Method and apparatus for variable bit rate clock recovery

• US 6,285,722 B1
• Filed: 11/25/1998
• Issued: 09/04/2001
• Est. Priority Date: 12/05/1997
• Status: Expired due to Term

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Telcordia Technologies Incorporated (Telefonaktiebolaget LM Ericsson)
• Inventors: Cheung, Nim K., Banwell, Thomas C.
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): CORRIELUS, JEAN B
• Application Number:
  US09/199,480
• Time in Patent Office: 1,014 Days
• Field of Search: 375/377, 375/324, 375/316, 375/326, 375/327, 375/354, 375/360, 375/225, 375/224, 375/359, 370/518, 327/291, 327/26, 327/37, 327/165
• US Class Current: 375/354
• CPC Class Codes: H04L 25/0262 Arrangements for detecting the data rate of an incoming signal
• CPC Class Codes: H04L 7/027 extracting the synchronising or clock signal from the received signal spectrum, e.g. by using a resonant or bandpass circuit
• CPC Class Codes: H04L 7/0334 Processing of samples having at least three levels, e.g. soft decisions

Abstract

Methods and apparatuses consistent with the present invention recover a clock signal from a variable bit rate data signal by estimating, in the time domain, the bit rate of the data signal, and based on the estimated variable bit rate, determining a center frequency of a narrow-band filter for extracting the clock signal from the data signal. A clock recovery circuit consistent with the present invention extracts a clock signal from a variable bit rate data signal by estimating a minimum time interval between transitions in the data signal, generating a plurality of pulses that correspond respectively to transitions in the data signal, adjusting the duration of each of the pulses based on the estimated minimum time interval and inputting into a narrow-band filter the adjusted pulses, determining a center frequency of the narrow-band filter based on the estimated minimum time interval, and extracting in the narrow-band filter the clock signal from the adjusted pulses.

Claims

1. A method for recovering a clock signal from an input signal having a variable bit rate, said method comprising the steps of:

estimating a minimum time interval between transitions in the input signal;

determining a center frequency of a narrow-band filter based on the estimated minimum time interval; and

extracting, at the determined center frequency, the clock signal from the input signal.

2. The method of claim 1 further comprises the steps of:

before the extracting step, generating a first plurality of pulses corresponding respectively to transitions in the input signal;

adjusting the duration of each of the first plurality of pulses based on the estimated minimum time interval; and

inputting into the narrow-band filter the adjusted first plurality of pulses.

3. The method of claim 1, wherein the estimating step further comprises the step of:

determining the variable bit rate of the input signal based on the estimated minimum time interval.

4. The method of claim 2, wherein the estimating step comprises the steps of:

generating a second plurality of pulses that correlate to the transitions in the input signal; and

adjusting the duration of each of the second plurality of pulses, such that minimum time intervals between the transitions in the input signal match the durations of the corresponding second plurality of pulses.

5. The method of claim 2, wherein the extracting step comprises the steps of:

generating a phase correction signal proportional to a difference between a phase of the clock signal and a phase of the first plurality of pulses; and

adding the phase correction signal to a center frequency of an oscillator generating the clock signal.

6. The method of claim 2, wherein the extracting step comprises the steps of:

generating a frequency correction signal proportional to a difference between a frequency of the clock signal and a frequency of the first plurality of pulses; and

adding the frequency correction signal to a center frequency of an oscillator generating the clock signal.

7. The method of claim 4, wherein the adjusting step of claim 4 comprises the steps of:

generating a voltage signal corresponding to the difference between the minimum time interval between transitions in the input signal and the duration of the corresponding second plurality of pulses; and

generating a current signal proportional to the voltage signal, wherein the current signal controls the durations of each of the second plurality of pulses.

8. A method for re covering a clock signal from an input signal having a variable bit rate, said method comprising the steps of:

estimating a minimum time interval between transitions in the input signal;

generating a first plurality of pulses corresponding respectively to transitions in the input signal;

adjusting duration of each of the first plurality of pulses based on the estimated minimum time interval and inputting into a narrow-band filter the adjusted first plurality of pulses;

determining a center frequency of the narrow-band filter based on the estimated minimum time interval; and

extracting in the narrow-band filter the clock signal from the adjusted first plurality of pulses.

9. The method of claim 8, wherein the estimating step comprises the steps of:

generating a set of delayed input signals by passing the input signal serially through a set of delay segments, wherein the set of delay segments delay the input signal based on a set of predetermined delay times, respectively;

comparing the input signal with the set of generated delayed input signals to determine which of the predetermined delay times are less than the minimum time interval between transitions in the input signal; and

generating a control signal based on a sum of the predetermined delay times that are less than the minimum time interval between transitions in the input signal.

