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Frequency Multiplier

  1. Nov 28, 2006 #1

    I Need to desing a variable frequency multiplier, I have a sinusoidal signal of 10Hz and I want to multiplier this signal and coverts it in a signal of 50Hz or 100Hz depending on a factor.

    I think that I can do it with a PLL but I don´t know how to do it. If someone knows where can I find information about it or can give me some I´ll be grateful.

  2. jcsd
  3. Nov 28, 2006 #2
    This should be moved to electrical, but I'll answer it here since I'm here at the moment. First, a couple of questions. Is the input signal always 10 hertz or does it change? If it changes, how much does it change? You only have 2 selections on output? PLL is a place to start.
    Last edited: Nov 28, 2006
  4. Nov 28, 2006 #3

    yes, the input is allways 10Hz. And I have more than 2 outputs, I have outputs from 50Hz to 300Hz, 10 by 10 ( 60,70.....110,120,....)
  5. Nov 28, 2006 #4

    I Need to desing a variable frequency multiplier, I have a sinusoidal signal of 10Hz ( It dosen´t change) and I want to multiplier this signal and coverts it in a signal of 50Hz or 100Hz or......, depending on a factor.

    I think that I can do it with a PLL but I don´t know how to do it. If someone knows where can I find information about it or can give me some I´ll be grateful.

  6. Nov 28, 2006 #5
    If the input is always 10 hertz then what is the point of even sampling it? Is this homework?
  7. Nov 28, 2006 #6


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    Staff: Mentor

    wikipedia.org is generally a good source for basic technical info like that (maybe not for more advanced info though):


    Basically you will have a variable frequency oscillator that you move up in frequency until a divided-down version matches your 10Hz reference.
  8. Nov 28, 2006 #7
    It's bad practice on this forum to double post. I thought a moderator would have moved your thread from Engineering systems and design to electrical but you started a new thread before anyone had the chance. From the things you've posted in the other thread I'd say you have been given an assignment to design a phase locked loop that uses a 10 hertz reference. Am I correct? You won't get people on this forum to do homework for you. But, there are a lot of knowlegeable people here and we'd love to hear what you know so we can help you.
  9. Nov 29, 2006 #8
    First of all, thanks berkeman.

    Sorry for double post, i didn´t Know that the moderator moves the threads that are in the wrong place. But I think you are wrong, i´m not asking for someone to solve my problem, i´m asking for information, because i don´t remenber how i have to chose the parameters of the VCO, and the filter to do the desing. I have seen in some examples that you have to put a gain in the open loop and this is the other problem I have.

    And if someone knows abaut a good book about PLL aplications, please tell me.
  10. Nov 29, 2006 #9
    First off, you may have trouble finding a VCO that covers the range you want. A single VCO that covers the range you want to can be done depending on what you yourself are able to do. I would do it with an op-amp triangle wave generator. You haven't said if the output of the synthesizer needs to be a sine wave or anything. The synthesizers that I have worked on usually had a pretty high loop gain. These were all oscillators running in the 100 to 1200 Mhz range. The final phase detector frequency was 10 Khz. Yours will be 10 Hz. The loop filter will be somewhat unusual due to the low frequency that your phase detector runs at. If you are looking to make a signal generator that does not need to be super accurate I wouldn't even consider PLL. Someone started a thread like this a while back and I put a bunch of input into it and of course like 99% of the threads like it, nothing became of it. As far as I know, the OP never built it. Here it is: https://www.physicsforums.com/showthread.php?t=119546&highlight=synthesizer
  11. Nov 29, 2006 #10


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    Staff: Mentor

    I merged the threads into this single one and moved it to the EE forum. It's a complicated enough project that I won't move it to homework for now.

    Patricia, can you state exactly what the project assignment calls for? And you can probably check out your university technical library to see what a few PLL books look like.
  12. Nov 29, 2006 #11


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    Staff: Mentor

    Oh, I guess you already gave us a fairly complete problem statement...

    input = 10Hz, output = 5x, 6x, 7x, ... , 30x

    But as was asked already, are the input and outputs square waves or another waveform shape? Does the output need to be phase locked to the input? If not, what is the required frequency accuracy? And in either case, what phase jitter is allowed? Phase jitter is one of the most important specs when it comes to PLLs and frequency multipliers.

    One way to design this would be to start with a higher frequency clock that you divide a constant amount and phase lock to the 10Hz input. Then run a separate variable divider down off the higher frequency clock to generate your 50Hz....300Hz signals. Quiz Question -- what is a good choice for that high-frequency clock? Why? (hint: choose the lowest frequency that will work for the divide ratios)
  13. Nov 30, 2006 #12

    I´ll try to answer your questions,
    1. The two signals must be in phase, that why i thougt abaul the PLL
    2. The two signals are sines, but yerterday i started designing one with an EXOR PD. I, m implementing this in simulation ( simulink of MATLAB), so is esay to transform sine wavws in square waves.
    3.- I´m sorry but i have no idea what the phase jitter that i need is. I work in system control, and I´m trying to control a motor with a big whell ( more or less) and to control the position ( phase) Y have to compare the 2 signals to see if they are the same ( If the output is like the input), and for it i need that the 2 signals run at the same frequency. So, i don´t understand to much how i have to desing it, that is an small part of my proyect.

    Thank you very much, i will read the tread you told me.
  14. Nov 30, 2006 #13
    Well this is much more informative. Thanks for the input. What type of motor is it? Are you basically replacing the VCO with the motor in your application or is it an AC induction motor?
  15. Nov 30, 2006 #14
    Freq Mult

    Well, is dificult to answer becase i don´t know any thing about the motor, I have used a basical model of an electrical motor. And sorry but i don´t usderstand the second question.
    I´ll try to send you the model of my system so you can make up an idea of what it is but i can´t give information about the components because the person that is doing this is still thinking about it, and i´m doing my work but is probably that in a few time i´ll have to chage it. But if i know how to choose the parameters for this case, i will be able to do it for an other case.

    I attach the transfer funtion of the motor+wheel, and the model



    I know what is the squeme that i have to follow to desing the sinthetizer but i still don´t know how to chose the parameters of the vco, for the PD i have put an EXOR, and for the filter a LPF Buterword, but for the VCO I have to chose the Quiescents Frequency and de sensitivity freq.

    I have try putting


    Because the VCO must be runing betwen 50 and 300 HZ and the input is 10Hz.

    And then i have to multiplies the output signal from the Analog Filter block by a constant to produce the control signal of the VCO. And here i have done "trial and error", and it goes, more or less, but i what to know how I have to choose it, please.

    Well i don´t know if is enough information for you to answer me.
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