Voltage controlled oscillator with adaptive closed loop coarse tune

• US 6,307,439 B2
• Filed: 11/23/1998
• Issued: 10/23/2001
• Est. Priority Date: 11/23/1998
• Status: Expired due to Fees

• Current Assignee: Garmin Corporation (Garmin Limited)
• Original Assignee: Garmin Corporation (Garmin Limited)
• Inventors: Cunning, Michael D.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Glenn, Kimberly E
• Application Number:
  US09/198,224
• Publication Number:
  US 20010013812A1
• Time in Patent Office: 1,065 Days
• Field of Search: 331/10, 331/177.R, 331/16, 331/17, 327/156
• US Class Current: 331/10
• CPC Class Codes: H03B 2201/0208 the means being an element with a variable capacitance, e.g. capacitance diode
• CPC Class Codes: H03L 2207/06 Phase locked loops with a controlled oscillator having at least two frequency control terminals
• CPC Class Codes: H03L 7/102 the additional signal being directly applied to the controlled loop oscillator
• CPC Class Codes: H03L 7/1075 by changing characteristics of the loop filter, e.g. changing the gain, changing the bandwidth H03L7/1072 takes precedence

Abstract

A voltage controlled oscillator circuit incorporating a closed loop coarse tuning mechanism. In this system, a reference oscillator is set with the desired frequency for the voltage controlled oscillator. A resulting voltage used to drive the oscillator is produced by a synthesizer connected in series with a loop filter. The resulting voltage is connected to a fine tune input of the voltage controlled oscillator and also to the input of an adaptive closed loop coarse tuning mechanism. The adaptive closed loop coarse tuning mechanism is comprised of an op amp configured in a noninverting feedback loop connected to a parallel resistor/adapt switch loop. The loop is followed by a shunt capacitor filter which is then connected directly to the coarse tune input of the VCO. If the adapt switch is closed, current from the coarse amp flows through a filter and to a coarse tune port of the VCO. The voltage resulting from the adaptive closed loop coarse tuning mechanism overrides any voltage being received in the fine tune port, making the coarse tune loop controlling in frequency acquisition. Throughout the entire coarse tune process, a feedback loop allows the synthesizer to adjust the control voltage as the VCO gets closer to the desired frequency. After a predetermined acquisition time, the adapt switch is opened. This virtually eliminates the adaptive closed loop tuning mechanism from the circuit because of the large time constant associated with the (closed) adapt switch/resistor circuit. At that point the fine tune port voltage will make any minor adjustments in driving the VCO to the desired frequency.

Claims

1. A voltage controlled oscillator circuit, said voltage controlled oscillator circuit comprising:

a fine tune mechanism;

a coarse tune mechanism;

a voltage controlled oscillator operably connected to said fine tun mechanisms and said coarse tuning mechanism, wherein said coarse tuning mechanism is comprised of an op amp circuit; and

wherein said fine tune mechanism and said coarse tuning mechanism operate in parallel closed loops, said fine tune mechanism having an output connected directly to an input of said coarse tune op amp circuit and also to a fine tune port input of said voltage controlled oscillator, wherein said op amp circuit is incorporated into a noninverting closed loop feedback configuration.

2. The voltage controlled oscillator circuit as recited in claim 1, further comprising a low impedance adapted switch connected in parallel with a resistor to an output of said noninverting closed loop feedback of said op amp.

3. The voltage controlled oscillator circuit as recited in claim 2, wherein said resistor in parallel is of a high resistance.

4. The voltage controlled oscillator circuit as recited in claim 2, further comprising a resistor with a shunt capacitor connected to said output of the op amp circuit and said parallel switch and resistor.

5. The voltage controlled oscillator circuit as recited in claim 4, wherein said parallel resistor is of a magnitude bigger than said resistor connected immediately in series with said parallel resistor.

6. The voltage controlled oscillator circuit as recited in claim 5, wherein the magnitude of difference in resistance value between said parallel resistor and said resistor in series is at least 10 to 1.

7. The voltage controlled oscillator as recited in claim 4, further comprising an output of said resistor and said shunt capacitor connected to a coarse tune port of said voltage controlled oscillator.

8. The voltage controlled oscillator circuit as recited in claim 1, wherein said fine tune mechanism is comprised of:

a frequency generator;

a synthesizer; and

a loop filter.

9. The voltage controlled oscillator circuit as recited in claim 8, further comprising a prescalar input from said voltage controlled oscillator connected to said synthesizer.

10. A voltage controlled oscillator circuit, said voltage controlled oscillator circuit comprising:

a fine tune mechanism, said fine tune mechanism comprised of a frequency generator, a synthesizer and a loop filter;

a voltage controlled oscillator, wherein said loop filter has an output connected to a fine tune port of said voltage controlled oscillator and said voltage controlled oscillator is connected to said synthesizer via a prescalar input line; and

a coarse tuning mechanism, said coarse tuning mechanism comprised of an op amp circuit configured in a noninverting closed loop feedback loop, a low impedance adapt switch connected in parallel with a resistor to an output of said noninverting closed loop feedback of said op amp circuit, a resistor and a shunt capacitor connected to said parallel switch and resistor, a coarse tune port of a voltage controlled oscillator connected to an output of said resistor and said shunt capacitor.

11. The voltage controlled oscillator circuit as recited in claim 10, wherein said voltage controlled oscillator circuit incorporated in combination with a communication device.

12. The voltage controlled oscillator circuit as recited in claim 11, where said communication device is capable of cellular communication.

13. The voltage controlled oscillator circuit as recited in claim 11, wherein said communication device further comprises a navigational aid.

14. The voltage controlled oscillator circuit as recited in claim 13, wherein said navigational aid has means for acquiring and processing global positioning system data.

15. The method of implementing an adaptive closed loop coarse tuning mechanism with a voltage controlled oscillator, said method comprising:

selecting a desired frequency as a reference;

comparing said reference frequency to a present

frequency of said voltage controlled oscillator;

producing a voltage corresponding to a phase difference

between said reference frequency and said present voltage

controlled oscillator frequency;

utilizing a closed adapt switch to drive an adaptive closed

loop coarse tuning mechanism with said voltage;

continuing to drive said adaptive closed loop coarse tune for a preset time; and

opening said adapt switch to end adaptive closed loop coarse tuning.

16. The method of implementing an adaptive closed loop coarse tuning mechanism as recited in claim 15, wherein said selection of a desired frequency as a reference is selected by an external control within a communication device.

17. A voltage controlled oscillator circuit, said voltage controlled oscillator circuit comprising:

a fine tune mechanism;

a coarse tuning mechanism;

a voltage controlled oscillator operably connected to said fine tune mechanism

and said coarse tuning mechanism, wherein said coarse tuning mechanism is comprised of an op amp circuit;

wherein said fine tune mechanism and said coarse tuning mechanism operate in parallel closed loops and wherein said fine tune mechanism is comprised of a frequency generator, synthesizer, and a loop filter; and

a prescaler input from said voltage controlled oscillator to said synthesizer.