Harmonic Characterization and Correction of Device Mismatch

• US 20070188244A1
• Filed: 12/29/2006
• Published: 08/16/2007
• Est. Priority Date: 02/16/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Staszewski, Robert B., Waheed, Khurram
• Granted Patent: US 7,714,665 B2
• Time in Patent Office: Days
• US Class Current: 331/16
• CPC Class Codes: H03L 2207/50 All digital phase-locked loop
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/113 using frequency discriminator

Abstract

A novel apparatus for and method of harmonic characterization and ratio correction of device mismatch between coarse and fine varactor tuning devices within a segmented unified varactor bank of a radio frequency (RF) digitally controlled oscillator (DCO). The DCO uses a single unified bank of varactors that is divided into an MSB bank, LSB bank and sigma-delta (SD-LSB) bank. Any ratio mismatches between MSBs and LSBs are digitally calibrated out using a DCO step-size pre-distortion scheme wherein the LSB steps are adjusted to account for the ratio mismatch between the MSB/LSB step sizes. A harmonic characterization technique is used to estimate the mismatches in the minimal size CMOS tuning varactors of a digitally controlled RF oscillator (DCO), wherein the nominal ratio mismatch between the MSB and LSB devices is estimated using hybrid stochastic gradient DCO gain estimation algorithms. The nominal ratio mismatch and the mismatches in the MSB and LSB banks are used to determine the average MSB/LSB mismatch. The average mismatch value is then used to correct the LSB steps.

Claims

1. An apparatus for correction of varactor mismatch of a single segmented unified tuning bank in a digitally controlled oscillator (DCO), said unified tuning bank having a coarse tuning bank comprising a plurality of coarse tuning devices and a fine tuning bank comprising a plurality of fine tuning devices, said apparatus comprising:

DCO gain estimation means; and

harmonic calibration means in combination with said DCO gain estimation means operative to determine a mismatch error value between said coarse tuning devices and said fine tuning devices.

2. The apparatus according to claim 1, wherein said harmonic calibration circuit comprises:

means for applying sinusoidal modulation to said DCO to yield a plurality of harmonics in an observable frequency modulated radio frequency (RF) spectrum; and

means for estimating said mismatch error value in said unified tuning bank utilizing a level of a second harmonic of said plurality of harmonics.

3. The apparatus according to claim 2, wherein said harmonic calibration circuit comprises a suitably programmed scripts processor (SCR).

4. The apparatus according to claim 2, further comprising means for tuning the magnitude of said applied sinusoidal modulation to average over a plurality of most significant bit (MSB) device combinations.

5. The apparatus according to claim 1, wherein said harmonic calibration means operates in a built-in self-test (BIST) manner.

6. The apparatus according to claim 1, wherein said coarse tuning bank comprises a 128-bit thermometer coded most significant bit (MSB) tuning bank.

7. The apparatus according to claim 1, wherein said fine tuning devices comprise inversion-type Complementary Metal Oxide Semiconductor (CMOS) tuning varactors.

8. The apparatus according to claim 1, wherein said fine tuning bank comprises a 16-bit thermometer coded least significant bit (LSB) tuning bank.

9. The apparatus according to claim 1, wherein said unified tuning bank further comprises a sigma-delta least significant bit (SD-LSB) tuning bank having a plurality of IX devices.

10. The apparatus according to claim 1, further comprising means for applying said mismatch error value to a pre-distortion circuit operative to compensate a DCO input signal for mismatches between said coarse tuning devices and said fine tuning devices to yield a compensated DCO input signal thereby.

11. The apparatus according to claim 10, wherein said pre-distortion circuit comprises means for multiplying said DCO input by said mismatch error value and adding a product generated thereby to said DCO input to generate said compensated DCO input signal.

12. A method of correction of device mismatch of a single segmented unified bank of conversion devices for use in a digital to analog quantity converter (DAC), said unified conversion bank having a coarse bank comprising a plurality of coarse conversion devices and a fine bank comprising a plurality of fine conversion devices, said method comprising the step of:

performing harmonic characterization of random conversion device mismatches in most significant bit (MSB) and least significant bit (LSB) devices;

said step of performing comprising the steps of;

applying a sinusoidal modulation to said DAC using one or more conversion device banks; and

estimating random mismatches in said DAC conversion device banks using the level of one or more harmonics in an observable frequency modulated RF spectrum output from said DAC.

