Memory access circuit and memory access system

• US 8,819,475 B2
• Filed: 03/20/2012
• Issued: 08/26/2014
• Est. Priority Date: 05/30/2011
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Iijima, Hiroaki
• Primary Examiner(s): Lee, Thomas
• Assistant Examiner(s): Chan, Danny
• Application Number:
  US13/425,338
• Publication Number:
  US 20120311372A1
• Time in Patent Office: 889 Days
• Field of Search: 713/503
• US Class Current: 713/503
• CPC Class Codes: G06F 1/08 Clock generators with changeable or programmable clock frequency
• CPC Class Codes: G06F 1/10 Distribution of clock signals , e.g. skew
• CPC Class Codes: G06F 1/12 Synchronisation of different clock signals provided by a plurality of clock generators

Abstract

According to one embodiment, a memory access circuit includes a PLL, a phy-clock tree, first, second, and master DLLs, and first and second PDs. The PLL generates a PLL output locked to a reference frequency. The phy-clock tree delays the PLL output and generates a reference clock signal. The first DLL corrects a clock skew between reference and system clock signals, and generates a source of the system clock signal. The second DLL corrects a clock skew between reference clock and phy-clock signals, and generates a source of the phy-clock signal. The first and second PDs detect a phase difference, and generate first and second detection signals. The master DLL counts the reference clock signal and generates a delay correction signal. The first and second DLLs determine a correction direction and a correction amount based on first and second detection and delay correction signals, respectively.

Claims

1. A memory access circuit connected to a memory comprising a parallel interface and a system circuit configured to issue a memory access command to command access to the memory, the memory access circuit comprising:

a phase locked loop configured to generate a PLL (Phase Locked Loop) output locked to a reference frequency of a reference signal;

a first phy-clock tree configured to delay the PLL output and to generate a reference clock signal;

a first delay locked loop configured to correct a clock skew between the reference clock signal and a system clock signal generated by the system circuit, and to generate a source signal of the system clock signal;

a second delay locked loop configured to correct a clock skew between the reference clock signal and a phy-clock signal used in the memory access circuit, and to generate a source signal of the phy-clock signal;

a first phase detector configured to detect a phase difference between the system clock signal and the phy-clock signal, and to generate a first detection signal corresponding to the phase difference;

a second phase detector configured to detect a phase difference between the system clock signal and the phy-clock signal, and to generate a second detection signal corresponding to the phase difference; and

a master delay locked loop configured to count the reference clock signal and to generate a delay correction signal, wherein

the first delay locked loop determines a correction direction and a correction amount based on the first detection signal and the delay correction signal, respectively; and

the second delay locked loop determines a correction direction and a correction amount based on the second detection signal and the delay correction signal, respectively.

2. The memory access circuit of claim 1, wherein

at least one of the first delay locked loop and the second delay locked loop comprises,

a plurality of reference phase multiplexers configured to select a plurality of reference phases in the reference clock signal,

a selection phase multiplexer configured to select a selection phase in the reference clock signals,

a plurality of delay element arrays configured to delay the reference clock signal of the reference phases and to generate a delayed reference clock signal of the reference phases,

a DLL (Delay Locked Loop) output multiplexer configured to select one of the reference phases in the delayed reference clock signal,

a phase comparator configured to compare the selection phase and the reference phase, and to generate a clock skew signal corresponding to a phase difference between the selection phase and the reference phase, and

a delay controller configured to control the reference phase multiplexer, the selection phase multiplexer, and the DLL output multiplexer in such a manner that a phase to be selected is switched on the basis of the clock skew signal, and to adjust number of delay elements to be operated on the basis of the delay correction signal with respect to the delay element array.

3. The memory access circuit of claim 1, further comprising:

a second phy-clock tree configured to delay the reference clock signal and to generate a DLL (Delay Locked Loop) clock signal;

a third phy-clock tree configured to delay the output of the second delay locked loop and to generate the phy-clock signal;

a third delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a strobe signal to be provided to the memory;

a fourth delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a data clock to be provided to the memory; and

a set angle calculating module configured to calculate a set angle to be provided to the third delay locked loop and the fourth delay locked loop based on the correction amount of the second delay locked loop;

wherein

the third delay locked loop and the fourth delay locked loop correct the clock skew based on the set angle.

