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Syncronizing a data acquisition device with a host

  • US 5,914,991 A
  • Filed: 06/30/1997
  • Issued: 06/22/1999
  • Est. Priority Date: 06/30/1997
  • Status: Expired due to Term
First Claim
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1. In a data acquisition pod of the type having a signal sampling A/D converter that is coupled to a host system via a data communication link, apparatus for synchronizing a host-derived reference clock signal with a clock signal in the data acquisition pod that operates the A/D converter, so that the A/D converter provides samples to the data communication link at the same rate as the rate at which the host system requests the samples, comprising:

  • a decoder having an input coupled to the data communication link for extracting from communication received from the host a host reference signal having a host reference frequency;

    a clock signal source for developing an A/D reference clock signal having a frequency that is offset a predetermined amount from the frequency of the host reference frequency;

    an A/D converter of the oversampling type having an A/D converter clock signal input; and

    a pulse modifying digital phase-locked loop (PLL) responsive to the A/D reference clock signal and the host reference signal for developing an A/D clock signal in which one of its clock periods is periodically modified, said A/D reference clock signal being coupled to said A/D converter clock signal input, thereby locking the rate at which the A/D converter develops samples to the rate at which the host system requests samples.

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