Phase Sensitive Demodulation

Discussion in 'General Electronics Chat' started by Dave, Apr 26, 2006.

  1. Dave

    Thread Starter Retired Moderator

    Nov 17, 2003
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    On a project I have recently been working on, I have come across a series of Phase Sensitive Demodulation (PSD) circuits. Although I understand the general principle of both switching-based PSD and multiplier-based PSD, I am struggling to find any concrete information about the whole concept of PSD, and I would like to at least have a better understanding on the topic.

    Does anyone have any good information about PSD or know of any good resources on the subject? I've tried looking around the web and in some of the more respected books on circuit theory with little success.

    Thanks.

    Dave
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Hi,

    Some years ago I worked on a couple of Princeton Applied Research lock-in amplifiers. They used a VCO in conjunction with a PLL to do synchronous demodulation.

    You might check PAR for equipment theories of operation, or search on lock-in amps to find some material. It may be a bit odd the PSD path, but the underlying principle should be quite similar. I think the error-correction voltage out of the PLL would work for PSD.
     
  3. Spoggles

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    Dec 2, 2005
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  4. Dave

    Thread Starter Retired Moderator

    Nov 17, 2003
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    Superb. That is the kind of information I am looking for. When I have analysed the PSD circuit in the lab I got the general idea that if the reference signal and the input signal are in phase, then the DC voltage at the output of the low-pass filter is positive. And if it is 180˚ output of phase the DC voltage is negative. But this does give a little extra information.

    Any further information would be appreciated.

    Dave
     
  5. RAH1379

    Well-Known Member

    Dec 13, 2005
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    wouldn't the chroma circuits of a tv receiver be the circuit your talking about here? at least in the ntsc system.
     
  6. Dave

    Thread Starter Retired Moderator

    Nov 17, 2003
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    Perhaps you could embellish what you mean? The PSD circuits I was refering to were a central SP element to an Magnetic Induction Tomography (MIT) system reported in a paper from a group at the University of Manchester who had developed one of only a hand full of MIT systems, I was merely trying to get a better understanding of the how PSD worked in the context of this system.

    DAve
     
  7. RAH1379

    Well-Known Member

    Dec 13, 2005
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    I would know nothing about that system but the color information in a ntsc television signal is a phase modulation system at 3.58 mhz where the phase of the carrier controls the addition of the three colors red green and blue to obtain all the colors you see on the screen.
     
  8. Dave

    Thread Starter Retired Moderator

    Nov 17, 2003
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    It is potentially a similar concept, but not having the details of my initial query to hand and not being massively familiar with NTSC, I cannot specifically comment at this point. If you can gain access to academic papers, this paper gives a detailed treatment of how PSD is utilised in an MIT (referred to as EMT here) system; section 2.2 and figure 2.

    Dave
     
  9. RAH1379

    Well-Known Member

    Dec 13, 2005
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    looks like some interesting stuff, by the way i work in a steel mill and have for 34 years this march 29th, i saved it to read later but i have to get a nap now because i have midnights tonight.After i read it i will find out if we use the same system or a different one in our caster or hot strip.
     
  10. Dave

    Thread Starter Retired Moderator

    Nov 17, 2003
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    Sure, I'll try and dig out the work I did purely on PSD - remember that paper you have there is image-application specific. If you find any literature about the phase modulation system in NTSC systems, I would be interested in having a look.

    Dave
     
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