Adaptive signal discrimination circuit and a method for discriminating high and low level of data signals

• US 4,939,750 A
• Filed: 03/14/1989
• Issued: 07/03/1990
• Est. Priority Date: 03/17/1988
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Nakamura, Seizo
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US07/323,382
• Time in Patent Office: 476 Days
• Field of Search: 375/4, 375/76, 358/282, 307/354, 307/358, 307/359, 328/146
• US Class Current: 375/317
• CPC Class Codes: H04L 25/061 providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset removal of dc offset in coupling arrangements H04L25/029, H04L25/0296

Abstract

An apparatus and a method for adaptively discriminating high and low levels of data signals to be demodulated into digital signals, which includes a reference signal generator, first and second sample and hold circuits, a discrimination signal generator, a timing signal generator and a discriminator. The first sample and hold circuit samples data signals at first discrete times at which the discriminator detects a high level of the data signal in relation to a discrimination level, and outputs a first sample signal whose level depends upon the level of the data signals at the first discrete times. Similarly, the second sample and hold circuit samples a low level of the data signals and outputs a second sample signal whose level depends upon the level of the data signals at the second discrete times. The apparatus further includes a signal generator which generates an average of an absolute value of the levels of the sample signal first and that of the second sample signal and a further signal generator which generates an inversion of the average signal. An additional signal generator has a low-pass filter and selector to selectively apply one of the average and inversion signals to the low-pass filter. The selector applies the inversion signal when the discriminator detects that the high level of the data signals has been inputted, otherwise, it applies the average signal. The output of the low-pass filter is a reference signal formed of a composite of the inversion and average signals. The reference signal is applied to the discrimination signal generator which produces the discrimination level so as to adjust the level of the discrimination level in proportion to the level reference signal.

Claims

1. An adaptive signal discrimination circuit for discriminating high and low levels of data signals, comprising:

means for generating a reference signal having a reference level;

means for receiving data signals having values which vary between high and low levels;

a first sampling means for sampling the data signals at first discrete times and outputting a first sample signal having a level indicative of the level of the data signals at the first discrete time;

a second means for sampling the data signals at second discrete times and outputting a second sample signal having a level indicative of the level of the data signals at the second discrete time;

means for generating a discrimination signal having a discrimination level which varies in proportion to the reference level;

means for generating timing signals;

means, responsive to each of the timing signals for discriminating between the high and low levels of the data signals in relation to the discrimination level of the discrimination signal, the first discrete times substantially coinciding with the times of detecting the high level, the second discrete time substantially coinciding with the times of detecting the low level; and

means for generating an average signal having a value indicative of an average of an absolute value of the level of the first sample signal and that of the second sample signal, and for generating an inversion signal having a value indicative of the inversion of the value of the average signal;

the reference signal generating means including a low-pass filter having input and output terminals and further including means for selectively applying one of the average signal and the inversion signal to said low-pass filter, said applying means applying the average signal to the input terminal of said low-pass filter when said discriminating means detects the low level of the data signal, said applying means applying the inversion signal to the input terminal of said low-pass filter when said discriminating means detects the high level of the data signal, the reference signal being generated from the output terminal of the said low-pass filter, whereby the discrimination signal adapts to variations of the data signals.

2. The circuit according to claim 1, wherein the discrimination signal is produced from the first, second and reference signals.

3. The circuit according to claim 1, wherein said discrimination signal generating means generates first and second discrimination signals, the first discrimination signal having a level intermediate of the level of the first sample signal and the reference signal the second discrimination signal having a level intermediate of the level of the reference signal and second sample signal.

4. The circuit according to claim 3, wherein the level of the first discrimination signal is substantially at the midpoint of the first sample signal and the reference signal and the level of the second discrimination signal is substantially at the midpoint of the levels of the reference signal and second sample signal.

5. The circuit according to claim 3, wherein said discriminating means further detects an intermediate level of the data signals, the intermediate level being intermediate of the levels of the first and second discrimination signals, the high level being above the levels of the first discrimination signal, the low level being below the level of the second discrimination signal.

