System and method for automatically correcting duty cycle distortion

• US 7,292,670 B2
• Filed: 08/06/2003
• Issued: 11/06/2007
• Est. Priority Date: 08/06/2003
• Status: Expired due to Fees

• Current Assignee: Semtech Canada Corp. (Semtech Corporation)
• Original Assignee: Gennum Corporation
• Inventors: d'Haene, Wesley C., Gupta, Atul K.
• Primary Examiner(s): Ha; Dac
• Assistant Examiner(s): Wang; Ted M.
• Application Number:
  US10/635,309
• Publication Number:
  US 20050031065A1
• Time in Patent Office: 1,553 Days
• Field of Search: 375/354, 375/355, 375/371, 375/376, 375/326
• US Class Current: 375/371
• CPC Class Codes: H03L 7/0812 and where no voltage or current controlled oscillator is used
• CPC Class Codes: H03L 7/087 using at least two phase detectors or a frequency and phase detector in the loop
• CPC Class Codes: H03L 7/0891 the up-down pulses controlling source and sink current generators, e.g. a charge pump
• CPC Class Codes: H03L 7/091 the phase or frequency detector using a sampling device H03L7/087 takes precedence
• CPC Class Codes: H03L 7/0998 using phase interpolation
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop

Abstract

In accordance with the teachings described herein, systems and methods are provided for automatically correcting duty cycle distortion. A slicer may be used to receive a data input signal and compare the data input signal with a slicer offset voltage to generate a sliced data signal. The slicer may also receive an offset control signal to automatically adjust the slicer offset voltage. A phase detector may be used to receive the sliced data signal and a recovered clock signal and to compare the sliced data signal with the recovered clock signal to generate a rising edge output signal and a falling edge output signal. The rising edge output signal may correspond to a phase difference between a rising edge of the sliced data signal and an edge of the recovered clock signal. The falling edge output signal may correspond to a phase difference between a falling edge of the sliced data signal and an edge of the recovered clock signal. A first feedback circuit may be used to phase-lock the recovered clock signal to the sliced data signal utilizing at least one of the rising edge output signal and the falling edge output signal. At least one of the rising edge output signal and the falling edge output signal may be configured in a second feedback circuit to generate the offset control signal.

Claims

1. A system for automatically correcting duty cycle distortion in a data input signal, comprising:

a slicer operable to receive the data input signal and compare the data input signal with a slicer offset voltage to generate a sliced data signal, the slicer being further operable to receive an offset control signal to automatically adjust the slicer offset voltage;

a phase detector circuit operable to receive the sliced data signal and a recovered clock signal and to compare the sliced data signal with the recovered clock signal to generate a rising edge output signal and a falling edge output signal, the rising edge output signal corresponding to a phase difference between a rising edge of the sliced data signal and an edge of the recovered clock signal, the falling edge output signal corresponding to a phase difference between a falling edge of the sliced data signal and an edge of the recovered clock signal;

a first feedback circuit operable to phase-lock the recovered clock signal to the sliced data signal utilizing at least one of the rising edge output signal and the falling edge output signal; and

at least one of the rising edge output signal and the falling edge output signal being configured in a second feedback circuit to generate the offset control signal;

wherein the first feedback circuit is operable to phase-lock the recovered clock signal to the sliced data signal utilizing both the rising edge output signal and the falling edge output signal.

2. The system of claim 1, wherein the first feedback circuit is a phase-locked loop circuit.

3. The system of claim 2, wherein the phase-locked loop circuit comprises:

a charge pump filter that receives at least one of the rising edge output signal and the falling edge output signal and generates a charge pump output signal with a polarity corresponding to at least one of the rising edge output signal and the falling edge output signal; and

a voltage-controlled oscillator that generates the recovered clock signal with a frequency that is a function of the charge pump output signal.

4. The system of claim 3, wherein the charge pump is a two-input charge pump.

5. The system of claim 2, wherein the phase detector circuit generates a feedback signal selected from the rising edge output signal and the falling edge output signal, and wherein the phase-locked loop circuit comprises:

a charge pump filter that receives the feedback signal and generates a charge pump output signal with a polarity corresponding to the feedback signal; and

a voltage-controlled oscillator that generates the recovered clock signal with a frequency that is a function of the charge pump output signal.

6. The system of claim 1, wherein the first feedback circuit is a delay-locked loop circuit.

7. The system of claim 6, wherein the first feedback circuit comprises:

a charge pump filter that receives at least one of the rising edge output signal and the falling edge output signal and generates a charge pump output signal with a polarity corresponding to at least one of the rising edge output signal and the falling edge output signal;

a fixed frequency signal generator that generates a reference clock signal; and

means for controlling the phase of the reference clock signal as a function of the charge pump output signal to generate the recovered clock signal.

8. The system of claim 7, wherein the controlling means is a phase interpolator coupled to the charge pump output signal and the reference clock signal and operable to control the phase of the reference clock signal as a function of the charge pump output signal to generate the recovered clock signal.

