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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 (LO). This would be typical of the normal operating mode of a packaged double balanced mixer, with the local oscillator drive considerably higher than the signal amplitude.
JC wept! As an engineer who uses mixers daily, I wouldn't recognize the article as being related to either a simple, or a pedantic, treatment of mixers. While most of the words written are true, they are irrelevant and uninformative, one would need to be an expert to understand in what sense they are true, a beginner would be hopelessly lost.
What is the purpose of the wiki? Is it to record some words vaguely related to the subject at hand, or is it to inform or educate? It might be easier to dig up any one of a dozen better written tutorials in the back pages of mixer manufacturers' catalogues, many available on the web and just point to them, than to write a new text which doesn't overtly plagiarise any of them.
For instance this link http://www.hobbyprojects.com/general_theory/mixer.html is very short, a bit confused (talking about fans beating) BUT the neophyte will come away from it understanding a damned sight more about mixers than from this article, and the expert will recognise it for what it is, a slightly flawed over simplificiation rather than the pile of dingoes kidneys that make up this article.
A mixer does not deal with sine waves, a simplified model of them does. A mixer is a component, not a mathematical equation. Exponential signal expansions convey nothing to somebody who wants to find out what a mixer does.
calms down, thinks, comes back
Perhaps I should be a bit more positive about this, but I'm not up to writing the article at the moment. I will present some definitions and ideas here in talk, and hope that others might consider whether the different approach has merit, and if so whether to modify, replace, rewrite or leave alone the main article. First some comments
The maths in the present article, the diode, exponential stuff etc. This should really be in a separate article entitled "How a non-linear system creates mixing products". It is all correct, just not really applicable to understanding what a "frequency mixer" is, how it's built, why it's used etc.
Proto-article
A frequency mixer is a component, that accepts two electrical signals, and is intended to produce as an output a signal, which has two frequency components, one at the sum of the two input signal frequencies and and one at the difference. Any mixer, whether practical or theoretical, will also produce other unwanted outputs. It is the reduction of these unwanted outputs that consumes most of the engineering time developing better mixers.
A mixer is used where frequencies must be changed for practical processing reasons. In a cell-phone for example, an input radio signal at 2GHz is mixed down to an intermediate frequency (or IF) of 70MHz using a local oscillator (or LO) of 1.93GHz. This is referred to as down-mixing. A transmitter will often use a frequency mixer to up-mix a low IF up to a high RF frequency for transmission.
The practice of mixers frequently uses jargon, so RF = radio frequency, usually the highest signal frequency, IF = Intermediate frequency, usually the lowest signal frequency, both relatively low level signals and often modulated, so not a single sine-wave. LO = local oscillator, a high level signal, always a single frequency, but may be sine or square.
There are two principal ways of performing the conversion. The first and mathematically simplest uses a multiplying mixer, usually abbreviated to multiplier, which is linear to the signal at each mixer port and performs the operation z(t) = y(t) * x(t), where x, y and z are the time varying voltages at each port. Multipliers tend to use semiconductor ICs, (496, what manufacturer, AD834 Analog Devices) but they are very noisy so have limited dynamic range. The second, and more commonly used, is a switching mixer, which performs the operation z(t) = y(t) * sign(x(t)), where again x, y and z are the voltages at each port. In the switching mixer, x is the LO.
A switching mixer usually works with diodes, the high level LO serves to switch the diodes rapidly from conducting to non-conducting, producing a switching action for the lower level signals. Recently, MOSFETs have begun to be used as the switching element in switching mixers, offering the advantage of lower power on the LO port.
The type of mixer is determined by the topology of diodes and balancing transformers are involved (a few diagrams here would not go amiss). A single diode mixer is unbalanced, has no isolation between ports, but is very simple and is the mixer of choice when frequencies are so ridiculously high that the only component that can be fabricated and got to work is a single diode (optical, teraHertz etc). Much better is a balanced mixer, which uses transformers and diodes to provide isolation between the ports. A double balanced mixer uses two transformers and four diodes, and provides isolation between all pairs of ports. The single balanced topolgy is sometimes used (one transformer, two diodes) at fairly high frequencies. A triple balanced topology (three transformers, 4 or more usually 8 diodes) is gaining popularity with its very good rejection of distortion products.
NeilUK 19:43, 5 June 2006 (UTC)
Isn't the output of the mixer a) a signal equal to the sum of the input frequencies (usually filterd) b) the difference of the frequencies (usually the IF) and c)TWICE the original input frequency? See for example heterodyne detection.
