Frequency Lock Stability in Device Using Overlapping VCO Bands

• US 20090147904A1
• Filed: 02/18/2009
• Published: 06/11/2009
• Est. Priority Date: 11/09/2006
• Status: Active Grant

• Current Assignee: MACOM Connectivity Solutions, LLC (MACOM Technology Solutions Holdings, Inc.)
• Original Assignee: Applied Micro Circuits Corporation (MACOM Technology Solutions Holdings, Inc.)
• Inventors: Pang, Simon, Do, Viet Linh, Eker, Mehmet Mustafa
• Granted Patent: US 8,121,242 B2
• Time in Patent Office: Days
• US Class Current: 375/376
• CPC Class Codes: H03L 7/0891 the up-down pulses controlling source and sink current generators, e.g. a charge pump
• CPC Class Codes: H03L 7/113 using frequency discriminator
• CPC Class Codes: H03L 7/1976 using a phase accumulator for controlling the counter or frequency divider
• CPC Class Codes: H04L 7/0004 Initialisation of the receiver H04L7/0075 and H04L7/10 take precedence
• 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

A system and method are provided for frequency lock stability in a receiver using overlapping voltage controlled oscillator (VCO) bands. An input communication signal is accepted and an initial VCO is selected. Using a phase-locked loop (PLL) and the initial VCO, the frequency of the input communication signal is acquired and the acquired signal tuning voltage of the initial VCO is measured. Then, the initial VCO is disengaged and a plurality of adjacent band VCOs is sequentially engaged. The acquired signal tuning voltage of each VCO is measured and a final VCO is selected that is able to generate the input communication signal frequency using an acquired signal tuning voltage closest to a midpoint of a predetermined tuning voltage range.

Claims

1. In a receiver device, a method for frequency lock stability using overlapping voltage controlled oscillator (VCO) bands, the method comprising:

in a receiving device including a plurality of VCOs with overlapping frequency bands, accepting an input communication signal;

selecting an initial VCO;

using a phase-locked loop (PLL) and the initial VCO, acquiring the frequency of the input communication signal;

measuring the acquired signal tuning voltage of the initial VCO;

disengaging the initial VCO and sequentially engaging a plurality of adjacent band VCOs;

measuring the acquired signal tuning voltage of each VCO; and

,

selecting a final VCO able to generate the input communication signal frequency using an acquired signal tuning voltage closest to a midpoint of a predetermined tuning voltage range.

2. The method of claim 1 wherein selecting the final VCO able to generate the input communication signal frequency includes:

dividing the tuning voltage range into a plurality of data points;

comparing the acquired signal tuning voltage of each VCO to the data points;

selecting the VCO with the fewest number of data points between the acquired signal tuning voltage and the midpoint of the tuning voltage range.

3. The method of claim 2 wherein selecting the VCO with the fewest number of data points between the acquired signal tuning voltage and the midpoint of the tuning voltage range includes:

for each VCO, counting the number of data points between the voltage range midpoint and the acquired signal tuning voltage;

comparing the count for each VCO; and

,

selecting the VCO with the lowest count.

4. The method of claim 3 wherein dividing the voltage range into a plurality of data points includes dividing the voltage range into a first plurality of low range data points between a minimum voltage and the midpoint of the tuning voltage range, and a second plurality of high range data points between a maximum voltage and the midpoint of the tuning voltage range;

wherein counting the number of data points between the voltage range midpoint and the acquired signal tuning voltage includes;

determining if an acquired signal is in a range selected from a group consisting of the high range and the low range; and

,

counting the number of data points in the selected range between the acquired signal tuning voltage and the midpoint of the tuning voltage range.

5. The method of claim 1 wherein the receiver is a clock and data recovery (CDR) device accepting the input communication signal includes accepting an input communication signal having a non-predetermined frequency;

and,

wherein selecting the initial VCO includes selecting the initial VCO in response to a coarse frequency acquisition (CFA) process.

6. The method of claim 5 wherein selecting the initial VCO in response to the CFA process includes:

initially determining a coarse clock frequency using a first sampling measurement;

finally determining the coarse clock frequency using a second sampling measurement;

subsequent to determining the coarse clock frequency, enabling a rotational frequency detector RFD to acquire the frequency of the input communication signal using a VCO signal generated by the initial VCO.

7. The method of claim 6 wherein initially determining the coarse clock frequency using the first sampling measurement includes:

selecting a high frequency first reference clock (Fref1);

counting the number of data transitions in a first time segment of the input communication signal at a plurality of sample frequencies equal to Fref1/n, where n is an integer ≧

1;

comparing the count for each sampling frequency, to the count for Fref1 (n=1);

determining the highest sampling frequency (n=x) having a lower count than Fref1; and

,

setting the coarse clock frequency to Fc1=Fref1/(x−

1).

8. The method of claim 7 wherein finally determining the coarse clock frequency using the second sampling measurement includes:

selecting a plurality of sub-reference clocks, the combination of which covers the frequency band between Fref1/x and Fref1/(x−

1);

counting the number of data transitions in the first time segment of the input communication signal at the plurality of sub-reference clock frequencies;

comparing the count for each sub-reference clock to the count for Fref1;

determining the lowest frequency sub-reference clock (Fc2) having a count equal to Fref1; and

,

selecting the final coarse clock frequency to Fc2 as the initial vco.

