Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1999-06-23
2002-07-23
Kinkead, Arnold (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S167000, C331S1070SL, C331S17700V
Reexamination Certificate
active
06424231
ABSTRACT:
Priority is claimed to Japanese Patent Application No. 10-182524 filed in Japan on Jun. 29, 1998, the entire contents of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a voltage controlled oscillation circuit, and particularly relates to a voltage controlled oscillation circuit used for mobile communication apparatuses, such as a portable telephone.
2. Description of the Related Art
With a size-reduction of mobile-communication apparatuses, such as portable telephones, the demand of a size-reduction of RF circuits including circuits such as voltage-controlled oscillation circuits and PLL circuits has become strong in recent years.
The circuit diagram of a conventional voltage controlled oscillation circuit is shown in FIG.
6
. The voltage controlled oscillation circuit
1
comprises an amplifier circuit
2
, a resonance circuit
3
, three capacitors C
1
, C
2
and C
3
, a varactor diode D
1
, and a choke element L
1
. The amplifier circuit
2
is connected to the resonance circuit
3
, and the varactor diode D
1
is connected in parallel to the resonance circuit
3
via a first capacitor C
1
. One end of the choke element L
1
is connected to the cathode of the varactor diode D
1
, and the other end of the choke element L
1
is connected to the ground via a third capacitor C
3
. Moreover, a second capacitor C
2
is connected in parallel to the choke element L
1
. The output of the amplifier circuit
2
is connected to an output terminal
4
, and the other end of the choke element L
1
is connected to a control voltage terminal
5
.
The control voltage terminal
5
is a terminal for changing the oscillation frequency of the voltage controlled oscillation circuit
1
. A DC voltage is applied to the varactor diode D
1
, the internal capacitance of the varactor diode D
1
is changed. The changes of the internal capacitance brings the changes of the resonance frequency of the resonance system including the resonance circuit
3
, the varactor diode D
1
or the like. As a result, the oscillation frequency of the voltage controlled oscillation circuit
1
varies accordingly. Moreover, the choke element L
1
is an inductor provided such that the load connected to the control voltage terminal
5
might not influence the resonance circuit
3
. For example, the choke element L
1
comprises of a microstrip line having a predetermined length and a narrow width. The third capacitor C
3
is a bypass capacitor. The second capacitor
2
is provided such that the second capacitor
2
is caused to be resonated with the choke element L
1
in the vicinity of the oscillation frequency and the impedance between the cathode of the varactor diode D
1
and the control voltage terminal
5
in an oscillation frequency is made as high as possible. In this way the second capacitor
2
compensates the characteristics, as the choke element L
1
does not necessarily work as an ideal choke element.
Usually, the control voltage terminal
5
of the voltage controlled oscillation circuit is connected to a loop filter when PLL circuit is formed. In
FIG. 6
, a loop filter
6
is shown. A resistor R
1
and a fourth capacitor C
4
are included in the output side of the loop filter
6
. When the loop filter
6
is connected to the control voltage terminal
5
of the voltage controlled oscillation circuit
1
, the resistor R
1
built in the loop filter
6
is connected in series to the control voltage terminal
5
of the voltage controlled oscillation circuit
1
. Moreover, the fourth capacitor C
4
is connected in parallel to the third capacitor C
3
of the voltage controlled oscillation circuit
1
.
When a demand for a size-reduction of RF circuit was not excessively strong, the voltage controlled oscillation circuit
1
and the loop filter
6
were able to be arranged with a wider distance between them. In this case, siring is formed, for example, on a mounting substrate from the output of the loop filter
6
to the control voltage terminal
5
of the voltage controlled oscillation circuit
1
, and this wiring works as an inductance in the high frequency corresponding to the oscillation frequency of the voltage controlled oscillation circuit
1
. Thus, the fourth capacitor C
4
in the output side of the loop filter
6
did not necessarily affect the characteristic of the voltage controlled oscillation circuit
1
.
However, when demand for a size-reduction of RF circuit becomes strong and the distance of the voltage controlled oscillation circuit
1
and the loop filter
6
becomes small, the inductance component of the wiring between them is almost eliminated, and the fourth capacitor C
4
in the output side of the loop filter
6
comes to be connected in parallel to the third capacitor C
3
of the voltage controlled oscillation circuit
1
.
At this time, a sub-resonance (i.e., a secondary resonance as a by-product) occurs in the resonance circuit of the voltage controlled oscillation circuit
1
by that the fourth capacitor C
4
is connected in parallel to the third capacitor C
3
. Particularly in order to improve a lock-up time, when the capacitance of the fourth capacitor C
4
in the output side of the loop filter
6
is made small, the frequency of the sub-resonance is generated in the vicinity of the original oscillation frequency of the voltage controlled oscillation circuit
1
. Conversely, when the distance of the voltage controlled oscillation circuit
1
and the loop filter
6
is made large, it means that the frequency of the sub-resonance is located far away from the original oscillation frequency since the inductance component of the wiring between the voltage controlled oscillation circuit
1
and the loop filter
6
is large.
In
FIG. 7
, the impedance of a resonance circuit
3
side ( mag (Z
11
), abbreviation of magnitude (Z
11
), logarithmic representation of the absolute value of Z
11
) is shown. The resonance circuit
3
side is viewed from the node of the amplifier circuit
2
of the voltage controlled oscillation circuit
1
, and the resonance circuit
3
side includes all of the varactor diode D
1
, the capacitor C
4
or the like.
As shown in
FIG. 7
, though the pole of the impedance (resonance point) is in the original oscillation frequency f
1
, another pole of the impedance (sub-resonance point) exists also in the frequency f
2
which is a little lower than the frequency f
1
. Due to this sub-resonance point, when the oscillation frequency of the voltage controlled oscillator
1
is changed, there is a problem that an abnormal oscillation depending on conditions occurs.
In
FIG. 8
, the relationship of a control voltage (DC voltage applied to the control voltage terminal
5
) and an oscillation frequency is shown when the fourth capacitor C
4
is connected in parallel to the control voltage terminal
5
of the voltage controlled oscillation circuit
1
. As is clear from
FIG. 8
, the abnormal oscillation occurs when the control voltage exceeded 2.6V, and a normal oscillation stops. When the control voltage is 2.8V, the oscillation resumes at the different frequency far away from the oscillation frequency whet the control voltage is 2.6V or less. When the control voltage is 2.6V or less, the oscillation frequency is a range from approximately 700 MHZ to 740 MHZ, on the other hand, when the control voltage is 2.8V, the oscillation frequency is approximately 820 MHZ. Moreover, changes of the oscillation frequency to changes of the control voltage also becomes small.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-described problems, and to provide the voltage controlled oscillation circuit preventing the influence due to the capacitor in the output side of the loop filter connected to a control voltage terminal.
In order to achieve the above-mentioned object, the present invention is to provide a voltage controlled oscillation circuit including an amplifier circuit, a resonance circuit connected to the amplifier circuit, a varactor ode connected to the resonance circuit, one end
Ryugo Koji
Takai Kiyofumi
Burns Doane , Swecker, Mathis LLP
Kinkead Arnold
Murata Manufacturing Co. Ltd.
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