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High Speed Equalizer Circuits

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  1. High Speed Equalizer Circuits ECE1352 Jenkin Wong November 28, 2003

  2. Agenda Background • Why Equalize? Equalization for 100Base-TX Ethernet • Introduction • Define Problem • Proposed Solution Jenkin Wong

  3. Background Why Equalize? • Non-ideal Channel • In frequency domain – Amplitude and Phase attenuation • In time domain – Intersymbol Interference (ISI) Maximize Data Rate on a Bandlimited Channel Jenkin Wong

  4. Equalizer for 10Mb/s and 100Mb/s Ethernet Background • A CMOS Transceiver for 10Mb/s and 100Mb/s Ethernet by Everitt, Parker, Hurst, Nack and Konda • Uses an Adaptive • Equalization scheme • implemented in the • analog domain • MLT3 Encoding • for 100Base-TX Focus on 100Base-TX Jenkin Wong

  5. Equalization for 100Base-TX What are the problems? • Attenuation vs. Frequency characteristic of the CAT-5 Cable, • At 62.5MHz, 18dB loss after 100m of cable • Baseline Wander • Worst case is when 56 consecutive zeros (max), followed by 4 ones • DC Insertion Loss of Cable • 2dB for 100m cable Jenkin Wong

  6. Equalization for 100Base-TX Solution • Adaptive Equalizer - Analog Implementation • Combines a coarse ADC and digital algorithms based on signal statistics to achieve equalization Jenkin Wong

  7. Equalization for 100Base-TX Equalization Control • Over-equalized – overshoot at each symbol transition • Under-equalized – Too much high frequency Attenuation Jenkin Wong

  8. Equalization for 100Base-TX Gain and DC wander Control • Too much Gain – always +1 error • Not enough Gain – always –1 error Jenkin Wong

  9. Equalization for 100Base-TX Adaptive Equalizer Block • Implementation issues • Position of Zero and Poles • Range of Gm • Controlling R Digital Logic will Tune Gm1 and Gm2 Jenkin Wong

  10. Equalization for 100Base-TX Transconductance Cell • Used in both the tuning PLL and the LPF • Bias for the LPF Gm cell is copied from the Gm-C cells inside PLL • R = 1/Gm Jenkin Wong

  11. Equalization for 100Base-TX Wander Cancellation Cell • Digital logic controls the charge pump changing the current Icp • Voltage I*R is add to cancel the DC wander Jenkin Wong

  12. Equalization for 100Base-TX Equalization performance at 100m The Eye is opened Jenkin Wong

  13. Equalization for 100Base-TX Performance Summary Equalization works! Jenkin Wong

  14. Equalization for 100Base-TX Conclusion • Crash course on Equalization • Analog Implementation of a High Speed adaptive equalization scheme for 100 Base-TX • Equalization is one of the many keys to reliable high speed digital data communication • ECE1392 – IC for Digital Communication • Q&A Jenkin Wong

  15. Equalization for 100Base-TX References • A CMOS Transceiver for 10Mb/s and 100Mb/s Ethernet by Everitt, Parker, Hurst, Nack and Konda • A Mixed-Signal Tuning Loop for Variable Bandpass Filter, A Final Report by Wee-Guan Ben Tan, EE, University of California • Slides from Research Overview in Analog IC Design by Prof. Phillip E. Allen, ECE Georgia Institute of Technology • Notes from Analog versus DSP for Disk Drive by Prof. Richard Spencer, University of California Jenkin Wong