SNAA386 November   2023 CDCE6214 , CDCE6214-Q1 , CDCE6214Q1TM , LMK00301 , LMK00304 , LMK00306 , LMK00308 , LMK00334 , LMK00334-Q1 , LMK00338 , LMK03318 , LMK03328 , LMK3H0102 , LMK6C , LMK6H , LMKDB1104 , LMKDB1108 , LMKDB1120 , LMKDB1202 , LMKDB1204

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Introduction to PCIe
    1. 2.1 The PCIe Link
  6. 3PCIe Clocking Architectures
    1. 3.1 Common Clock Architecture
    2. 3.2 Separate Reference Architecture
    3. 3.3 Spread Spectrum Clocking
    4. 3.4 PCIe REFCLK Topology
    5. 3.5 Noise Folding
  7. 4PCIe Clocking Specifications
    1. 4.1 REFCLK Output Format
    2. 4.2 PCIe Jitter Requirements
    3. 4.3 PCIe Time Domain Requirements
  8. 5REFCLK Measurement Technique
    1. 5.1 Clock Generator Measurement Results
      1. 5.1.1 PNA Measurement Result without SSC
      2. 5.1.2 PCIe Filtered PNA Result without SSC
      3. 5.1.3 PNA Measurement Result, With SSC
      4. 5.1.4 PCIe Filtered PNA Result, With SSC
      5. 5.1.5 Time Domain PCIe Measurement Result
    2. 5.2 Clock Buffer Measurement Results
      1. 5.2.1 PNA Measurement Result
      2. 5.2.2 PCIe Filtered PNA Result
      3. 5.2.3 Time Domain PCIe Measurement Result
  9. 6Texas Instruments Products with PCIe Compliance
  10. 7Summary
  11. 8References

7 Summary

Systems that use PCIe must take care to plan the architecture appropriately. Each of the different architectures has tradeoffs, and the system designer must determine which one meets the requirements of their system. The addition of Spread Spectrum Clocking is an excellent choice for reducing EMI, but at the cost of adding complexity to the REFCLK design.

Both frequency and time domain specifications must be met to be compliant to PCIe. Selecting a low RMS jitter clock source is critical. Measuring PCIe jitter requires understanding PCIe filtering. Using a newer PNA allows for simple collection of non-SSC and SSC phase noise data for frequency domain analysis. The Texas Instruments PCIe Reference Clock Analysis Tool allows for rapid analysis of PNA and oscilloscope data to determine PCIe compliance.

The widespread use of PCIe and the need for increased data throughput needs requires clocking products. Texas Instruments offers a broad portfolio of clock generator and clock buffer products that meet the most demanding PCIe Gen 6.0 compliance. The Texas Instruments Clocks and Timing Overview provides further information on the PCIe compliant products available.