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A Method for Synchronizing Clock Domains of Different Frequencies

IP.com Disclosure Number: IPCOM000009807D
Publication Date: 2002-Sep-19
Document File: 5 page(s) / 274K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method to synchronize different clock domains by using the high-speed clock from the PLL VCO. Benefits include using existing clocks efficiently without adding additional hardware.

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A Method for Synchronizing Clock Domains of Different Frequencies

Disclosed is a methodto synchronize different clock domains by using the high-speed clock from the PLL VCO. Benefits include using existing clocks efficiently without adding additional hardware.

Background

Synchronizing different clock domains is an important problem to solve in high-performance designs. This is particularly important in high-performance chipsets where minimizing latency between the host system bus and memory system bus is essential. Existing methods rely on using DLL circuitry to offset the clocks to a known phase relationship, which can be quite area intensive if there are a large number of clock domains to synchronize.

General Description

In order to generate the various clock domains needed on a chipset memory controller, the VCO frequency is based on the minimum frequency needed to generate these clocks by integer division.

Table 1 shows the VCO frequency and the divider settings needed to generate the various clocks in a memory controller:


  Cfg   hclk   vco clk   D P R E D I V   M P R E D I V   C P R E D I V   F P O S T D I V   D P O S T D I V   M P O S T D I V   M I O P O S T D I V   D L L P O S T D I V   C P O S T D I V   ddiv clk   mdiv clk   cdiv clk   dclk   fclk   mclk   mio clk   cclk   dll ref clk
  1   100   1600   4   4   2   1   4   4   2   2   4   400   400   800   100   400   100   200   200   400
  2   100   1600   4   3   2   1   4   4   2   2   4   400   533   800   100   400   133   266   200   400
  3   133   1600   3   4   2   1   4   4   2   2   4   533   400   800   133   533   100   200   200   400
  4   133   1600   3   3   2   1   4   4   2   2   4   533   533   800   133   533   133   266   200   400
  5...