VCO CAPACITOR BANK TRIMMING AND CALIBRATION

• US 20090278620A1
• Filed: 05/07/2008
• Published: 11/12/2009
• Est. Priority Date: 05/07/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Lee, Sang-Oh, Taghivand, Mazhareddin, Yang, Jeongsik
• Granted Patent: US 7,855,610 B2
• Time in Patent Office: Days
• US Class Current: 331/36.C
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/10 for assuring initial synchronisation or for broadening the capture range

Abstract

Techniques are disclosed for trimming a capacitance associated with a capacitor bank for use in a voltage-controlled oscillator (VCO). In an embodiment, each capacitance is sub-divided into a plurality of constituent capacitances. The constituent capacitances may be selectively enabled or disabled to trim the step sizes of the capacitor bank. Further techniques are disclosed for calibrating the trimmable capacitance to minimize step size error for the capacitor bank.

Claims

1. A capacitor bank for a voltage-controlled oscillator (VCO), the capacitor bank comprising a plurality of nominal selectable capacitances, at least one of the nominal selectable capacitances comprising:

at least one sub-capacitance configurable to contribute to the capacitance of the at least one selectable capacitance based on a trim setting control signal, the at least one sub-capacitance having a capacitance less than the nominal value of the at least one of the nominal selectable capacitances.

2. The capacitor bank of claim 1, each of the plurality of nominal selectable capacitances comprising:

at least one sub-capacitance configurable to contribute to the capacitance of the at least one selectable capacitance based on the trim setting control signal, the at least one of the sub-capacitance having a capacitance less than the nominal value of the at least one of the nominal selectable capacitances.

3. The capacitor bank of claim 1, at least one of the nominal selectable capacitances comprising:

a plurality of sub-capacitances configurable to contribute to the capacitance of the at least one selectable capacitance based on the trim setting control signal, each of the plurality of sub-capacitances having a capacitance less than the nominal value of the at least one of the nominal selectable capacitances.

4. The capacitor bank of claim 2, each of the plurality of nominal selectable capacitances comprising:

a corresponding plurality of sub-capacitances configurable to contribute to the capacitance of the corresponding nominal selectable capacitance based on the trim setting control signal, each of the plurality of sub-capacitances having a capacitance less than the nominal value of the corresponding nominal selectable capacitance.

5. The capacitor bank of claim 1, the trim setting control signal comprising multiple control signals, each control signal opening or closing a switch to disable or enable a corresponding capacitance.

6. The capacitor bank of claim 1, the at least one sub-capacitance comprising a plurality of binary-weighted sub-capacitances.

7. The capacitor bank of claim 1, the at least one sub-capacitance comprising a plurality of sub-capacitances having a total capacitance greater than the nominal capacitance of the corresponding nominal selectable capacitance.

8. The capacitor bank of claim 1, the at least one sub-capacitance comprising a plurality of sub-capacitances having a total capacitance equal to the nominal capacitance of the corresponding nominal selectable capacitance.

9. The capacitor bank of claim 1, the VCO coupled to a frequency measurement module for measuring an output frequency of the VCO, the frequency measurement module coupled to a capacitor bank calibration module, the calibration module comparing the measured output frequency of the VCO with the nominal frequency of the VCO.

10. The capacitor bank of claim 9, the VCO coupled to a translation module for translating a nominal frequency control signal to a trim setting control signal for the capacitor bank.

11. The capacitor bank of claim 10, the translation module comprising a look-up table.

12. The capacitor bank of claim 1, the VCO being an analog VCO further comprising a varactor having a capacitance adjustable by an analog control signal.

13. The capacitor bank of claim 1, the VCO being a digital VCO, the DCO further comprising a digital capacitance bank for fine adjustment of the DCO resonant frequency.

14. A voltage-controlled oscillator (VCO) comprising:

a capacitor bank comprising a plurality of nominal selectable capacitances, at least one of the nominal selectable capacitances comprising;

at least one sub-capacitance configurable to contribute to the capacitance of the at least one selectable capacitance based on a trim setting control signal, the at least one sub-capacitance having a capacitance less than the nominal value of the at least one of the nominal selectable capacitances.

15. The VCO of claim 14, further comprising:

a frequency measurement module for measuring an output frequency of the VCO, the frequency measurement module coupled to the output of the VCO;

a capacitor bank calibration module, the calibration module comparing the measured output frequency of the VCO with the nominal frequency of the VCO; and

a translation module for translating a nominal frequency control signal to a trim setting control signal for the capacitor bank.

