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

5 Passing Out Of Band (OOB) Signals

Out of Band (OOB) Signaling is used in SATA and SAS to enable device-to-device communication and negotiation in a storage environment. This signaling uses a series of Idle and Active periods with specific timing. Any impact to this timing could cause major problems within a storage system. This makes undistorted propagation of the OOB signaling extremely important to a storage system design engineer.

Highlighting some key OOB signaling specifications from SATA3.1 gives some guidelines for the type of OOB and signal noise which could be encountered in a real storage system.

Table 5. OOB Specifications

PARAMETER UNITS LIMIT ELECTRICAL SPECIFICATION
Gen 1 Gen 2 Gen 3
VTHRESH: OOB Signal Detection Threshold mVppd Min 50 75 75
Nom 100 125 125
Max 200 200 200
COMINIT/COMRESET and COMWAKE Transmit Burst Length ns Min 103.5
Nom 106.7
Max 109.9
COMINIT/COMRESET Transmit Gap Length ns Min 310.4
Nom 320.0
Max 329.6
COMWAKE Transmit Gap Length ns Min 103.5
Nom 106.7
Max 109.9

Using the COMWAKE waveform burst timing and a noise level equal to the typical OOB signal detection threshold represents a very difficult problem for most re-driver components. With a fully linear datapath, the DS125BR820 overcomes any distortion issues while propagating this waveform across SAS/SATA links ensuring robust OOB communication.

The visible noise injected in Figure 11 is 100 mVpp in amplitude at a frequency of 200 MHz.

oob_signaling_ds125br820_input_snla236.pngFigure 11. OOB Signaling at DS125BR820 Input
oob_signaling_ds125br820_output_snla236.pngFigure 12. OOB Signaling at DS125BR820 Output