Problem with appnote XAPP622 (SDR LVDS)

Hi,

in the introduction i find: "At SDR clock frequencies below the maximum operating frequency (420 MHz) of the Virtex-II Digital Clock Manager (DCM), implementing a single data rate design can be easily accomplished using standard design techniques. This application note describes a method of implementing an SDR interface at clock frequencies higher than the maximum operating frequency of the DCM, without exceeding the AC timing specifications of the Virtex-II devices."

but later on, on page 3, the input ref_clk is connected to a DCM. Why is that possible? I thought the frequency is higher than the max DCM input frequency?

regards, Benjamin

Reply to
Benjamin Menküc
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The maximum operating frequency of the DCM is not a function of the input clock, but of the internal delay lines. The Virtex-II and above families include a divide by two function on the CLKIN pin of the DCM dropping the frequency from 622 to 311 MHz for the delay lines in the DCM which is within the operating range of the DCM.

Ed

Benjam> Hi,

Reply to
Ed McGettigan

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