System and method to speed up PLL lock time on subsequent calibrations via stored band values

1. A phase lock loop (PLL) calibration apparatus for phased lock loop (PLL) circuit having a voltage controlled oscillator (VCO) providing an output frequency, said apparatus comprising:

a logic circuit for setting an initial frequency band value for use in prior calibrating a PLL circuit, and iteratively incrementing said frequency band value settings for said prior PLL circuit calibrating until achieving a PLL circuit lock condition at a particular operating frequency; and

a memory storage device operably coupled to said logic circuit for storing said frequency band value setting used for achieving said PLL circuit lock condition at the particular operating frequency,

a reset signal received at said logic circuit for triggering a new PLL circuit calibration at said particular operating frequency;

a fast calibration signal received at said logic circuit and asserted to directly forward said stored frequency band value setting stored in said memory storage device to said VCO for said new PLL circuit calibration,

wherein said VCO uses said frequency band value setting from the prior PLL calibration stored in said memory storage device as said initial frequency for said new PLL circuit calibration,

wherein the PLL lock in said new calibration is achieved in a reduced amount of time.

2. The PLL calibration apparatus as claimed in claim 1 , wherein said initial frequency band value setting corresponds to a base frequency band which is a lowest frequency band among a plurality of sequentially higher frequency bands to be used with said PLL circuit calibrating, said memory storage device storing said initial frequency band value setting.

3. The PLL calibration apparatus as claimed in claim 2 , wherein said logic circuit receives the reset signal and a de-asserted fast calibration signal and responsively initiating, at said logic circuit, a triggering of said new calibration of said PLL circuit using the base frequency band value setting.

4. The PLL calibration apparatus as claimed in claim 2 , wherein said logic circuit further comprises:

a multiplexor circuit, receiving at a first input said initial base frequency band value setting, and receiving at a second input said stored achieved frequency band value setting, said multiplexor circuit responsive to a receipt of said asserted fast calibration signal for outputting said stored achieved frequency band value setting.

5. The PLL calibration apparatus as claimed in claim 1 , wherein said logic circuit, upon receiving said reset signal and an asserted fast calibration signal, responsively initiates triggering of said subsequent calibration of said PLL circuit using a frequency band value setting that corresponds to a lower frequency band than said stored prior achieved frequency band value setting, said frequency band value setting that corresponds to a lower frequency band being used as said initial frequency.

6. The PLL calibration apparatus as claimed in claim 5 , wherein said stored prior achieved frequency band value setting corresponds to a frequency band N, said frequency band value setting that corresponds to a lower frequency band corresponds to a frequency band N−1 or a frequency band less than N−1.

7. The PLL calibration apparatus as claimed in claim 6 , wherein for said PLL calibrating, said PLL calibration apparatus initiates a sweeping of frequency bands from a frequency band value setting corresponding to a lower frequency band N−1 setting or lower frequency band setting, and incrementing said bands in achieving a PLL lock condition from said frequency band N−1 or a lower band setting, to account for any variations in a temperature or a voltage used in said PLL circuit.

8. The PLL calibration apparatus as claimed in claim 6 , further comprising: reporting an error in calibration when it is determined that a current frequency band has been stepped up to the maximum frequency band of the plurality of bands and the size of the smallest selection window is equal to a preset maximum size and without the calibration of the PLL circuit device having been completed.

9. A method of calibrating a phase lock loop (PLL) circuit having a voltage controlled oscillator (VCO) providing an output frequency comprising:

setting, at a calibration logic circuit device, an initial frequency band value for use in prior calibrating a PLL circuit, and during the prior PLL calibrating, iteratively incrementing said frequency band value settings until achieving a PLL circuit lock condition at a particular operating frequency; and

storing, in a memory storage device operably coupled to said logic circuit, said frequency band value setting used for achieving said PLL circuit lock condition at the particular operating frequency,

receiving at said logic circuit device, a reset signal for triggering a new PLL circuit calibration at said particular operating frequency;

receiving at said logic circuit device, a fast calibration signal asserted to directly forward said stored frequency band value setting stored in said memory storage device to said VCO for said new PLL circuit calibration,

wherein said VCO uses said frequency band value setting from the prior PLL calibration stored in said memory storage device as said initial frequency for said new PLL circuit calibration,

wherein the PLL lock in said subsequent calibration is achieved in a reduced amount of time.

10. The method as claimed in claim 9 , wherein said initial frequency band value setting corresponds to a base frequency band which is a lowest frequency band among a plurality of sequentially higher frequency bands to be used with said PLL circuit calibrating, said memory storage device storing said initial frequency band value setting.

11. The method as claimed in claim 10 , further comprising:

receiving, at said calibration logic circuit device, the reset signal and a de-asserted fast calibration signal and responsively initiating, at said logic circuit, a triggering of said new calibration of said PLL circuit using the base frequency band value setting.

12. The method as claimed in claim 10 , wherein said calibration logic circuit device comprises a multiplexor device, said method further comprising:

receiving, at a first input of said multiplexor device, said initial base frequency band value setting;

receiving at a second input of said multiplexor device said stored achieved frequency band value setting, and

said multiplexor device responding to receipt of said asserted fast calibration signal for outputting said stored achieved frequency band value setting.

13. The method as claimed in claim 9 , wherein in response to receiving at said calibration logic circuit said reset signal and an asserted fast calibration signal, initiating triggering of said subsequent calibration of said PLL circuit using a frequency band value setting that corresponds to a lower frequency band than said stored prior achieved frequency band value setting, said frequency band value setting that corresponds to a lower frequency band being used as said initial frequency.

14. The method as claimed in claim 13 , wherein said stored prior achieved frequency band value setting corresponds to a frequency band N, said frequency band value setting that corresponds to a lower frequency band corresponds to a frequency band N−1 or a frequency band less than N−1.

15. The method as claimed in claim 14 , wherein said PLL calibrating comprises:

sweeping of applied frequency bands from a frequency band value setting corresponding to a lower frequency band N−1 setting or lower frequency band setting, and incrementing said bands in achieving a PLL lock condition from said frequency band N−1 or a lower band setting, to account for any variations in a temperature or a voltage used in said PLL circuit.

16. The method as claimed in claim 14 , further comprising: reporting an error in calibration when it is determined that a current frequency band has been stepped up to the maximum frequency band of the plurality of bands and the size of the smallest selection window is equal to a preset maximum size and without the calibration of the PLL circuit device having been completed.

17. A computer program product for calibrating a phase lock loop (PLL) circuit having a voltage controlled oscillator (VCO) providing an output frequency comprising:

a computer readable storage medium having program instructions embodied therewith, wherein the computer readable storage medium is not a transitory signal per se, the program instructions readable by a processing circuit to cause the processing circuit to perform a method to:

set, at a calibration logic circuit device, an initial frequency band value for use in prior calibrating a PLL circuit, and during the prior PLL calibrating, iteratively increment said frequency band value settings until achieving a PLL circuit lock condition at a particular operating frequency; and

store, in a memory storage device operably coupled to said logic circuit, said frequency band value setting used for achieving said PLL circuit lock condition at the particular operating frequency,

receive at said calibration logic circuit device, a reset signal for triggering a new PLL circuit calibration at said particular operating frequency;

receive at said calibration logic circuit device, a fast calibration signal asserted to directly forward said stored frequency band value setting stored in said memory storage device to said VCO for said new PLL circuit calibration,

wherein said VCO uses said frequency band value setting from the prior PLL calibration stored in said memory storage device as said initial frequency for said new PLL circuit calibration,

wherein the PLL lock in said subsequent calibration is achieved in a reduced amount of time.