High Speed Equalizer Circuits
ECE1352Jenkin Wong
November 28, 2003
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AgendaBackground
• Why Equalize?
Equalization for 100Base-TX Ethernet• Introduction• Define Problem• Proposed Solution
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Why Equalize?• Non-ideal Channel• In frequency domain – Amplitude and Phase
attenuation• In time domain – Intersymbol Interference (ISI)
Background
Maximize Data Rate on a Bandlimited Channel
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Equalizer for 10Mb/s and 100Mb/s EthernetBackground
• 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 Encodingfor 100Base-TX
Focus on 100Base-TX
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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
f
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Equalization for 100Base-TXSolution
• Adaptive Equalizer - Analog Implementation Combines a coarse ADC and digital algorithms
based on signal statistics to achieve equalization
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Equalization for 100Base-TX
Equalization Control
• Over-equalized – overshoot at each symbol transition
• Under-equalized – Too much high frequency Attenuation
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Equalization for 100Base-TX
Gain and DC wander Control
• Too much Gain – always +1 error• Not enough Gain – always –1 error
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Equalization for 100Base-TXAdaptive Equalizer Block
• Implementation issues Position of Zero and Poles Range of Gm Controlling R
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Digital Logic will Tune Gm1 and Gm2
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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
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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
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Equalization for 100Base-TX
Equalization performance at 100m
The Eye is opened
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Equalization for 100Base-TX
Performance Summary
Equalization works!
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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
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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
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