Apparatus and method thereof for clock and data recovery of N-PAM encoded signals using a conventional 2-PAM CDR circuit

• US 8,594,262 B2
• Filed: 06/10/2011
• Issued: 11/26/2013
• Est. Priority Date: 06/17/2010
• Status: Active Grant

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Transwitch Corporation
• Inventors: Slezak, Yaron, Veytsman, Genady
• Primary Examiner(s): Bayard, Emmanuel
• Application Number:
  US13/157,526
• Publication Number:
  US 20110311008A1
• Time in Patent Office: 900 Days
• Field of Search: 375/257, 375/353, 375/354, 375/368, 375371-376, 375/287, 375/360
• US Class Current: 375/353
• CPC Class Codes: H03M 9/00 Parallel/series conversion or vice versa digital stores in which the information is moved stepwise per se G11C19/00
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/0053 Closed loops
• CPC Class Codes: H04L 2027/0067 Phase error detectors
• CPC Class Codes: H04L 2027/0069 Loop filters
• CPC Class Codes: H04L 25/03133 with a non-recursive structure H04L25/03127 takes precedence
• CPC Class Codes: H04L 25/4917 using multilevel codes
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657
• CPC Class Codes: H04L 7/0087 Preprocessing of received signal for synchronisation, e.g. by code conversion, pulse generation or edge detection
• 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

An interface circuit for enabling clock and data recovery (CDR) of N-level pulse amplitude modulation (N-PAM) modulated data streams using a 2-PAM CDR circuit. The circuit comprises a number of N−1 comparators for comparing an input data stream to N−1 configurable thresholds, the input data stream is N-PAM modulated and the N−1 configurable thresholds are N−1 different voltage levels; a number of N−1 of edge detectors respectively connected to the N−1 comparators for detecting transitions from one logic value to another logic value, N is a discrete number greater than two; and a determination unit for determining if the detected transitions is any one of a major transition and a minor transition and asserting a transition signal if only a major transition or a minor transition has occurred, the transition signal is fed into a 2-PAM CDR circuit and utilized for recovering a clock signal of the input data stream.

Claims

1. An interface circuit for enabling clock and data recovery (CDR) of N-level pulse amplitude modulation (N-PAM) modulated data streams using a 2-PAM CDR circuit, comprising:

a number of N−

1 comparators for comparing an input data stream to N−

1 configurable thresholds, wherein the input data stream is N-PAM modulated and the N−

1 configurable thresholds are N−

1 different voltage levels;

a number of N−

1 of edge detectors respectively connected to the N−

1 comparators for detecting transitions from one logic value to another logic value, wherein N is a discrete number greater than two;

a determination unit for determining if a detected transition is any one of a major transition and a minor transition, wherein a major transition is a logic value change in a most significant bit (MSB) and a least significant bit (LSB) remains at a low-logic value, and a minor transition is a logic value change in a LSB or a logic value change in the MSB and the LSB remains at a high-logic value, wherein the MSB and LSB are two bits out of 2 bits in the input data stream; and

asserting a transition signal if only a major transition or a minor transition has occurred, wherein the transition signal is fed into a 2-PAM CDR circuit and utilized for recovering a clock signal of the input data stream by phase aligning to the transitions in the input data stream.

2. The interface circuit of claim 1, further comprising:

a decoder for mapping N−

1 outputs of the N−

1 comparators to bit-data streams and timing the output of the transition signal with the bit-data streams, wherein the number of bit-data stream is based on the number of voltage levels in the input modulated data stream.

3. The interface circuit of claim 2, wherein N equals to four, thereby the interface circuit enables clock and data recovery of 4-PAM modulated data streams using the 2-PAM CDR circuit.

4. The interface circuit of claim 1, wherein the threshold levels are set according to voltage levels of signals transmitter by a transmitter.

5. The interface circuit of claim 1, wherein the threshold levels are calibrated during power up of the interface circuit.

6. The interface circuit of claim 3, wherein the input data stream is compared to three configurable thresholds.

7. The interface circuit of claim 6, wherein a first configurable threshold is set to a common-mode voltage level plus a reference value representing an upper least significant bit (LSB) threshold value, a second configurable threshold is set to a common-mode voltage level representing a most significant bit (MSB) threshold value, and a third configurable threshold is set to a common-mode voltage level minus a reference value representing a lower LSB threshold value.

8. The interface circuit of claim 7, wherein the number of N−

1 of edge detectors includes three edge detectors, wherein a first edge detector detects crossing of the upper LSB threshold, a second edge detector detects crossing of the MSB threshold, and a third edge detector detects crossing of the lower LSB threshold.

9. The interface circuit of claim 8, wherein the determination unit asserts the transition signal when only one of the edge detectors detects crossing or when all of the edge detectors detect crossing.

10. The interface circuit of claim 7, wherein the decoder maps outputs of the first comparator, the second comparator, and the third comparator to two separate bit-data streams respective of the input data stream, thus providing recovered bit-data streams.

