JP2912203B2 - Voltage controlled oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator for a radio device requiring a wide oscillation frequency band,
In particular, the present invention relates to a voltage controlled oscillator such as a Colpitts oscillator including an inductive circuit section including a parallel circuit of an inductance element having one end at a ground potential and a varicap diode for changing a capacitance value by a change in an applied reverse bias voltage.

[0002]

2. Description of the Related Art In a conventional voltage-controlled oscillator of this type, in order to widen the oscillation frequency, a super step-junction type whose capacitance value with respect to a change in reverse bias voltage can be largely changed is often used as a varicap diode. But,
In this method, since the APC sensitivity (voltage-to-oscillation frequency change ratio) increases, there is a disadvantage that the S / N or C / N of the oscillation signal deteriorates. There is also a method of increasing the change width of the reverse bias voltage applied to the varicap diode. However, in this method, the variable width of the oscillation frequency becomes extremely small in the high reverse bias voltage region of the varicap diode because the voltage is in the nonlinear region of the change in capacitance, so that this voltage-controlled oscillator is used as a synthesizer (or a phase locked loop). ), The loop gain of the synthesizer loop (or phase lock loop) is reduced.

As a voltage-controlled oscillator for solving the above-mentioned problem, there is a technique disclosed in Japanese Patent Application Laid-Open No. 3-160801. In this voltage controlled oscillator, a plurality of varicap diodes (variable capacitance diodes in the disclosure example, hereinafter also referred to as varicaps) are connected in an alternating manner, and a reverse bias voltage is individually applied to each of them.

In order to adjust the oscillation center frequency of the voltage controlled oscillator, a trimmer capacitor is connected in parallel to the varicap diode,
As disclosed in Japanese Patent Application Laid-Open No. 5 (1999) -2005, there is an example in which a microstrip line is added to the varicap diode as a trimming stub.

[0005]

In the first example of the disclosed voltage controlled oscillator, when the reverse bias voltage applied to the first varicap is low and the capacitance value of the first varicap is large, Even if the capacitance value of the second varicap is changed by changing the reverse bias voltage applied to the second varicap, the capacitance value of the variable capacitance portion is equal to the capacitance value of the first varicap. Since this is the sum of the capacitance value of the second varicap and the change in the oscillation frequency due to the change in the reverse bias voltage applied to the second varicap, there is a drawback.

When the reverse bias voltage applied to the first varicap is high and the capacitance value of the first varicap is small, the change in the oscillation frequency is caused by the change in the capacitance value of the second varicap. However, there is a disadvantage that the method of setting the reverse bias voltage to the first and second varicaps for changing the oscillation frequency in a wide band becomes complicated.

Further, the second example has a drawback that broadband oscillation cannot be performed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, and to easily control the oscillation frequency over a wide band while ensuring a high S / N or high C / N of the oscillation signal. It is to provide a voltage controlled oscillator that can be used.

[0009]

One of the voltage controlled oscillator SUMMARY OF THE INVENTION The present invention is seen containing a parallel circuit of a varicap diode to vary the capacitance value by the change in inductance element and applying a reverse bias voltage, one end grounded A voltage-controlled oscillator having an inductive circuit portion having a potential, a first capacitive stub having one end connected to the other end of the inductive circuit portion, and at least one n-th (n is an integer of 2 or more) A capacitive stub, a (n + 1) -th capacitive stub having the other end as an open end, and the first to (n + 1) -th capacitive stubs according to the supplied stub length control signal. A diode switch circuit that can be cascade-connected one by one at the ends .
n farther from the inductance element of the capacitive stub
One end of 1/4 wavelength stub is connected to the tip of
The other end of each of the quarter-wave stubs has one end grounded.
The other ends of the diodes are connected respectively.

[0010]

[0011]

[0012] The voltage controlled oscillator, the diode switch circuit, in the case of cascade connecting n or (n + 1) of the capacitive stubs to said inductance element, said capacitive having ordinal number less than the n or n + 1 A configuration can be adopted in which all the diodes connected to the stub-connected quarter-wavelength stub are turned on.

