Basic phase shifter circuit

Discussion in 'General Electronics Chat' started by sdh314, Dec 12, 2011.

  1. sdh314

    Thread Starter New Member

    Jun 2, 2011
    18
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    Hello all,

    I'm building a lock-in amplifier circuit based on the AD630 chip for an optical measurement system (circuit is similiar to this one: http://blockyourid.com/~gbpprorg/mil/cavity/lock/SimpleLockInAmplifier.pdf)

    Anyways, I've noticed that the output is negative, so I need to modify the phase of the reference signal. I've found a simple phase shifter circuit (attached), but I can't find a lot of info on the circuit itself. After building it (with R = 10k and C = 23nF) I get a 90degree phase change of a square wave input at each extreme of the potentiometer (100k pot), but in between these two extremes the waveform changes significantly from a square wave profile. I believe the choice of components are designed for a 5kHz, can anyone suggest suitable values for a 1kHz wave (I'm assuming that that is the reason the output isn't square-wave like.

    Also, do I need to use an op-amp with both negative and postive supply rails? (I'm just using a single supply op-amp (TLC271)).

    Any info (links or otherwise) would be much appreciated.

    Thanks!
     
  2. Tesla23

    Active Member

    May 10, 2009
    318
    67
    To change the phase of the reference signal by 180 degrees, simply swap the connections to pins 9 and 10 of the AD630.
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    If your output is negative use a Inverting amplifier. http://en.wikipedia.org/wiki/Operational_amplifier
    Yes indeed. What is your supply voltage at the moment? I am not sure that the TLC271 is the best selection for your project. Do you use a sine wave or a square wave as source.
    Also strictly speaking your setup is not a lock-in amplifier. As it have no (phase-locked loop) PLL thats lock on to some external reference signal. Your setup is basically a synchronous demodulator followed by a low-pass filter. The heart in every lock-in amplifier :)
     
    Last edited: Dec 12, 2011
  4. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    The AD630 has differential inputs for the reference signal, so you just reverse the input signal connection at pins 9 and 10 to change the phase by 180 degrees and thus the polarity of the output signal.
     
  5. sdh314

    Thread Starter New Member

    Jun 2, 2011
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    Thanks all, much appreciated. And saved me messing around with a phase shifter :)

    I've got a few other questions on the AD630, but I'll start another thread for them :)
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    NO stay in this thread. I think it will provide a better background. I have used the AD630 in some AC skin conductance measurement equipment. Very like your application. A nice chip, but somewhat expensive
     
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