10. The method of claim 8, wherein the estimating step comprises the steps of:

generating a set of delayed input signals by passing the input signal serially through a set of programmable delay segments, wherein the set of programmable delay segments delay the input signal based on a set of pre-determined delay times, respectively;

comparing the input signal with the set of generated delayed input signals to determine which of the pre-determined delay times are less than the minimum time interval between transitions in the input signal; and

generating a control signal based on a sum of the pre-determined delay times that are less than the minimum time interval between transitions in the input signal.

11. The method of claim 8, wherein the estimating step comprises the steps of:

generating one or more delayed transitions by passing the input signal through a programmable time interval generator, wherein said one or more delayed transitions are generated based on a set of delay time values, respectively;

comparing transitions in the input signal with the generated delayed transitions; and

adjusting one or more of the delay time values, such that one of the delay time values matches the minimum time interval between transitions in the input signal.

12. An apparatus for recovering a clock signal from an input signal having a variable bit rate, said apparatus comprising:

a rate detector for estimating a minimum time interval between transitions in the input signal;

a transition detector for generating a first plurality of pulses corresponding respectively to transitions in the input signal;

a narrow-band filter for extracting the clock signal from an adjusted first plurality of pulses; and

a rate selector for adjusting, based on the estimated minimum time interval, duration of each of the first plurality of pulses and a center frequency of the narrow-band filter that receives the adjusted first plurality of pulses.

13. The apparatus of claim 12, wherein said rate detector comprises:

a set of delay segments connected in series for generating a set of delayed input signals based on a set of pre-determined delay times, respectively; and

a set of latches connected to the set of delay segments, respectively, for comparing the set of delayed input signals with the input signal to determine which of the pre-determined delay times are less than the minimum time interval between transitions in the input signal and generating a control signal based on a sum of the pre-determined delay times that are less than the minimum time interval between transitions in the input signal.

14. The apparatus of claim 12, wherein said rate detector comprises:

a programmable time interval generator for generating a set of delayed transitions based on a set of delay time values, respectively; and

an edge transition comparator connected to the programmable time interval generator for comparing the set of delayed transitions with transitions in the input signal and adjusting one or more of the delay time values, such that one of the delay time values matches the minimum time interval between the transitions in the input signal.

15. The apparatus of claim 12 further comprises:

a calibration source for generating a calibration signal having a set of pre-determined reference bit rates, wherein the rate detector estimates the pre-determined reference bit rate of the calibration signal; and

a response monitor for determining differences between the pre-determined reference bit rates and the estimated pre-determined reference bit rate and for adjusting the rate selector until one of determined differences equals zero.

16. The apparatus of claim 12, wherein the rate detector comprises:

an interval generator for generating a second plurality of transitions that correlate to the transitions in the input signal;

a transition comparator for determining a difference between the duration of each of the second plurality of transitions and a time interval between each of the transitions in the input signal; and

a feedback means for adjusting the duration of each of the second plurality of transitions until the determined difference equals zero.

17. The apparatus of claim 12, wherein the narrow-band filter comprises:

a phase comparator for generating a phase correction signal proportional to a difference between a phase of the clock signal and a phase of the adjusted first plurality of pulses; and

a first adder for adding the phase correction signal to a center frequency of an oscillator generating the clock signal.

18. The apparatus of claim 17, wherein the narrow-band filter further comprises:

a frequency comparator for generating a frequency correction signal proportional to a difference between a frequency of the clock signal and a frequency of the adjusted first plurality of pulses; and

a second adder for adding the frequency correction signal to the center frequency of the oscillator generating the clock signal.

19. The apparatus of claim 16, wherein the interval generator comprises:

an edge triggered one-shot for generating the second plurality of pulses that correlate to the transitions in the input signal.

20. The apparatus of claim 16, wherein the interval generator comprises:

one or more resettable edge triggered delay elements for generating the second plurality of pulses that correlate to the transitions in the input signal.

21. An apparatus for recovering a clock signal from an input signal having a variable bit rate, said apparatus comprising:

a rate detector for estimating a minimum time interval between transitions in the input signal;

a rate selector connected to the rate detector;

a transition detector connected to the rate selector; and

a narrow-band filter connected to the transitions detector and the rate selector, such that the rate selector adjusts, based on the estimated minimum time interval, duration of each of a plurality of pulses generated by the transition detector and a center frequency of the narrow-band filter for extracting the clock signal from the input signal.