9. The method of claim 8 wherein selecting the plurality of sub-reference clocks includes selecting a plurality of tunable sub-reference clocks, the combination of which can be tuned to cover the frequency band between Fref1/x and Fref1/(x−

1);

wherein counting the number of data transitions in the first time segment of the input communication signal at the plurality of sub-reference clock frequencies includes;

tuning each sub-reference clock to the low end of its frequency sub-band; and

counting data transitions; and

,

wherein determining the lowest frequency sub-reference clock (Fc2) having a count equal to Fref1 includes determining the highest frequency sub-reference clock having a lower count than Fref1.

10. The method of claim 1 further comprising:

subsequent to acquiring the frequency of the input communication signal using the final VCO, substituting a phase detector (PHD) for the frequency detector in the PLL; and

,

acquiring the phase of the input communication signal.

11. In a receiver using a plurality of voltage controlled oscillators (VCOs) with overlapping frequency bands, a system for frequency lock stability comprising:

a plurality of VCOs for generating VCO signals in overlapping frequency bands;

a phase-locked loop (PLL) including;

a frequency detector to acquire the frequency of an input communication signal with respect to a VCO signal, and an output to supply a VCO tuning voltage;

an initial VCO having an input to accept the tuning voltage and an output to supply the VCO signal;

a multiplexer (MUX) having an input to accept the tuning voltage from the frequency detector, a control signal input, and a plurality of selectable outputs, each output connected to a corresponding VCO to supply the tuning voltage in response to the control signal;

a frequency stability module (FSM) having an interface to measure tuning voltage and an output to supply the control signal to the MUX, the FSM measuring the acquired signal tuning voltage of the initial VCO, disengaging the initial VCO and sequential engaging a plurality of adjacent band VCOs, the FSM measuring the acquired signal tuning voltage of each VCO and selecting a final VCO able to generate the input communication signal frequency using an acquired signal tuning voltage closest to a midpoint of a predetermined tuning voltage range.

12. The system of claim 11 wherein the FSM includes:

a controller to supply data point voltages;

a comparator having a first input to accept the acquired signal tuning voltage, a second input to accept the data point voltages, and an output to supply a voltage comparison;

a memory to record the voltage comparisons for each VCO;

wherein the controller having an interface to access the record of voltage comparisons in memory and an output to supply a control signal to the MUX, selecting the final VCO as the one with the fewest number of data points between the acquired signal tuning voltage and the midpoint of the tuning voltage range.

13. The system of claim 12 wherein the memory records a count of the number of data points between the tuning voltage range midpoint and the acquired signal tuning voltage for each VCO;

and,

wherein the controller accesses the count for each VCO from memory and selects the VCO with the lowest count.

14. The system of claim 13 wherein the controller supplies the comparator with data points for each VCO selected from a group consisting of a first plurality of low range data points between a minimum voltage and the midpoint of the tuning voltage range, and a second plurality of high range data points between a maximum voltage and the midpoint of the tuning voltage range;

and,

wherein the memory records a count of the number of data points in the selected range between the acquired signal tuning voltage and the midpoint of the tuning voltage range.

15. The system of claim 11 wherein the receiver is a clock and data recovery (CDR) device;

wherein the PLL accepts an input communication signal having a non-predetermined frequency; and

,

the system further comprising;

a coarse determination module (CDM) having an input to accept the input communication signal and an output to supply a control signal to the MUX selecting the initial VCO.

16. The system of claim 15 wherein the CDM initially determines the coarse clock frequency using a first sampling measurement and supplies a finally determined coarse clock frequency using a second sampling measurement;

and,

wherein the PLL frequency detector in a rotational frequency detector (RFD) selectively enabled subsequent to determining the coarse clock frequency, to acquire the frequency of the input communication signal using a VCO signal generated by the initial VCO.

17. The system of claim 16 further comprising:

a reference clock having an output to supply a high frequency first reference clock frequency Fref1;

wherein the CDM has an input connected to the reference clock output, the CDM initially determining the coarse clock frequency as follows;

counting the number of data transitions in a first time segment of the input communication signal at a plurality of sample frequencies equal to Fref1/n, where it is an integer ≧

1;

comparing the count for each sampling frequency, to the count for Fref1 (n=1);

determining the highest sampling frequency (n=x) having a lower count than Fref1; and

,

setting the coarse clock frequency to Fc1=Fref1/(x−

1).

18. The system of claim 17 wherein the CDM further comprising:

a plurality of sub-reference clocks, the combination of which covers the frequency band between Fref1/x and Fref1/(x−

1);

wherein the CDM finally determines the coarse clock frequency as follows;

counting the number of data transitions in the first time segment of the input communication signal at the plurality of sub-reference clock frequencies;

comparing the count for each sub-reference clock to the count for Fref1;

determining the lowest frequency sub-reference clock (Fc2) having a count equal to Fref1; and

,

setting the final coarse clock frequency to Fc2 and selecting the lowest sub-reference clock as the initial VCO.

19. The system of claim 18 wherein the plurality of sub-reference clocks are tunable sub-reference clocks, the combination of which can be tuned to cover the frequency band between Fref1/x and Fref1/(x−

1);

wherein the CDM counts the number of data transitions in the first time segment of the input communication signal at the plurality of sub-reference clock frequencies as follows;

tuning each sub-reference clock to the low end of its frequency sub-band;

counting data transitions; and

,

determining the highest frequency sub-reference clock having a lower count than Fref1.

20. The system of claim 11 wherein the frequency detector is a selectively enabled;

and,

wherein the PLL includes a phase detector (PHD) selectively enabled subsequent to the frequency detector acquiring the frequency of the input communication signal using the final VCO, to acquire the phase of the input communication signal.