JP2006352423A - Voltage control oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage control oscillator in which abnormal oscillations of a resonator and a spurious component of an oscillation signal are removed even while imparting the linearity to the change of a junction capacity of a variable capacity element, and also, the occurrence of thermal noise is suppressed. <P>SOLUTION: The voltage control oscillator 11 is provided with a resonance circuit 12 and an amplifier circuit 13. The resonance circuit 12 is provided with a variable capacity element circuit 14 in which the plurality of variable capacity elements VD1, VD2 are connected in series. A control voltage for reversely biasing the variable capacity elements VD1, VD2 is inputted from a control voltage input terminal Vc1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a voltage controlled oscillator that includes a resonance circuit and an amplifier circuit and controls an oscillation frequency by a control voltage from a control voltage input terminal.

  Conventionally, in a resonant circuit of a voltage controlled oscillator, a variable capacitance element such as a varactor diode (varicap diode) is connected to an oscillator such as an LC oscillation circuit or a crystal oscillator, and an active element for amplification such as a transistor is connected in an amplifier circuit. It acts as a negative resistance and is configured by connecting a resonance circuit and an amplifier circuit.

  The resonance circuit is provided with a control voltage input terminal for changing the junction capacitance of the variable capacitance element, and is variable by applying a control voltage from the outside to the control voltage input terminal so that the variable capacitance element is reverse-biased. The oscillation frequency is controlled by changing the junction capacitance of the capacitive element and changing the combined capacitance of the resonance circuit.

  Here, FIG. 1 shows a configuration example of a conventional voltage controlled oscillator with reference to Patent Document 1. The voltage controlled oscillator 1 includes a resonance circuit 2 and an amplifier circuit 3.

  In the resonance circuit 2, a parallel circuit of a trimmer capacitor TC1 and a capacitor C2 for adjusting and setting the oscillation frequency is connected to one end of the crystal resonator XD1, and the other end of the parallel circuit is grounded. By adjusting the trimmer capacitor TC1, the oscillation frequency of the voltage controlled oscillator 1 is set to a design value. Further, the amplifier circuit 3 is connected to the other end of the crystal resonator XD1 via a current blocking capacitor C3, and one end of the capacitor C1 is connected. The other end of the capacitor C1 is connected to the cathode of the varactor diode VD1, and the anode of the varactor diode VD1 is grounded. Further, a resistance voltage dividing circuit comprising resistors R1 and R2 is connected to the control voltage input terminal Vc, and the other end of the resistor R2 is grounded. A connection point between the resistor R1 and the resistor R2 is connected to the cathode of the varactor diode VD1 and the capacitor C1.

  In the voltage controlled oscillator 1 having such a configuration, when a control voltage is applied to the control voltage input terminal Vc so that the varactor diode VD1 is reverse-biased, the control voltage is divided by the resistance voltage dividing circuit. The control voltage is applied to the varactor diode VD1, acts as a reverse bias voltage, changes the junction capacitance of the varactor diode VD1, changes the equivalent inductance component of the resonance circuit 2, and makes it possible to control the oscillation frequency. there were.

  Varactor diodes used in such voltage controlled oscillators are usually less sensitive to changes in junction capacitance with respect to the amount of change in reverse bias voltage when the reverse bias voltage is high, and reverse bias voltage when the reverse bias voltage is low. The change in the junction capacitance with respect to the amount of change in the reverse bias voltage is non-linear depending on the magnitude of the reverse bias voltage, such that the sensitivity of the change in the junction capacitance with respect to the amount of change in voltage is high.

  This nonlinearity is a property that is unnecessary in some cases for a circuit that determines an external control voltage (hereinafter referred to as an external control voltage circuit), and a property in which the change in junction capacitance is linear (hereinafter, this property is referred to as a capacitance). Sometimes called linearity of change).

Therefore, in the above-described configuration example, the control voltage is divided by the resistance voltage dividing circuit, so that the change range of the reverse bias voltage is narrowed and the capacitance change of the varactor diode is relatively linear. Is configured.
JP-A-8-46427

By the way, in the voltage controlled oscillator 1 having the above-described configuration, since the resistance voltage dividing circuit including the resistor R1 and the resistor R2 is connected to the control voltage input terminal Vc, the resistor R1 and the resistor R2 are connected from the control voltage input terminal Vc. A current will flow through to ground.
Then, when an external control voltage circuit is connected to the control voltage input terminal Vc, a current flows from the external control voltage circuit to the control voltage input terminal Vc.

