Active Cabling Specifications - SFP+ Active Cable Specifications and Alternate Test Methods

SFF Committee
SFF-8461 Specifications for SFP+ Active Cable Specifications and Alternate Test Methods —— Chapter 2 Active Cabling Specifications

Chapter 2        Active Cabling Specifications
2.1Introduction.....................................................................................................................................3
2.2Cable Applications Reference Model........................................................................................3
2.310GSFP+Ac Direct Attach Construction....................................................................................3
2.4SFP+ ACTIVE CABLE HIGH-SPEED ELECTRICAL SPECIFICATION.................................4
2.5SFP+ ACTIVE CABLES TYPE I (FOR OPERATION WITH A LIMITING HOST)....................5
2.6SFP+ ACTIVE CABLES TYPE II...................................................................................................5
Table 2See D.7 in SFF-8431.............................................................................................................6

2.1 INTRODUCTION

High speed cabling specifications are based on SFI signalling as defined in SFF-8431 supporting either a limiting or linear host. Active cable assemblies may be used to provide operation over longer or thinner cables than achievable with direct attach copper assemblies. This section defines electrical specification and compliance testing methodology for such assemblies.

2.2 CABLE APPLICATIONS REFERENCE MODEL

A compliant active cable assembly is designated as 10GSFP+ACA and it can be identified by reading the memory map of SFF-8472.

The compliance points for SFP+ Active Cables(10GSFP+ACA) are the same as host compliance test points in 3.3.1 and the module compliance test points in 3.3.2 of SFF-8431.

All SFI test equipment must have 50 Ohms single ended impedance on all test ports.

Tx_Disable contacts in the module for cable assembly with active transmitter shall enable or disable the transmitter. For a passive assembly it shall be pulled to VccT with a 4.7 k? to 10 k?. The RX_LOS contact in the module for a cable assembly with active receiver shall be connected to the receiver IC loss of signal. A passive cable assembly RX_LOS contact shall be pulled low in the module. Direct connection of RX_LOS to VeeR is allowed for a cable assembly with passive receiver.

This specification does not assume transmit pre-emphasis beyond the level defined in SFF-8431.

Warning: 10GSFP+Cu can only be used on systems with common grounds. Connecting systems with different ground potential with SFP+ direct attach cable results in a short and may cause damage.

2.3 10GSFP+AC DIRECT ATTACH CONSTRUCTION

10GSFP+ACA SFP+ active cable assemblies could be copper or optical, providing either a linear or a limiting output. While particular implementations are not specified by this standard, it is expected that SFP+ Active Cables operate with either linear or limiting hosts as defined in section X.2.

An example of active cable assembly with active transmitter is shown in Figure 1. The cable assembly shown has an active transmitter and active receiver. Other implementation possible are active-passive and passive-active. The cable assembly shall incorporate DC blocking capacitors with at least 4.3 V rating between any signal commissioning IC and the SFP+ edge card connector1. The DC blocking capacitor shall have high pass pole of between 20 kHz and 100 kHz. For a copper cable assembly, the drain wire is connected to VeeT and to VeeR and the cable shield directly connects the module A and B cases.

2.4 SFP+ ACTIVE CABLE HIGH-SPEED ELECTRICAL SPECIFICATION

This section defines the high-speed electrical specification for implementations with limiting or linear outputs. Active Cables designed to operate with limiting hosts are broadly defined as Type I, while Active Cables designed tooperate with linear Hosts are broadly defined as Type II. The test setup for both Type I and Type II Active Cables is shown in Figure 2.

2.5 SFP+ ACTIVE CABLES TYPE I (FOR OPERATION WITH A LIMITING HOST)

SFP+ Active Cable’s Type I are assemblies that operate with the SFP+ limiting hosts defined in Chapter 3 of SFF-8431. Specifically, the active cable input must satisfy the SFP+ module transmitter input specifications at B’ in Table 16 of SFF-8431 and tolerance specifications at B” in Table 17 of SFF-8431. The active cable output must satisfy the SFP+ Limiting Module Receiver Output Electrical Specifications at C’ in Table 18 of SFF-8431and the SFP+ Limiting Module Receiver Output Jitter and Eye Mask Specifications Table 19 of SFF-8431. These output specifications must be met with worst case input allowed by Table 16 and Table 17 of SFF-8431.

2.6 SFP+ ACTIVE CABLES TYPE II

SFP+ Active Cables Type II are cables that operate with the linear hosts defined in Chapter 3 of SFF-8431. To ensure this, SFP+ Active Cables Type II must comply with the following specifications. The active cable input must satisfy the SFP+ module transmitter input specifications at B’ in Table 16 of SFF-8431 and tolerance specifications at B” in Table 17 of SFF-8431. The output at C’ of Active Cables Type II must satisfy the requirements of Table 18 of SFF-8431. In addition, it must meet the specifications in Table 2.

S-Parameters test method is an alternate method of calculating 10GSFP+Cu cable parameters for passive cable assembly. The advantage of the S-parameters method is that it can give consistent results without requiring extensive adjustment to the SerDes driver. This method gives equivalent result to direct measurement of cable dWDP, VMA loss, and VCR per definition of SFF-8431 Appendix E.4.
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