4. The memory access circuit of claim 2, further comprising:

a second phy-clock tree configured to delay the reference clock signal and to generate a DLL (Delay Locked Loop) clock signal;

a third phy-clock tree configured to delay the output of the second delay locked loop and to generate the phy-clock signal;

a third delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a strobe signal to be provided to the memory;

a fourth delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a data clock to be provided to the memory; and

a set angle calculating module configured to calculate a set angle to be provided to the third delay locked loop and the fourth delay locked loop based on the correction amount of the second delay locked loop;

wherein

the third delay locked loop and the fourth delay locked loop correct the clock skew based on the set angle.

5. The memory access circuit of claim 1, wherein at least one of the first delay locked loop and the second delay locked loop comprises,

a reference phase multiplexer configured to select one reference phase in the reference clock signal,

a delay element array configured to delay the reference clock signal of the reference phase and to generate a delayed reference clock signal, and

a delay controller configured to control the reference phase multiplexer to switch a phase to be selected on the basis of the delay correction signal, and to adjust number of delay elements to be operated with respect to the delay element array.

6. The memory access circuit of claim 2, wherein the delay controller calculates the correction amount for every phase in the reference clock signal.

7. The memory access circuit of claim 4, wherein the delay controller calculates the correction amount for every phase in the reference clock signal.

8. The memory access circuit of claim 5, wherein the delay controller calculates the correction amount for every phase in the reference clock signal.

9. A memory access system comprising:

a memory comprising a parallel interface;

a system circuit configured to issue a memory access command to command an access to the memory; and

a memory access circuit connected to the memory and the system circuit;

wherein

the memory access circuit comprises,

a phase locked loop configured to generate a PLL (Phase Locked Loop) output locked to a reference frequency of a reference signal,

a first phy-clock tree configured to delay the PLL output and to generate a reference clock signal,

a first delay locked loop configured to correct a clock skew between the reference clock signal and a system clock signal generated by the system circuit, and to generate a source signal of the system clock signal,

a second delay locked loop configured to correct a clock skew between the reference clock signal and a phy-clock signal used in the memory access circuit, and to generate a source signal of the phy-clock signal,

a first phase detector configured to detect a phase difference between the system clock signal and the phy-clock signal, and to generate a first detection signal corresponding to the phase difference,

a second phase detector configured to detect a phase difference between the system clock signal and the phy-clock signal, and to generate a second detection signal corresponding to the phase difference; and

a master delay locked loop configured to count the reference clock signal and to generate a delay correction signal, wherein

the first delay locked loop determines a correction direction and a correction amount based on the first detection signal and the delay correction signal, respectively; and

the second delay locked loop determines a correction direction and a correction amount based on the second detection signal and the delay correction signal, respectively.

10. The memory access system of claim 9, wherein

at least one of the first delay locked loop and the second delay locked loop comprises,

a plurality of reference phase multiplexers configured to select a plurality of reference phases in the reference clock signal,

a selection phase multiplexer configured to select a selection phase in the reference clock signals,

a plurality of delay element arrays configured to delay the reference clock signal of the reference phases and to generate a delayed reference clock signal of the reference phases,

a DLL (Delay Locked Loop) output multiplexer configured to select one of the reference phases in the delayed reference clock signal,

a phase comparator configured to compare the selection phase and the reference phase, and to generate a clock skew signal corresponding to a phase difference between the selection phase and the reference phase, and

a delay controller configured to control the reference phase multiplexer, the selection phase multiplexer, and the DLL output multiplexer in such a manner that a phase to be selected is switched on the basis of the clock skew signal, and to adjust number of delay elements to be operated on the basis of the delay correction signal with respect to the delay element array.

11. The memory access system of claim 9, further comprising:

a second phy-clock tree configured to delay the reference clock signal and to generate a DLL (Delay Locked Loop) clock signal;

a third phy-clock tree configured to delay the output of the second delay locked loop and to generate the phy-clock signal;

a third delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a strobe signal to be provided to the memory;

a fourth delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a data clock to be provided to the memory; and

a set angle calculating module configured to calculate a set angle to be provided to the third delay locked loop and the fourth delay locked loop based on the correction amount of the second delay locked loop;

wherein

the third delay locked loop and the fourth delay locked loop correct the clock skew based on the set angle.