  However, the external control voltage circuit may be designed on the assumption that no current flows into the control voltage input terminal Vc of the voltage controlled oscillator 1, and such an external control voltage circuit is used as the control voltage input terminal Vc. In the case of connection to the control voltage, the control voltage input from the external control voltage circuit is not a specified value, and abnormal oscillation may occur in the voltage controlled oscillator 1 or a spurious component may be included in the oscillation signal.

  In addition, when the resistance voltage dividing circuit is provided, the resistors R1 and R2 may cause thermal noise, and the phase noise of the voltage controlled oscillator may be deteriorated.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a voltage controlled oscillator that eliminates abnormal oscillation of a resonator and spurious components of an oscillation signal, and further suppresses the generation of thermal noise, while giving the variable capacitance element linearity of capacitance change. There is to do.

  In order to solve the above problems, the voltage controlled oscillator according to the present invention has the following configuration.

  In a voltage controlled oscillator comprising: a resonance circuit including a variable capacitance element; and an amplification circuit connected to the resonance circuit, wherein a control voltage input terminal for inputting a control voltage of the variable capacitance element is provided in the resonance circuit. The resonance circuit includes a variable capacitance element circuit in which a plurality of the variable capacitance elements are connected in series, and the control voltage is directly applied to the variable capacitance element circuit.

  As described above, in the voltage controlled oscillator, the control voltage is divided by being provided with a variable capacitance element circuit in which a plurality of variable capacitance elements are connected in series without being provided with a resistance voltage dividing circuit, and applied to each variable capacitance element. The divided voltage is the reverse bias voltage. As a result, the junction capacitance of the variable capacitance element can be made linear without the need for a resistance voltage dividing circuit, and therefore no current flows through the control voltage input terminal, resulting in abnormal oscillation in the voltage controlled oscillator. There is no problem, no problem that the oscillation signal includes spurious components, or the problem that the resistor causes thermal noise and the phase noise of the voltage controlled oscillator deteriorates.

  The voltage controlled oscillator according to the present invention has the following configuration.

  The variable capacitance element is a varactor diode, and the variable capacitance element circuit is formed by connecting the varactor diodes in series in the same direction.

  In this way, a variable capacitance element circuit can be configured using a varactor diode as a variable capacitance element.

  As described above, in the present invention, the control voltage is divided by the variable capacitance element circuit in which a plurality of variable capacitance elements are connected in series, thereby narrowing the change range of the reverse bias voltage and linearizing the capacitance change of the variable capacitance element. You can have it. In addition, the provision of the variable capacitance element circuit eliminates the need to divide the control voltage using a resistor, and naturally eliminates the flow of current through the control voltage input terminal, resulting in abnormal oscillation of the resonator. In addition, the spurious component of the oscillation signal can be reliably eliminated. Further, the thermal noise caused by the resistor is eliminated, and the deterioration of the phase noise characteristic of the oscillator due to this can be eliminated.

Next, the voltage controlled oscillator according to the first embodiment will be described with reference to FIG.
FIG. 2 is a circuit diagram of the voltage controlled oscillator 11 of the present embodiment. In this voltage controlled oscillator 11, the resonance circuit 12 and the amplifier circuit 13 are coupled by a coupling capacitor C13.

The amplifier circuit 13 includes a transistor Tr11 that functions as an amplification stage and a transistor Tr12 that functions as a buffer stage.
The transistor Tr11 in the amplification stage is configured to input the resonance signal from the resonance circuit 12 to the base. A base bias voltage is applied to the base of the transistor Tr11 from a base bias circuit including resistors R11, R12, and R13. The collector of the transistor Tr11 is connected to the emitter of the transistor Tr12 in the buffer stage, and the collector is grounded at a high frequency via a capacitor C16, which is a bypass capacitor. It is operated with the emitter grounded. The emitter of the transistor Tr11 is grounded via a capacitor C17 and a resistor R14. Further, an output voltage is obtained by the resistor R14, and this output voltage is applied to the base of the transistor Tr12 via the capacitor C15. Further, a feedback capacitor C14 feeds back a signal from the emitter to the base of the transistor Tr11. The amplification circuit of the amplification stage and the resonance circuit 12 form an oscillation circuit that is a modified Colpitts type.

