Design and Simulation of cross-coupled VCO in ADS

Discussion in 'Wireless & RF Design' started by rkhandare, Aug 13, 2019.

  1. rkhandare

    Thread Starter New Member

    Aug 13, 2019
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    Hello everyone. I am currently designing a low power consumption and low phase noise cross-coupled VCO in ADS. But I'm not getting the oscillating waveform when performing the transient response. Can anyone please help me with the issue. Thanks in advance.
     
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  2. danadak

    Distinguished Member

    Mar 10, 2018
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    Sure seems the collector supply at 1V too low ?


    Regards, Dana.
     
  3. rkhandare

    Thread Starter New Member

    Aug 13, 2019
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    Lower the voltage supply, lesser will be the power consumption.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    C1 and C2 should connect to respective transistor bases, not to each other.
    If the simulator is to be believed, you've created a -333 megaVolt generator :).
     
  5. rkhandare

    Thread Starter New Member

    Aug 13, 2019
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    Thankyou for your reply. May I know how do I make the circuit oscillate after connecting the capacitors to the base of the transistors.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I don't use ADS, but in the LTspice simulator you can specify a start-up condition, e.g. by giving one of the capacitors an initial voltage so that the circuit isn't completely symmetrical to start with.
     
  7. rkhandare

    Thread Starter New Member

    Aug 13, 2019
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    Ok.thanks.
     
  8. danadak

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    Mar 10, 2018
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    I understand that. But at 1V do you have enough reverse bias on collectors
    to get transistors to function as transistors, especially on c old side of operation ?


    Regards, Dana.
     
  9. rkhandare

    Thread Starter New Member

    Aug 13, 2019
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    Thanks for your reply. May I know how much supply voltage would you recommend to function the transistors properly?
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Something missing from your circuit, once you have the caps connected properly, is a respective pull-up resistor from each base to the +ve supply rail.
     
  11. danadak

    Distinguished Member

    Mar 10, 2018
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    Depends on part.

    This shows at low Vce you are close to saturation, and given your Vbe is relatively
    fixed this tells you what Vcb should be doing. You don't want clipping if you are trying
    to amp a signal. This also effects dynamic range of signal swing at collector.

    upload_2019-8-13_9-16-59.png


    Regards, Dana.
     
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