6. The circuit according to claim 5, wherein said applying means connects the input terminal of said low-pass filter to a ground potential when said discriminating means detects the intermediate level.

7. The circuit according to claim 1, wherein said timing signal generating means includes means for comparing the data signals with the reference signals and for the data signals substantially varying in accordance with a predetermined eye-pattern having eye opening portions at third discrete times, produces the timing signals so as to coincide with every third discrete time of said eye opening portion.

8. The circuit according to claim 7, wherein said timing signal generating means generates a respective sampling pulse at a certain time interval after each timing signal is generated.

9. The circuit according to claim 8, wherein said certain time interval substantially coincides with an interval of time during which discrimination between the high and low level is completed by said discriminating means.

10. The circuit according to claim 9, wherein said discriminating means comprises means for selectively applying the sampling pulse to said first sampling means upon detecting the high level and to said second sampling means upon detecting the low level and wherein said first and second sampling means are respectively responsive to receipt of the sampling pulse to perform said sampling of the data signals.

11. The circuit according to claim 1, wherein said first sampling means includes first holding means for holding first difference signals having respective levels successively indicative of the difference between the level of the data signal and the level of the reference signal at the first discrete times and wherein said second sampling means includes second holding means for holding second difference signals having respective levels successively indicative of the difference between the level of the data signal and the level of the reference signal at the second discrete times.

12. The circuit according to claim 11, wherein

said data signals, reference signals and first and second difference signals are voltages, said first and second sampling means respectively have resistance, and said first and second holding means respectively have capacitance which hold the voltages of the first and second difference signals;

the first difference signal is successively renewed at each of the first discrete times so that the voltage of the first difference signals at the time of being renewed is intermediate of the voltage of the first difference signals prior to being renewed and a value indicative of the difference between the voltage of the data signal and the voltage of the reference signal at the time of the first difference signal being renewed;

the second signal is successively renewed at each of the second discrete times so that the voltage of the second difference signal at the time of being renewed is intermediate of the voltage of second difference signal prior to being renewed and a value indicative of the difference between the voltage of the data signals and the voltage of the reference signal, at the time of the second difference signal being renewed;

the level of the first sample signal is substantially equal to the sum of the voltage of the first difference signal and the voltage of the reference signal; and

the level of the second sample is substantially equal to the sum of the voltage of the reference signal and the voltage of the second difference signal.

13. The circuit according to claim 1, wherein said low-pass filter has a first cut-off frequency equal to a cut-off frequency of through a transmission line.

14. The circuit according to claim 1, wherein said receiving means has a high-pass filter which transmits the data signals therethrough, said high-pass filter having a second cut-off frequency, and wherein said low-pass filter has a cut-off frequency equal to said second cut-off.

15. The circuit according to claim 14, wherein the second cut-off frequency is higher than a first cut-off frequency of a transmission line through which said receiving means the data signals.

16. A method for discriminating high and low levels of transmitted comprising the steps of:

generating a reference signal having a reference level;

receiving data signals having values which vary between high and low levels;

sampling the data signals at first discrete times;

outputting, following each successive sampling at the first discrete times, a first sample signal having a level indicative of the level of the data signals at the first discrete times;

sampling the data signals at second discrete times;

outputting, following each successive sampling at the second discrete times, a second sample signal having a level indicative of the level of the data signals at the second discrete times;

generating a discrimination signal having a discrimination level which varies is proportion to the reference level;

generating timing signals;

discriminating, in response to each of the timing signals, between the high and low levels of the data signals in relation to the discrimination level of the discrimination signal, the first discrete times substantially coinciding with the times of detecting the high level during said step of discriminating, the second discrete times substantially coinciding with the times of detecting the low level during said step of discriminating;

generating an average signal having a value indicative of to an average of an absolute value of the level of the first sample signal and that of the second sample signal upon detecting the low level during said step of discriminating;

generating an inversion signal having a value indicative of the inversion of the average signal upon detecting the high level during said step of discriminating; and

forming a composite signal from the average and inversion signals;

said step of forming a reference signal including the step of filtering the composite signal so as to reduce relatively high frequency portions thereof and pass the relatively low frequency portions as the reference signal.