  In the transistor Tr12 in the buffer stage, a power supply voltage is applied to the collector via the inductor L13, a base bias circuit composed of resistors R11, R12, and R13 is connected to the base, and the emitter of the transistor Tr11 and the transistor Tr12 are connected. A capacitor C15 is connected between the bases. An output voltage from the transistor Tr11 in the amplification stage is input to the base of the transistor Tr12 in the buffer stage through the capacitor C15, and an oscillation signal is output through the capacitor C18 connected to the collector. The capacitor C19 is a high frequency bypass capacitor.

  For such a configuration, the amplifier circuit 13 supplies an appropriate base bias current to the transistor Tr11 from the power supply voltage terminal Vb1, thereby amplifying and oscillating the resonance signal from the resonance circuit 12 by the transistor Tr11. The oscillation signal is output from the output terminal Vout1 through the buffer stage by the transistor Tr12.

  In the resonance circuit 12, one end of the high frequency bypass capacitor C11 and one end of the inductor L12 are connected to the control voltage input terminal Vc1, the other end of the capacitor C11 is grounded, and the cathode of the varactor diode VD11 is connected to the other end of the inductor L12. Connected. The anode of the varactor diode VD11 is further connected to the cathode of the varactor diode VD12, and the anode of the varactor diode VD12 is grounded. The variable capacity element circuit 14 of the present invention is formed by the above varactor diodes VD11 and VD12. The cathode of the varactor diode VD11 is connected to a capacitor C12 that functions as a capacitance and DC cut for the LC resonance circuit, and this capacitor C12 is grounded via an inductor L11 that mainly functions as an inductance of the LC resonance circuit. is doing. A connection point between the capacitor C12 and the inductor L11 is connected to a capacitor C13 for coupling with the amplifier circuit 13.

  Thus, in the present embodiment, the resonance circuit 12 is a parallel LC resonance circuit in which an inductance and a capacitance are connected in parallel. The inductance by the inductor L11 and the combined capacitance (the combined capacitance) of the capacitor C12 and the varactor diodes VD11 and VD12. ) Determines the resonance frequency.

  In the resonance circuit 12, the varactor diodes VD11 and VD12 are elements having substantially the same characteristics, and the anode of the varactor diode VD11 and the cathode of the varactor diode VD12 are connected, so that the directions of the cathode and the anode are the same in series. The variable capacitance element circuit 14 is connected so as to be oriented, and a control voltage is applied to both ends of the variable capacitance element circuit 14.

  Then, a voltage obtained by dividing the control voltage by the number of varactor diodes (here, 2) is applied as a reverse bias voltage to each of the varactor diodes VD11 and VD12. Becomes narrow, and the change in the junction capacitance of each of the varactor diodes VD11 and VD12 becomes relatively linear. As shown here, the characteristics of the varactor diodes VD11 and VD12 are improved by making the characteristics of the plurality of varactor diodes substantially the same, and the setting of the varactor diodes VD11 and VD12 is easier. Thus, the circuit design of the voltage controlled oscillator 11 can be contributed.

  The characteristics of the plurality of varactor diodes are not necessarily substantially the same, and even if they are not the same, the varactor diodes VD11 and VD12 are connected in series to form the variable capacitance element circuit 14. The reverse bias voltage applied to each of the varactor diodes VD11 and VD12 is divided according to the respective junction capacitance. Thereby, it is possible to provide a voltage controlled oscillator in which the linearity of the change in the junction capacitance of the varactor diodes VD11 and VD12 is improved.

  In the present embodiment, since the variable capacitance element circuit 14 is used to reduce the reverse bias voltage applied to the varactor diode, no resistance voltage dividing circuit is required, and it is assumed that a control voltage is input from the control voltage input terminal Vc1. However, no current flows through the control voltage input terminal Vc1.

  Thereby, the external control voltage circuit connected to the control voltage input terminal Vc1 can surely prevent the voltage controlled oscillator 11 from oscillating abnormally and the spurious component from being included in the oscillation signal. Since no resistor is included in 12, generation of thermal noise can be suppressed, and generation of phase noise can be suppressed.

