Clock data recovery circuit

Patent metadata

Field	Value
Publication number	US-9413518-B2
Application number	US-201313964448-A
Country	US
Kind code	B2
Filing date	Aug 12, 2013
Priority date	Aug 12, 2013
Publication date	Aug 9, 2016
Grant date	Aug 9, 2016

Abstract

Systems and methods for stabilizing clock data recovery (CDR) by filtering the abrupt phase shift associated with data pattern transition in the input signal. The CDR circuit includes a data pattern detector coupled to a data pattern filter. The data pattern detector is capable of detecting the data patterns of the input signal. Accordingly, the data pattern filter can selectively generate a filter indication indicating to freeze or suppress the CDR phase caused by data pattern transition. The filter indication can be incorporated to a phase error signal, a gain function, and/or the control voltage driving the VCO.

First claim

What is claimed is:

1. A method of reconstructing clock signals according to input signals in a data transmission receiver, said method comprising:
receiving an input signal comprising a plurality of data patterns;
detecting a phase difference between said input signal and a feedback signal of a clock data recovery (CDR) circuit;
detecting a data pattern of said input signal;
generating a control signal in accordance with said phase difference and said data pattern, wherein said generating comprises attenuating said control signal responsive to detection of a data pattern transition; and
providing said control signal to an oscillator circuit to generate an output signal of said CDR circuit.

2. The method of claim 1 , wherein said plurality of data patterns comprises a first data pattern and a second data pattern, and further comprising:
generating a first phase error signal based on said phase difference;
modifying said first phase error signal to generate a second phase error signal in response to detection of said first data pattern within said input signal until detection of said second data pattern within said input signal; and
generating said control signal based on said second phase error signal.

3. The method of claim 2 , wherein said modifying said first phase error signal comprises:
outputting logic “0”s; and performing an AND logic operation on said logic “0”s and said first phase error signal to generate said second phase error signal.

4. The method of claim 3 further comprising adding a time delay to said second phase error signal.

5. The method of claim 1 , wherein said plurality of data patterns comprises a first data pattern and a second data pattern, and further comprising:
generating a phase error signal based on said phase difference; and
converting said phase error signal to a voltage of said control signal by multiplying said phase error signal with a gain function, wherein said gain function is configured to be a minimal value if said first data pattern is detected within said input signal until said second data pattern is detected within said input signal subsequently.

6. The method of claim 3 further comprising adding an 8-bit delay to said second phase error signal in response to detection of said first data pattern.

7. The method of claim 1 , wherein said first data pattern comprises a clock pattern, and wherein said second data pattern comprises a scrambled data pattern.

8. The method of claim 1 , wherein said input signal comprises an ordered set block and a data block in compliance with a version of a PCIe 3.0 encoding scheme.

9. A clock data recovery (CDR) circuit comprising:
a phase frequency detector configured to receive an input signal comprising a first data pattern and a second data pattern, and to generate a phase error signal representing a phase difference between said input signal and a feedback signal of said CDR circuit;
a data pattern filter configured to detect data patterns of said input signal and to generate a filtering indication in response to detection of said first data pattern within said input signal; and
an oscillating element coupled to said data pattern filter, said oscillating element configured to generate an output signal of said CDR circuit in response to a control signal that is determined by said phase difference and said filtering indication, wherein said control signal is attenuated responsive to detection of a data pattern transition.

10. The CDR circuit of claim 9 further comprising:
an up/down counter coupled to said phase frequency detector and operable to convert phase differences to control signals for controlling said oscillating element; and
a low pass filter coupled between said up/down counter and said oscillating element.

11. The CDR circuit of claim 10 , wherein said data pattern filter is integrated with said phase frequency detector, and wherein said data pattern filter comprises:
a lookup table configured to: detect data patterns of said input signal; output a logic “0” as said filtering indication in response to detection of said first data pattern within said input signal; and output a logic “1” in response to detection of said second data pattern within said input signal; and
an AND logic module coupled to said lookup table and configured to: perform an AND operation between an output of said lookup table and said phase error signal to generate a modified phase error signal that is provided to said up/down counter.

12. The CDR circuit of claim 11 , wherein said data pattern filter further comprises a delay circuit coupled between said lookup table and said AND logic module, wherein said delay circuit is configured to add a configurable time delay to an output of said lookup table.

13. The CDR circuit of claim 10 , wherein said data pattern filter comprises:
a lookup table coupled to said phase frequency detector and configured to: detect data patterns of said input signal; and output a minor coefficient as said filter indication upon detection of said first data pattern within said input signal; and
multiplication logic coupled to said lookup table and said up/down counter, wherein said multiplication logic is configured to multiply said minor coefficient with a control signal output from said up/down counter in response to detection of said first data pattern; and to output a scaled control signals that is provided to said oscillating element.

14. The CDR circuit of claim 13 , wherein said first data pattern corresponds to a clock pattern, wherein said second data pattern corresponds to a scrambled pattern, and wherein said first data pattern and said second data pattern are transmitted in different bit rates.

15. An integrated circuit for clock and data recovery from data received through a series link, said integrated circuit comprising:
a phase frequency detector configured to: receive an input signal comprising a first component and a second component; detect a phase difference between said input signal and a feedback signal of a clock data recovery (CDR) loop; and generate a first phase error signal;
a lookup table configured to: identify said first component within said input signal; and output a filter indication in response to identifying said first component; and
a voltage controlled oscillator (VCO) configured to generate a clock signal at an output of said CDR in response to a control signal that is determined by said phase difference and said filter indication, wherein said control signal is attenuated responsive to detection of a data pattern transition.

16. The integrated circuit of claim 15 , wherein said first component corresponds to a header of a data block, wherein said second component corresponds to a payload of a data block.

17. The integrated circuit of claim 15 , wherein said lookup table is an integral part of said phase frequency detector and operable to output logic “1”s as said filter indication, further comprising:
a summing module coupled to said lookup table;
AND logic configured to perform AND logic operation on said filter indication and said first phase error signal to generate a second phase error signal; and
an up/down counter coupled to said phase frequency detector and operable to convert said second phase error signal to said control signal.

18. The integrated circuit of claim 15 further comprising:
an up/down counter coupled to said phase frequency detector and operable to output a first control signal proportional to said detected phase difference; and
a multiplication unit coupled to said up/down

Assignees

• Nvidia Corp

Inventors

• Chang Yu
• Chen Huabo
• Ozguc Hakki
• Hopgood Michael

Classifications

• H04L27/2273

  associated with quadrature demodulation, e.g. Costas loop · CPC title

• H04L2027/0057

  quadrature phase · CPC title

• H04L7/0041 Primary

  Delay of data signal · CPC title

• H04L7/0016

  correction of synchronization errors · CPC title

• H04L7/0083 Primary

  taking measures against momentary loss of synchronisation, e.g. inhibiting the synchronisation, using idle words or using redundant clocks · CPC title