Frequency synthesizer using a VCO having a controllable operating point, and calibration and tuning thereof

• US 6,744,324 B1
• Filed: 04/14/2003
• Issued: 06/01/2004
• Est. Priority Date: 03/19/2001
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Adams, Andrew R., Weste, Neil H., Avery, Stephen C.
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US10/413,862
• Time in Patent Office: 414 Days
• Field of Search: 331/1.A, 331/8, 331/10, 331/12, 331/17, 331/18, 331/25, 331/44, 331/179, 332/127, 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 7/113 using frequency discriminator
• 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 frequency synthesizer, a calibrator thereof, and an operating controller thereof are described. The synthesizer comprises a main charge pump that drives a voltage controlled oscillator (VCO) through a loop filter. The calibrator includes a second, replica charge pump that can also drive the VCO, but is set up to output only its maximum or minimum 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. The operating point controller includes a sensor to sense the operating point and a controller that provides a switching input to a switchable bank of capacitors to change the operating point. The change can be determined according to calibration data.

Claims

1. A frequency synthesizer calibrator, comprising:

a replica charge pump for duplicating at least two outputs expected to be produced by a main charge pump,

wherein, the replica charge pump includes controls for enabling its at least two 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, wherein the two outputs are the minimum and maximum value outputs.

3. The calibrator of claim 2, further comprising:

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

4. The calibrator of claim 3, further comprising:

a voltage-controlled oscillator (VCO) connected to receive output 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.

5. The calibrator of claim 4, 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.

6. The calibrator of claim 5, wherein the frequency measurement device includes a counter and measures the frequency in relation to a reference frequency provided by a reference oscillator.

7. The calibrator of claim 5, 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.

8. The calibrator of claim 2, 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.

9. The calibrator of claim 8, 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.

10. The calibrator of claim 9, 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.

11. The calibrator of claim 10, 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.

12. A frequency synthesizer, 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 capacitor input;

a switchable bank of capacitors having a switch input, and connected to said capacitor input, the switchable capacitor bank 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 rending 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.

13. The frequency synthesizer of claim 12, further comprising:

a sensor connected to the control input of the VCO providing an indication of the magnitude of the control signal; and

a controller connected to the switch input and accepting the control signal magnitude indication, the controller providing control to the switchable capacitor bank to maintain the operating point of the VCO close to a desirable operating point.

14. The frequency synthesizer of claim 13, fabricated on a single substrate using a metal oxide semiconductor process.

15. The frequency synthesizer of claim 13, wherein the sensor provides an analog output, and wherein the controller is a digital controller that accepts a digital input, the frequency synthesizer further comprising

an analog to digital converter (ADC) to convert the analog sensor output to the magnitude indication accepted by the digital controller.

16. The frequency synthesizer of claim 15, wherein the digital controller detects when the operating point veers from the desirable operating point by more than a threshold and generates the control to the switchable capacitor bank when the threshold is exceeded.

17. A frequency synthesizer, 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 capacitor input;

a bank of capacitors connected to said 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 rading 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.

18. The frequency synthesizer of claim 17, further comprising:

a sensor connected to the control input of the VCO providing an indication of the magnitude of the control signal; and

a controller connected to the switch input and accepting the control signal magnitude indication, the controller providing control to the capacitor bank to maintain the operating point of the VCO close to a desirable operating point.

19. The frequency synthesizer of claim 18, fabricated on a single substrate using a metal oxide semiconductor process.

20. The frequency synthesizer of claim 18, wherein the sensor provides an analog output, and wherein the controller is a digital controller that accepts a digital input, the frequency synthesizer further comprising

an analog to digital converter (ADC) to convert the analog sensor output to the magnitude indication accepted by the digital controller.

21. The frequency synthesizer of claim 20, wherein the digital controller detects when the operating point veers from the desirable operating point by more than a threshold and generates the control to the capacitor bank when the threshold is exceeded.

22. A method for operating a frequency synthesizer that depends on a voltage controlled oscillator with an operating frequency range that depends on the setting of a selectable bank of capacitors and on the magnitude of a control signal, the method comprising the steps of:

predeterming 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 to a new operating frequency range based on said minimum and maximum output frequencies in said list.

23. The method of claim 22, wherein the step of predetermining includes the steps of:

generating the output of a replica charge pump to provide the control input of said VCO as an alternate to a main charge pump that drives said VCO;

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

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

24. The method of claim 23, wherein the stop of tabulating includes the steps of:

manipulating said replica charge pump to drive said matching minimum and matching maximum 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.

25. The method of claim 22, further including the step of:

starting the calibration method when an on-chip temperature measurement exceeds a previously obtained temperature measurement by a temperature threshold.

26. The method of claim 24, further comprising:

sensing the VCO output to provide an indication of the magnitude of the control signal;

controlling the range of operating said VCO using a range controller connected to the VCO; and

controlling the range controller to maintain the operating point of the VCO close to a desirable opening point using the control signal magnitude indication.

27. The method of claim 26, wherein the sensing provides an analog output, and wherein the controlling is carried out digitally, the method further comprising

converting the analog sensor output to a digital quantity, and providing the digital quantity as the magnitude indication.

28. The method of claim 27, wherein the controlling includes detecting when the operating point veers from the desirable operating point by more than a threshold and generating a control to the range controller when the threshold is exceeded.

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

means for pertaining 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;

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

means for providing the drive of said VCO from the output of a replica charge pump as an alternate to a main charge pump that drives said VCO, the replica pump constructed such that the electronics of said replica charge pump simulate that of said an 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.

30. The means of claim 29, 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.

31. The means of claim 30, further comprising:

sensing means coupled to the VCO output to provide an indication of the magnitude of the control signal;

range control means connected to the VCO for controlling the range of operating said VCO; and

controller means connected to and accepting the control signal magnitude indication, the controller providing control to the range control means to maintain the operating point of the VCO close to a desirable operating point.

32. The means of claim 31, wherein the sensing means provides an analog output, and wherein the controller means is a digital device that accepts a digital input, the means of operating the synthesizer further comprising

analog to digital converter (ADC) means to convert the analog sensor output to the magnitude indication accepted by the digital controller.

33. The means of claim 32, wherein the digital controller detects when the operating point veers from the desirable operating point by more than a threshold and generates the control to the switchable capacitor bank when the threshold is exceeded.