  Further, for example, when a charge pump of a PLL circuit is used as the external control voltage circuit and the charge pump terminal is connected to the control voltage input terminal Vc1, normally, a current of 1 nA or more flows from the PLL circuit to the control voltage input terminal Vc1. Although the reference leak performance in the PLL circuit deteriorates and causes abnormal oscillation, the deterioration of the reference leak performance is suppressed by preventing the current from flowing through the control voltage input terminal Vc1 as in the present embodiment. it can.

  Conventionally, for example, the reference leak can be suppressed even if the voltage is divided by a high-resistance resistor of 1000 MΩ or more. However, in such a case, the size of the high-resistance resistor becomes very large. For example, it is not practical in terms of cost and size to be realized as an electronic component such as an IC.

  On the other hand, if the voltage controlled oscillator 11 that divides the voltage by the variable capacitance element circuit 14 is used as in the present embodiment, the reference leak is suppressed, and it is practical in terms of cost and size, for example, an electronic device such as an IC. The voltage-controlled oscillator 11 that is very miniaturized as a component can be realized.

  The amplifier circuit 13 shown here is not necessarily limited to this configuration in the implementation of the present invention, and the present invention is not limited by the configuration of the amplifier circuit 13. For example, as the transistor included in the amplifier circuit 13, a bipolar transistor having a control terminal “base” and a current controlled terminal “collector” is used in the above description, but instead, the control terminal is “gate”, A unipolar transistor (FET) having a current controlled terminal as a “drain” may be used, or an oscillation circuit other than a Colpitts type may be configured.

  Further, although the varactor diode has been mainly described as the variable capacitance element of the present invention, another type of variable capacitance element in which the linearity of the capacitance change is not so good may be used instead.

  Next, a second embodiment of the present invention will be described. FIG. 3 shows the voltage controlled oscillator of this embodiment.

  FIG. 3 is a circuit diagram of the voltage controlled oscillator 21 of the present embodiment. In this voltage controlled oscillator 21, the resonance circuit 22 and the amplifier circuit 23 are coupled by a coupling capacitor C23. Note that the amplifier circuit 23 of the present embodiment has substantially the same configuration as the amplifier circuit 13 of the first embodiment described above, and will not be described here. Further, the resonance circuit 22 of the present embodiment has a configuration similar to that of the resonance circuit 12 of the first embodiment described above, mainly in that the variable capacitance element circuit 24 is formed by connecting more variable capacitance elements in series. Different.

  In the resonance circuit 22, one end of the high frequency bypass capacitor C21 and one end of the inductor L22 are connected to the control voltage input terminal Vc2, the other end of the capacitor C21 is grounded, and the cathode of the varactor diode VD21 is connected to the other end of the inductor L22. is doing. The anode of the varactor diode VD21 is further connected to the cathode of the varactor diode VD22. The anode of the varactor diode VD22 is further connected to the cathode of the varactor diode VD23. The anode of the varactor diode VD23 is grounded. The varactor diodes VD21, VD22, and VD23 form the variable capacitance element circuit 24 of the present invention. The cathode of the varactor diode VD21 is connected to a capacitor C22 that acts as a capacitance and DC cut for the LC resonance circuit, and this capacitor C22 is grounded via an inductor L21 that mainly acts as an inductance of the LC resonance circuit. is doing. A connection point between the capacitor C22 and the inductor L21 is connected to a capacitor C23 for coupling with the amplifier circuit 23.

  As described above, in this embodiment, the resonance circuit 22 and the amplifier circuit 23 are connected, the varactor diodes VD21, VD22, and VD23 that are variable capacitance elements are provided in the resonance circuit 22, and the control voltage input terminal Vc2 is further provided. Further, when the control voltage is applied to the control voltage input terminal Vc2, the junction capacitances of the varactor diodes VD21, VD22, and VD23 change, and the combined capacitance of the junction capacitance and the capacitor C22 causes the resonance circuit 22 The oscillation frequency is determined.

  In the resonance circuit 22, the varactor diodes VD 21, VD 22, and VD 23 are connected in series so that the directions of the cathode and the anode are the same direction, and a control voltage is applied to both ends of the variable capacitance element circuit 24. Applied. In this way, by connecting more variable capacitance elements in series, the change range of the reverse bias voltage can be further narrowed, and the linearity of the capacitance change of each varactor diode can be further improved.

