US3798576A
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US
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Automatic equalization method and apparatus
Assignee: Xerox Corp
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Filing: 1971-12-30
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Granted: 1974-03-19
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Expires: 1991-12-30
Abstract
Abstract This invention relates to a method of and an apparatus for providing equalization to frequency dependent delay and amplitude distortions in a transmission line. The apparatus includes an adjustable equalizer having a plurality of delay networks, an amplifier, a peak-to-average difference detector, and a control logic for selectively switching the delay networks and amplifier into and out of the path for the incoming signal. Adjustment of the equalizer to a given transmission line is carried out under the control of the control logic and in response to peak-toaverage difference signals supplied by the detector. To that end, a train of test pulses is transmitted to the equalizer via the transmission line, and the delay networks and amplifier are selectively switched into and out of the signal path in timed synchronism with successive ones of those pulses, thereby providing different combinations of phase and/or amplitude compensation for such pulses. The peak-to-average difference detector responds to the compensated pulses to identify the particular delay network or delay network/amplifier combination that best compensates for the distortion introduced by the transmission line, and the control logic locks that combination into the signal path. In the case where the equalizer is used in an FM transmission system, it is interposed between the transmission line and the FM demodulator so that the equalization takes place prior to the recovery of the demodulated baseband signal.
Inventors
- 👤 J Torpie
- 👤 A Bell
- 👤 M Gorham
- 👤 W Keating
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 07:59
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/04; H04B3/14; H04B3/141; H04B3/146; H04B3/148; H04B3/46; H04B3/462
Claims Analysis
Total Claims: 37
Claim 1
Independent Claim
83 words
An adjustable equalizer for use in a receiving means of a transmission system for correcting frequency dependent distortion introduced into the incoming signal pulses by the transmission medium, comprising: an adjustable equalization means including a plurality of allpass delay networks having different delay versus frequency characteristics; and control means for selecting and identifying a particular combination of said delay networks which provides best equalization and enabling said adjustable equalization means to insert said particular combination into the path of the incoming signal pulses.
Claim 2
Dependent Claim
83 words
An adjustable equalizer for use in a receiving means of a transmission system for correcting frequency dependent distortion introduced into the incoming signal pulses by the transmission medium, comprising: an adjustable equalization means including a plurality of allpass delay networks having different delay versus frequency characteristics; and control means for selecting and identifying a particular combination of said delay networks which provides best equalization and enabling said adjustable equalization means to insert said particular combination into the path of the incoming signal pulses.
Claim 3
Dependent Claim
98 words
The equalizer according to claim 1 wherein said control means includes: means for sequentially inserting different combinations of said delay networks in different combinations into a path provided for the incoming signal pulses; means for determining the amounts of distortion of the signals caused by the insertion of each of said combinations and for generating separate output signals indicating the amount of distortion caused by each of said combinations; means for selecting the one distortion indicating signal which represents the least amount of distortion to thereby identify the particular combination of delay networks which provides the best equalization.
Claim 4
Dependent Claim
50 words
The equalizer according to claim 1, including means for detecting a mode identifying signal from the received signal, and means responsive to said mode identifying means for enabling said control means to insert particular ones of delay networks that provide a fixed delay versus frequency characteristics without the selection process.
Claim 5
Dependent Claim
39 words
The equalizer according to claim 1 including, at least one frequency dependent amplifier, means for selectively inserting said amplifier into the path of the incoming signal to equalize substantially the frequency dependent amplitude attenuation introduced by the transmission medium.
Claim 6
Dependent Claim
25 words
The equalizer according to claim 4 said control means and said switching means are arranged to connect said amplifier and said delay networks in parallel.
Claim 7
Dependent Claim
38 words
The equalizer according to claim 4, including a plurality of switching means for use by said control means in inserting said amplifier and said plurality of delay networks in different combinations into the path of the incoming signals.
Claim 8
Dependent Claim
25 words
The equalizer according to claim 6, wherein said switching means includes a pair of field effect transistors arranged in a single throw double pole configuration.
Claim 9
Dependent Claim
25 words
The equalizer according to claim 6, said control means and said switching means are arranged to connect said amplifier and said delay networks in series.
Claim 10
Dependent Claim
52 words
The equalizer according to claim 1, wherein said distortion measuring means includes means for comparing the peak values of the distorted wave to its DC average value and for generating a DC voltage representing the difference between the peak values and the DC average value as a measure of the delay distortion.
Claim 11
Dependent Claim
73 words
The equalizer according to claim 9 wherein said means for determining the amount of distortion includes means for detecting and producing a positive peak value, a negative peak value, and an average value from said distorted signal, and means for producing a peak-to-average difference from said positive and negative peak values and said average value, with the peak-to-average difference representing the positive peak value, less the negative peak value and the average value.
