Self-tuning and temperature compensated voltage controlled oscillator

• US 6,023,198 A
• Filed: 06/08/1998
• Issued: 02/08/2000
• Est. Priority Date: 06/08/1998
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Cruger, Lorenzo, McKinney, John K., Avanic, Branko
• Primary Examiner(s): Lee, Benny
• Assistant Examiner(s): Choe, Henry
• Application Number:
  US09/093,238
• Time in Patent Office: 610 Days
• Field of Search: 331/176, 331/DIG. 2, 331/17
• US Class Current: 331/17
• CPC Class Codes: H03L 1/02 against variations of temperature only
• CPC Class Codes: H03L 2207/06 Phase locked loops with a controlled oscillator having at least two frequency control terminals
• CPC Class Codes: H03L 7/095 using a lock detector H03L7/087 takes precedence
• 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 7/189 comprising a D/A converter for generating a coarse tuning voltage

Abstract

A self-tuning VCO (116) receives a control voltage input (Vcont) (114) and an adjustable programmable voltage (Vadj) (122) and provides optimized locked conditions even under variations in temperature. A radio temperature is measured and stored (204) while Vadj (122) is initialized and stepped and Vcont (114) attempts to lock the VCO on frequency. Once a locked condition is achieved, the Vcont (114) is monitored to determine if it falls within a predetermined voltage range. If a non-optimized condition is detected, then the Vadj (122) is automatically adjusted until the VCO (116) becomes locked with a Vcont which falls within the predetermined voltage range. When a locked condition is achieved, the radio temperature is monitored and compared (212) to the original stored temperature (204). If a temperature threshold limit is reached (216) then the VCO is re-checks itself for a locked condition and re-optimizes itself to accommodate for the variations in temperature.

Claims

1. A method of self-tuning a voltage controlled oscillator (VCO) circuit in a radio, comprising the steps of:

internally measuring the radio'"'"'s initial temperature;

storing the radio'"'"'s initial temperature;

initializing a programmable voltage;

applying the programmable voltage to the VCO to tune the VCO;

applying a control voltage to the VCO to lock the VCO;

determining if the VCO is in a locked condition;

measuring the control voltage internally to the radio if the VCO is in a locked condition;

comparing the control voltage of the VCO in the locked condition to a predetermined control voltage range stored in the radio;

automatically adjusting the programmable voltage if the VCO is in an unlocked condition or if the control voltage does not fall within the predetermined control voltage range;

repeating the steps of determining, measuring, comparing, and automatically adjusting, until the VCO is locked and the control voltage falls within the predetermined control voltage range;

monitoring the radio temperature when the VCO is locked and the control voltage falls within the predetermined control voltage range;

calculating the difference between the radio'"'"'s initial temperature and the monitored temperature to determine whether a predetermined delta temperature threshold has been reached; and

returning to the step of determining, if a predetermined temperature threshold has been reached.

2. The method of claim 1, wherein the programming voltage is generated by a digital-to-analog (D/A) converter.

3. The method of claim 2, wherein the step of adjusting comprises the step of incrementing the D/A.

4. The method of claim 2, where in the step of adjusting comprises the step of decrementing the D/A.

5. The method of claim 1, further including the step of storing the programmable voltage prior to the step of monitoring.

6. The method of claim 5, wherein the step of initializing includes the step of initializing the programmable voltage using the stored programmable voltage.

7. A method of self-tuning a VCO circuit in a radio, comprising the steps of:

selecting a control voltage range for the VCO;

initializing a programmable voltage corresponding to a predetermined tuning frequency;

applying a control voltage to the VCO to attempt to lock the VCO on the predetermined tuning frequency;

measuring the control voltage internally to the radio;

adjusting the tuning frequency through the programmable voltage until the VCO locks on frequency at a control voltage that falls within the selected control voltage range; and

monitoring the radio temperature internally to the radio and returning to the step of measuring the control voltage if the radio temperature reaches a predetermined delta temperature threshold.

8. The method of claim 7, wherein the step of adjusting includes the steps of incrementing and decrementing the programming voltage until the control voltage falls within the selected control voltage range.

9. The method of claim 7, further including the step of storing the programming voltage prior to the step of monitoring.

10. The method of claim 9, wherein the step of initializing comprises the step of initializing the programmable voltage using the stored programmable voltage.

11. A phase locked loop for a radio, comprising:

a VCO receiving a programmable voltage and a control voltage and generating a radio frequency (RF) output in response thereto, the VCO being characterized by a Ko value dependent on the control voltage;

a loop divider for dividing the VCO RF output frequency signal into a divided RF signal;

a phase detector for comparing a reference frequency to the divided RF signal and producing an error signal;

a loop filter for filtering the error signal and generating the control voltage for steering the VCO;

a microprocessor for measuring the control voltage and adjusting the programmable voltage until the VCO automatically locks on frequency with the control voltage that falls within predetermined control voltage limits, the predetermined control voltage limits being set for optimized Ko conditions;

a temperature detect circuit for measuring the temperature of the radio; and

the microprocessor monitoring the temperature detect circuit in order to detect an out of range delta temperature condition, and the microprocessor checking for a locked VCO within predetermined control voltage limits, and, if needed, adjusting the programmable voltage until the control voltage falls within the predetermined control voltage limits.

12. A phase locked loop as described in claim 11, wherein the adjustable programmable voltage is generated by a digital-to-analog (D/A) converter.

13. A phase locked loop as described in claim 11, wherein the microprocessor stores the predetermined control voltage limits.

14. A phase locked loop as described in claim 11, wherein the microprocessor stores the out of range delta temperature condition.