One alternative of the voltage controlled oscillator [0013] The present invention is seen containing a parallel circuit of a varicap diode to vary the capacitance value by the change in Lee <br/> inductance element and applying a reverse bias voltage, one end grounded In a voltage controlled oscillator provided with an inductive circuit unit for setting a potential, a first capacitive stub having one end connected to the other end of the inductive circuit unit, and one end connected to the other end of the first capacitive stub circuit A 波長 wavelength stub, a first diode having one end connected to the other end of the 波長 wavelength stub and the other end grounded, a second capacitive stub having the other end as an open end, A second diode that connects the other end of the first capacitive stub to one end of the second capacitive stub; and a first diode that turns on the first diode and turns off the second diode. Stub length control mode And a stub length control circuit having both a second stub length control mode to ON and the first and second diodes.

[0014]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a voltage controlled oscillator according to the present invention.

This voltage controlled oscillator has a transistor TR
1 is an oscillator, and is a Colpitts oscillator in which the base of a transistor TR1 is grounded at high frequency by a capacitor C6. A capacitor C5 representing a capacitive impedance is provided between the collector and the emitter of the transistor TR1, a capacitor C7 representing a capacitive impedance is provided between the emitter and the base, and an inductive circuit section 1 representing an inductive impedance is provided between the collector and the base. Each is connected. The collector of the transistor TR1 is connected to a power supply voltage Vcc from a power supply terminal Pp via a coil L2 for preventing oscillation signal leakage.
Is supplied to the base, and a voltage obtained by dividing the power supply voltage Vcc by the resistors R2 and R3 is supplied to the base, and the emitter is grounded via an auto-bias resistor R4. The output signal of the voltage controlled oscillator is output from the emitter of the transistor TR1 to the output terminal Po through the capacitor C8.

The inductive circuit section 1 includes a resonator Z1 which is an inductance element exhibiting an inductive impedance at the oscillation frequency of the voltage controlled oscillator, and an anode grounded varicap connected in parallel to the resonator Z1 in a high frequency manner. A diode X1. The capacitance of the diode X1 changes in response to a variable control voltage Vv that is a reverse bias voltage applied to the control terminal Pv, and the oscillation frequency of the voltage controlled oscillator changes in response to the change in the capacitance. For example, the capacitance value of the diode X1 makes the oscillation frequency of the voltage controlled oscillator lower than the resonance frequency of the resonator Z1, but the increase of the capacitance value of the diode X1 further lowers the oscillation frequency. The control terminal Pv and the diode X
A resistor R1 for protecting the diode X1 and a filter composed of the coil L1 and the capacitor C1 are connected in series between the first cathode and the first cathode. This filter blocks the passage of high frequency signals between the inductive circuit part 1 and the diode X1. The capacitors C2 and C3 are coupling capacitors between the diode X1 and the resonator 12, and the capacitor C4 is a coupling capacitor for blocking a direct current between the resonator Z1 and the collector of the transistor TR1 and for passing an oscillation signal component. Exhibits almost zero impedance. The resonator Z1 generally uses a high-Q resonator such as a quartz resonator or a dielectric resonator, but may use a relatively low-Q resonator such as a stripline resonator. The voltage-controlled oscillator according to this embodiment uses a 2SC4266 type transistor (manufactured by NEC Corporation) for the transistor TR1, a dielectric resonator having a resonance frequency of about 2 GHz for the resonator Z1, and a capacitance value of the diode X1 of tens pF. An oscillation signal having an oscillation frequency of about 900 MHz is generated.

The voltage controlled oscillator according to the present embodiment further includes stub circuits 11, 12, 13 and 14 for adding an additional capacitance Ca to the inductive circuit unit 1. The stub circuits 11 to 14 are formed on a microstrip line.

The stub circuit 11 has one end connected to a capacitor C2.
Stub S1 connected between C1 and C3, and a quarter-wave stub S connected at one end near the other end of the capacitive stub S1.
5 and a cathode grounded PIN diode X5 whose anode is connected to the other end of the quarter-wave stub S5. The capacitive stub S1 is formed of a strip line having a wide strip conductor (having a low characteristic impedance) and a short length, and exhibits a capacitance near the oscillation frequency of the voltage controlled oscillator. The 波長 wavelength stub S5 is formed of a strip line having a relatively high characteristic impedance with a length of about １ ／ wavelength near the oscillation frequency. The PIN diode has a low high-frequency resistance value when conducting (ON) and is non-conducting (O
FF) has a high high-frequency resistance and a small inter-terminal capacitance, and thus is suitable as a diode X5 used as a high-frequency switch. A high-frequency varactor having the above-described ON / OFF characteristics can be used instead of the PIN diode X5.

