Impulse Noise Measurement Test Setup

Transcription

1 Impulse Noise Measurement Test Setup 1/27/2015 Ramin Shirani Larry Cohen

2 Impulse Noise Problem Overview Problem: Impulse noise events in the enterprise environment may degrade the operational BER of otherwise compliant NGBase-T links to unacceptable levels Impulse noise effects in the enterprise environment on systems with bandwidth beyond 1000Base-T are not fully understood What we already know 10GBase-T is mainly deployed in the data center environment so the existing knowledge base is not fully applicable to the enterprise environment 1000Base-T equipment is known to operate properly in the enterprise environment First step: Create a test setup to capture, record, and analyze the characteristics of impulse noise waveforms in the enterprise environment and measure the important characteristics that could affect NGBase-T link quality Frequency of occurrence (inter-arrival time) Signal bandwidth and the effect of AFE lowpass filtering Common-mode and differential-mode waveforms (peak-to-peak voltage) induced in cabling; main interest is worst-case differential waveforms Determine relative susceptibility of different cable and connector categories 1/27/2015 2

3 Impulse Noise Measurement Considerations Instrumentation must be placed at multiple locations to obtain a valid (and useful) noise profile of the enterprise environment Example location #1: Wired port in an office bullpen cubicle Lots of human activity in an area with no ESD mitigation Potential for lots of ESD induced impulse noise events near LAN ports Additional potential for on/off switch arc transient induced impulse noise events Example location #2: Wireless access point placement Less nearby human activity; potentially less ESD events Potential for on/off switch arc transient induced impulse noise events Relevant for all locations How bad is the impulse noise produced from office HVAC equipment? Are there additional unexpected noise sources picked up due to cable routing (floor and/or ceiling) and other office equipment? 1/27/2015 3

4 Impulse Noise Event Capture Test Setup #1 Control Computer (PC with GPIB) GPIB 100 Differential-mode and Commonmode for all four pairs CM-DM Block L (1 to 10 meters) Optional Keystone or inline connector This is the receive "antenna" Cable channel under test (Cat 5e/6/6a UTP) All unused pairs terminated with Shielded -to-sma Breakout/ Board 0-degree splitter for common-mode Digital Storage Oscilloscope Scope channel should have at least 500 MHz bandwidth, 2 Gsps sampling rate, and samples memory capture depth (5 usec time span) LNA is mainly required to capture low-level differential-mode waveforms Lowpass filter simulates effect of AFE and adds additional anti-alias filtering Impulse capture threshold controlled by scope trigger level Captured impulse waveforms recorded on control computer for later analysis Proper site placement of noise survey instrumentation is critical to gathering valid data Power Splitter 180-degree splitter for differential-mode +20 db Gain LNA Low-pass filter (f 3dB = 200 MHz to 400 MHz) 1/27/2015 4

5 Impulse Noise Event Capture Test Setup #2 100 Differential-mode and Commonmode for all four pairs L (1 to 10 meters) This is the receive "antenna" All unused pairs terminated with Control Computer (PC with GPIB) GPIB CM-DM Block Optional Keystone or inline connector Cable channel under test (Cat 5e/6/6a UTP) Shielded -to-sma Breakout/ Board Matched coaxial cable pair CH1 CH2 Digital Storage Oscilloscope Captures both common-mode and differential mode impulses simultaneously, but requires better scope with more bandwidth, memory depth, and sensitivity Scope channels should have at least 1 GHz MHz bandwidth, 5 Gsps sampling rate, and samples memory capture depth (5 usec time span) Use post-processing of captured waveforms to generate common-mode and differential mode impulse noise events and simulate any AFE lowpass filtering Scope vertical sensitivity may limit resolution of differential-mode waveforms Impulse capture threshold controlled by scope trigger level 1/27/2015 Impulse noise in the enterprise environment 5

6 Design of CM-DM Block Block (R DM = 100 R CM = 50 Edge of connector enclosure should be at the edge of the board. Pair 1 Proposed symmetrical PCB layout of resistors to preserve termination balance. 1 Via to ground Shielded Connector Pair 2 Pair 4 Resistor values: = /- 0.1% = /- 1% 8 Use "tab up" jack Pair 3 All signal traces are 100 Ohms (+/- 10%) weakly coupled matched differential pairs, and all are the same length. 1/27/2015 6