Ring oscillator

Discussion in 'General Electronics Chat' started by Ahmad Aldabbagh, Jun 5, 2015.

  1. Ahmad Aldabbagh

    Thread Starter New Member

    Jun 5, 2015
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    Hi all


    Could you help me please to design a ring oscillator circuit using MOSFET inverters ( 5 stages ) to get a frequency about 20 MHz ?

    - recommended software is LTspice or Multisim


    Thanks in advance for your help
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    Is this a school/college project?
     
  3. Ahmad Aldabbagh

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    Jun 5, 2015
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    no
     
  4. bertus

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  5. crutschow

    Expert

    Mar 14, 2008
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    If this is not homework, who recommended LTspice or Multisim?
     
  6. Ahmad Aldabbagh

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    Jun 5, 2015
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    I need to work on these two programs
     
  7. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Google for application notes from National Semiconductors. I recall at least two of them explaining the basics.
     
    Last edited: Jun 8, 2015
  8. AnalogKid

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    The problem with the ring oscillator is that it is critically dependent on device factors that are not critically controlled during manufacture. Beyond the obvious suggestion of an integrated or discrete crystal oscillator, there are other non-resonant oscillator structures that give you more control over its design and operation. 20 MHz might be a bit high for a classic phase-shift oscillator, but you could do one with ECL gates.

    ak
     
  9. Ahmad Aldabbagh

    Thread Starter New Member

    Jun 5, 2015
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    Yes that is right. Actually I have to use MOSFET in order to save power and in the meanwhile I got 25 Mhz using 3 stages inverters and supply voltage of 8v. This voltage is considered high and I need to reduce it but the problem is that there no output waveform when the voltage reduced below 8v. do you have suggestion about what type of MOSFET I have to use with low voltage needed?
     
  10. AnalogKid

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    Can you post your schematic?

    ak
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    For a 5 gate ring oscillator wich should produce 20 Mhz, you would need a propagation delay of total 50 nS.
    This will yield to a propagation delay of 10 nS for one gate.
    This can be found in TTL chips, but cmos will be most likely to slow.

    Bertus
     
  12. Ahmad Aldabbagh

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    Jun 5, 2015
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    Please find the attached schematic
     
  13. dl324

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    Are you trying to design with 5 stages, or 3? What is your desired operating voltage? Any reason why you're using high current devices?
     
  14. Ahmad Aldabbagh

    Thread Starter New Member

    Jun 5, 2015
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    dear Dennis,
    '' Are you trying to design with 5 stages, or 3?'' ....... I need to design both of them.

    ''What is your desired operating voltage?'' ................ the desired voltage is 3.3 v .

    ''Any reason why you're using high current devices?'' ............. no, please advise me if you have suggestion about type and serial number of the MOSFET transistor.

    thanks
     
  15. dl324

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    Mar 30, 2015
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    Look for some low threshold voltage devices. I think it's going to be difficult to get 5 stages to work at 3.3V; even 3 stages may be difficult. Don't use power devices; larger devices mean more parasitics and you don't need the drive capability.
     
  16. AnalogKid

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    Aug 1, 2013
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    With all of its amplitude and frequency stability issues, why are you focused on a ring architecture?

    ak
     
  17. Ahmad Aldabbagh

    Thread Starter New Member

    Jun 5, 2015
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    I need it in a specific application
     
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