17. The method according to claim 16, wherein said step of generating the discrimination signal includes generating the discrimination signal from the first sample signal, the second sample signal and the reference signal.

18. The method according to claim 16, wherein said step of generating the discriminating signal includes generating a first discrimination signal with a first discrimination level intermediate of the level of the first sample signal and the level of the reference signal and generating a second discrimination signal with a second discrimination level intermediate of the level of the reference signal and the level of the second sample signal.

19. The method according to claim 18, wherein the first discrimination signal has a level which is substantially at the midpoint of the respective levels of the first sample signal and the level of the reference signal and the second discrimination signal has a level which is substantially at the midpoint of the respective levels of the reference signal and the second sample signal.

20. The method according to claim 18, wherein said step of discriminating further comprises the step of detecting an intermediate level of the data signals, intermediate of the first and second discrimination levels, the high level being above the first discrimination level, the low level being below the second discrimination level.

21. The method according to claim 20, further comprising the step of equating the composite signal to a ground potential upon detecting the intermediate level during said step of discriminating.

22. The method according to claim 16, further comprising the step of receiving data signals which vary substantially in accordance with a predetermined eye-pattern having eye opening portions at third discrete times, wherein said step of generating the timing signals comprises generating the timing signals so as to coincide with the third discrete times of the eye opening portions.

23. An adaptive discrimination circuit for discriminating high and low levels of transmitted data signals, comprising:

means for receiving the transmitted data signals which vary between high and low levels;

means for generating a compensation signal having a compensation level;

means for producing a compensated data signal having a level indicative of a sum of the level of the transmitted data signal and the compensation level;

a first sampling means for sampling the compensated data signals at first discrete times and outputting a first sample signal having a level indicative of the level of the compensated data signals at the first discrete times;

a second sampling means for sampling the compensated data signal at second discrete times and outputting a second sample signal having a level indicative of the level of the compensated data signals at the second discrete times;

means for generating a discrimination signal having a level intermediate the levels of the first and second sample signals;

means for generating timing signals;

means, responsive to each of the timing signals, for discriminating between high and low levels of the compensated data signals in relation to the discrimination level of the discrimination signal, the first discrete times substantially coinciding with the time of detecting the high level, the second discrete times substantially coinciding with the time of detecting the low level; and

means for generating an average signal having a value indicative of an average of an absolute value of the level of the first sample signal and that of the second sample signal, and for generating an inversion signal having a value indicative of the inversion of the value of the average signal;

the compensation signal generating means including a low-pass filter having input and output terminals and further including means for selectively applying one of the average signal and the inversion signal to said low-pass filter, said applying means applying the average signal to the input terminal of said low-pass filter when said discriminating means detects the high level of the compensated data signal, said applying means applying the inversion signal to the input terminal of said low-pass filter when said discriminating means detects the low level of the compensated data signal, the compensation signal being generated from the output terminal of said low-pass filter, whereby the discrimination signal adapts to variations of the transmitted data signals.

24. The circuit according to claim 23, wherein said discrimination signal generating means generates first and second discrimination signals, the first dicrimination signal having a level intermediate of the levels of the first sample signal and a ground potential, the second discrimination signal having a level intermediate of the ground potential and the level of the second sample signal.

25. The circuit according to claim 24, wherein the level of the first discrimination signal is substantially at the midpoint of the first sample signal and the ground potential and wherein the level of the second discrimination signal is substantially at the midpoint of the ground potential and the level of the second sample signal.

26. The circuit according to claim 24, wherein said discriminating means further detects an intermediate level of the compensated data signals, the intermediate level being intermediate of the levels of the first and second discrimination signals, the high level being above the level of the first discrimination signal, the low level being below the level of the second discrimination signal.

27. The circuit according to claim 26, wherein said applying means connects the input terminal of said low-pass filter to the ground potential when said discriminating means detects the intermediate level.

