Oscillators – Solid state active element oscillator – Significant distributed parameter resonator
Reexamination Certificate
2001-11-06
2003-09-30
Pascal, Robert (Department: 2817)
Oscillators
Solid state active element oscillator
Significant distributed parameter resonator
C331S03600C, C331S1170FE
Reexamination Certificate
active
06628174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage-controlled oscillator capable of changing an oscillation frequency by voltage control and a communication device employing the same.
2. Description of the Background Art
In general, a voltage-controlled oscillator employing a variable capacitance element such as a varactor diode is proposed. In the conventional voltage-controlled oscillator, the capacity-control voltage characteristic of the varactor diode employed as a tuning element is improved for attaining a broadband tuning range (width of change of the oscillation frequency with respect to change of a control voltage), optimizing the tuning range or improving linearity of change of the oscillation frequency with respect to change of the control voltage.
However, such improvement of the capacity-control voltage characteristic of the varactor diode is too limited to sufficiently broaden the band of the tuning range, sufficiently optimize the tuning range or sufficiently improve the linearity of change of the oscillation frequency with respect to change of the control voltage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a voltage-controlled oscillator capable of attaining a broadband tuning range and optimizing the tuning range while improving linearity of change of an oscillation frequency with respect to change of a control voltage and a communication device employing the same.
A voltage-controlled oscillator according to an aspect of the present invention comprises an oscillation part performing oscillation and a tuning part resonating within the oscillation frequency band of the oscillation part, while the tuning part includes an impedance transformer including a transmission line and a variable reactance circuit, connected between an end of the transmission line and the oscillation part, including a variable capacitance element having a capacitance value varying with a control voltage and an inductive component, a locus drawn by the impedance of the tuning part as viewed from the node between the oscillation part and the tuning part in response to change of the control voltage includes a point where reactance reaches substantially zero, and the characteristic impedance of the transmission line is so set that the rate of change of the capacitance value of the variable capacitance element with respect to change of the oscillation frequency is minimized within a prescribed range of the characteristic impedance of the transmission line.
In the voltage-controlled oscillator according to the present invention, the tuning part resonates in the oscillation frequency band of the oscillation part. When the control voltage is changed, the impedance of the tuning part as viewed from the node between the oscillation part and the tuning part draws a locus including a point where the reactance reaches substantially zero. In this case, the rate of change of the oscillation frequency with respect to change of the control voltage can be increased. The characteristic impedance of the transmission line is so set that the rate of change of the capacitance value of the variable capacitance element with respect to change of the oscillation frequency is minimized within a prescribed range of the characteristic impedance of the transmission line, whereby the rate of change of the oscillation frequency with respect to change of the capacitance value of the variable capacitance element is increased. Therefore, the rate of change of the oscillation frequency with respect to change of the control voltage is so increased that a broadband tuning range can be attained.
A desired range can be selected from the broadband tuning range, whereby the tuning range can be optimized.
Further, a range having excellent linearity of the capacity-control voltage characteristic of the variable capacitance element can be selectively used due to the broadband tuning range. Thus, linearity of change of the oscillation frequency with respect to change of the control voltage for the voltage-controlled oscillator is improved.
A necessary tuning range can be ensured by small change of the capacitance value of the variable capacitance element, whereby capacity change in the tuning range is reduced and change of a series resistance component of the variable capacitance element is also reduced. Therefore, fluctuation of a phase noise characteristic caused by change of the oscillation frequency is reduced.
The Q-value of the tuning part as well as the phase noise characteristic are improved by performing tuning in a region of the control voltage having a small dc resistance component of the variable capacitance element.
The impedance of the tuning part as viewed from the node between the oscillation part and the tuning part at the central value of the control voltage may be so set that the reactance substantially reaches zero. Thus, the rate of change of the oscillation frequency with respect to change of the control voltage can be increased.
The other end of the transmission line may be opened, the reactance of the variable reactance circuit may be inductive at the central value of the control voltage, and the characteristic impedance of the transmission line may be set to the minimum value within the prescribed range.
When the other end of the transmission line is opened and the reactance of the variable reactance circuit is inductive at the central value of the control voltage, the rate of change of the capacitance value of the variable capacitance element with respect to change of the oscillation frequency is reduced as the characteristic impedance of the transmission line is reduced. Therefore, the rate of change of the oscillation frequency with respect to change of the capacitance value of the variable capacitance element can be increased by setting the characteristic impedance of the transmission line to the minimum value within the prescribed range. Consequently, the rate of change of the oscillation frequency with respect to change of the control voltage can be increased, for attaining a broadband tuning range.
The characteristic impedance of the transmission line may be set lower than 50&OHgr;. When the other end of the transmission line is opened and the reactance of the variable reactance circuit is capacitive at the central value of the control voltage, the rate of change of the capacitance value of the variable capacitance element with respect to change of the oscillation frequency is reduced as the characteristic impedance of the transmission line is reduced. Therefore, the rate of change of the oscillation frequency with respect to change of the control voltage can be increased for attaining a broadband tuning range by setting the characteristic impedance of the transmission line lower than 50&OHgr;.
The other end of the transmission line may be opened, the reactance of the variable reactance circuit may be inductive at the central value of the control voltage, and the characteristic impedance of the transmission line may be so set as to minimize the rate of change of the capacitance value of the variable capacitance element with respect to change of the oscillation frequency.
When the other end of the transmission line is opened and the reactance of the variable reactance circuit is capacitive at the central value of the control voltage, the rate of change of the capacitance value of the variable capacitance element with respect to change of the oscillation frequency has the minimum value. Therefore, the rate of change of the oscillation frequency with respect to change of the capacitance value of the variable capacitance element can be increased by setting the characteristic impedance of the transmission line to minimize the rate of change of the capacitance value of the variable capacitance element with respect to change of the oscillation frequency. Consequently, the rate of change of the oscillation frequency with respect to change of the control voltage can be increased for attaining a broadband tuning range.
The characteristi
Imaoka Toshikazu
Onoda Katsuaki
Glenn Kimberly E
Sanyo Electric Co,. Ltd.
LandOfFree
Voltage-controlled oscillator and communication device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Voltage-controlled oscillator and communication device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Voltage-controlled oscillator and communication device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3098131