Claim 12
Dependent Claim
126 words
An adjustable equalizer for use in a transmission system for correcting the incoming sequence of pulses in series subjected to frequency dependent distortions by the transmission medium, comprising: a plurality of delay networks having different delay versus frequency characteristics; means for inserting a plurality of different combinations of said delay networks in succession into the path of the incoming signal in synchronization therewith; means for obtaining a measure of the amount of the frequency dependent distortions introduced by said plurality of different combinations of delay networks in series with the transmission medium; and means for selecting a combination of said delay networks which provide least amount of frequency dependent distortions and latching said combination into the path of the incoming signal for providing an optimum equalization.
Claim 13
Dependent Claim
126 words
An adjustable equalizer for use in a transmission system for correcting the incoming sequence of pulses in series subjected to frequency dependent distortions by the transmission medium, comprising: a plurality of delay networks having different delay versus frequency characteristics; means for inserting a plurality of different combinations of said delay networks in succession into the path of the incoming signal in synchronization therewith; means for obtaining a measure of the amount of the frequency dependent distortions introduced by said plurality of different combinations of delay networks in series with the transmission medium; and means for selecting a combination of said delay networks which provide least amount of frequency dependent distortions and latching said combination into the path of the incoming signal for providing an optimum equalization.
Claim 14
Dependent Claim
165 words
The equalizer according to claim 11, further including switching means interposed between different pairs of said delay networks, a demodulator interposed between the output of the delay networks and an output utilization means, means connected to said demodulator for deriving a carrier detection signal in response to said signal pulses for successively actuating the said switching means in different combinations in synchronization with said pulses to thereby enable said inserting means to set said different combinations of said delay networks into the path of the incoming signal pulses, said distortion measuring means includes means for producing peak-to-average difference signals giving a measure of the amount of distortion of the pulses from the output of said demodulator in terms of the delay characteristics of the transmission introduced by said different combinations of the delay networks combination and the transmission line; and said selecting means includes a comparator for comparing the successive distortion level indicating signals to identify the one which indicates a minimum amount of distortion.
Claim 15
Dependent Claim
63 words
The equalizer according to claim 11 further including means for indicating a condition of the transmission system requiring elimination of the selection operation and means interposed between said condition indicating means and said selection means for disabling said selection means and for inserting a predetermined combination of said delay networks into the path of incoming signal pulses upon the occurrence of said condition.
Claim 16
Dependent Claim
26 words
The equalizer according to claim 11 including means for reducing the number of different combinations of said delay networks being selectively interposed in the incoming path.
Claim 17
Dependent Claim
23 words
The equalizer according to claim 11 including means for selectively inserting at least one frequency dependent amplifier in series with said delay networks.
Claim 18
Dependent Claim
30 words
The equalizer according to claim 11 means for inserting a predetermined combination of frequency dependent amplifier and delay networks selectively and permanently in the path of the incoming signal pulses.
Claim 19
Dependent Claim
34 words
The equalizer according to claim 11 wherein said equalizer is interposed between a frequency demodulator and a transmission medium for providing equalization prior to demodulation of a frequency modulated incoming train of signal pulses.
Claim 20
Dependent Claim
28 words
The equalizer according to claim 11 further including means for inserting a predetermined combination of delay networks into said signal path when said selection means fails to function.
Claim 21
Dependent Claim
33 words
The equalizer according to claim 11, wherein said distortion measuring means includes means for deriving voltages substantially proportional to the level of the distortions introduced by said different combinations of said delay networks.
Claim 22
Dependent Claim
63 words
The equalizer according to claim 19 wherein the distortion measuring means includes means for detecting the positive and negative peak and DC average values of the signal pulses after distortion by the corresponding ones of the delay network combinations, and means for deriving a peak-to-average difference signal by subtraction of the negative peak value and the average value from the positive peak value.
Claim 23
Dependent Claim
60 words
The apparatus according to claim 11 wherin said selection means includes logic conTrol circuitry adapted to enable said distortion measuring means and said selecting means to complete selection function during a single cycle of time duration during which a number of said signal pulses corresponding to the number of different combinations of said delay networks are applied thereto in succession.
Claim 24
Dependent Claim
81 words
The equalizer according to claim 21 wherein said distortion level indicating means includes means for detecting voltage outputs substantially inversely proportional to the level of distortion provided by corresponding combinations of delay networks and transmission; said selection means includes means for storing the largest voltage in response to enabling signals from said logic control circuitry; and said logic circuitry includes means responsive to the largest output of said selection means for latching selected ones of switches into the incoming signal path.