11. The interface circuit of claim 10, wherein the decoder is adapted to output a logic value ‘

00’

when all comparators result in crossing of their respective thresholds, output a logic value ‘

01’

when the second and third comparators result in crossing of their respective thresholds;

output a logic value ‘

10’

when the third comparator results in crossing of its respective threshold; and

output a logic value ‘

11’

when none of the comparators result in crossing of their respective thresholds.

12. The interface circuit of claim 1, is further capable of processing 2-PAM modulated input data streams.

13. A receiver connected to a serial multimedia interface for processing high-speed multimedia signals transmitted by a transmitter over the serial multimedia interface, comprising:

an adaptive equalizer for receiving an input data stream over the serial multimedia interface and generating an equalized input data stream, wherein the input data stream is a N-level pulse amplitude modulation (N-PAM) modulated data stream;

an interface circuit connected to the adaptive equalizer for generating a transition signal indicating only major and minor transitions in the equalized input data stream and generating bit-data streams from the equalized input data stream, wherein N is a discrete number greater than two and the number of bit-data streams is based on the number of voltage levels in the input modulated data stream;

a 2-PAM clock and data recover (CDR) circuit for locking on a signal used in transmission of the input data stream by phase aligning to the transitions in the input data stream based, in part, on the transition signal; and

a data sampler for sampling the bit-data stream and generating serial bit streams, each of the serial bit streams includes k bits, wherein a major transition is a logic value change in a most significant bit (MSB) and a least significant bit (LSB) remains at a low-logic value, and a minor transition is a logic value change in a LSB or a logic value change in the MSB and the LSB remains at a high-logic value, wherein the MSB and LSB are two bits out of 2 bits in the input data stream.

14. The receiver of claim 13, wherein the interface circuit comprises:

a number of N−

1 comparators for comparing the equalized input data stream to N−

1 configurable thresholds, wherein the N−

1 configurable thresholds are N−

1 different voltage levels;

a number of N−

1 of edge detectors respectively connected to the N−

1 comparators for detecting transitions from one logic value to another logic value; and

a determination unit for determining if the detected transitions include any one of a major transition and a minor transition and asserting a transition signal if only a major transition or a minor transition has occurred.

15. The receiver of claim 13, wherein the data sampler comprises:

a number of flip-flops as the number of bit-data streams and each samples one of the bit-data streams using the clock signal provided by the 2-PAM CDR circuit; and

a number of de-serializers as the number of flip-flops each respectively connected to the flip-flops and each de-serializer generates a single serial bit stream from a bit-data stream sampled by a flip-flop.

16. The receiver of claim 13, wherein the serial multimedia interface comprises at least one of:

a high-definition multimedia interface (HDMI), a digital video interface (DVI), a DisplayPort (DP), and a universal serial bus (USB).

17. The receiver of claim 13, wherein N equals to four, thereby the receiver enables clock and data recovery of 4-PAM modulated data streams using the 2-PAM CDR circuit.

18. A method for enabling clock and data recovery (CDR) of N-level pulse amplitude modulation (N-PAM) modulated data streams using a 2-PAM CDR circuit comprising:

comparing an input data stream to N−

1 configurable thresholds, wherein the input data stream is N-PAM modulated and the N−

1 configurable thresholds are N−

1 different voltage levels;

detecting transitions from one logic value to another logic value based on comparisons of the input data stream to the N−

1 configurable thresholds, wherein N is a discrete number greater than two; and

determining if the detected transitions include any one of a major transition and a minor transition; and

asserting a transition signal if only a major transition or a minor transition has occurred, wherein the transition signal is fed into a 2-PAM CDR circuit and utilized for recovering a clock signal of the input data stream by phase aligning to the transitions in the input data stream based, in part, on the transition signal, wherein a major transition is a logic value change in a most significant bit (MSB) and a least significant bit (LSB) remains at a low-logic value, and a minor transition is a logic value change in a LSB or a logic value change in the MSB and the LSB remains at a high-logic value, wherein the MSB and LSB are two bits out of 2 bits in the input data stream.

19. The method of claim 18, further comprising:

mapping N−

1 outputs of the N−

1 comparators to bit-data streams; and

timing the outputs of the transition signal with the bit-data streams, the number of bit-data stream is based on the number of voltage levels in the input modulated data stream.

20. The method of claim 18, wherein N equals to four, thereby enabling clock and data recovery of 4-PAM modulated data streams using the 2-PAM CDR circuit.

21. The method of claim 20, wherein the input data stream is compared to three configurable thresholds, wherein a first configurable threshold is set to a common-mode voltage level plus a reference value representing an upper LSB threshold value, a second configurable threshold is set to a common-mode voltage level representing a MSB threshold value, and a third configurable threshold is set to a common-mode voltage level minus a reference value representing a lower LSB threshold value.

22. The method of claim 21, wherein detecting transitions from one logic value to another logic value further comprising:

detecting crossing of the upper LSB threshold, the MSB threshold, and the lower LSB threshold.

23. The method of claim 22, wherein the transition signal is asserted when crossing of only one threshold is detected or crossing or crossing of all the threshold is detected.