Linear phase interpolator and phase detector

• US 20090103675A1
• Filed: 04/15/2008
• Published: 04/23/2009
• Est. Priority Date: 10/19/2007
• Status: Active Grant

• Current Assignee: Rambus Inc.
• Original Assignee: Diablo Technologies Incorporated (Rambus Inc.)
• Inventors: Yousefi Moghaddam, Gholamreza, Kanesapillai, Sivakumar, Pfaff, Dirk
• Granted Patent: US 8,218,705 B2
• Time in Patent Office: Days
• US Class Current: 375/376
• CPC Class Codes: H03L 7/0995 the oscillator comprising a ring oscillator
• CPC Class Codes: H03L 7/10 for assuring initial synchronisation or for broadening the capture range
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

A novel interpolating phase detector for use in a multiphase PLL is described comprising an array of individual phase comparators, all operating at essentially the same operating point which permits the circuits to be designed simultaneously for high speed and for low power consumption. Two adjacent phase outputs of a multi-phase VCO may be selected and interpolated in between, by selectively attaching a variable number of phase comparators to each phase output and summing their phase error outputs. By varying the number of phase comparators attached to each phase output, interpolation can be achieved with high linearity.

Claims

1. An interpolating phase detector array for comparing a phase of a reference clock signal with phases of a set of K phase shifted clock signals and generating a phase error output signal, the interpolating phase detector array comprising:

a plurality of N phase detector columns, each column including;

a plurality of M exclusive-OR (XOR) blocks, each block having;

inputs for receiving the reference clock signal, receiving two of the phase shifted clock signals, receiving “

coarse”

control signals for enabling said received phase shifted clock signals; and

a phase error output;

a steerable current source having first and second current sink outputs for delivering a bias current to two distinct sets of XOR blocks, and having an input to receive a “

fine”

control signal for directing the bias current to one of said distinct sets; and

a current output IOUT for delivering the phase error output signal formed by joining phase error outputs of the XOR blocks.

2. The interpolating phase detector array as described in claim 1, wherein the received phase shifted clock signals are selected from the set of K phase shifted clock signals to have phases differing by 180 degrees.

3. The interpolating phase detector array as described in claim 1, wherein each of the received phase shifted clock signals is connected to one of the XOR-blocks in each phase detector column.

4. The interpolating phase detector array as described in claim 1, wherein all N steerable current sources are designed to deliver substantially the same unit strength of the bias current.

5. The interpolating phase detector array as described in claim 1, wherein N−

1 steerable current sources are designed to deliver substantially the same unit strength of the bias current, and one steerable current source is designed to deliver the bias current with a strength of ½

unit.

6. The interpolating phase detector array as described in claim 1, wherein M=4 and K=8.

7. The interpolating phase detector array as described in claim 1, wherein N=9.

8. An interpolating phase detector array for comparing a phase of a reference clock signal with phases of a set of K phase shifted clock signals and generating a phase error output signal, the phase detector array comprising:

a matrix of M rows by N columns of exclusive-OR (XOR) blocks, and a set of N steerable current sources;

each of the XOR blocks including a reference clock input connected to the reference clock signal, further including first and second phase shifted clock inputs connected to selected ones of the set of phase shifted clock signals, a bias current input, and a phase error output, the phase error outputs of all XOR blocks being joined into a current output IOUT for delivering the phase error output signal; and

each of the N steerable current sources being assigned to a distinct one of the columns of the XOR-blocks, each steerable current source including a first current sink output connected to the bias current inputs of the XOR-blocks of odd-numbered rows, and second current sink outputs connected to the bias current inputs of the XOR-blocks of even-numbered rows.

9. The interpolating phase detector array as described in claim 8, wherein each XOR block further includes first and second “

coarse”

control inputs for enabling corresponding first and second phase shifted clock inputs, and wherein each steerable current source further includes a “

fine”

control input for steering the bias current to either the first or second current sink outputs.

