Method and apparatus to tune and calibrate an on-chip oscillator in a wireless transceiver chip

• US 6,512,419 B1
• Filed: 09/14/2001
• Issued: 01/28/2003
• Est. Priority Date: 03/19/2001
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Systems Wireless Networking (Australia) Pty Limited (Cisco Systems, Inc.)
• Inventors: Avery, Stephen, Adams, Andrew, Weste, Neil
• Primary Examiner(s): Mis, David C.
• Application Number:
  US09/952,925
• Time in Patent Office: 501 Days
• Field of Search: 331/1.A, 331/8, 331/10, 331/12, 331/17, 331/18, 331/25, 331/44, 331/179, 327/11, 327/156-159, 360/51, 375/376, 455/260
• US Class Current: 331/17
• CPC Class Codes: H03F 1/0277 Selecting one or more amplifiers from a plurality of amplifiers
• CPC Class Codes: H03F 2203/45418 the CMCL comprising a resistor addition circuit
• CPC Class Codes: H03F 2203/45652 the LC comprising one or more further dif amp stages, either identical to the dif amp or not, in cascade
• CPC Class Codes: H03F 2203/7203 the gated amplifier being switched on or off by a switch in the bias circuit of the amplifier controlling a bias current in the amplifier
• CPC Class Codes: H03F 2203/7224 the gated amplifier being switched on or off by clamping by a switch at the output of the amplifier
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence
• CPC Class Codes: H03F 3/45659 Controlling the loading circuit of the differential amplifier
• CPC Class Codes: H03F 3/72 Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03L 7/07 using several loops, e.g. for redundant clock signal generation
• 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 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/104 using an additional signal from outside the loop for setting or controlling a parameter in the loop H03L7/107, H03L7/12 take precedence
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence
• CPC Class Codes: H03L 7/185 using a mixer in the loop H03L7/187 - H03L7/195 take precedence

Abstract

A local oscillator calibrator comprises a main charge pump that drives a voltage controlled oscillator (VCO) through a loop filter. A second, replica charge pump can also drive the VCO, but is setup to output only its most positive or most negative analog output control voltage. Since the construction and characteristics of the replica charge pump duplicate the main charge pump, the main charge pump'"'"'s minimum and maximum analog control outputs can be cloned out to the VCO on demand. A VCO calibration procedure therefore includes switching the VCO to each of its ranges set by a bank of fixed capacitors, and using the replica charge pump to drive the VCO to its minimum and maximum frequency for each range setting. The min-max frequency data is stored in a lookup table, and operational requests to switch to a new channel frequency can be supported with a priori information about which fixed-capacitor range selection will be best.

Claims

1. A local oscillator calibrator, comprising:

a replica charge pump for duplicating a minimum and a maximum output control signal expected to be produced by a main charge pump;

wherein, the replica charge pump includes controls for enabling its minimum and maximum outputs; and

wherein, the replica charge pump is connected to a voltage controlled oscillator that includes a bank of fixed-value capacitors for range selection.

2. The calibrator of claim 1, further comprising:

a main charge pump constructed similar to the replica charge pump and drawing its operating power from the same sources such that its range of output voltage-controlled oscillator (VCO) control signal magnitudes match those of the replica charge pump.

3. The calibrator of claim 2, further comprising:

a voltage-controlled oscillator (VCO) connected to receive outputs from both the replica charge pump and the main charge pump, and providing a frequency output; and

a bank of fixed-value capacitors providing a selectable range of operating frequencies for the VCO.

4. The calibrator of claim 3, further comprising:

a frequency measurement device providing for a frequency reading of a frequency output of the VCO for each of said selectable range of operating frequencies produced by individual ones of the bank of fixed-value capacitors.

5. The calibrator of claim 4, further comprising:

a calibration table constructed of a plurality of said frequency measurements taken while the replica charge pump is driving the VCO at a predetermined control signal magnitude.

6. The calibrator of claim 1, further comprising:

a main charge pump constructed similar to the replica charge pump and drawing its operating power from the same sources such that its minimum and maximum output voltage-controlled oscillator (VCO) control signal magnitudes match those of the replica charge pump.

7. The calibrator of claim 6, further comprising:

a voltage-controlled oscillator (VCO) connected to receive outputs from both the replica charge pump and the main charge pump, and providing a frequency output; and

a bank of fixed-value capacitors providing a selectable range of operating frequencies for the VCO.

8. The calibrator of claim 7, further comprising:

a frequency measurement device providing for a frequency reading of a frequency output of the VCO for each of said selectable range of operating frequencies produced by individual ones of the bank of fixed-value capacitors.