Here, the capacitive stub S of the stub circuit 11
1 has a control voltage V from a control terminal P1 via a low-pass filter including a coil L11 and a capacitor C11.
Have received one. Now, when a positive voltage V1 is applied to the control terminal P1, the PIN diode X5 is turned on and the
The other end of the wavelength stub S5 is a short-circuit point, and one end of the quarter-wave stub S5 is an open point. Therefore, 1 /
The four-wavelength stub S5 and the PIN diode X5 have no effect on the susceptance exhibited by the capacitive stub S1 and may be treated as being absent.

The stub circuit 12 includes a PIN diode X2 having a cathode connected to the other end of the capacitive stub S1, a capacitive stub S2 having one end connected to the anode of the PIN diode X2, and one end connected to the other end of the capacitive stub S2. It has a quarter-wave stub S6 connected in the vicinity, and a cathode-grounded PIN diode X6 whose anode is connected to the other end of the quarter-wave stub S6. The capacitive stub S2 of the stub circuit 12 includes a coil L12 and a capacitor C1.
2 receives a control voltage V2 from a control terminal P2 via a low-pass filter composed of two.

The stub circuit 13 includes a PIN diode X3 having a cathode connected to the other end of the capacitive stub S2, a capacitive stub S3 having one end connected to the anode of the PIN diode X3, and one end connected to the other end of the capacitive stub S3. There is a quarter-wave stub S7 connected in the vicinity, and a cathode grounded PIN diode X7 having an anode connected to the other end of the quarter-wave stub S7. The capacitive stub S3 of the stub circuit 13 includes a coil L13 and a capacitor C1.
3 receives the control voltage V3 from the control terminal P3 via the low-pass filter composed of the control voltage V3.

The stub circuit 14 includes a PIN diode X4 having a cathode connected to the other end of the capacitive stub S3, and a capacitive stub S3 having one end connected to the anode of the PIN diode X4. The capacitive stub S4 of the stub circuit 14 includes a coil L14 and a capacitor C1.
4 receives a control voltage V4 from a control terminal P4 via a low-pass filter composed of the control signal V4.

The capacitive stubs S2, S3 and S4 in the stub circuits 12, 13 and 14 have almost the same function as the capacitive stub S1 of the stub circuit 11. Similarly, 1
Since the quarter-wavelength stubs S6 and S7 have almost the same function as the capacitive stub S1, and the PIN diodes X6 and X7 have almost the same function as the PIN diode X5, the functions of the stub circuits 12, 13 and 14 are related. Description is omitted.

The inductive circuit unit 1 includes control terminals P1 to P
By appropriately selecting the values of the control voltages V1 to V4 to be supplied to the power supply 4, the additional capacitance Ca is changed stepwise, and the oscillation frequency of the voltage controlled oscillator can be changed over a wide band. The gradual change of the additional capacitance Ca is caused by adding capacitive stubs S1, S to a parallel circuit of the resonator Z1 and the varicap diode X1.
2, S3 and S4 are sequentially cascaded one by one at the ends of these capacitive stubs.

FIG. 2 is a diagram summarizing the operation of controlling the length of the capacitive stub in the present embodiment.

Referring to FIGS. 1 and 2, in order to connect only the capacitive stub S1 to the parallel circuit, the PIN diode X5 is turned on and the PIN diode X is turned on.
2 needs to be turned off. Diode X2 is OFF
, The influence of the circuit elements farther from the parallel circuit than the diode X2 is eliminated, so that the PIN diode X3
ON / OFF of X4, X6 and X7 is optional. To realize this diode ON / OFF state, the control voltage V1 is set to a positive voltage, and the control voltage V2 is set to 0V or a negative voltage. The control voltages V3 and V4 are arbitrary, but in order to further reduce the influence of the capacitive stubs S2, S3 and S4, it is preferable that the control voltages V3 and V4 be 0 V or a negative voltage. In addition, the negative voltage is more negative than 0V.
The ON / OFF ratio of the IN diode is improved.

