Pulse or digital communications – Equalizers – Automatic
Utility Patent
1998-03-19
2001-01-02
Bocure, Tesfaldet (Department: 2731)
Pulse or digital communications
Equalizers
Automatic
C333S018000, C333S02800T
Utility Patent
active
06169764
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to data communication circuitry, and in particular to an adaptive line equalizer circuit that is particularly suited for high speed, low power data communication.
In high-speed data communication, such as Fast Ethernet (e.g. 100BASE-T), the mere filtering of the receive signal (to remove unwanted noise and other corruptive signals) is not sufficient for recovering the data with small bit error rate (BER). In the case of 100BASE-T communication, for example, dispersion-loss of the cable is linearly proportional to the cable's length and square-root of the data rate. A cable equalizer circuit is therefore necessary in order to compensate for the cable's losses and to improve the inter-symbol interference (ISI) of the received data. The function of the equalizer is to synthesize a frequency response that is inversely proportional to that of the cable's. When using an adaptive equalizer there is an added advantage in that it enables the receiver to handle variable cable lengths without significantly altering the ISI of the recovered data. Depending on the required degree of cable loss, compensation over different cable lengths and frequency bandwidths, first or second order high-pass filtering is required.
Conventional prior art adaptive equalizers have typically used peak detection circuitry to detect the level (or strength) of the received signal at the input of the slicing comparator. The peak detection approach, however, is highly susceptible to jitter, which results in increased bit error rate (BER) for the adaptive equalizer at higher data transmission rates. An improved adaptive equalizer architecture based on a high speed bipolar implementation was proposed by Alan J. Baker in “An Adaptive Cable Equalizer for Serial Digital Video Rates to 400 Mb/s,” 1996, IEEE Int'l Solid-State Circuits Conf., p. 174. Baker's adaptive equalizer applies the signal to a slicing comparator after some initial high-pass filtering. The slope of the comparator input signal is adjusted against that of the comparator output signal by means of a servo loop involving the input high-pass filter. By incorporating a two-stage quantized feedback comparator this circuit can handle base-line wander problem that is common to those data communication standards that allow long consecutive identical digits.
While Baker's approach improves the performance of the adaptive equalizer, it's implementation requires a fast bipolar/CMOS (BiCMOS) process running with a 5 volt power supply. Baker's equalizer is therefore more costly to fabricate and consumes more power.
There is a need for an improved adaptive equalizer that can be implemented in a cost-efficient manner and with reduced power consumption.
SUMMARY OF THE INVENTION
The present invention provides a low cost and low power adaptive cable equalizer that is particularly suitable for fast Ethernet data communication. In a specific embodiment, the present invention implements an adaptive equalizer using CMOS continuous-time analog signal processing, with variable resistors, linear capacitors and high-speed operational amplifiers. First, second and higher order adaptive equalizers can be implemented using the teachings of the present invention.
Accordingly, in one embodiment, the present invention provides an adaptive line equalizer including a high-pass filter having an input terminal coupled to receive an input signal, a slicing comparator having an input terminal coupled to the output terminal of the high-pass filter, and a servo control block having a first input coupled to the input of the comparator and a second input coupled to the output of the comparator, and an output coupled to a control input of the high-pass filter, wherein, the servo control block further comprises a squaring circuit. IN a preferred embodiment, the various elements of the adaptive equalizer are implemented with fully differential architecture.
A better understanding of the nature and advantages of adaptive cable equalizer of the present invention may be had with reference to the detailed description and drawings below.
REFERENCES:
patent: 4607231 (1986-08-01), Nakayama
patent: 5481564 (1996-01-01), Kakuishi et al.
patent: 5708703 (1998-01-01), Nagaraj
patent: 5764695 (1998-06-01), Nagaraj et al.
patent: 5978417 (1999-11-01), Baker et al.
Bocure Tesfaldet
Plato Labs, Inc.
Townsend and Townsend / and Crew LLP
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