13. The method according to claim 12, wherein said digital to analog quantity converter comprises a digitally controlled oscillator (DCO).

14. The method according to claim 12, further comprising the step of measuring gain for each conversion device bank to estimate a nominal ratio mismatch between most significant bit (MSB) and least significant bit (LSB) devices.

15. The method according to claim 14, further comprising the step of computing an average ratio mismatch between most significant bit (MSB) and least significant bit (LSB) devices using said nominal ratio mismatch estimate and individual random mismatch estimates measured in each conversion device bank.

16. The method according to claim 14, wherein said method is implemented in a suitably programmed scripts processor (SCR).

17. A transmitter comprising:

a frequency synthesizer for performing a frequency modulation;

said frequency synthesizer comprising a digitally controlled oscillator (DCO);

said DCO comprising;

a single segmented unified tuning bank comprising;

a coarse tuning bank comprising a plurality of coarse tuning devices adapted to provide coarse frequency tuning control of said DCO;

a fine tuning bank comprising a plurality of fine tuning devices adapted to provide fine frequency tuning control of said DCO; and

harmonic calibration means for determining an average ratio mismatch error value between said coarse tuning devices and said fine tuning devices.

18. The transmitter according to claim 17, wherein said DCO further comprises a pre-distortion circuit operative to compensate a DCO input signal for mismatches between said coarse tuning devices and said fine tuning devices utilizing said mismatch error value to yield a compensated DCO input signal thereby.

19. A method of ratio estimation between coarse and fine varactor tuning devices in a digitally controlled oscillator (DCO), said method comprising the steps of:

measuring DCO gain (KDCO) for each varactor bank in said DCO to estimate a nominal ratio mismatch between most significant bit (MSB) and least significant bit (LSB) devices;

performing harmonic characterization of random varactor mismatches in most significant bit (MSB) and least significant bit (LSB) devices;

said step of performing comprising the steps of;

applying a sinusoidal modulation to said DCO using one or more varactor banks;

estimating random mismatches in said DCO varactor banks using the level of one or more harmonics in an observable frequency modulated RF spectrum output from said DCO; and

computing an average ratio mismatch between most significant bit (MSB) and least significant bit (LSB) devices using said nominal ratio estimate and individual random mismatch estimates measured in each varactor bank.

20. The method according to claim 19, wherein the level of a second harmonic is used as a measure to estimate said MSB/LSB mismatch.

21. The method according to claim 19, further comprising the step of digitally calibrating out said MSB/LSB mismatch by adjusting LSB steps to account for said mismatch between MSB and LSB step sizes.

22. A transmitter comprising:

a frequency synthesizer for performing a frequency modulation;

said frequency synthesizer comprising a digitally controlled oscillator (DCO);

said DCO comprising;

a single segmented unified tuning bank comprising;

a coarse tuning bank comprising a plurality of coarse tuning devices adapted to provide coarse frequency tuning control of said DCO;

a fine tuning bank comprising a plurality of fine tuning devices adapted to provide fine frequency tuning control of said DCO; and

means for interfacing said transmitter to a scripts processor, said scripts processor suitably programmed to perform harmonic calibration by determining an average ratio mismatch error value between said coarse tuning devices and said fine tuning devices.

23. A method of harmonic calibration of random varactor mismatches between most significant bit (MSB) device of an MSB varactor bank and least significant bit (LSB) devices of an LSB varactor bank in a digitally controlled oscillator (DCO), said method comprising the steps of:

applying a single frequency modulation tone to said DCO; and

estimating random mismatches in said DCO varactor banks using the level of one or more harmonics in an observable frequency modulated RF spectrum output from said DCO.

24. The method according to claim 23, wherein said method is implemented in a suitably programmed scripts processor (SCR).

25. The method according to claim 23, further comprising the step of measuring DCO gain (KDCO) for each varactor bank in said DCO to estimate a nominal ratio mismatch between most significant bit (MSB) and least significant bit (LSB) devices.

26. The method according to claim 25, further comprising the step of computing an average ratio mismatch between most significant bit (MSB) and least significant bit (LSB) devices using said nominal ratio estimate and individual random mismatch estimates measured in each varactor bank.