In order to cascade-connect the capacitive stubs S1 and S2 to the above-described parallel circuit by performing the same examination as described above, the control voltages V1 and V3 are set to 0V (or a negative voltage, the same applies hereinafter).
And the control voltage V2 is set to a positive voltage, the PIN diodes X2, X5 and X6 are turned on, and the PIN diode X
3 is turned OFF. Also, capacitive stubs S1, S2 and S
3 in cascade with the parallel circuit, the control voltage V
1, V2 and V4 are set to 0 V, the control voltage V3 is set to a positive voltage, and the PIN diodes X2, X3, X5 to X7 are set to O.
N, and the PIN diode X4 is turned off. Further, in order to cascade connect all the capacitive stubs S1 to S4 to the parallel circuit, the control voltages V1 to V3 are set to 0 V, the control voltage V4 is set to a positive voltage, and all the PIN diodes X2
To X7 are turned ON.

The connection directions of the PIN diodes X2 to X7 in the present embodiment can be made opposite to each other. In this case, the control voltages V1 to V4 need to be reversed from those in FIG.

FIG. 3 is a diagram showing the relationship between the additional capacitance Ca and the oscillation frequency F with respect to the length of the capacitive stub in the voltage controlled oscillator according to the present embodiment. Here, the capacitive stub S
The lengths of 1 to S4 are represented by reference numerals of the components, and the capacitances generated by the respective capacitive stubs are all the same. Further, the oscillation frequency F decreases linearly with an increase in the additional capacitance value Ca.

When the capacitive stubs S1 to S1 are sequentially connected in cascade to the parallel circuit of the varicap diode X1 and the resonator Z1, the total length of these capacitive stubs becomes 1/8.
When the wavelength is less than the wavelength, the additional capacitance Ca increases almost in proportion to the total length. Therefore, when the reverse bias voltage Vv of the diode X1 is a fixed value, the oscillation frequency F decreases stepwise. If the only capacitive stub connected to the parallel circuit is S1, the oscillation frequency F is the highest frequency F1a when the reverse bias voltage of the diode X1 is the maximum value. When the reverse bias voltage of the diode X1 is the minimum value, the oscillation frequency F becomes the lowest frequency F1b. Frequency F1a
A band between F1b and F1b is defined as band A. Similarly, if the connection capacitive stubs are S1 and S2, the oscillation frequency F will be in the range of the band B between the highest frequency F2a and the lowest frequency F2b. Hereinafter, similarly, in the connection of the capacitive stubs S1, S2, and S3, the oscillation frequency F is in the range of the band C between the highest frequency F3a and the lowest frequency F3b, and the capacitive stubs S1, S2, S3, and S4 The oscillation frequency F is in the range of the band D between the highest frequency F4a and the lowest frequency F4b.

Here, the capacitance value Ca exhibited by the capacitive stubs S1 to S4 in the present embodiment will be discussed in detail. The stubs S1 to S4 are microstrip lines using a glass epoxy resin having a relative dielectric constant of 4.8 as a substrate. This strip line has a substrate thickness of 0.2 m
m, the width of the strip conductor is 0.4 mm, the conductor thickness of the strip conductor is 18 μm, the characteristic impedance Z0 is 50Ω at a frequency of 900 MHz, the wavelength shortening rate α is 0.524, and thus one wavelength (λ) is 174 mm. .

The relationship between the stub length 1 of the strip line and the capacitance value Ca is shown in equation (1). Here, ω is an angular frequency (= 2πF). Note that the lengths of the PIN diodes X2 to X4 are ignored.

Ca = {1 / (ωZ0)} tan (2πl / λ) (1) According to the equation (1), when the total length of the capacitive stubs S1 to S4 is 21.8 mm (λ / 8), Ca is 3.5p
F and the capacity Ca at 38.1 mm (7λ / 32)
Is 17.8 pF. The voltage controlled oscillator of FIG. 1 can obtain an oscillation band of about 50 MHz by changing the additional capacitance Ca from 1 pF to 15 pF. Note that the characteristic impedance Z0 of the stubs S1 to S4 is 50Ω as described above.
, The capacitance value Ca changes abruptly near the stub length λ / 4, so that the line width of the stubs S1 to S4 is widened so that the characteristic impedance Z0 is lower than 50Ω and the line length l
A more appropriate design is to improve the linearity of the capacitance value Ca with respect to.

As described above, the voltage-controlled oscillator according to the present embodiment divides the oscillation frequency into four steps to broaden the oscillation frequency by appropriately selecting the values of the control voltages V1 to V4 supplied to the control terminals P1 to P4. Can change. Therefore, the control voltage V applied to the varicap diode X1
Since the range of v can be easily limited to a range in which the oscillation frequency F changes linearly and the voltage-to-capacity change ratio is large, a high S / N ratio can be maintained.

