Method and apparatus for calibrating a frequency adjustable oscillator in an integrated circuit device

• US 20010020875A1
• Filed: 04/02/2001
• Published: 09/13/2001
• Est. Priority Date: 05/03/1999
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Silicon Wave, Inc. (Qorvo, Inc.)
• Inventors: Jansson, Lars Gustaf
• Granted Patent: US 6,323,736 B2
• Time in Patent Office: Days
• US Class Current: 331/44
• CPC Class Codes: H01L 27/0805 Capacitors only
• CPC Class Codes: H03B 2201/0266 the means comprising a transistor
• CPC Class Codes: H03B 2201/0283 the means functioning digitally
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1231 the amplifier comprising one or more bipolar transistors
• CPC Class Codes: H03B 5/124 the means comprising a voltage dependent capacitance
• CPC Class Codes: H03B 5/1265 switched capacitors
• CPC Class Codes: H03F 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H03F 2203/45631 the LC comprising one or more capacitors, e.g. coupling capacitors
• CPC Class Codes: H03F 2203/45638 the LC comprising one or more coils
• CPC Class Codes: H03F 3/45085 Long tailed pairs H03F3/45112, H03F3/45139 take precedence
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• 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
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

A method and apparatus for digitally controlling the capacitance of an integrated circuit device using MOS-FET devices. In accordance with one aspect of the present invention, a one-bit or “binary” varactor is presented wherein the gate-to-bulk capacitance of the MOS-FET device exhibits dependency to a D.C. voltage applied between its gate and well implant regions. The capacitance-voltage characteristic of the binary capacitor has three major regions: (1) a first relatively flat region having little or no voltage dependency and having a capacitance equal to a first low capacitance of C₁; (2) a sloped region wherein a voltage dependency exists; and (3) a second relatively flat region where there is little or no voltage dependency and where the capacitance equals a second higher capacitance of C₂. The capacitance of the binary capacitor can be changed from C₁ to C₂ simply by changing the polarity of the applied D.C. voltage from a positive to a negative value. A plurality of binary capacitors are configured in a parallel arrangement to produce a digitally controlled capacitor. The digitally controlled capacitor can be used in any integrated circuit requiring a tightly controlled tuned network. One application is a voltage-controlled oscillator (VCO) wherein the center output frequency of the VCO is calibrated by digitally modifying the capacitance of the VCO'"'"'s digitally controlled capacitor. A means for determining whether the VCO requires calibration and a means for calibrating the center output frequency of the VCO is presented.

Claims

1. A method of calibrating a frequency adjustable oscillator circuit in an integrated circuit device, wherein the frequency adjustable oscillator circuit includes an inductor coupled in parallel to a plurality of multiple capacitance level capacitors, each multiple capacitance level capacitor having a plurality of steady-state capacitance levels, and wherein each multiple capacitance level capacitor is coupled to an associated and corresponding control signal, and wherein the capacitance level measured across the plurality of capacitors varies as a function of the corresponding control signal, the method comprising the steps of:

a) tuning the oscillator circuit to a desired center frequency;

b) measuring an actual center frequency generated by the oscillator circuit;

c) comparing the actual center frequency measured in step (b) to the desired center frequency; and

d) varying the control signals applied to the plurality of multiple capacitance level capacitors until the actual center frequency measured in step (b) is approximately equal to the desired center frequency of the oscillator circuit.

2. The method of calibrating a frequency adjustable oscillator as set forth in

claim 1

, wherein the tuning step (a) comprises the step of applying a DC control voltage (V_tune) to a tuning varactor coupled in parallel to the plurality of multiple capacitance level capacitors.

3. The method of calibrating a frequency adjustable oscillator as set forth in

claim 1

, wherein the measuring step (b), comparing step (c), and varying step (d) are manually performed during a production testing phase, and wherein the control signals are manually varied in step (d) until the actual measured center frequency is approximately equal to the desired center frequency of the oscillator.

4. The method of calibrating a frequency adjustable oscillator as set forth in

claim 3

, wherein the control signals are stored in a non-volatile memory device and subsequently used to calibrate the oscillator circuit.

5. The method of calibrating a frequency adjustable oscillator as set forth in

claim 1

, wherein the measuring step (b), comparing step (c), and varying step (d) are automatically performed when power is first supplied to the oscillator.

6. The method of calibrating a frequency adjustable oscillator as set forth in

claim 5

, wherein the control signals are controlled by a microprocessor.

7. The method of calibrating a frequency adjustable oscillator as set forth in

claim 5

, wherein the control signals are controlled by a field programmable gate array device.

