VOLTAGE CONTROLLED OSCILLATOR WITH ADAPTIVE CLOSED LOOP COARSE TUNE

• US 20010013812A1
• Filed: 11/23/1998
• Published: 08/16/2001
• Est. Priority Date: 11/23/1998
• Status: Active Grant

• Current Assignee: Garmin Corporation (Garmin Limited)
• Original Assignee: Garmin Corporation (Garmin Limited)
• Inventors: CUNNING, MICHAEL D.
• Granted Patent: US 6,307,439 B2
• Time in Patent Office: Days
• 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, currentfrom 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 varactor;

a coarse tune varactor; and

a voltage controlled oscillator.

2. The voltage controlled oscillator circuit as recited in

claim 1

, wherein said coarse tune varactor is comprised of an op amp circuit.

3. The voltage controlled oscillator circuit as recited in

claim 2

, said fine tune varactor 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.

4. The voltage controlled oscillator circuit as recited in

claim 3

, wherein said op amp circuit is incorporated into a noninverting closed loop feedback configuration.

5. The voltage controlled oscillator circuit as recited in

claim 4

, further comprising of a low impedance adapt switch connected in parallel with a resistor to an output of said noninverting closed loop feedback of op amp.

6. The voltage controlled oscillator circuit as recited in

claim 5

, wherein said resistor in parallel is of a high resistance.

7. The voltage controlled oscillator circuit as recited in

claim 3

, further comprising a resistor and a shunt capacitor connected to said output of the op amp circuit and said parallel switch and resistor.

8. The voltage controlled oscillator circuit as recited in

claim 7

, wherein said parallel resistor is of a magnitude bigger than said resistor connected immediately in series with said parallel resistor.

9. The voltage controlled oscillator circuit as recited in

claim 8

, wherein the magnitude of difference in resistance value between said parallel resistor and said resistor in series is at least 10 to 1.

10. The voltage controlled oscillator circuit as recited in

claim 2

, further comprising an output of said resistor and said shunt capacitor connected to a coarse tune port of said voltage controlled oscillator.

11. The voltage controlled oscillator circuit as recited in

claim 1

, wherein said fine tune varactor is comprised of:

a frequency generator;

a synthesizer; and

a loop filter.

12. The voltage controlled oscillator circuit as recited in

claim 1

, further comprising a prescalar input from said voltage controlled oscillator connected to said synthesizer.

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

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

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

a coarse tune varactor, said coarse tune varactor 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.

14. The voltage controlled oscillator circuit as recited in

claim 13

, wherein said voltage controlled oscillator circuit incorporated in combination with a communication device.

15. The voltage controlled oscillator circuit as recited in

claim 14

, where said communication device is capable of cellular communication.

16. The voltage controlled oscillator circuit as recited in

claim 14

, wherein said communication device further comprises a navigational aid.

17. The voltage controlled oscillator circuit as recited in

claim 16

, wherein said navigational aid has means for acquiring and processing global positioning system data.

18. 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.

19. The method of implementing an adaptive closed loop coarse tuning mechanism as recited in

claim 18

, wherein said selection of a desired frequency as a reference is selected by an external control within a communication device.