12. The memory access system of claim 10, further comprising:

a second phy-clock tree configured to delay the reference clock signal and to generate a DLL (Delay Locked Loop) clock signal;

a third phy-clock tree configured to delay the output of the second delay locked loop and to generate the phy-clock signal;

a third delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a strobe signal to be provided to the memory;

a fourth delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a data clock to be provided to the memory; and

a set angle calculating module configured to calculate a set angle to be provided to the third delay locked loop and the fourth delay locked loop based on the correction amount of the second delay locked loop;

wherein

the third delay locked loop and the fourth delay locked loop correct the clock skew based on the set angle.

13. The memory access system of claim 9, wherein

at least one of the first delay locked loop and the second delay locked loop comprises,

a reference phase multiplexer configured to select one reference phase in the reference clock signal,

a delay element array configured to delay the reference clock signal of the reference phase and to generate a delayed reference clock signal, and

a delay controller configured to control the reference phase multiplexer to switch a phase to be selected on the basis of the delay correction signal, and to adjust number of delay elements to be operated with respect to the delay element array.

14. The memory access system of claim 10, wherein the delay controller calculates the correction amount for every phase in the reference clock signal.

15. The memory access system of claim 12, wherein the delay controller calculates the correction amount for every phase in the reference clock signal.

16. The memory access system of claim 13, wherein the delay controller calculates the correction amount for every phase in the reference clock signal.

17. A memory access circuit connected to a memory comprising a parallel interface and a system circuit configured to issue a memory access command to command access to the memory and to generate a system clock signal;

the memory access circuit comprising;

a phase locked loop configured to generate a PLL (Phase Locked Loop) output locked to a reference frequency of a reference signal from the system clock signal;

a first phy-clock tree configured to delay the PLL output and to generate a reference clock signal;

a delay locked loop configured to correct a clock skew between the reference clock signal and a phy clock signal used in the memory access circuit and to generate a source signal of the phy-clock signal;

a phase detector configured to detect a phase difference between the reference clock signal and the phy-clock signal, and to generate a detection signal corresponding to the phase difference; and

a master delay locked loop configured to count the reference clock signal and to generate a delay correction signal, wherein

the delay locked loop determines a correction direction and a correction amount based on the detection signal and the delay correction signal, respectively.

18. The memory access circuit of claim 17, wherein

at least one of the first delay locked loop and the second delay locked loop comprises,

a plurality of reference phase multiplexers configured to select a plurality of reference phases in the reference clock signal,

a selection phase multiplexer configured to select a selection phase in the reference clock signals,

a plurality of delay element arrays configured to delay the reference clock signal of the reference phases and to generate a delayed reference clock signal of the reference phases,

a DLL (Delay Locked Loop) output multiplexer configured to select one of the reference phases in the delayed reference clock signal,

a phase comparator configured to compare the selection phase and the reference phase, and to generate a clock skew signal corresponding to a phase difference between the selection phase and the reference phase, and

a delay controller configured to control the reference phase multiplexer, the selection phase multiplexer, and the DLL output multiplexer in such a manner that a phase to be selected is switched on the basis of the clock skew signal, and to adjust number of delay elements to be operated on the basis of the delay correction signal with respect to the delay element array.

19. The memory access circuit of claim 17, further comprising:

a second phy-clock tree configured to delay the reference clock signal and to generate a DLL (Delay Locked Loop) clock signal;

a third phy-clock tree configured to delay the output of the second delay locked loop and to generate the phy-clock signal;

a third delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a strobe signal to be provided to the memory;

a fourth delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a data clock to be provided to the memory; and

a set angle calculating module configured to calculate a set angle to be provided to the third delay locked loop and the fourth delay locked loop based on the correction amount of the second delay locked loop;

wherein the

third delay locked loop and the fourth delay locked loop correct the clock skew based on the set angle.

20. The memory access circuit of claim 18, further comprising:

a second phy-clock tree configured to delay the reference clock signal and to generate a DLL (Delay Locked Loop) clock signal;

a third phy-clock tree configured to delay the output of the second delay locked loop and to generate the phy-clock signal;

a third delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a strobe signal to be provided to the memory;

a fourth delay locked loop configured to correct a clock skew between the reference clock signal and the DLL clock signal, and to generate a source signal of a data clock to be provided to the memory; and

a set angle calculating module configured to calculate a set angle to be provided to the third delay locked loop and the fourth delay locked loop based on the correction amount of the second delay locked loop;

wherein

the third delay locked loop and the fourth delay locked loop correct the clock skew based on the set angle.