Voltage multiplier

Discussion in 'Homework Help' started by Josato, Nov 7, 2012.

  1. Josato

    Thread Starter New Member

    Mar 8, 2011
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    Hi all!

    As part of a group project I have to design a circuit that involves a frequency mixer in cadence allegro.

    I have to do this to exploit the fact that cos(A)*cos(B) = 1/2(cos(A+B) + cos(A-B)).

    Anyway, for the moment I just put in an analogue behavioral model mixer, which does the job perfectly https://en.wikipedia.org/wiki/Frequency_mixer . What I have to do next is replace that component with a circuit.

    I have looked for circuits, but I don't know what is really suitable for the project. I have opamps and p and n type mosfets available to use (don't really know what the type is or whether it matters).



    [​IMG]

    Sadly, there is also a current limit on the design so that's something I have to factor in too. Can anyone help? I see that a 'gilbert cell' does the job, but I can't find a mosfet implementation. Why is a voltage controlled amplifer not ok?

    If anyone could help or pointers (or even feedback on my question phrasing), I would be extremely appreciative (I know this doesn't translate to much, but there you go)

    Jo
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,179
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    The circuit you want is called a mixer. It does multiplication and produces sidebands at A+B and at A-B. Were you expecting some kind of magic?
    Minicircuits and others make such circuit components.
     
  3. Josato

    Thread Starter New Member

    Mar 8, 2011
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    Hi, thanks for your reply.

    Yes, but the idea isn't that I purchase a mixer, it is that I design one using op-amps and/or possibly MOSFETs
     
  4. Papabravo

    Expert

    Feb 24, 2006
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  5. Josato

    Thread Starter New Member

    Mar 8, 2011
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    Diodes and transformers... I suppose I will have to ask the tutor. I did see that a few designs used diodes and transformers though.

    Thank you very much for the link! On this page: http://www.radio-electronics.com/info/rf-technology-design/mixers/fet-mixers.php

    There is a diagram of applying both the signals to a dual gate MOSFET... I can't synthesize one out of the MOSFET I have can I? And I can only use MOSFETS and FETs interchangeably if they are only used for switching?

    That isn't a circuit I can build, is it?
     
  6. Josato

    Thread Starter New Member

    Mar 8, 2011
    17
    0
    Hi,

    I got in contact with the tutor and he suggested using a 'switched gain demodulator'... But when I google it I don't get any results. What is that?

    I think I know what the principle is: you multiply your signal by 1 or -1 based on the frequency of modulation you want, and that is like mixing. Only question is, how to do?
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
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    Have you considered an NMOS or BJT balanced modulator? Google LM1496.
     
  8. Josato

    Thread Starter New Member

    Mar 8, 2011
    17
    0
    Thank you very much my good man! This appears to be exactly the sort of thing I was looking for.
     
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