FAST START-UP SYSTEM FOR TRANSVERSAL EQUALIZERS

• US 3,715,666 A
• Filed: 03/30/1971
• Issued: 02/06/1973
• Est. Priority Date: 03/30/1971
• Status: Expired due to Term

• Current Assignee: David Adams Spaulding, Kurt Hugo Mueller
• Original Assignee: David Adams Spaulding, Kurt Hugo Mueller
• Inventors: Mueller, Kurt Hugo, Spaulding, David Adams
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US05/129,328
• Time in Patent Office: 679 Days
• Field of Search: 325/42,65 178/69R,69.5R 179/170.2 328/165 333/17,18
• US Class Current: 375/231
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

Initial convergence of automatic transversal equalizer tap gain settings is rapidly achieved without first establishing synchronization between a test signal incoming at a receiving location over a distorting transmission channel and a locally generated ideal reference signal. Identical periodic digital patterns of fixed length equal to the number of taps available on the equalizer comprise the respective test and reference signals. Error signals obtained from a comparison of test and reference signals at an arbitrary speed which need not be related to the data rate assigned to the transmission channel are correlated with tap signals to obtain a sequence of coarse tap gain coefficients. Just prior to message data transmission this sequence is cyclically shifted with respect to the tap locations to align the highest of them at an assigned reference location.

Claims

1. In combination with a distorting transmission medium and a synchronous data transmission system a transversal equalizer having a delay line portion with equally spaced taps therealong, an adjustable attenuator for each such tap including a reference tap, and a summing circuit for selectively attenuated tap outputs:

means for achieving fast initial adjustment of said attenuators from a preset substantially equal value condition comprising matching pseudorandom word generators associated respectively with the transmitting end of said medium and with said equalizer, the number of bits in each pseudorandom word being identical and equal to the number of taps on said delay line, means for comparing the output of said summing circuit with said matching word in the output of the generator associated with said equalizer to derive an error signal, means for correlating said error signal with signals at the inputs to said attenuators for establishing an order set of gain coefficients for said attenuators, mean for measuring the largest of said gain coefficients, and means for cyclically shifting said gain coefficients to align the largest such coefficient with said reference tap.

2. The combination defined in claim 1 in which said circulating means comprises a plurality of synchronized switches for group sequentially connecting each of the taps on said delay line to said adjustable attenuators.

3. In combination with a distorting transmission medium and a synchronous data transmission system a transversal equalizer having a delay line portion with equally spaced taps therealong, an adjustable attenuator for each such tap including a reference tap, and a summing circuit for selectively attenuated tap outputs:

means for achieving fast initial adjustment of said attenuators comprising matching pseudorandom word generators associated respectively with the transmitting end of said medium and with said equalizer, the number of bits in each pseudorandom word being identical and equal to the number of taps on said delay line, means responsive to the storing of one complete word which has traversed said transmission meDium in said delay line for repeatedly circulating said stored word relative to the inputs to said adjustable attenuators, means for comparing said circulating word in the output of said summing circuit with said matching word in the output of the generator associated with said equalizer to derive an error signal, means for correlating said error signal with signals at the inputs to said attenuators for establishing an ordered set of gain coefficients for said attenuators, means for measuring the largest of said gain coefficients, and means for cyclically shifting said gain coefficients to align the largest such coefficient with said reference tap. 4 The combination defined in claim 3 also comprising first clock means operating at said synchronous data rate for timing in common the word generator associated with said equalizer and said circulating means.

5. The combination defined in claim 4 further comprising second clock means operating at a rate different from said synchronous data rate for timing in common the word generator associated with said equalizer and said circulating means, and means for switching between said first and second clock means upon storing one complete transmitted word in said delay line.

6. The combination defined in claim 3 in which said circulating means comprises a feedback connection between the tap of greatest delay and the input of said delay line.

7. Apparatus for obtaining rapid initial convergence of the gain settings in a transversal equalizer including a tapped delay line, an adjustable attenuator for each tap and a summation circuit based on the minimization of the mean-square error between identical pseudorandom binary test and reference patterns, one of which has traversed a distorting transmission medium, comprising means for generating said identical patterns as a periodic sequence having the same number of binary elements per period as there are taps on said delay line at the synchronous transmission rate of said medium without prior pattern synchronization, means for storing one period of the transmitted test pattern in said delay line, means for iteratively circulating the stored pattern from output to input of said delay line and generating the reference pattern at a rate substantially higher than said synchronous rate, means for comparing said stored and reference patterns with each other element by element at the output of said summation circuit to obtain an error signal, means for correlating said error signal with samples of the transmitted pattern at the several taps on said delay line to furnish control signals for adjusting attenuators associated with said taps, means for adjusting responsive to said control signals said attenuators until said error signal is minimized, means for measuring the values of the gain coefficients effective at said attenuators to identify the largest such coefficient, and means for cyclically shifting the gain coefficients characterizing the adjustments of said attenuators relative to the taps on said delay line so that the largest gain coefficient is effective at the tap designated as a reference tap.

8. A method for obtaining rapid initial convergence of the gain settings in a transversal equalizer including a tapped delay line, an adjustable attenuator for each tap and a summation circuit based on the minimization of the mean-square error between identical binary test and reference patterns, one of which was traversed a distorting transmission medium, comprising the steps of generating said identical patterns as a periodic sequence having the same number of elements per period as there are taps on said delay line but without first synchronizing said patterns, comparing said patterns element by element at the output of said summation circuit to obtain an error signal, correlating said error signal with samples of the transmitted pattern at the several taps on said delay line to furnish contRol signals for adjusting attenuators associated with said taps, adjusting responsive to said control signals said attenuators until said error signal is minimized, measuring the gain coefficients applied to said attenuators to identify the largest such coefficient, and cyclically shifting the gain coefficients characterizing the adjustments of said attenuators relative to the taps on said delay line so that the largest gain coefficient is effective at the tap designated as a reference tap.