9.1.1 Signal Integrity in 10G-KR Applications

When configured in "KR Mode", using either the VOD_SEL and MODE pin setting or SMBus register control, the DS100BR111 is designed to operate transparently within a KR backplane channel environment. Installing a DS100BR111 repeater within the KR backplane channel splits the total channel attenuation into two parts. In other words, operating in "KR Mode" implies that signals will pass through the repeater with a linearized output. Ideally the repeater can be placed near the middle of the channel, maximizing the signal-to-noise ratio across the bidirectional interface.

In order to maximize the 10G-KR solution space, the 802.3ap specification calls for an optimization of the Tx partner signal conditioning coefficients based on feedback from the KR Rx ASIC endpoint. This link optimization sequence is commonly referred to as "link training" and is performed at speed (10.3125 Gbps). Setting the DS100BR111 active CTLE to compensate for the channel loss from each of the KR transmitters will reduce the transmit and receive equalization settings required on the KR physical layer devices. This central location keeps a larger signal-to-noise ratio at all points in the channel, extending the available solution space and increasing the overall margin of almost any channel. Suggested initial settings for the DS100BR111 are given in Table 10 and Table 11. Further adjustments to EQx, DEMx, and VODx settings may optimize signal margin on the link for different system applications.

The SMBus Slave Mode code example in Table 12 may be used to program the DS100BR111 with the recommended device settings.

9.1.2 OOB (Out-of-Band) Functionality in SAS/SATA Applications

For SAS/SATA systems, a low speed OOB (Out-of-Band) communication sequence is used to detect and communicate device capabilities between host ASIC and link partners. These OOB signals, including COMWAKE, COMINIT, COMRESET, and COMSAS, are a series of burst, idle, and negation times transmitted and detected across the SAS/SATA link. These bursts occur at a rapid rate, with the COMWAKE signal having the most stringent requirement of 106.6 ns active followed by 106.6 ns idle. Normally, if the device is set in 10G-KR mode (MODE pin floating), the device goes idle-to-active in approximately 150 ns. If the device is set to SAS mode (MODE pin tied via 1 kΩ to VDD (2.5 V mode) or VIN (3.3 V mode)), the device goes idle-to-active in approximately 3 to 4 ns. This fast idle-to-active time is critical to pass OOB signaling, and when operating in pin mode, the MODE pin should be tied high. If operating in SMBus slave mode, the user can set Reg 0x28 to 0x4C for this faster idle-to-active response.

9.2.1 Design Requirements

As with any high speed design, there are many factors that influence the overall performance. Below are a list of critical areas for consideration during design.

• Use 100 Ω impedance traces. Length matching on the P and N traces should be done on the single-ended segments of the differential pair.
• Use uniform trace width and trace spacing for differential pairs.
• Place AC-coupling capacitors near to the receiver end of each channel segment to minimize reflections.
• The maximum body size for AC-coupling capacitors is 0402.
• Back-drill connector vias and signal vias to minimize stub length.
• Use Reference plane vias to ensure a low inductance path for the return current.

9.2.2 Detailed Design Procedure

The DS100BR111 is designed to be placed at an offset location with respect to the overall channel attenuation. In order to optimize performance, the repeater requires optimization to extend the reach of the cable or trace length while also recovering a solid eye opening. To optimize the repeater in a 10G-KR environment, the settings mentioned in Table 10 (for Pin Mode) and Table 11 (for SMBus Modes) are recommended as a default starting point. For a generic 10GbE application where link training is not required, the following settings in Table 13 and Table 14 may be referenced as an initial starting point:

Examples of the repeater performance are illustrated in the performance curves in the next section.

9.2.3 Application Performance Plots

The lab setups referenced in Figure 10 to Figure 12 were used to collect typical performance data on FR4 and cable media. For all measurements, Mode Pin = Float.

