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

4.2 Channel Extension

In order to assess channel extension in a system environment, a PCB with the DS125BR401A and miniSAS-HD connectors was developed.

sas3_system_test_setup_snla236.gifFigure 7. SAS-3 System Test Setup

The following EQ, VOD, DEM, and VOD_DB settings have been tested for SAS-3 12 Gbps operation with a SAS-3 Expander ASIC. The cable lengths tested ranged from 1 – 12 meters with no more than 7 meters on one side of the DS125BR401A. The test data is shown in the table below.

Table 4. DS125BR401A Settings Used for Testing

CABLE LENGTHS DS125BR401A SETTINGS BER Testing Result
Cable1 Cable 2 CH-A
EQ		 CH-A
VOD		 CH-A
DEM		 CH-B
EQ		 CH-B
VOD		 CH-B
DEM
2m 7m 0x03’h 110’b 0x00’h 0x03’h 1.4Vpp 0x00’h Pass
3m 7m 0x03’h 110’b 0x00’h 0x03’h 1.4Vpp 0x00’h Pass
5m 7m 0x03’h 110’b 0x00’h 0x03’h 1.4Vpp 0x00’h Pass
7m 2m 0x03’h 110’b 0x00’h 0x00’h 1.4Vpp 0x00’h Pass
7m 3m 0x03’h 110’b 0x00’h 0x00’h 1.4Vpp 0x00’h Pass
7m 5m 0x03’h 110’b 0x00’h 0x00’h 1.4Vpp 0x00’h Pass

NOTE

Channel-A DEM is listed as VOD_DB in the device datasheet.

The mini-SAS HD cable running from the system ASIC to the DS125BR401A (Table 4, Column 2) connects to the top connector on the DS125BR401A SAS board given the orientation shown in Figure 8. The mini-SAS HD cable running from the DS125BR401A to the system ASIC (Table 4, Column 4) connects to the bottom connector.

tida00425_12gbps_sas3_link_extender_board_snla236.pngFigure 8. TIDA-00425, 12 Gbps SAS-3 Link Extender Board

Although testing was completed with DS124BR401A CTLE = 0x03’h for Channel A, lower levels of equalization should be used if the attenuation between the SAS-3 ASIC Tx and the DS125BR401A inputs is less than 8-10 dB at 6 GHz.

With the miniSAS-HD cables removed, the TIDA-00425 “SAS-3 Link Extender” design can be tested directly using SMA to miniSAS-HD breakout cables. Under this condition, high quality waveforms are observed on the output ports.

12gbps_sas3_waveform_output_link_extender_board_snla236.pngFigure 9. 12 Gbps SAS-3 Waveform Output from “Link Extender Board”

Additional testing with the DS125BR820 using the setup in Figure 10 shows SAS-3 channel extension of approximately 10 dB is possible with good isolation between channels. This diagram shows DS125BR820 placement at both 10 dB and 25 dB away from the SAS-3 ASIC Tx. Further testing verified that all locations between 10 – 25 dB resulted in error free system performance.

12gbps_sas3_testing_system_asic_snla236.pngFigure 10. 12 Gbps SAS-3 Testing with System ASIC