28. The circuit according to claim 23, wherein said timing signal generating means includes means for comparing the levels of the compensated data signals with ground potential, and wherein for compensated data signals substantially varying in accordance with a predetermined eye-pattern having eye opening portions at third discrete times, said timing signal generating means produces the timing signals so as to coincide with the respective third discrete times of said eye opening portions.

29. The circuit according to claim 28, wherein said timing signal generating means generates a respective sampling pulse at a certain time interval after each timing signal is generated.

30. The circuit according to claim 29, wherein said certain time interval substantially coincides with an interval of time during which discriminating between the high and low levels is completed by said discriminating means.

31. The circuit according to claim 30, wherein said discriminating means comprises means for selectively applying the sampling pulse to said first sampling means upon detecting the high level and said second sampling means upon detecting the low level and wherein said first and second sampling means are respectively responsive to receipt of the sampling pulse to perform said sampling of the compensated data signals.

32. The circuit according to claim 23, wherein said low-pass filter has a first cut-off frequency equal to a cut-off frequency of a transmission line through which said receiving means receives the transmitted data signals.

33. The circuit according to claim 23, wherein said receiving means has a high-pass filter which transmits the transmitted data signal therethrough, said high-pass filter having a second cut-off frequency, and wherein said low-pass filter has a cut-off frequency equal to said second out-off frequency.

34. The circuit according to claim 33, wherein the second cut-off frequency is higher than a first cut-off frequency of a transmission line through which said receiving means receives the transmitted data signals.

35. A method for discriminating high and low levels of transmitted data signals, comprising the steps of;

receiving transmitted data signals having values which vary between high and low levels;

generating compensation signals having a compensation level;

producing compensated data signals having a level indicative of the sum of the level of the transmitted data signal and the compensation level;

sampling the compensated data signals at first discrete times;

outputting, following each successive sampling at the first discrete times, a first sample signal having a level indicative of the level of the compensated data signals at the first discrete time;

sampling the compensated data signals at second discrete times;

outputting, following each successive sampling at the second discrete times, a second sample signal having a level indicative of the level of the compensated data signals at the second discrete time;

generating a discrimination signal having a level intermediate of the levels of the first and second sample signals;

generating timing signals;

discriminating, in response to each of the timing signals, between the high and low levels of the compensated data signals in relation to the level of the discrimination signal, the first discrete times substantially coinciding with the times of detecting the high level during said step of discriminating, the second discrete times substantially coinciding with the times of detecting the low level during said step of discriminating;

generating an average, signal having a value indicative of an average of an absolute value of the level of the first sample signal and that of the second sample signal upon detecting the high level during said step of discriminating;

generating an inversion signal having a value indicative of the inversion of the average signal upon detecting the low level during said step of discriminating; and

forming a composite signal from the average and inversion signals;

said step of forming a compensation signal including the step of filtering the composite signal so as to reduce relatively high frequency portions and pass the relatively low frequency portions thereof as the compensation signal.

36. The method according to claim 35, wherein said step of generating the discrimination signal includes generating a first discrimination signal with a first discrimination level intermediate of the level of the first sample signal and a ground potential, and generating a second discrimination signal with a second discrimination level intermediate of the ground potential and the level of the second sample signal.

37. The method according to claim 36, wherein the first discrimination signal has a level which is substantially at the midpoint respective of the level of the first sampling signal and the ground potential and wherein the second discrimination signal has a level which is substantially at the midpoint respectively of the ground potential and the level of the second sample signal.

38. The method according to claim 36, wherein said step of discriminating further comprises the step of detecting an intermediate level of the compensated date signals, intermediate of the first and second discrimination levels, the high level being above the first discrimination level, the low level being below the second discrimination level.

39. The method according to claim 38, wherein said method further has a step of equating the composite signal to the ground potential upon detecting the intermediate level during said step of discriminating.

40. The method according to claim 35, further comprising the step of receiving transmitted data signals which vary substantially in accordance with a predetermined eye-pattern having eye opening portions at third discrete times, wherein said step of generating the timing signals comprises generating the timing signals so as to coincide with the third discrete times of the eye opening portions.