High Frequency Full Wave Rectifier

Discussion in 'The Projects Forum' started by synws93, Nov 20, 2016.

  1. synws93

    Thread Starter New Member

    Nov 18, 2016
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    <Moderator's note: This post was moved from http://forum.allaboutcircuits.com/threads/high-frequency-full-wave-rectifier.116931/#post-1062554 to create a new thread. It is not homework.>

    Hi @dl324 ,

    I've found out the schematic that you have been talking about. Is it possible to use MCP6292 for this application? Sorry I'm quite new to electronics, and I have to do a project with precision full wave rectifier.
    MCP629x specification sheet: http://ww1.microchip.com/downloads/en/DeviceDoc/21812e.pdf

    This is the schematic that I've found out.

    [​IMG]

    Thanks in advance.
     
    Last edited by a moderator: Nov 20, 2016
  2. DickCappels

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    What are the performance requirements for your circuit?
     
  3. crutschow

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    Your post title says "high frequency".
    What is high?
     
  4. crutschow

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    Here's the LTspice simulation of a simplified version of the no-diode precision rectifier.
    I used a different op amp but it should also work with the Microchip device.

    upload_2016-11-20_0-49-27.png
     
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  5. synws93

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    Nov 18, 2016
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    In my project, the input of the signal will be around 400 - 500kHz. And I want to rectify my signal to a precision full wave.

    It will be around 400 - 500 kHz signal.

    Sorry for the late replies, as I was not aware that my post was moved to a new thread.
     
  6. synws93

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    Nov 18, 2016
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    Wow, thank you so much as I have no idea on how to use LTspice. I shall try it later on my breadboard and hope it will work.
     
  7. dannyf

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    Sep 13, 2015
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    If you don't mind non linearity, a set of germanium diodes will do just fine.
     
  8. synws93

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    Nov 18, 2016
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    Hi dannyf, where can I put the set of germanium diodes? Is IN4148 considered germanium diodes as I have a few in hand.
     
  9. bertus

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  10. dannyf

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    you are looking for small signal germanium or shottky diodes. There are tons of them and they are very inexpensive.

    If you cannot find any, use small signal transistors. for your frequency range, 2n2222 would be more than enough. or 2n390x for higher frequency, or s901x into 100Mhz or over. or jfets.

    choices are literally endless.
     
  11. synws93

    Thread Starter New Member

    Nov 18, 2016
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    Let's say I'm using crutschow's circuit, where do I place these germanium diodes?

    Thanks in advance. PS: I'm quite new to electronics.
     
  12. bertus

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    Hello,

    The circuit of crutschow does not use diodes.
    There are two opamps. U2 determines if the signal is positive or negative,
    U3 amplifies the signal by +1 or -1 depending on the signal from U2.

    @crutschow , please correct me if I amwrong.

    Bertus
     
  13. synws93

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    Nov 18, 2016
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    Hi Bertus, yes I know that crutschow's circuit does not use diodes.

    But dannyf suggested that if I don't mind non-linearity, I can put in germanium diodes. I'm just not sure where can I put the suggested diodes into my circuit.
     
  14. crutschow

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    If you use diodes and don't mind some non-linearity, then you don't need the op amps.
    Note that a diode will only give half-wave rectification, not the full-wave of the op amp circuit.
     
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  15. synws93

    Thread Starter New Member

    Nov 18, 2016
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    Thanks for sharing this information.

    Means if i need linearity in my signal, op amps are needed.

    If I need non-linearity in my signal, I can basically use diodes for my precision full wave rectifier.
     
  16. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    If you use diodes it won't be a "precision full wave rectifier".
     
  17. crutschow

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    Basically yes.
    The circuit requires a single-supply opamp with its negative power supply being ground, and thus U2 simply is unable to generate a negative output.
    Thus for the positive polarity input U2 and U3 amplify the signal, both as followers.
    For negative input, U2's output must stay at zero and U3 then amplifies the signal as an inverter.
     
  18. dannyf

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    Sep 13, 2015
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    I don't see every post so cannot help you there.

    I think if all you want is a full-wave rectifier, a few diodes / transistors will do just fine, as I laid out earlier.
     
  19. DickCappels

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  20. synws93

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    Nov 18, 2016
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    Hi DickCappels, I tried to use your circuit. I have input 500kHz sine wave and I got back a 500kHz sine wave too but not rectified. Not sure where is the problem. I've attached to you the images of my set-up.

    [​IMG]
    [​IMG]
    [​IMG]
     
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