8. A calibrating frequency adjustable oscillator circuit in an integrated circuit device, wherein the frequency adjustable oscillator circuit includes an inductor coupled in parallel to a plurality of multiple capacitance level capacitors, each multiple capacitance level capacitor having a plurality of steady-state capacitance levels, and wherein each multiple capacitance level capacitor is coupled to an associated and corresponding control signal, and wherein the capacitance level measured across the plurality of capacitors varies as a function of the corresponding control signal, the oscillator circuit comprising:

a) means for tuning the oscillator circuit to a desired center frequency;

b) means, coupled to the oscillator circuit, for measuring an actual center frequency generated by the oscillator circuit;

c) means, coupled to the measuring means, for comparing the actual center frequency to the desired center frequency; and

d) means, responsive to the comparing means, for varying the control signals applied to the plurality of multiple capacitance level capacitors until the actual center frequency is approximately equal to the desired center frequency of the oscillator circuit.

9. A method of automatically calibrating a voltage controlled oscillator (VCO) in an integrated circuit device, wherein the VCO includes at least one tuning varactor coupled in parallel to at least one inductor, and wherein the at least one inductor is coupled in parallel to a plurality of multiple capacitance level capacitors, each multiple capacitance level capacitor having a plurality of steady-state capacitance levels, and wherein each multiple capacitance level capacitor is coupled to an associated and corresponding control signal, and wherein the capacitance level measured across the plurality of capacitors varies as a function of the corresponding control signal, and wherein the control signals together comprise a control word, the method comprising the steps of:

a) tuning the VCO to a desired center frequency;

b) measuring an output frequency generated by the VCO;

c) comparing the VCO output frequency measured in step (b) to the desired center frequency; and

d) varying the control word applied to the plurality of multiple capacitance level capacitors until the VCO output frequency measured in step (b) is approximately equal to the desired center frequency.

10. The automatic VCO calibration method as set forth in

claim 9

, wherein the tuning step (a) comprises the step of applying a DC control voltage (V_tune) to a tuning varactor coupled in parallel to the plurality of multiple capacitance level capacitors.

11. The automatic VCO calibration method as set forth in

claim 9

, wherein the measuring step (b) is performed by a phase-locked loop circuit coupled to receive the VCO output frequency.

12. The automatic VCO calibration method as set forth in

claim 11

, wherein the VCO output frequency is compared with a reference frequency, and wherein the control word applied to the plurality of multiple capacitance level capacitors is varied responsive to the comparison.

13. A calibrating voltage controlled oscillator (VCO) in an integrated circuit device, wherein the VCO includes at least one tuning varactor coupled in parallel to at least one inductor, and wherein the at least one inductor is coupled in parallel to a plurality of multiple capacitance level capacitors, each multiple capacitance level capacitor having a plurality of steady-state capacitance levels, and wherein each multiple capacitance level capacitor is coupled to an associated and corresponding control signal, and wherein the capacitance level measured across the plurality of capacitors varies as a function of the corresponding control signal, and wherein the control signals together comprise a control word, the VCO comprising:

a) means for tuning the VCO to a desired center frequency;

b) means, coupled to the VCO, for measuring an output frequency generated by the VCO;

c) means, coupled to the measuring means, for comparing the VCO output frequency to the desired center frequency; and

d) means, responsive to the comparing means, for varying the control word applied to the plurality of multiple capacitance level capacitors until the VCO output frequency is approximately equal to the desired center frequency.

14. A self-calibrating voltage controlled oscillator (VCO), wherein the self-calibrating VCO is capable of being calibrated to produce a desired output frequency f_o based upon a selected tuning voltage and a selected digital control word, the VCO comprising:

a) at least one inductor;

b) a tuning varactor coupled to the at least one inductor, wherein the capacitance of the tuning varactor is controlled by a selected tuning voltage (V_tune);

c) a plurality of multiple capacitance level capacitors coupled in parallel to the tuning varactor, each multiple capacitance level capacitor having a plurality of steady-state capacitance levels, wherein each multiple capacitance level capacitor is coupled to an associated and corresponding control signal, and wherein the capacitance level measured across the plurality of capacitors varies as a function of the corresponding control signal, and wherein the control signals together comprise a digital control word;

d) an amplifier coupled to the at least one inductor; and

e) a current source coupled in serial to the amplifier;

and wherein the digital control word applied to the plurality of multiple capacitance level capacitors is dynamically varied until the output frequency of the VCO is approximately equal to the desired output frequency.

15. A self-calibrating voltage controlled oscillator (VCO), wherein the self-calibrating VCO is capable of being calibrated to produce a desired output frequency f_o based upon a selected tuning voltage and a selected digital control word, the VCO comprising:

a) at least one inductor means;

b) means for tuning the VCO to an initial output frequency, wherein the tuning means is controlled by a selected tuning voltage (V_tune);

c) means, for digitally controlling a plurality of multiple capacitance level capacitors coupled in parallel to the tuning means, each multiple capacitance level capacitor having a plurality of steady-state capacitance levels, wherein each multiple capacitance level capacitor is coupled to an associated and corresponding digital control signal, and wherein the capacitance level measured across the plurality of capacitors varies as a function of the corresponding control signal, and wherein the control signals together comprise a digital control word;

d) amplifying means, coupled to the at least one inductor means; and

e) current source means coupled in serial to the amplifier;

and wherein the digital control word applied to the plurality of multiple capacitance level capacitors is dynamically varied until the output frequency of the VCO is approximately equal to the desired output frequency.

