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 Effect of load capacitor at the output of an oscillator 

Last post Tue, Apr 17 2012 9:57 AM by Jithin. 3 replies.
Started by Jithin 12 Apr 2012 09:58 AM. Topic has 3 replies.
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  • Thu, Apr 12 2012 9:58 AM

    • Jithin
    • Top 500 Contributor
    • Joined on Wed, Mar 7 2012
    • Posts 17
    • Points 250
    Effect of load capacitor at the output of an oscillator Reply

    Hi,

    While designing an oscillator ,which had a ring oscillator(differential ended) architecture , the frequency sensitivity of the vco had changed, that is if initially my vco works in a frequency range of 300MHz - 500MHz aor a control voltage range (1.3V-1.85V). After adding a capacitor

    at the output,say 400fF of each differential amplifier stage then the same frequency(300MHz- 500MHz) swings at a voltage range of (.9V - 1.65V).Thereby decreasing the  gain of vco. The problem is that I can't find a reason for this phenomenon and can't answer the questions like how the range of the control voltage had changed due to the addition of a load capacitor.

    Please help me.

    Thanking you in advance.

    with regards,

    Jithin 
    • Post Points: 20

  • Fri, Apr 13 2012 4:51 AM

    • Quek
    • Top 10 Contributor
    • Joined on Wed, Oct 14 2009
    • Singapore, 00-SG
    • Posts 944
    • Points 14,305
    Re: Effect of load capacitor at the output of an oscillator Reply

    Hi Jithin

    It seems that this is a design issue and it would be a little hard for us to help. : )  Hope that you will be able to get more help in the designer's forum.

    Best regards
    Quek
    • Post Points: 20

  • Fri, Apr 13 2012 4:54 AM

    Re: Effect of load capacitor at the output of an oscillator Reply

    Especially without seeing the design - you didn't even say how the control voltage controls the VCO frequency, for example. But Quek's right - a more design-centric forum would probably make more sense.

    Andrew.

    • Post Points: 5

  • Tue, Apr 17 2012 9:57 AM

    • Jithin
    • Top 500 Contributor
    • Joined on Wed, Mar 7 2012
    • Posts 17
    • Points 250
    Re: Effect of load capacitor at the output of an oscillator Reply
    Thank you Andrew .
    • Post Points: 5
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Started by Jithin at 12 Apr 2012 09:58 AM. Topic has 3 replies.