URGENT - AD9913 - quartz cristal characteristics

  • Hello

AD9913 datasheet does not specify quartz cristal characteristics

What are the absolute maximum for 25MHz cristal characteristics to be used together with 39pF capacitors

- ppm ? 10 - 50 ppm ?

- capacitance ? 4,8, 12, 16, 20 pF ?

- ESR ? 50 / 70 / 100 Ohms ?

Thank you in advance

STH



typo
[edited by: STH at 12:37 PM (GMT -4) on 10 May 2021]

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  • +1
    •  Analog Employees 
    on May 12, 2021 3:19 AM

    Hi,

    I would recommend using the crystals used in some of the DDS evaluation boards: HC49SD_25MHZ or FOXSDLF/250F-20. You can then use the specifications of these crystals as a guide for the absolute maximum values.

    Best regards,

    Mark

  • Hello

    I could find a book that details maths for Pierce oscillator: Les oscillateurs en électronique / Gérard Couturier. ISBN 2-7298-2290-9. Part III provides details about Pierce oscillator equations.

    1. Stability Condition

    C1 >> Cq and C2 >> Cq. Used capacitors shall be bigger than Quartz

    2. Oscillation Condition

    C1 = Ce + C1' + Cp with Ce entry capacitance, Cp pcb capacitance and C1' the first capacitance arbitrarily defined

    C2 = C2' + Cp

    Cq = C1.C2/(C1+C2) or C2 = Cq.C1/(C1-Cq)

    with Ce = 3pF, Cp = 1.2pF, C1'=39pF, C2'=39pF.

    We get Cq = 43.2 . 40.2 / (43.2 + 40.2) = 20.8pF

    Suggested component is 25MHz / 20pF. We do agree

    In this case, C2' = 20 . 43.2 / ( 43.2 - 20 ) - 1.2 = 36pF.

    I would suggest to add these figures to the datasheet because 20pF Quartz are not always offered by manufacturers. Engineers might choose components with different characteristics because they can not find it.

    I could find that 18pF Quartz are much easier to find on the market and thus less expensive.

    In this case C2' = 18 . 43.2 / ( 43.2 - 18 ) - 1.2 = 29.6pF.

    If someone enventually try this configuration. Thank you to confirm it is working with AD9913.

    Thank You

    Simon

Reply
  • Hello

    I could find a book that details maths for Pierce oscillator: Les oscillateurs en électronique / Gérard Couturier. ISBN 2-7298-2290-9. Part III provides details about Pierce oscillator equations.

    1. Stability Condition

    C1 >> Cq and C2 >> Cq. Used capacitors shall be bigger than Quartz

    2. Oscillation Condition

    C1 = Ce + C1' + Cp with Ce entry capacitance, Cp pcb capacitance and C1' the first capacitance arbitrarily defined

    C2 = C2' + Cp

    Cq = C1.C2/(C1+C2) or C2 = Cq.C1/(C1-Cq)

    with Ce = 3pF, Cp = 1.2pF, C1'=39pF, C2'=39pF.

    We get Cq = 43.2 . 40.2 / (43.2 + 40.2) = 20.8pF

    Suggested component is 25MHz / 20pF. We do agree

    In this case, C2' = 20 . 43.2 / ( 43.2 - 20 ) - 1.2 = 36pF.

    I would suggest to add these figures to the datasheet because 20pF Quartz are not always offered by manufacturers. Engineers might choose components with different characteristics because they can not find it.

    I could find that 18pF Quartz are much easier to find on the market and thus less expensive.

    In this case C2' = 18 . 43.2 / ( 43.2 - 18 ) - 1.2 = 29.6pF.

    If someone enventually try this configuration. Thank you to confirm it is working with AD9913.

    Thank You

    Simon

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