9. The system of claim 7, wherein the controlling means is a voltage controlled delay circuit coupled to the charge pump output signal and the reference clock signal and operable to control the phase of the reference clock signal as a function of the charge pump output signal to generate the recovered clock signal.

10. The system of claim 7, wherein the controlling means is a current controlled delay circuit coupled to the charge pump output signal and the reference clock signal and operable to control the phase of the reference clock signal as a function of the charge pump output signal to generate the recovered clock signal.

11. The system of claim 6, wherein the phase detector circuit generates a feedback signal selected from the rising edge output signal and the falling edge output signal, and wherein the first feedback circuit comprises:

a charge pump filter that receives the feedback signal and generates a charge pump output signal with a polarity corresponding to the feedback signal;

a fixed frequency signal generator that generates a reference clock signal; and

means for controlling the phase of the reference clock signal as a function of the charge pump output signal to generate the recovered clock signal.

12. The system of claim 11, wherein the controlling means is a phase interpolator coupled to the charge pump output signal and the reference clock signal and operable to control the phase of the reference clock signal as a function of the charge pump output signal to generate the recovered clock signal.

13. The system of claim 11, wherein the controlling means is a voltage controlled delay circuit coupled to the charge pump output signal and the reference clock signal and operable to control the phase of the reference clock signal as a function of the charge pump output signal to generate the recovered clock signal.

14. The system of claim 11, wherein the controlling means is a current controlled delay circuit coupled to the charge pump output signal and the reference clock signal and operable to control the phase of the reference clock signal as a function of the charge pump output signal to generate the recovered clock signal.

15. The system of claim 1, wherein the phase detector circuit synchronizes the sliced data signal with the recovered clock signal to generate a retimed data signal.

16. The system of claim 15, wherein the phase detector circuit comprises:

a retiming stage coupled to the sliced data signal and the recovered clock signal, wherein the retiming stage is triggered by the recovered clock signal and samples the sliced data signal to generated the retimed data signal and a synchronization signal; and

a synchronization stage coupled to the synchronization signal and the retimed data signal, wherein the synchronization stage is triggered by the retimed data signal and samples the synchronization signal to generate the rising edge output signal and the falling edge output signal.

17. The system of claim 16, wherein the retiming stage of the phase detector circuit comprises:

a first retiming stage latch coupled to the sliced data signal and the recovered clock signal that samples the sliced data signal on a rising edge of the recovered clock signal to generate the retimed data signal; and

a second retiming stage latch coupled to the sliced data signal and the recovered clock signal that samples the sliced data signal on the falling edge of the recovered clock signal to generate the synchronization signal.

18. The system of claim 16, wherein the synchronization stage of the phase detector circuit comprises:

a first synchronization stage latch coupled to the retimed data signal and the synchronization signal that samples the synchronization signal on the rising edge of the retimed data signal to generate the rising edge output signal; and

a second synchronization stage latch coupled to the retimed data signal and the synchronization signal that samples the synchronization signal on the falling edge of the retimed data signal to generate the falling edge output signal.

19. The system of claim 16, wherein the phase detector circuit generates a feedback signal selected from the rising edge output signal and the falling edge output signal and the first feedback circuit is operable to phase-lock the recovered clock signal to the sliced data signal utilizing the feedback signal, and wherein the synchronization stage of the phase detector circuit comprises:

a first synchronization stage latch coupled to the retimed data signal and the synchronization signal that samples the synchronization signal on the rising edge of the retimed data signal to generate the rising edge output signal;

a second synchronization stage latch coupled to the recovered clock signal and the synchronization signal that samples the synchronization signal on the falling edge of the recovered clock signal to generate the falling edge output signal; and

a multiplexer having a first data input coupled to the rising edge output signal, a second data input coupled to the falling edge output signal and a select input coupled to the retimed data signal, wherein the select input controls whether the multiplexer selects the rising edge output signal or the falling edge output signal to generate the feedback signal.

20. The system of claim 16, wherein the phase detector circuit generates a feedback signal selected from the rising edge output signal and the falling edge output signal and the feedback signal is configured in the second feedback circuit to generate the offset control signal, and wherein the synchronization stage of the phase detector circuit comprises:

a first synchronization stage latch coupled to the retimed data signal and the synchronization signal that samples the synchronization signal on the rising edge of the retimed data signal to generate the rising edge output signal;

a second synchronization stage latch coupled to the retimed data signal and the synchronization signal that samples the synchronization signal on the falling edge of the retimed data signal to generate the falling edge output signal; and

a multiplexer having a first data input coupled to the rising edge output signal, a second data input coupled to a logical inversion of the falling edge output signal and a select input coupled to the retimed data signal, wherein the select input controls whether the multiplexer selects the rising edge output signal or the falling edge output signal to generate the feedback signal.

