1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Clapp oscillator 150 mhz

  1. Apr 8, 2017 #1
    • Thread moved to the Homework forums, and new poster reminded to show their efforts in their threads
    hi , i want to design a clapp oscillator with output frequency up to 150 MHZ , inductance value must be 0.24 u , who can help me please?? i need it for my project
     
    Last edited by a moderator: Apr 8, 2017
  2. jcsd
  3. Apr 8, 2017 #2

    anorlunda

    User Avatar
    Science Advisor
    Gold Member

  4. Apr 8, 2017 #3
    i saw the references but i don't have any solutions
     
  5. Apr 8, 2017 #4
    here is my oscillator design , the output frequency must be 150 MHZ but the simulation in ltspice is 147 MHZ
     

    Attached Files:

  6. Apr 8, 2017 #5

    anorlunda

    User Avatar
    Science Advisor
    Gold Member

    Tagging @berkeman
     
  7. Apr 8, 2017 #6

    davenn

    User Avatar
    Science Advisor
    Gold Member

    I don't know why you must keep the value of the inductor what it is ??

    have you considered experimenting with the values of C1 and C2 C1=C2 but change the values to 33pF instead of your 50pF
    as according to the freq formula for a Clapp Osc, they will also help set the frequency

    upload_2017-4-9_8-32-24.png

    you just haven't done enough experimenting


    Dave
     
  8. Apr 8, 2017 #7
    i'm working in model , so that the inductor value must be kept at 0.24 uH , the VCC must be 3.3 V , and i must use a JFET , the output frequency must be 150 MHZ , can you help me with others design ?
     
  9. Apr 8, 2017 #8

    davenn

    User Avatar
    Science Advisor
    Gold Member

    I really don't see the reason for all those musts, except for maybe the voltage

    I have given you an option go try it in your simulator and experiment with the values of C1 and C2
    come back with your results


    Dave
     
  10. Apr 8, 2017 #9
    i tried your option but i found 144 MHZ
     

    Attached Files:

  11. Apr 8, 2017 #10

    davenn

    User Avatar
    Science Advisor
    Gold Member

    sooo ... did you think of trying other values ??
    start thinking about the problem
    so if you went to 33p and the freq dropped, what do you think that is telling you ?
    what should you try next ?
     
  12. Apr 8, 2017 #11
    really i don't know , i tried many values but always the same problem
     
  13. Apr 8, 2017 #12

    davenn

    User Avatar
    Science Advisor
    Gold Member

    come on .... seriously ??

    so if the 33p dropped the freq .... how about something higher than 50p ..... say 60p or 75p
    see what that does
     
  14. Apr 8, 2017 #13

    davenn

    User Avatar
    Science Advisor
    Gold Member

    I want you to find a pair of values that will take you a little above 150 MHz
    THEN you can change out C3 for a trimmer cap with a centre value of ~ 10p
    and use that to adjust to your wanted frequency


    Dave
     
  15. Apr 8, 2017 #14
    I Tried with c1=c2 = 50 pF and C3 = 5.5 pF i found 150 MHZ :) but when i calculated i found 153 MHZ !!
     
  16. Apr 8, 2017 #15

    Baluncore

    User Avatar
    Science Advisor

    AHMEDbr.
    The LTspice circuit shown in post #4 has D1 as a bias or limiter component, but D1 is the wrong way round to DC bias an N-JFET.

    In post #9 the diode has gone, but there is still no gate DC bias.
    You need to DC bias the gate by replacing D1 with a 47k resistor between ground and JFET gate.
     
  17. Apr 8, 2017 #16

    berkeman

    User Avatar

    Staff: Mentor

    Thread closed for Moderation...

    EDIT -- Thread re-opened after being moved to the Homework Help forums. Reminder to all to please use the Report link to let the Mentors know about newbies misplacing schoolwork questions in the technical forums. Especially with so little effort shown initially. Thank you.
     
    Last edited: Apr 8, 2017
  18. Apr 8, 2017 #17

    berkeman

    User Avatar

    Staff: Mentor

    Have you actually looked at the equations for the frequency of oscillation of this design? What is the exact homework problem statement? With a circuit like you show in your simulation schematic, the oscillation frequency will vary a lot with temperature and component tolerance. If you need that exact oscillation frequency, you will need to do a lot more than what is shown in your schematic...
     
  19. Apr 8, 2017 #18

    davenn

    User Avatar
    Science Advisor
    Gold Member


    I had asked/commented about that way back in post #6 :wink:
     
  20. Apr 8, 2017 #19

    davenn

    User Avatar
    Science Advisor
    Gold Member

    so apart from the missing bias resistor, baluncore pointed out. What other things do you think would
    cause a difference between what freq you got in the sim and the freq you got for an actual circuit ?
     
  21. Apr 9, 2017 #20
    hi everybody , i replaced the diode with a bias resistor as Baluncore said , but i found 147 MHZ , should i add a temperature compensation to my circuit ???
     

    Attached Files:

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Clapp oscillator 150 mhz
  1. Ring oscillator (Replies: 1)

  2. Opamp oscillator (Replies: 1)

Loading...