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Frequency Mulitplier not working

Discussion in 'General Electronics Discussion' started by Smada, Feb 2, 2016.

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  1. Smada

    Smada

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    0
    Feb 2, 2016
    Hi, I have been trying to make a frequency multiplier for a project but it will not work. I have tried using both a sa612a chip and even making my own gilbert cell for the purpose! I expect an output as shown below, but get nothing like that.[​IMG]

    The sa612a data sheet is found here: http://www.nxp.com/documents/data_sheet/SA612A.pdf

    I have been trying the multiplier with test frequencies of 100hz and 1000hz.

    So I have put 100hz into pin1.
    Pin 2 to ground
    Pin 3 to ground
    1000hz into pin 6.
    Pin 7 to ground.
    5 volts into pin 8.

    Measuring the frequency from either of the output pins (4 or 5) does not give the expected output wave. I have experimented with the inputs/ outputs and general setup but nothing seems to work. I feel I am missing some key part of the whole thing!!!

    I have also created a gilbert cell similar to the one shown below.[​IMG]

    I have tried this setup in several ways:

    With both RF inputs (base of Q2 and Q6) at 100hz and all LO inputs (base of Q1 Q4 Q3 and Q5) at 1000hz. Then measured the output with / without parallel resistance connected to supply rail but it does not work.

    Also with just Q2 receiving 100hz and Q6 just getting a bias voltage, and Q1 / Q5 getting 1000hz and Q4 / Q3 getting a bias voltage. Again measuring the outputs with / without some load resistors. Again does not seem to work!

    Any help with both / either of these circuits would be greatly appreciated, I feel I have reached a dead end with what should be a simple thing so please help me!!
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Impossible to evaluate your circuit without seeing it. I suggest that you post your schematic.

    Also: You do realize that all three inputs must be balanced circuitry? IE. not referenced to GND Common.

    Chris
     
  3. davenn

    davenn Moderator

    13,620
    1,882
    Sep 5, 2009

    Hi Smada
    welcome to EP :)

    This chip ISNT a frequency multiplier, it's primary use is a mixer ( can also be used as an oscillator and type of filter)

    I suggest you refer to Fig 8 example in the datasheet

    SA612A Mixer.GIF

    1) Honestly, I don't know how it will respond to frequencies as low as you are trying to use
    I have always use them at much higher MHz freq's in radio receiver applications as it is intended for

    2) your description of how you used the pins suggests you didn't understand that it has balanced inputs ... ie you cant just ground one pin

    3) your higher freq should be going into pins 1 and 2 and your lower mixer freq should be going into pins 6 and 7


    will let you consider those points and see what you come up with

    cheers
    Dave
     
  4. Smada

    Smada

    3
    0
    Feb 2, 2016
    Hi Dave, I always thought a mixer and a multiplier are the were the same thing? My purpose is to multiply the two signals together and then filter out the difference between them - the data sheet doesn't mention anything about minimum frequencies so I was just using those values to test. Can I use this chip for my intended purpose or am I better served just making my own using the Gilbert cell - something which I have also been failing to do! I have tried the chip with the 1000Hz signal going into both pins 1 and 2, and the 100Hz signal going into pins 6 and 7 but it didn't work. Thanks for your reply.
     
  5. Smada

    Smada

    3
    0
    Feb 2, 2016
    Hi guys, I want to use the mixer as the guy does in this video (he is also using what seems to be the same chip) .

    He also has uploaded the drawn set up here http://www.qsl.net/w2aew//youtube/RFmixersheterodyne.pdf . Do the transformers on the input and output make a significant difference?
     
  6. davenn

    davenn Moderator

    13,620
    1,882
    Sep 5, 2009
    no, very different beasts, you are using the wrong description
    when you MULTIPLY a frequency, you can double or triple etc it to a much higher frequency.
    Multiply = same thing that is does in maths 2 x 3 = 6

    Mixing is when you take a freq and mix it with another freq and you end up with 2 resulting freq's
    the input freq + the mixing freq ( the Local Oscillator freq)
    and the input freq - the LO freq

    so in your case you should have 1000Hz input and a LO of 100 Hz and with that you end up with 2 resulting freq's
    1100 Hz and 900 Hz. You then filter out the one you don't want and use the other for whatever purpose


    and that's how it works :)


    Dave
     
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