22. The method of claim 15, the determining a trim setting control signal for the capacitor bank corresponding to said at least one nominal frequency control signal comprising:

setting the nominal frequency control signal to first, second, and third nominal frequencies, and measuring corresponding first, second, and third output frequencies, the first nominal frequency being larger than the second nominal frequency by a nominal step size, the second nominal frequency being larger than the third nominal frequencies by the same nominal step size, the difference between the first and second output frequencies being a first actual step size, the difference between the second and third output frequencies being a second actual step size;

if the second actual step size is less than zero, adjusting a trim setting control signal to increase a selectable capacitance in the capacitor bank associated with the first nominal frequency; and

if the second actual step size is greater than the first actual step size, adjusting a trim setting control signal to decrease a selectable capacitance in the capacitor bank associated with the first nominal frequency.

23. The method of claim 22, the determining a trim setting control signal for the capacitor bank corresponding to said at least one nominal frequency control signal further comprising:

repeating the steps of setting the nominal frequency control signal to first, second, and third nominal frequencies, and adjusting the trim setting control signal for a plurality of the nominal selectable capacitances in the capacitor bank.

24. The method of claim 22, further comprising determining a trim setting control signal for the capacitor bank corresponding to each of the plurality of nominal frequency control signals.

16. A method for adjusting the output frequency of a voltage-controlled oscillator (VCO), the VCO comprising a capacitor bank, the capacitor bank comprising a plurality of nominal selectable capacitances, the method comprising:

during a calibration phase, providing at least one nominal frequency control signal to the capacitor bank in the VCO, and determining a trim setting control signal for the capacitor bank corresponding to said at least one nominal frequency control signal;

during an operation phase, applying the at least one nominal frequency control signal to said capacitor bank in the VCO in conjunction with the corresponding trim setting control signal determined during said calibration phase.

17. The method of claim 16, the determining a trim setting control signal for the capacitor bank comprising:

measuring a first output frequency of the VCO corresponding to a first trim setting control signal;

measuring a second output frequency of the VCO corresponding to a second trim setting control signal;

selecting the trim setting control signal corresponding to a VCO output frequency being closer to the at least one nominal frequency control signal.

18. The method of claim 17, the applying the at least one nominal frequency control signal to said capacitor bank in the VCO in conjunction with the corresponding trim setting control signal comprising:

selectively enabling a plurality of sub-capacitances associated with the nominal selectable capacitances in the VCO, the plurality of sub-capacitances configurable to contribute to the capacitance of the at least one selectable capacitance.

19. The method of claim 18, each of the plurality of sub-capacitances having a capacitance less than the nominal value of the corresponding nominal selectable capacitance.

20. The method of claim 18, the trim setting control signal comprising multiple control signals, each control signal opening or closing a switch to disable or enable a corresponding capacitance.

21. The method of claim 18, the plurality of sub-capacitances comprising a plurality of binary-weighted sub-capacitances.

25. A voltage-controlled oscillator (VCO) comprising:

means for, during a calibration phase, providing at least one nominal frequency control signal to the capacitor bank in the VCO, and determining a trim setting control signal for the capacitor bank corresponding to said at least one nominal frequency control signal; and

means for, during an operation phase, applying the at least one nominal frequency control signal to said capacitor bank in the VCO in conjunction with the corresponding trim setting control signal determined during said calibration phase.

26. The VCO of claim 25, the means for applying the at least one nominal frequency control signal comprising:

means for selectively enabling a plurality of sub-capacitances associated with the nominal selectable capacitances in the VCO, the plurality of sub-capacitances configurable to contribute to the capacitance of the at least one selectable capacitance.

27. A computer program product for adjusting the output frequency of a voltage-controlled oscillator (VCO), the VCO comprising a capacitor bank, the capacitor bank comprising a plurality of nominal selectable capacitances, the product comprising:

computer-readable medium comprising;

code for causing a computer to, during a calibration phase, provide at least one nominal frequency control signal to the capacitor bank in the VCO, and determine a trim setting control signal for the capacitor bank corresponding to said at least one nominal frequency control signal;

code for causing a computer to, during an operation phase, apply the at least one nominal frequency control signal to said capacitor bank in the VCO in conjunction with the corresponding trim setting control signal determined during said calibration phase.

28. The computer program product of claim 27, the code for causing a computer to apply the at least one nominal frequency control signal during operation further comprising:

code for causing a computer to measure a first output frequency of the VCO corresponding to a first trim setting control signal;

code for causing a computer to measure a second output frequency of the VCO corresponding to a second trim setting control signal;

code for causing a computer to select the trim setting control signal corresponding to a VCO output frequency being closer to the at least one nominal frequency control signal.

29. A capacitor bank for a voltage-controlled oscillator (VCO), the capacitor bank comprising a plurality of nominal selectable capacitances, the plurality of nominal selectable capacitances comprising a minimum capacitance associated with a least significant bit (LSB), the capacitor bank further comprising:

a trim network comprising a plurality of selectable trim capacitances for adjusting the capacitance of the capacitor bank, the plurality of selectable trim capacitances comprising at least one trim capacitance less than the capacitance associated with the (LSB).