crystal oscillator circuit

Discussion in 'General Electronics Chat' started by whale, Dec 17, 2009.

  1. whale

    Thread Starter Active Member

    Dec 21, 2008
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    hello everyone,

    i have a crystal oscillator circuit

    iam verymuch confused about the term EQUIVALENT SERIES RESISTANCE.

    for an AT CUT crystal operating in fundamental parallel resonant mode is it enough if we just match the load capacitance of the crystal with the circuit?

    OR , we too want to consider in matching EQUIVALENT SERIES RESISTANCE of the crystal?

    iam going to change the frequency of the oscillator circuit above to
    13.25 MHZ by changing the crystal unit , give me some suggestions.

    i have a crystal piece with 13.2520 MHZ of fundamental frequency, but i don't know where to find its .i dont know to which manufacture it belong to .
    the wordings stamped on the crystal are,

    at front side of crystal,

    DY-8
    13.252083

    and at back side of the crystal,

    WXL
    B/0 05

    the crystal is about 1.3 CM in length, and 1 CM in width and the thickness is about 2 CM.with two leads at its base.

    how can i get its data?
    and how to match with above circuit?
     
    Last edited: Dec 17, 2009
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287

    Greetings:

    There's a lot of good information on this in the ARRL Handbook, in Chapter 10

    The ESR is about 7 ohms for a 10HMZ crystal AT cut. In a SERIES resonant mode, this is the limiting factor for the Q. (Equivalent inductance for such a crystal is about 9.8 mH.

    For a series mode crystal, you want the LOAD and SOURCE impedances to both be as low as possible. This allows you to approach the theoretical Q that the ESL will allow.

    For a PARALLEL resonant mode, the opposite is true, you want as LITTLE loading on the crystal as possible. However, in order to supply any current to the crystal you have to have SOME finite loading somewhere!

    Because any crystal has two significant capacitances, the series capacitance and the shunt capacitance, the maximum impedance will not occur at the 180 degree phase shift point. (They are nearly identical in the series mode, but can diverge significantly in the parallel mode)

    The optimum capacitive loading (external to the crystal) will depend on the type of oscillator and the required phase shift to maintain oscillation.

    Hope this helps!

    Eric
     
  3. whale

    Thread Starter Active Member

    Dec 21, 2008
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    thanks for your reply eric ,

    can you please tell me from the circuit, what type of oscillator is this?
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yes, that's a Pierce oscillator....probably the most straightforward crystal oscillator.

    eric
     
  5. whale

    Thread Starter Active Member

    Dec 21, 2008
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    to change the circuit to operate at 13.25 mhz by using a 13.25 mhz crystal what should i do?
     
  6. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    You MIGHT be able to "pull" the frequency of the crystal by trimmer capacitors, but that's a fairly large step. Since you want to go DOWN in frequency, you might be more successful with a series resoanant mode with some inductive loading, Look up "VXO" circuits on the web.

    Eric
     
  7. whale

    Thread Starter Active Member

    Dec 21, 2008
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    now i have 13.25 MHZ crystal unit in my hand, if i replace the crystal unit in the above circuit with 13.25 MHZ crystal, will it work?

    or do i want to match the load capacitance?

    its enterer if my oscillator work at the range of 13 to 14 mhz
     
  8. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    It should work, but it might not be on the exact frequency. Do you have a frequency counter?

    Eric
     
  9. whale

    Thread Starter Active Member

    Dec 21, 2008
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    No eric, but iam pleased to hear it will work.
    Ok i'll try it.
     
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