SNAA435 April   2025 CDC6C-Q1 , LMK3C0105-Q1 , LMK3H0102-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2FPD-Link REFCLK Requirements and Jitter Definitions
    1. 2.1 FPD-Link III REFCLK Requirements
    2. 2.2 FPD-Link IV REFCLK Requirements
  6. 3FPD-Link Clocking Selection Guide
  7. 4EMI Considerations
  8. 5Summary
  9. 6References

2 FPD-Link REFCLK Requirements and Jitter Definitions

FPD-Link REFCLK jitter requirements are generally specified in either the time-domain or frequency-domain. Frequency-domain jitter measurements are taken with a phase noise analyzer (PNA), such as the Keysight E5052. To calculate RMS phase jitter, the measured phase noise curve is integrated over a defined frequency band (usually 12kHz to 20MHz) and normalized based on the carrier frequency.

Frequency-Domain Jitter Measurement Setup With PNA Figure 2-1 Frequency-Domain Jitter Measurement Setup With PNA
Phase Noise Measurement Example Figure 2-2 Phase Noise Measurement Example

Time-domain jitter measurements are taken with a jitter analysis software suite on a high-speed oscilloscope. TI commonly uses the DPOJET jitter and eye analysis tool provided on Tektronix oscilloscopes for such measurements. In this case, TI recommends measuring the total jitter (TJ) at a given bit error rate (BER) with the clock recovery settings designed to match the input PLL characteristic of the serializer device. The following sections provide more details on how to configure the jitter analysis tool.

To open DPOJET, launch One Touch Jitter or Serial Data/Jitter Wizard from the utilities menu. Launching the tool can automatically set the acquisition settings and vertical and horizontal scaling based on the active input signal. A new window is also opened with various configuration options and measurement results. To configure FPD-Link REFCLK time-domain jitter measurements, enter the Select tab and add a measurement for TJ@BER with a BER setting of 10-10. The clock recovery filters can be set in the Configure tab and needs to be set based on the FPD-Link device as described in Section 2.1.

DPOJET Jitter Measurement Configuration Figure 2-3 DPOJET Jitter Measurement Configuration
DPOJET Clock Recovery Filter Configuration Figure 2-4 DPOJET Clock Recovery Filter Configuration