Pulse or digital communications – Receivers – Automatic baseline or threshold adjustment
Reexamination Certificate
1998-05-12
2001-01-09
Vo, Don N. (Department: 2734)
Pulse or digital communications
Receivers
Automatic baseline or threshold adjustment
C375S232000, C375S346000, C327S307000
Reexamination Certificate
active
06173019
ABSTRACT:
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the patent and trademark office, patent file or records, but otherwise reserves all copyright rights whatsoever.
This application is submitted with a microfiche appendix containing copyrighted material, copyright 1996, National Semiconductor Corporation. Such appendix consists of 3 microfiche transparencies with a total of 293 frames.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to data receivers for receiving high data rate signals from long lengths of cable, and in particular, data receivers for receiving high data rate, binary or MLT3 encoded data signals from long lengths of cable, while providing signal baseline restoration, adaptive signal equalization and dynamic data signal slicing.
2. Description of the Related Art
Recovering data which has been transmitted over a long length of cable at high rates requires that such data be equalized in order to compensate for the loss and phase dispersion of the cable. Further, in those applications where the cable length may vary, such equalization must be based upon a complementary transfer function which is capable of adapting accordingly since the transfer function of the cable varies with the length of the cable. This type of data recovery is generally done using three functions: a filter function; a dc restoration and slicing function; and an adaptation control, or servo, function.
The filter function is performed using a complementary (with respect to the complex cable loss characteristic) filter which synthesizes the inverse of the transfer function of the cable. Since the bit error rate (BER) is directly related to jitter, an important performance metric for an equalizer is jitter within the output waveform. The extent to which the equalizer is able to match the inverse of the complex cable loss characteristic determines the extent to which inter-symbol interference induced jitter is eliminated.
The dc restoration function is necessary to ensure that the equalized incoming signal is properly centered within the dynamic range of the data recovery system so as to allow for accurate signal slicing. The slicing function is used to extract the data from the equalized signal.
The adaptation control, or servo, function is necessary to ensure that the data recovery system is able to adapt to changes in the incoming data signal, such as increases and decreases in signal amplitude and changes in signal phase, as well as changes in the operating environment.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a control loop for controlling a baseline correction of a data signal includes a baseline correction circuit, a data signal peak detection circuit, a data signal mean detection circuit, a signal processing circuit and a baseline control circuit. The baseline correction circuit is configured to receive and combine a baseline correction signal and an input data signal having a data signal baseline associated therewith and in accordance therewith provide a corrected data signal with a substantially fixed baseline. The data signal peak detection circuit is coupled to the baseline correction circuit and is configured to receive and detect the corrected data signal and in accordance therewith provide a plurality of peak parameter signals which indicates whether the corrected data signal has transcended a plurality of predetermined signal levels including predetermined minimum and maximum signal levels. The data signal mean detection circuit is coupled to the baseline correction circuit and is configured to receive and detect the corrected data signal and in accordance therewith provide a first baseline parameter signal which indicates whether the corrected data signal is within a predetermined range of values intermediate to the predetermined minimum and maximum signal levels, and provide a second baseline parameter signal which indicates a polarity of the corrected data signal relative to a measured mean value of the corrected data signal. The signal processing circuit is coupled to the data signal peak detection circuit and is configured to receive and process the plurality of peak parameter signals and in accordance therewith provide a third baseline parameter signal which indicates a difference between the corrected data signal and the measured mean value of the corrected data signal. The baseline control circuit is coupled to the data signal mean detection circuit, the signal processing circuit and the baseline correction circuit, and is configured to receive and process the first, second and third baseline parameter signals and in accordance therewith provide the baseline correction signal.
In accordance with another embodiment of the present invention, a method of controlling a baseline correction of a data signal with a control loop includes the steps of:
receiving and combining a baseline correction signal and an input data signal having a data signal baseline associated therewith and in accordance therewith generating a corrected data signal with a substantially fixed baseline;
detecting the corrected data signal and in accordance therewith generating a plurality of peak parameter signals which indicates whether the corrected data signal has transcended a plurality of predetermined signal levels including predetermined minimum and maximum signal levels;
detecting the corrected data signal and in accordance therewith generating a first baseline parameter signal which indicates whether the corrected data signal is within a predetermined range of values intermediate to the predetermined minimum and maximum signal levels, and generating a second baseline parameter signal which indicates a polarity of the corrected data signal relative to a measured mean value of the corrected data signal;
processing the plurality of peak parameter signals and in accordance therewith generating a third baseline parameter signal which indicates a difference between the corrected data signal and the measured mean value of the corrected data signal; and
processing the first, second and third baseline parameter signals and in accordance therewith generating the baseline correction signal.
These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.
REFERENCES:
patent: 3851266 (1974-11-01), Conway
patent: 4575683 (1986-03-01), Roberts et al.
patent: 5844941 (1998-12-01), Mack et al.
patent: 5940442 (1999-08-01), Wong et al.
Hee Wong
Phanse Abhijit
Baker & MacKenzie
National Semiconductor Corporation
Phu Phuong
Vo Don N.
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