10. The interpolating phase detector array as described in claim 8, wherein all N steerable current sources are designed to deliver substantially the same unit strength of the bias current.

11. The interpolating phase detector array as described in claim 8, wherein N−

1 steerable current sources are designed to deliver substantially the same unit strength of the bias current, and one steerable current source is designed to deliver the bias current with a strength of ½

unit.

12. The interpolating phase detector array as described in claim 8, wherein M=4 and K=8.

13. The interpolating phase detector array as described in claim 8, wherein N=9.

14. A method for detecting a phase error in an interpolating phase detector array, including the steps of:

providing an array of XOR blocks arranged in M rows and N columns for comparing a phase of a reference clock signal with phases of a set of K phase shifted clock signals;

enabling a first subset of the XOR blocks in one of the M rows to perform the comparison with the phase of a first one of the K phase shifted clock signals, under control of a first “

coarse”

control signal;

enabling a second subset of the XOR blocks in a different one of the M rows to perform the comparison with the phase of a second one of the K phase shifted clock signals, under control of a second “

coarse”

control signal, the phase of the second phase shifted clock signal differing from the phase of the first phase shifted clock signal by approximately 360/K degrees;

providing each enabled XOR block with a bias current of unit strength; and

generating a phase error output signal by combining comparison outputs from all enabled XOR blocks.

15. The method for detecting a phase error of claim 14, wherein providing each enabled XOR block with a bias current includes steering the bias current from one of N steerable current sources individually assigned to a column to XOR blocks in the column in odd-numbered and even-numbered rows respectively, dependent on the state of a “

fine”

control signal applied to the steerable current source.

16. The method for detecting a phase error of claim 15, further comprising the step of selecting a combination of states of the N “

fine”

control signals to steer the bias current to a first and second subsets of the XOR blocks in the odd-numbered and even-numbered rows respectively.

17. The method for detecting a phase error of claim 16, further comprising the step of combining the phase error outputs from the enabled XOR blocks of the each subset yielding a combined phase error output current of a strength in proportion to a size of the respective subset.

18. The method for detecting a phase error of claim 15, wherein M=4, K=8, and N=9.

19. A phase lock loop (PLL) including a multiphase voltage controlled oscillator (VCO) generating a set of K phase shifted clock signals whose frequency is controlled through a frequency control input, and an interpolating phase detector array designed for comparing a phase of a reference clock signal with phases of the phase shifted clock signals and for generating a phase error output signal, the interpolating phase detector array comprising:

a plurality of N phase detector columns, each phase detector column including;

a plurality of M exclusive-OR (XOR) blocks, each having inputs for receiving the reference clock signal, receiving two of the phase shifted clock signals, receiving “

coarse”

control signals for enabling said received phase shifted clock signals, and having a phase error output; and

a steerable current source having first and second current sink outputs for delivering a bias current to two distinct sets of XOR blocks, and having an input to receive a “

fine”

control signal for directing the bias current to one of said distinct sets; and

the phase error outputs of all XOR blocks being joined into a current output IOUT for delivering the phase error output signal.

20. The PLL as described in claim 19 further including a current to voltage converter coupled to the current output IOUT, for converting the phase error output current IOUT into a voltage phase error voltage SEC coupled to the frequency control input of the VCO.

21. The PLL as described in claim 19, wherein each of the received phase shifted clock signals is connected to one of the XOR blocks in each phase detector column.

22. The PLL as described in claim 19, wherein all N steerable current sources are designed to deliver substantially the same unit strength of the bias current.

23. The PLL as described in claim 19 wherein N−

1 steerable current sources are designed to deliver substantially the same unit strength of the bias current, and one steerable current source is designed to deliver the bias current with a strength of ½

unit.

24. The PLL as described in claim 19, wherein M=4 and K=8.

25. The PLL as described in claim 19, wherein N=9.