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

 

  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

5 REFCLK Measurement Technique

For measuring the performance of REFCLK, a Phase Noise Analyzer (PNA) can be used to measure the frequency-domain of the jitter, the phase noise. The output trace can be output to a text file, which can then be post-process through a PCIe processing tool. Newer PNAs, such as the R&S® FWSP used in this paper, are able to support both SSC and non-SSC phase noise data collection, allowing for post-processing of spread-spectrum clocks. Figure 5-1 shows the test setup for the PNA measurements. Table 5-1 lists the equipment and devices used in the REFCLK measurements.

GUID-20231120-SS0I-SPCX-PNNW-0PSVFMG9GTT9-low.svg Figure 5-1 PNA Measurement Test Setup
Table 5-1 Equipment Used in REFCLK Measurements
Low-Noise Source Devices Under Test (DUTs) Balun Measurement Equipment

R&S® SMA100B

Agilent E5052B

LMK3H0102

LMKDB1120(1)

 Mini-Circuits® ADTL2-18 R&S® FSWP(2)

Agilent DSO80804B(3)
(1) The LMKDB1120 device uses the R&S® SMA100B as the low-noise clock source for PCIe measurements. Using a low noise source is critical for accurate jitter measurements.
(2) R&S® FSWP used for frequency domain measurements.
(3) Agilent DSO80804B used for time domain measurements.