16. A method of automatically calibrating a voltage controlled oscillator (VCO) in an integrated circuit device, wherein the VCO produces an output frequency signal and wherein the VCO includes at least one tuning varactor coupled in parallel to at least one inductor, and wherein the capacitance of the tuning varactor is controlled by an analog tuning voltage V_tune, and wherein the at least one inductor is coupled in parallel to a plurality of multiple capacitance level capacitors, each multiple capacitance level capacitor having a plurality of steady-state capacitance levels, and wherein each multiple capacitance level capacitor is coupled to an associated and corresponding control signal, and wherein the capacitance level measured across the plurality of capacitors varies as a function of the corresponding control signal, and wherein the control signals together comprise a control word, the method comprising the steps of:

a) applying a selected initial control word to the plurality of multiple capacitance level capacitors;

b) waiting for a first pre-determined settling period to allow the VCO output signal time to settle, and then proceeding to step (c);

c) comparing the analog tuning voltage V_tune to a predetermined low output threshold value V_outL, and proceeding to step (d) if V_tune is less than V_outL, else proceeding to step (h);

d) waiting for a second pre-determined settling period to allow the VCO output signal time to settle, and then proceeding to step (e);

e) comparing the analog tuning voltage V_tune to a predetermined high output threshold value V_outH, and returning to step (c) if V_tune is greater than V_outH, else proceeding to step (f);

f) comparing the analog tuning voltage V_tune to the predetermined low output threshold value V_outL, and proceeding to step (g) if V_tune is less than V_outL, else returning to step (c);

g) varying the control word applied to the plurality of multiple capacitance level capacitors by increasing the control word by one least significant bit (LSB) value, and then returning to step (c);

h) comparing the analog tuning voltage V_tune to the predetermined high output threshold value V_outH, and proceeding to step (i) if V_tune is greater than V_outH, else returning to step (c);

i) waiting for the second predetermined settling period to allow the VCO output signal time to settle, and then proceeding to step (j);

j) comparing the analog tuning voltage V_tune to the predetermined low output threshold value V_outL, and returning to step (c) if V_tune is less than V_outL, else proceeding to step (k);

k) comparing the analog tuning voltage V_tune to the predetermined high output threshold value V_outH, and proceeding to step (1) if V_tune is greater than V_outH, else returning to step (c); and

l) varying the control word applied to the plurality of multiple capacitance level capacitors by decreasing the control word by one least significant bit (LSB) value, and returning to step (c).

17. The method of automatically calibrating a VCO as set forth in

claim 16

, wherein the steps are executed in software instructions by a microprocessor that is operatively coupled to the VCO.

18. The method of automatically calibrating a VCO as set forth in

claim 16

, wherein the initial control word applied in step (a) is approximately equal to one-half of a maximum attainable value of the control word.

19. The method of automatically calibrating a VCO as set forth in

claim 16

, wherein the second pre-determined settling period is approximately equal to 100 microseconds.

20. The method of automatically calibrating a VCO as set forth in

claim 16

, wherein the method does not proceed beyond step (b) if the VCO is being used in a radio system and wherein the radio system is currently receiving or transmitting voice or data information.

21. The method of automatically calibrating a VCO as set forth in

claim 16

, wherein the VCO is used in a frequency hop transceiver capable of generating receive and transmit frequencies in a wireless Time-Division Duplex scheme.

22. The method of automatically calibrating a VCO as set forth in

claim 21

, the method further comprising the steps of:

a) after the step (b) of waiting for a first pre-determined settling period, proceeding to sub-step (i);

i) determining whether the VCO is currently operating during a receive or transmit time slot;

ii) if the VCO is currently operating during a receive or transmit time slot, returning to sub-step (i), else proceeding to sub-step (iii);

iii) determining whether a channel jump or channel hop condition exists, and if no channel jump condition exists, proceeding to step (c) of

claim 16

, else proceeding to sub-step (iv);

iv) determining a difference in VCO center frequency required by the channel hop condition determined in sub-step (iii); and

v) updating the control word responsive to the difference determined during sub-step (iv).

23. The method of automatically calibrating a VCO as set forth in

claim 22

, wherein the control word that is applied to the plurality of multiple capacitance level capacitors represents a number of channels that is jumped during the channel jump condition determined during sub-step (iii).

24. The method of automatically calibrating a VCO as set forth in

claim 22

, wherein the control word is updated during sub-step (v) if and only if a channel jump exceeding a predetermined channel jump threshold is determined during sub-step (iii).