Although the voltage controlled oscillator shown in FIG. 1 has four stub circuits 11 to 14, the stub circuits 12 and 13 are omitted, and the stub circuit 11 is omitted.
And 14 can also be directly connected. In this case, when the control voltage V1 is set to the positive voltage, the control voltage V4 is set to 0V, and the PIN diode X5 is turned on and the PIN diode X4 is turned off, only the capacitive stub S1 is connected in parallel with the varicap diode X1 and the resonator Z1. Connected to the circuit. Also,
In order to cascade-connect the capacitive stubs S1 and S4 to the parallel circuit, the control voltage V1 is set to 0V and the control voltage V4 is set to a positive voltage.

It is needless to say that any number of circuits equivalent to the stub circuits 11 and 12 may be connected in cascade between the stub circuits 11 and 14.

[0038]

As described above, according to the present invention, there are provided a first capacitive stub having one end connected to the other end of the inductive circuit portion, an n-th (n is an integer of 2 or more) capacitive stub, The (n + 1) -th capacitive stub having the other end as an open end and the capacitive stubs from the first to (n + 1) -th capacitive stubs are sequentially arranged at the tips of these capacitive stubs in accordance with the supplied stub length control signal. Since a diode switch circuit that can be cascaded one by one is provided, there is an effect that an oscillation signal having a good linearity of control voltage versus oscillation frequency in a wide band can be easily generated while maintaining a high S / N ratio.

Further, the present invention has an effect that the oscillation frequency can be changed in a wide band with a low control voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a voltage controlled oscillator according to the present invention.

FIG. 2 is a diagram summarizing a control operation of a capacitive stub length in the present embodiment.

FIG. 3 is a diagram illustrating a relationship between an additional capacitance Ca and an oscillation frequency F with respect to a capacitive stub length in the voltage controlled oscillator according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inductive circuit part 11-14 Stub circuit C1-C8, C11-C14 Capacitor L1, L2, L11-L14 Coil P1-P4 Stub length control terminal Pv Capacitance control terminal Pp power terminal Po Output terminal R1-R4 Resistor S1- S4 Capacitive stub S5 to S7 Quarter wavelength stub TR1 Transistor X1 Varicap diode X2 to X7 PIN diode Z1 Resonator

Claims (3)

(57) [Claims] 1. A saw including a parallel circuit of a inductance element and the applied reverse bias voltage varicap diodes to vary the capacitance value by the change of the voltage controlled oscillator comprising an inductive circuit for one end and the ground potential, one end Are connected to the other end of the inductive circuit section, at least one n-th (n is an integer of 2 or more) capacitive stub, and (n + 1) ) And a diode switch circuit capable of sequentially cascading the first to (n + 1) th capacitive stubs one by one at the tips of the capacitive stubs in accordance with a supplied stub length control signal. further comprising the inductance of said first through capacitive stubs of the n
One end of a 1/4 wavelength stub at the tip farthest from the element
And the other end of each of the 波長 wavelength stubs
Is connected to the other end of the diode, one end of which is grounded.
It characterized in that it has a voltage-controlled oscillator. 2. The method according to claim 1, wherein the number of said diode switch circuits is n.
Others when cascading the n + 1 of the capacitive stubs to the inductance element, the said capacitive stubs connected with ordinal number less than the n or n + 1 1/4
Voltage controlled oscillator according to claim 1, characterized in that all the diodes connected to the wavelength stub ON. 3. A saw including a parallel circuit of a inductance element and the applied reverse bias voltage varicap diodes to vary the capacitance value by the change of the voltage controlled oscillator comprising an inductive circuit for one end and the ground potential, one end A first capacitive stub connected to the other end of the inductive circuit unit, a 波長 wavelength stub having one end connected to the other end of the first capacitive stub circuit, and a 波長 wavelength stub. A first diode having one end connected to the other end and the other end grounded, a second capacitive stub having the other end as an open end, the other end of the first capacitive stub, and the second capacitor A second diode connecting one end of the conductive stub, a first stub length control mode for turning on the first diode and turning off the second diode, and both the first and second diodes. A stub length control circuit having a second stub length control mode to be turned on.