which passes one radio frequency, or band of frequencies, and excludes others, by using electrical resonance. A tuner performs the process of selecting the desired signal but its output is not directly usable and must be sent to another device....
  • Variable-frequency oscillator
    Variable-frequency oscillator

    A variable frequency oscillator in electronics is a oscillator with an oscillation frequency that can be electronically changed . It is a necessary component in any radio receiver or transmitter that works by the superheterodyne principle, and controls the radio frequency to which the apparatus is tuned....


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