Answers Database Can an FPGA be used in combination with an external crystal oscillator as an amplifier? Record #4071 Product Family: Hardware Product Line: Spartan Product Part: S10 Problem Title: Can an FPGA be used in combination with an external crystal oscillator as an amplifier? Problem Description: Urgency: Standard General Description: People familiar with the 3000 series onboard oscillator may want to try to make an amp with a Spartan or similar FPGA by attaching a crystal oscillator externally. Solution 1: It is not recommended to use a crystal oscillator with a XC9500, XC5200, XC4000E/EX/XL/XLA, Virtex/VirtexE or Spartan/SpartanXL/Spartan-II to create a clock signal. Using an FPGA or CPLD to act as a crystal oscillator is wasteful in power, and also in pins. A ready-made oscillator is more beneficial as it is put together with the appropriate circuitry to maintain a valid clock signal. It starts up reliably and consumes a minimum of power. For all frequencies: Using two IOBs, one as input, the other as output, results in a multi-stage linear amplifier with too much gain, too fast a gain roll-off and thus high phase distortion, all resulting in instability, on top of high power consumption. Regarding very low frequencies: A 32 kHz crystal ( used in every modern watch ) has relatively high impedance and needs more gain than the high-frequency crystals we normally work with. So don't try to use it with an XC3000 type FPGA. End of Record #4071 - Last Modified: 02/01/00 14:56

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