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    HOW TO DEBUG vco

    i DESIGN A VCO,BUT it doesn't oscillate,which aspects should we consider about no ocsalliating?how to debug a vco?thank u

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    Re: HOW TO DEBUG vco

    1. Check if it is free running?
    Check the amplifier has sufficient gain. Remove all feedback elements.

    hope this helps
    brmadhukar



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    Re: HOW TO DEBUG vco

    no free running :(



    •   Alt22nd March 2005, 01:59

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    Re: HOW TO DEBUG vco

    brmadhukar:
    How can i do?
    in the simulation ,it works well.



    •   Alt24th March 2005, 09:10

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    Re: HOW TO DEBUG vco

    Could you possibly clue us in as to what you are talking about? Bipolar, Fet, reflection (negative resistance) oscillator, transmission oscillator, frequency, circuit schematic, phase of the moon?



    •   Alt25th March 2005, 01:46

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    Re: HOW TO DEBUG vco

    ok.this is the sch



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    Re: HOW TO DEBUG vco

    this is the pcb,my first pcb,not good.:)



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    Re: HOW TO DEBUG vco

    hi liberal.

    1) you mean no free running -> is it not working or you do no expect it to work?

    2) can you check it as an amplifier -- feed some input at required frequency and check the output

    3) PCB is critical-- I hope you have filtered the power supply and you do not have any switching elements.

    4) I may be able to help you out in details. But I shall be very slow in replying. If it is OK send me a PM.

    brmadhukar



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    HOW TO DEBUG vco

    PCB is not visible. Try to post once again.
    If substrate is FR4 (as it seems...) increase to 0.02 the loss tangent (more similar to real value) and see if it oscillates.
    Use, instead of ideal passive components, vendor library component models (Q and SRF can be important).
    I hope it can help.
    Mazz



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    Re: HOW TO DEBUG vco

    To brmadhukar:
    Thanks for your valuable advice,I will try again tomorrow.and i have a little request,if u make my sch to a pcb,how do u place it?can u send a jpg,i want to get some experience.:)
    To mazz:
    i don't konw why the pcb is not visible.i send it again.hope your help:)
    http://img41.photo.163.com/liberal_l.../143497891.jpg
    change "** "to "tt"



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    Re: HOW TO DEBUG vco

    You schematic is not making sense to me. What is all that crap to the right
    of C6 for? Get rid of it for now.

    Is this a reflection or a transmission oscillator? The reason I ask is that is looks a little like a reflection oscillator (you are trying to make a negative resistance at the collector to resonate with the ceramic resonator, but why is there a C1 capacitor?).



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    Re: HOW TO DEBUG vco

    To biff44:
    The components in the right of C6 is a model of a varator(smv1233),not crap.
    and this oscilator is a colpitt sch,it can also be classified as a reflective oscillator.



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    Re: HOW TO DEBUG vco

    Colpitts oscillators are transmission type oscillators. You build an amplifier with some gain G and phase shift P. You place a tuned circuit in the feedback path with Loss L and phase shift Q.

    IF G > L, AND P + Q = n2Π, it will oscillate.

    You might want to break the circuit into pieces and measure the gain and phase shift of the amplifier part, measure the loss and phase shift of the ceramic resonator part, and fix what is not meeting the above criteria.



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    HOW TO DEBUG vco

    To liberal
    link is forbidden for me...
    Mazz



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    Re: HOW TO DEBUG vco

    again



    •   Alt29th March 2005, 06:41

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    HOW TO DEBUG vco

    From layout photo the prototype seems well done.
    I'm assuming that the board is double layer and vias are plated through holes.
    I can only suggest (once again) to make simulation with real capacitors models and lossy transmission lines.
    I hope it can help.
    Mazz



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