Voltage-controlled oscillation circuit

Details Voltage-controlled oscillation circuit Voltage-controlled oscillation circuit

2002-08-06

2004-04-13

Ton, My-Trang Nu (Department: 2816)

Oscillators

Solid state active element oscillator

Transistors

Reexamination Certificate

active

06720835

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a voltage-controlled oscillation circuit (VCO circuit), and for example, to a RF-CMOS VCO circuit used for a high frequency band.
2. Description of the Related Art
FIG. 13
is a circuit diagram showing a conventional RF-CMOS voltage-controlled oscillation (VCO) circuit
900
used for a high frequency band. Such a conventional RF-CMOS VCO circuit used for a high frequency band, is disclosed in the IEE JOURNAL OF SOLID-STATE CIRCUITS VOL. 32, NO. 5, pp. 736-744, “A 1.8-GHz Low-Phase Noise CMOS VCO using Optimized Hollow Spiral Inductors”, published in May 1997. The conventional RF-CMOS VCO circuit
900
includes a pair of inductors
901
a
and
901
b
, a pair of variable capacitance elements
902
a
and
902
b
, a pair of MOS transistors M
1
and M
2
each of which operates as a negative resistance, and a pair of MOS transistor M
3
and M
4
each of which operates as a current generator.
The variable capacitance elements
902
a
and
902
b
are, for example, a pair of pn-connection diodes or a pair of MOS condensers. A capacitance value of the variable capacitance elements
902
is controlled by changing a voltage level, which is applied, to the variable capacitance elements
902
a
and
902
b.
When an inductance of the inductor
901
is L and a capacitance value of the variable capacitance element
902
is C, an oscillation frequency f is 1/[2 Π{square root over ( )}LC]. When a change of voltage applied to the variable capacitance element
902
is &Dgr;V, and then a change of the capacitance value C is &Dgr;C, a ratio &Dgr;C/&Dgr;V between the change &Dgr;V of the voltage applied to the variable capacitance element
902
and the change &Dgr;C of the capacitance value is determined on the basis of kind of the variable capacitance elements that are used. Then, a change of the oscillation frequency &Dgr;f=[−f/2C])×&Dgr;C. A ratio &Dgr;f/&Dgr;V between the change &Dgr;f of the oscillation frequency and the change &Dgr;V of the voltage applied to the variable capacitance element
902
is designated a frequency sensitivity &Dgr;f/&Dgr;V=[−f/2C]×[&Dgr;C/&Dgr;V]. Specifically, two outputs (oscillation frequency &Dgr;f=[−f/2C]×&Dgr;C and frequency sensitivity &Dgr;f/&Dgr;V =[−f/2C]×[&Dgr;C/&Dgr;V] is determined on the basis of two parameters (inductance L and capacitance value C). A center capacitance value of the variable capacitance element
902
, or a capacitance value when a tuning voltage is 0 V, can be used as the capacitance value C.
In the conventional RF-CMOS VCO circuit used for a high frequency band, the oscillation frequency f is used around 1 GHz, the inductance L used is around a few nH, and the capacitance value C of the variable capacitance element
902
is around a few pF. The inductor
901
has a series resistance (wiring resistance) which even increases in accordance with an increase of the inductance L. The series resistance of the inductor
901
is larger than the wiring resistance of another connection of the conventional RF-CMOS VCO circuit. Therefore, the series resistance of the inductor
901
deteriorates a quality factor Q of the conventional RF-CMOS VCO circuit.
When the inductor
901
having a smaller series resistance and the variable capacitance element
902
having a larger variable capacitance are used in the conventional RF-CMOS VCO circuit, the conventional RF-CMOS VCO circuit can obtain a larger quality factor Q. However, in such a case, the frequency sensitivity &Dgr;f/&Dgr;V=−f/(2C)×(&Dgr;C/&Dgr;V)deteriorates.
SUMMARY OF THE INVENTION
The present invention is therefore directed to providing a voltage-controlled oscillation (VCO) circuit which substantially overcome one or more of the problems due to the limitations and disadvantages of the related art.
It is an objective of the invention to provide a voltage-controlled oscillation (VCO) circuit, including a current generator, a variable capacitor having a capacitance value which changes in accordance with a tuning voltage, and which is electrically connected to the current generator in series, an inductor which is electrically connected to the variable capacitor in parallel, a fixed capacitor which is electrically connected to the variable capacitor in parallel, and which has a set capacitance.
According to the present invention, the oscillation frequency, the frequency sensitivity and the quality factor can be set to a desired value, individually. Further, a phase noise can be reduced.


REFERENCES:
patent: 4918406 (1990-04-01), Baumbach et al.
patent: 5920235 (1999-07-01), Beards et al.
patent: 6097258 (2000-08-01), Van Veenendaal
patent: 6225871 (2001-05-01), Chien
patent: 6411171 (2002-06-01), Itoh
patent: 6556093 (2003-04-01), Craninckx et al.

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