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Altera_Forum
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16 years ago

How to run crystal??

I have

The Connor-Winfield CS-023 3.2x2.5mm Surface Mount Crystal.It has 4 pins.Datasheet shows to ground 1,4 pins.I have read somewhere that for 4 pin crystal one dnt need an external electronic inverter/Buffer to run the crystal.I am confused about what to do? If i go for inverter,inverters with such a low t(THL) transition from high to low are not available easily...i want to connect this crystal to my altera CPLD(EPM7064S).

Do not know where to supply Vcc becoz its not in datasheet.

5 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    Yes, it's a crystal, not a crystal oscillator. The latter is used mostly as a FPGA/CPLD clock. To run the crystal, you need an unbuffered inverter and load capacitors, typically also a series resistance to adjust the drive level.

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    I have found an inverter 74LVC1Gx04 for my 114.25Mhz crystal...will they work with each other? What else i have to connect except load capacitances and resistor.Any issues?

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    As I already mentioned, an unbuffered inverter is needed to build a crystal oscillator. 74LVC1GU04 is an example of an unbuffered inverter, standard SN74LVC1G04 is a buffered (three inverter) gate.

    Usual crystal manufacturer application notes don't cover logic gate oscillators for the said frequency range. A 114 MHz crystal is at least 3rd overtone and won't operate at the right frequency without at least a parallel inductor or LC circuit. Most designers would use a classical one transistor crystal oscillator and a logic gate as a level translator, if forced to design an oscillator.
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    Thanks for your help.I got busy with something else.Kindly can you send me curcuit diagram for 3rd ovetone operation.