I'm removing the {{tone}} template from the top of this article. It has been there for some time with no explanation, and with no discussion here. I assume it was added because someone saw the word we in the text. Looking at WP:Manual of Style#Avoid first-person pronouns and one, mathematical discussions such as where we may be found here are clearly made an exception to the normal rule: "It is also acceptable to use “we” in mathematical derivations; for example: “To normalize the wavefunction, we need to find the value of the arbitrary constant A.”" -- Nigelj 00:30, 11 November 2006 (UTC)
These either need to be properly refactored or merged. The same maths is shown under two different titles.Either we put all the maths under 'heterodyne' and use this article to talk about devices (such as the fabled and much edited Pentagrid converter) or else put it all in one place. REferences would be handy, too. -- Wtshymanski ( talk) 06:24, 28 November 2010 (UTC)
The current lead sentence says: "In electronics a mixer is a nonlinear electrical circuit which produces an output signal that is the product of two input signals." This gives the erroneous impression that a mixer is identical to an analog multiplier. I think the essential points in the definition of a mixer are that (1) its purpose is to generate new frequencies from the input frequencies, and (2) it does this by the heterodyning process. I think the lead should include these two points. -- Chetvorno TALK 09:09, 28 November 2010 (UTC)
The ideal mixer is indeed a four-quadrant multiplier, and that is not a nonlinear device. The basic identity establishing the sum/difference frequency behaviour is the prosthaphaeresis formula sin (ω1t)⋅sin (ω2t) = cos(ω1t − ω2t) − cos(ω1t + ω2t)/2. There is a huge tradeoff between DC accuracy and bandwidth among analog multipliers; balanced RF mixers such as the Gilbert cell and its vacuum tube complement, the beam deflection tube, are designs optimized for bandwidth.
Nonlinear devices are a faster and/or cheaper substitute that merely emulate a 1-quadrant multiplier by having the oscillator move the input signal up and down their nonlinear gain curve. The best results can be obtained with a quadratic curve, since a⋅b = (a+b)2 − (a−b)2/4 where one of the quadratic terms can be omitted in the circuit if the mixer output is fed into an IF bandpass anyway, as with triode mixers in historic VHF/UHF receivers. Today's bipolar semiconductors behave exponentially, distorting the IF bandpass input signal some more. -- Mkratz ( talk) 22:43, 26 June 2013 (UTC)
If the two circuits are the same, why are they called by different names? Why are there separate chapters in engineering books on mixers and analog multipliers? -- Chetvorno TALK 18:15, 9 July 2013 (UTC)
If all we're arguing about is whether to add the word "multiplier" to the lead, I say we stop arguing. The lead reads nicely enough as it stands. ~ KvnG 22:28, 9 July 2013 (UTC)
This is the
talk page for discussing improvements to the
Frequency mixer article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
![]() | This ![]() It is of interest to the following WikiProjects: | ||||||||||||||||||||
|
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 (LO). This would be typical of the normal operating mode of a packaged double balanced mixer, with the local oscillator drive considerably higher than the signal amplitude.
JC wept! As an engineer who uses mixers daily, I wouldn't recognize the article as being related to either a simple, or a pedantic, treatment of mixers. While most of the words written are true, they are irrelevant and uninformative, one would need to be an expert to understand in what sense they are true, a beginner would be hopelessly lost.
What is the purpose of the wiki? Is it to record some words vaguely related to the subject at hand, or is it to inform or educate? It might be easier to dig up any one of a dozen better written tutorials in the back pages of mixer manufacturers' catalogues, many available on the web and just point to them, than to write a new text which doesn't overtly plagiarise any of them.
For instance this link http://www.hobbyprojects.com/general_theory/mixer.html is very short, a bit confused (talking about fans beating) BUT the neophyte will come away from it understanding a damned sight more about mixers than from this article, and the expert will recognise it for what it is, a slightly flawed over simplificiation rather than the pile of dingoes kidneys that make up this article.
A mixer does not deal with sine waves, a simplified model of them does. A mixer is a component, not a mathematical equation. Exponential signal expansions convey nothing to somebody who wants to find out what a mixer does.
calms down, thinks, comes back
Perhaps I should be a bit more positive about this, but I'm not up to writing the article at the moment. I will present some definitions and ideas here in talk, and hope that others might consider whether the different approach has merit, and if so whether to modify, replace, rewrite or leave alone the main article. First some comments
The maths in the present article, the diode, exponential stuff etc. This should really be in a separate article entitled "How a non-linear system creates mixing products". It is all correct, just not really applicable to understanding what a "frequency mixer" is, how it's built, why it's used etc.
Proto-article
A frequency mixer is a component, that accepts two electrical signals, and is intended to produce as an output a signal, which has two frequency components, one at the sum of the two input signal frequencies and and one at the difference. Any mixer, whether practical or theoretical, will also produce other unwanted outputs. It is the reduction of these unwanted outputs that consumes most of the engineering time developing better mixers.
A mixer is used where frequencies must be changed for practical processing reasons. In a cell-phone for example, an input radio signal at 2GHz is mixed down to an intermediate frequency (or IF) of 70MHz using a local oscillator (or LO) of 1.93GHz. This is referred to as down-mixing. A transmitter will often use a frequency mixer to up-mix a low IF up to a high RF frequency for transmission.
