100 Gb/s Ethernet 100GBASE-CR4 practical implementation of testing the receiver, transmitter, and cable assembly parameters at their compliance test points

摘要

Ethernet physical layer specifications, referred to as PHY specifications, contain the types of transmitters and receivers and the functions that translate the data into signals (encoding), which are compatible with the link segment specification. The portion of the physical layer responsible for interfacing to the transmission medium is called the Physical Medium Dependent layer (PMD). 100GBASE-CR4 PMD is an Ethernet port type supporting a signaling rate of 25.78125 GBd on four lanes of twinaxial copper cable assemblies achieving 100 Gb/s transmission with a reach of up to at least 5 meters. In prior generations of Ethernet copper port types (e.g., 1000BASE-T, 10GBASE-T), the Medium Dependent Interfaces (MDIs) are specified but the mechanism of testing the physical media signals at the MDI were not addressed leaving the details to the implementer. The inclusion of test points and test fixtures represent a milestone in the testability of Ethernet physical layer signals for conformance to the standard and a precursor to enabling interoperability between multivendor equipment. This paper will provide a detailed technical overview and the practical implementation of testing the 100GBASE-CR4 receiver and transmitter at their compliance test points utilizing test fixtures (i.e., Module and Host Compliance Boards) verified to the test fixture specifications. An implementation of cable assembly testing is provided figuratively. This paper is a follow-on to the DesignCon 2015 paper "100 Gb/s Ethernet 100GBASE-CR4 Test Points and Test Fixtures" that details the validation of the 100GBASE-CR4 test fixture specifications to implement the testing of the transmitter, receiver and copper cable assemblies. Test methodology and test equipment will be described and illustrated for: 1. Transmitter parameters: differential and common mode voltages, return loss, transmitted waveform characteristics, linear fit pulse peak and associated coefficients, signal-to-noise-and-distortion ratio and jitter. 2. Receiver parameters; receiver input amplitude tolerance, return loss and interference tolerance. Specification parameters and illustrations will be provided for: 1. Compliance test fixtures specified in a mated state. 2. Cable assembly. 3. Channel Operating Margin (COM).