9. The calibrator of claim 8, further comprising:

a calibration table constructed of a plurality of said frequency measurements taken while the replica charge pump is driving the VCO at a maximum or a minimum control signal magnitude.

10. A local oscillator, comprising:

a voltage-controlled oscillator (VCO) providing a variable frequency output that depends, in part on an analog control input signal, and in part on a capacitance connected to a fixed-capacitor input;

a bank of fixed-value capacitors connected to said fixed-capacitor input and providing a selectable range of operating frequencies for the VCO;

a main charge pump connected to control the VCO and having a first analog output control signal that can span between a minimum and a maximum output magnitude which are dependent on operating conditions and electronic construction;

a replica charge pump having an electronic construction and operating conditions that duplicate the main charge pump such that it provides a second analog output with minimum and maximum output VCO-control signal magnitudes that match those of said first analog output;

a frequency measurement device providing for a frequency reading of a frequency output of the VCO for each of said selectable range of operating frequencies produced by individual ones of the bank of fixed-value capacitors; and

a calibration table constructed of a plurality of said frequency measurements taken while said second analog output from the replica charge pump is driving the VCO at said minimum and maximum output VCO-control signal magnitudes.

11. A local oscillator, comprising:

a voltage-controlled oscillator (VCO) providing a variable frequency output that depends, in part on an analog control input signal, and in part on a capacitance connected to a fixed-capacitor input;

a bank of fixed-value capacitors connected to said fixed-capacitor input and providing a selectable range of operating frequencies for the VCO;

a main charge pump connected to control the VCO and having a first analog output control signal that can span between a minimum and a maximum output magnitude which are dependent on operating conditions and electronic construction;

a replica charge pump having an electronic construction and operating conditions that duplicate the main charge pump such that it provides a second analog output with a predetermined output VCO-control signal magnitude that matches those of said first analog output;

a frequency measurement device providing for a frequency reading of a frequency output of the VCO for each of said selectable range of operating frequencies produced by individual ones of the bank of fixed-value capacitors; and

a calibration table constructed of a plurality of said frequency measurements taken while said second analog output from the replica charge pump is driving the VCO at said predetermined output VCO-control signal magnitude.

12. A method for operating a local oscillator that depends on a voltage controlled oscillator with a selectable bank of fixed-value range capacitors, the method comprising the steps of:

predetermining what minimum and maximum output frequencies result from driving a control input of a voltage-controlled oscillator (VCO) at the minimum and maximum outputs obtainable from a main charge pump;

tabulating a list of said minimum and maximum output frequencies obtained in the step of predetermining; and

responding to a request to move a new operating frequency based on said minimum and maximum output frequencies in said list.

13. The method of claim 12, wherein the step of predetermining includes the steps of:

paralleling the output of a main charge pump that drives said VCO with the output of a replica charge pump;

constructing the electronics of said replica charge pump to simulate that of said main charge pump; and

operating said main charge pump and said replica charge pump under the same operating conditions to obtain at least matching minimum and matching maximum outputs that drive said VCO.

14. The method of claim 13, wherein the step of tabulating includes the steps of:

manipulating said replica charge pump to drive said matching minimum and matching maxim outputs to said VCO;

measuring a resulting VCO output frequency; and

building a lookup table of frequency ranges obtained for each one of a selectable bank of fixed-value range capacitors switched on to said VCO.

15. The method of claim 12, further including the step of:

compensating according to on-chip temperature measurements and a priori data related to the effects of temperature.

16. A means for operating a local oscillator that depends on a voltage controlled oscillator with a selectable bank of fixed-value range capacitors, comprising:

means for predetermining what minimum and maximum output frequencies result from driving a control input of a voltage-controlled oscillator (VCO) at the minimum and maximum outputs obtainable from a main charge pump;

means for tabulating a list of said minimum and maximum output frequencies obtained in the step of predetermining; and

means for responding to a request to move a new operating frequency based on said minimum and maximum output frequencies in said list.

17. The means of claim 16, wherein the means for predetermining includes:

means for paralleling the output of a main charge pump that drives said VCO with the output of a replica charge pump;

means for constructing the electronics of said replica charge pump to simulate that of said main charge pump; and

means for operating said main charge pump and said replica charge pump under the same operating conditions to obtain at least matching minimum and matching maximum outputs that drive said VCO.

18. The means of claim 16, wherein tabulating means includes:

means for manipulating said replica charge pump to drive said matching minimum and matching maxim outputs to said VCO;

means for measuring a resulting VCO output frequency; and

means for building a lookup table of frequency ranges obtained for each one of a selectable bank of fixed-value range capacitors switched on to said VCO.

19. The means of claim 16, further comprising:

means for compensating according to on-chip temperature measurements and a priori data related to the effects of temperature.