21. A system for automatically correcting duty cycle distortion in a data input signal, comprising:

a slicer operable to receive the data input signal and compare the data input signal with a slicer offset voltage to generate a sliced data signal, the slicer being further operable to receive an offset control signal to automatically adjust the slicer offset voltage;

a phase detector circuit operable to receive the sliced data signal and a recovered clock signal and to compare the sliced data signal with the recovered clock signal to generate a rising edge output signal and a falling edge output signal, the rising edge output signal corresponding to a phase difference between a rising edge of the sliced data signal and an edge of the recovered clock signal, the falling edge output signal corresponding to a phase difference between a falling edge of the sliced data signal and an edge of the recovered clock signal;

a first feedback circuit operable to phase-lock the recovered clock signal to the sliced data signal utilizing at least one of the rising edge output signal and the falling edge output signal; and

at least one of the rising edge output signal and the falling edge output signal being configured in a second feedback circuit to generate the offset control signal;

wherein the phase detector circuit generates a feedback signal selected from the rising edge output signal and the falling edge output signal, and wherein the feedback signal is configured in the second feedback circuit to generate the offset control signal.

22. The system of claim 21, wherein the second feedback circuit includes a charge pump filter that receives the feedback signal and generates the offset control signal with a polarity corresponding to the feedback signal.

23. A system for automatically correcting duty cycle distortion in a data input signal, comprising:

a slicer operable to receive the data input signal and compare the data input signal with a slicer offset voltage to generate a sliced data signal, the slicer being further operable to receive an offset control signal to automatically adjust the slicer offset voltage;

a phase detector circuit operable to receive the sliced data signal and a recovered clock signal and to compare the sliced data signal with the recovered clock signal to generate a rising edge output signal and a falling edge output signal, the rising edge output signal corresponding to a phase difference between a rising edge of the sliced data signal and an edge of the recovered clock signal, the falling edge output signal corresponding to a phase difference between a falling edge of the sliced data signal and an edge of the recovered clock signal;

a first feedback circuit operable to phase-lock the recovered clock signal to the sliced data signal utilizing at least one of the rising edge output signal and the falling edge output signal; and

at least one of the rising edge output signal and the falling edge output signal being configured in a second feedback circuit to generate the offset control signal;

wherein both the rising edge output signal and the falling edge output signal are configured in the second feedback circuit.

24. The system of claim 23, wherein the second feedback circuit includes a two-input charge pump filter that receives the rising edge output signal and the falling edge output signal and generates the offset control signal.

25. The system of claim 23, wherein the second feedback circuit compares the rising edge output signal and the falling edge output signal to generate a combined feedback signal and generates the offset control signal as a function of the combined feedback signal.

26. The system of claim 25, wherein the second feedback circuit includes a charge pump filter that receives the combined feedback signal and generates the offset control signal with a polarity corresponding to the combined feedback signal.

27. A system for automatically correcting duty cycle distortion in a data input signal, comprising:

a slicer operable to receive the data input signal and compare the data input signal with a slicer offset voltage to generate a sliced data signal, the slicer being further operable to receive an offset control signal to automatically adjust the slicer offset voltage;

a phase detector circuit operable to receive the sliced data signal and a recovered clock signal and to compare the sliced data signal with the recovered clock signal to generate a rising edge output signal and a falling edge output signal, the rising edge output signal corresponding to a phase difference between a rising edge of the sliced data signal and an edge of the recovered clock signal, the falling edge output signal corresponding to a phase difference between a falling edge of the sliced data signal and an edge of the recovered clock signal;

a first feedback circuit operable to phase-lock the recovered clock signal to the sliced data signal utilizing at least one of the rising edge output signal and the falling edge output signal; and

at least one of the rising edge output signal and the falling edge output signal being configured in a second feedback circuit to generate the offset control signal;

wherein the phase detector circuit generates a feedback signal selected from the rising edge output signal and the falling edge output signal, and wherein the first feedback circuit is operable to phase-lock the recovered clock signal to the sliced data signal utilizing the feedback signal.

28. A system for automatically correcting duty cycle distortion in a data input signal, comprising:

a slicer operable to receive the data input signal and compare the data input signal with a slicer offset voltage to generate a sliced data signal, the slicer being further operable to receive an offset control signal to automatically adjust the slicer offset voltage;

a phase detector circuit operable to receive the sliced data signal and a recovered clock signal and to compare the sliced data signal with the recovered clock signal to generate a rising edge output signal and a falling edge output signal, the rising edge output signal corresponding to a phase difference between a rising edge of the sliced data signal and an edge of the recovered clock signal, the falling edge output signal corresponding to a phase difference between a falling edge of the sliced data signal and an edge of the recovered clock signal;

a first feedback circuit operable to phase-lock the recovered clock signal to the sliced data signal utilizing at least one of the rising edge output signal and the falling edge output signal; and

at least one of the rising edge output signal and the falling edge output signal being configured in a second feedback circuit to generate the offset control signal;

wherein the second feedback circuit includes a charge pump filter that receives at least one of the rising edge output signal and the falling edge output signal and generates the offset control signal with a polarity corresponding to at least one of the rising edge output signal and the falling edge output signal.