The practice of mixers frequently uses jargon, so RF = radio frequency, usually the highest signal frequency, IF = Intermediate frequency, usually the lowest signal frequency, both relatively low level signals and often modulated, so not a single sine-wave. LO = local oscillator, a high level signal, always a single frequency, but may be sine or square.
There are two principal ways of performing the conversion. The first and mathematically simplest uses a multiplying mixer, usually abbreviated to multiplier, which is linear to the signal at each mixer port and performs the operation z(t) = y(t) * x(t), where x, y and z are the time varying voltages at each port. Multipliers tend to use semiconductor ICs, (496, what manufacturer, AD834 Analog Devices) but they are very noisy so have limited dynamic range. The second, and more commonly used, is a switching mixer, which performs the operation z(t) = y(t) * sign(x(t)), where again x, y and z are the voltages at each port. In the switching mixer, x is the LO.
A switching mixer usually works with diodes, the high level LO serves to switch the diodes rapidly from conducting to non-conducting, producing a switching action for the lower level signals. Recently, MOSFETs have begun to be used as the switching element in switching mixers, offering the advantage of lower power on the LO port.
The type of mixer is determined by the topology of diodes and balancing transformers are involved (a few diagrams here would not go amiss). A single diode mixer is unbalanced, has no isolation between ports, but is very simple and is the mixer of choice when frequencies are so ridiculously high that the only component that can be fabricated and got to work is a single diode (optical, teraHertz etc). Much better is a balanced mixer, which uses transformers and diodes to provide isolation between the ports. A double balanced mixer uses two transformers and four diodes, and provides isolation between all pairs of ports. The single balanced topolgy is sometimes used (one transformer, two diodes) at fairly high frequencies. A triple balanced topology (three transformers, 4 or more usually 8 diodes) is gaining popularity with its very good rejection of distortion products.
NeilUK 19:43, 5 June 2006 (UTC)
Isn't the output of the mixer a) a signal equal to the sum of the input frequencies (usually filterd) b) the difference of the frequencies (usually the IF) and c)TWICE the original input frequency? See for example heterodyne detection.
I'm removing the {{tone}} template from the top of this article. It has been there for some time with no explanation, and with no discussion here. I assume it was added because someone saw the word we in the text. Looking at WP:Manual of Style#Avoid first-person pronouns and one, mathematical discussions such as where we may be found here are clearly made an exception to the normal rule: "It is also acceptable to use “we” in mathematical derivations; for example: “To normalize the wavefunction, we need to find the value of the arbitrary constant A.”" -- Nigelj 00:30, 11 November 2006 (UTC)
These either need to be properly refactored or merged. The same maths is shown under two different titles.Either we put all the maths under 'heterodyne' and use this article to talk about devices (such as the fabled and much edited Pentagrid converter) or else put it all in one place. REferences would be handy, too. -- Wtshymanski ( talk) 06:24, 28 November 2010 (UTC)
The current lead sentence says: "In electronics a mixer is a nonlinear electrical circuit which produces an output signal that is the product of two input signals." This gives the erroneous impression that a mixer is identical to an analog multiplier. I think the essential points in the definition of a mixer are that (1) its purpose is to generate new frequencies from the input frequencies, and (2) it does this by the heterodyning process. I think the lead should include these two points. -- Chetvorno TALK 09:09, 28 November 2010 (UTC)
The ideal mixer is indeed a four-quadrant multiplier, and that is not a nonlinear device. The basic identity establishing the sum/difference frequency behaviour is the prosthaphaeresis formula sin (ω1t)⋅sin (ω2t) = cos(ω1t − ω2t) − cos(ω1t + ω2t)/2. There is a huge tradeoff between DC accuracy and bandwidth among analog multipliers; balanced RF mixers such as the Gilbert cell and its vacuum tube complement, the beam deflection tube, are designs optimized for bandwidth.
Nonlinear devices are a faster and/or cheaper substitute that merely emulate a 1-quadrant multiplier by having the oscillator move the input signal up and down their nonlinear gain curve. The best results can be obtained with a quadratic curve, since a⋅b = (a+b)2 − (a−b)2/4 where one of the quadratic terms can be omitted in the circuit if the mixer output is fed into an IF bandpass anyway, as with triode mixers in historic VHF/UHF receivers. Today's bipolar semiconductors behave exponentially, distorting the IF bandpass input signal some more. -- Mkratz ( talk) 22:43, 26 June 2013 (UTC)
If the two circuits are the same, why are they called by different names? Why are there separate chapters in engineering books on mixers and analog multipliers? -- Chetvorno TALK 18:15, 9 July 2013 (UTC)
If all we're arguing about is whether to add the word "multiplier" to the lead, I say we stop arguing. The lead reads nicely enough as it stands. ~ KvnG 22:28, 9 July 2013 (UTC)