SNLA236 September   2015 DS125BR111 , DS125BR401A , DS125BR820

 

  1.   Linear Repeaters Used in SAS/SATA Applications
    1.     Trademarks
    2. 1 Introduction
    3. 2 SAS-3 Transmit Waveforms
      1. 2.1 Default Transmit Equalization Coefficients
      2. 2.2 Using Linear Equalization to Recover Tx FIR Information
      3. 2.3 Linear Equalization Effects on Jitter Due to Attenuation
    4. 3 Equalizer Placement within a SAS-3 Channel
    5. 4 System Results Using Linear Equalization
      1. 4.1 Linear Equalization Effects on Jitter Due to Attenuation
      2. 4.2 Channel Extension
    6. 5 Passing Out Of Band (OOB) Signals
    7. 6 Conclusions
    8. 7 Appendix A: Layout Considerations
  2.   Revision History

2 SAS-3 Transmit Waveforms

SAS-3 is a serial interface which is often grouped in a x4 lane arrangement supported by miniSAS-HD connectors. Due to the link attenuation supported by SAS-3 devices, the SAS-3 transmitter must contribute some Tx equalization to help compensate for the total channel attenuation or loss at high frequencies. The transmitter must be able to produce individual pre- and post- cursor equalization coefficients based on the table below.

Table 1. SAS-3 Transmitter Equalization

SIGNAL CHARACTERISTIC MINIMUM NOMINAL MAXIMUM UNITS
Precursor Equalization Ratio RPRE 1 1.66 V/V
Post Cursor Equalization Ratio RPOST 1 3.33 V/V
Peak to Peak Voltage (Differential VP-P) 850 1200 mV
Transmitter Device Off Voltage 50 mV

NOTE

When pre- and post-cursor energy is applied, the combined equalization may be higher.

The experiments in this report demonstrate the DS125BR820’s ability to reproduce this type of transmitted waveform using active continuous time linear equalization. This capability works well with system Tx-Rx training algorithms, allowing for increased reach in SAS-3 applications.