9.2.3.1 Equalization Results (Pre-Channel Only)

No Repeater Used

Figure 13. TL = 5 Inch 4–Mil FR4 Trace,
No Repeater, 8 Gbps

No Repeater Used

Figure 15. TL = 10 Inch 4–Mil FR4 Trace,
No Repeater, 10.3125 Gbps

No Repeater Used

Figure 17. TL = 15 Inch 4–Mil FR4 Trace,
No Repeater, 10.3125 Gbps

No Repeater Used

Figure 19. TL = 20 Inch 4–Mil FR4 Trace,
No Repeater, 10.3125 Gbps

No Repeater Used

Figure 21. TL = 30 Inch 4–Mil FR4 Trace,
No Repeater Used, 10.3125 Gbps

No Repeater Used

Figure 23. TL = 35 Inch 4–Mil FR4 Trace,
No Repeater Used, 10.3125 Gbps

No Repeater Used

Figure 25. TL = 3-Meter 30-AWG 100 Ω Twin-Axial Cable,
No Repeater, 10.3125 Gbps

No Repeater Used

Figure 27. TL = 7-Meter 30-AWG 100 Ω Twin-Axial Cable,
No Repeater, 10.3125 Gbps

No Repeater Used

Figure 29. TL = 10-Meter 30-AWG 100 Ω Twin-Axial Cable,
No Repeater, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x01, DEMA = 000'b,

VOD = 000'b

Figure 14. TL = 5 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x02, DEMA =000'b,

VODA = 000'b

Figure 16. TL= 10 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x03, DEMA = 000'b,

VOD = 000'b

Figure 18. TL = 15 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x07, DEMA = 000'b,

VOD = 000'b

Figure 20. TL = 20 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x0F, DEMA = 000'b,

VOD = 000'b

Figure 22. TL = 30 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x1F, DEMA = 000'b,

VOD = 000'b

Figure 24. TL = 35 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x03, DEMA = 000'b,

VODA = 000'b

Figure 26. TL = 3-Meter 30-AWG 100 Ω Twin-Axial Cable,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x0F, DEMA = 000'b,

VODA = 011'b

Figure 28. TL = 7-Meter 30-AWG 100 Ω Twin-Axial Cable,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x2F, DEMA = 000'b,

VODA = 000'b

Figure 30. TL = 10-Meter 30-AWG 100 Ω Twin-Axial Cable,
DS100BR111 CHA, 10.3125 Gbps

9.2.3.2 Equalization and De-Emphasis Results
(Pre-channel and Post-channel, No Tx Source De-emphasis)

No Repeater Used

Figure 31. TL1 = 15 Inch 4–Mil FR4 Trace,
TL2 = 10 Inch 4–Mil FR4 Trace,
No Repeater, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x0B, DEMA = 010'b,

VOD = 101'b

Figure 32. TL1 = 15 Inch 4–Mil FR4 Trace,
TL2 = 10 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

9.2.3.3 Equalization and De-Emphasis Results
(Pre-channel and Post-channel, -6 dB Tx Source De-emphasis)

No Repeater Used

Figure 33. TL1 = 15 Inch 4–Mil FR4 Trace,
TL2 = 10 Inch 4–Mil FR4 Trace,
No Repeater, 10.3125 Gbps

No Repeater Used

Figure 35. TL1 = 30 Inch 4–Mil FR4 Trace,
TL2 = 10 Inch 4–Mil FR4 Trace,
No Repeater, 10.3125 Gbps

No Repeater Used

Figure 37. TL1 = 40 Inch 4–Mil FR4 Trace,
TL2 = 10 Inch 4–Mil FR4 Trace,
No Repeater, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x00, DEMA = 000'b,

VOD = 011'b

Figure 34. TL1 = 15 Inch 4–Mil FR4 Trace,
TL2 = 10 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x03, DEMA = 010'b,

VOD = 101'b

Figure 36. TL1 = 30 Inch 4–Mil FR4 Trace,
TL2 = 10 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps

DS100BR111 Settings: EQA = 0x03, DEMA = 100'b,

VOD = 101'b

Figure 38. TL1 = 40 Inch 4–Mil FR4 Trace,
TL2 = 10 Inch 4–Mil FR4 Trace,
DS100BR111 CHA, 10.3125 Gbps