Claim 25
Dependent Claim
136 words
The equalizer according to claim 21 wherein said distortion measuring means includes means for generating successive peak-to-average difference signals including means for generating the positive and negative peak value, and the DC average value of the distorted pulse from the outputs of the corresponding combinations of delay networks, said selection means including storage means and comparing means: said logic control circuitry compares subsequent peak-to-average signals means with a prior peak-to-average signal stored in said storage means to detect any peak-to-average signal which equals or exceeds the stored peak-to-average signal; and said logic circuitry including a temporary buffer for storing in said storage means the last detected peak-to-average signal representing the combination of delay networks which provides the best equalization, and means for latching said combination into the incoming signal path at the end of the cycle.
Claim 26
Dependent Claim
132 words
The equalizer according to claim 23 wherein said logic circuitry is adapted to enable said delay distortion measuring means to generate peak-to-average signals for different combinations of delay networks during each of two successive cycles pulses ariving in series and storing, said storage means stores the maximum peak-to-average signal reading derived during the first cycle, and said comparing means compares the stored peak-to-average signal reading with each of the peak-to-average signals provided during the second cycle to generate a selection signal when a PAD reading of the second cycle equals or exceeds the stored PAD reading, and said logic circuitry includes means responsive to said selection signal from said comparator for activating selected combinations of said switches to interpose selected combinations of said delay network into the path of the incoming signals.
Claim 27
Independent Claim
76 words
A method of equalizing frequency dependent delay distortion introduced to incoming signal pulses by a transmission medium comprising the steps of: passing said signal pulses through different combinations of a plurality of networks having different delay versus frequency and attenuation versus frequency characteristics, selecting as a preferred combination the combination of networks which results in the least amount of frequency dependent distortion, and inserting said preferred combination of networks into the path of the incoming signal.
Claim 28
Independent Claim
76 words
A method of equalizing frequency dependent delay distortion introduced to incoming signal pulses by a transmission medium comprising the steps of: passing said signal pulses through different combinations of a plurality of networks having different delay versus frequency and attenuation versus frequency characteristics, selecting as a preferred combination the combination of networks which results in the least amount of frequency dependent distortion, and inserting said preferred combination of networks into the path of the incoming signal.
Claim 29
Dependent Claim
55 words
The method according to claim 25 including the steps of detecting a mode identifying signal indicating that the selection steps are unnecessary, and bypassing said selection steps and inserting a combination of networks having a predetermined delay versus frequency and attenuation versus frequency characteristics into the signal path in response to such a mode signal.
Claim 30
Dependent Claim
33 words
The method according to claim 25 including the steps of inserting at least one frequency dependent amplitude shaping network in the path of the incoming signal in combination with said selected delay networks.
Claim 31
Dependent Claim
33 words
The method according to claim 25 wherein a selected combination of delay networks and amplitude shaping networks are inserted in parallel between the transmission medium and a receiving means to provide the equalization.
Claim 32
Dependent Claim
69 words
The method according to claim 25 wherein the preferred combination is selected by passing separate pulses through the different combinations of networks to derive a series of signals individually indicative of the distortion resulting from different ones of said combinations, and then sensing a peak-to-average difference for each of said distortion indicative signals to identify the combination which results in the least amount of distortion of the received signal.
Claim 33
Dependent Claim
47 words
The method according to claim 29 wherein said peak-to-average differences are obtained by deriving from each of said distortion indicative signals a positive peak value and a DC average value and by then subtracting the negative peak value and the average value from the positive peak value.
Claim 34
Dependent Claim
28 words
The method according to claim 30 wherein said combinations are sequentially inserted in synchronization with said pulses into the incoming signal path to derive said distortion indicative signals.
Claim 35
Dependent Claim
69 words
The method according to claim 31 wherein the combination which results in the least amount of distortion is selected within a single cycle by comparing each succeeding peak-to-average difference against the preceding peak-to-average difference of greatest amplitude storing the peak-to-average difference of greatest amplitude until the end of the cycle, and then inserting into the signal path the combination of networks which provided the peak-to-average difference of greatest amplitude.
Claim 36
Dependent Claim
84 words
The method according to claim 31 wherein the combination which results in the least amount of distortion is selected in two cycles by storing the maximum peak-to-average difference obtained during the first cycle, successively comparing the stored peak-to-average difference against separate peak-to-average differences derived during the second cycle to identify any of the second cycle derived peak-to-average differences which equals or exceeds the stored peak to average difference, and latching into the signal path a delay network combination which yields an identified peak-to-average difference.
Claim 37
Dependent Claim
57 words
The method according to claim 33 further including the steps of detecting any failure to identify during the second cycle a peak-to-average signal difference equal to or exceeding the stored peaked to average signal difference, and inserting a network having a predetermined delay versus frequency characteristic into the signal path in the event of such a failure.
References Cited (Backward Citations)
US3670269A
Cited
US3665171A
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-03-18 | 1977-09-17 | 1978-03-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-03-18 | 1981-09-17 | 1982-03-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-03-18 | 1985-09-17 | 1986-03-19 | $7700.00 | Window Closed / Lapsed |