  Further, when the varactor diodes VD21, VD22, and VD23 exhibit substantially the same characteristics, the voltage obtained by dividing the control voltage by the number of varactor diodes (here, 3) is used as each reverse varactor diode. Since it is applied to VD21, VD22, VD23, the change range of the reverse bias voltage is narrowed, and the linearity of the capacitance change of each varactor diode VD21, VD22, VD23 with respect to the control voltage operation is improved. By making the characteristics of the plurality of varactor diodes substantially the same as shown here, the setting of each element becomes easier and it can contribute to circuit design.

  Even if the varactor diodes VD21, VD22, and VD23 do not have substantially the same characteristics, the varactor diodes VD21, VD22, and VD23 are connected in series to form the variable capacitance element circuit 24. The reverse bias voltages applied to VD21, VD22, and VD23 are divided according to the respective junction capacitances, and the change in the junction capacitances of the varactor diodes VD21, VD22, and VD23 can be made linear.

  As described above, in this embodiment, since the variable capacitance element circuit 24 is used to reduce the reverse bias voltage applied to the varactor diode, a resistance voltage dividing circuit is not required, and the control voltage is input from the control voltage input terminal Vc2. However, current does not flow through the control voltage input terminal Vc2.

  As a result, the external control voltage circuit connected to the control voltage input terminal Vc2 can reliably prevent the voltage controlled oscillator 21 from oscillating abnormally and the oscillation signal from including spurious components. Since no resistor is included in 22, generation of thermal noise can be suppressed, and generation of phase noise can be suppressed.

  Next, a third embodiment of the present invention will be described. FIG. 4 shows the voltage controlled oscillator of this embodiment.

  FIG. 4 is a circuit diagram of the voltage controlled oscillator 31 of the present embodiment. In this voltage controlled oscillator 31, a resonance circuit 32 and an amplifier circuit 33 are coupled by a coupling capacitor C33.

  Note that the amplifier circuit 33 of this embodiment has substantially the same configuration as the amplifier circuit 13 of the first embodiment described above, and a description thereof is omitted here.

  In this embodiment, the resonance circuit 32 is a series LC resonance circuit in which an inductance and a capacitance are connected in series. The inductance by the inductor L31 and the combined capacitance (synthetic capacity) of the varactor diodes VD31, VD32, and VD33. Thus, the resonance frequency is determined. Thus, it differs from the above-mentioned embodiment by the point that the resonance circuit 32 is a series LC resonance circuit.

  In the resonance circuit 32, one end of the high frequency bypass capacitor C31 and one end of the inductor L32 are connected to the control voltage input terminal Vc3, the other end of the capacitor C31 is grounded, and the cathode of the varactor diode VD31 is connected to the other end of the inductor L32. is doing. The anode of the varactor diode VD31 is further connected to the cathode of the varactor diode VD32. The anode of the varactor diode VD32 is further connected to the cathode of the varactor diode VD33, and the anode of the varactor diode VD33 is grounded. The variable capacitance element circuit 34 of the present invention is formed by the varactor diodes VD31, VD32, and VD33 described above, and the combined capacitance mainly acts as the capacitance of the LC resonance circuit. Further, an inductor L31 mainly acting as an inductance of the LC resonance circuit is connected to the cathode of the varactor diode VD31. The other end of the inductor L31 is connected to a capacitor C33 for coupling and DC cut with the amplifier circuit 33.

  Thus, in this embodiment, since a resistance voltage dividing circuit for reducing the reverse bias voltage applied to the varactor diode is not required, even if the control voltage is input from the control voltage input terminal Vc3, the control voltage input terminal No current flows through Vc3.

  As a result, the external control voltage circuit connected to the control voltage input terminal Vc3 can reliably prevent the voltage controlled oscillator 31 from oscillating abnormally and the oscillation signal from including spurious components. Since no resistor is included in 32, generation of thermal noise can be suppressed, and generation of phase noise can be suppressed.

  Next, a fourth embodiment of the present invention will be described. FIG. 5 shows the voltage controlled oscillator of this embodiment.

  FIG. 5 is a circuit diagram of the voltage controlled oscillator 41 of the present embodiment. In this voltage controlled oscillator 41, a resonance circuit 42 and an amplifier circuit 43 are coupled by a coupling capacitor C43.

  Note that the amplifier circuit 43 of this embodiment has substantially the same configuration as the amplifier circuit 13 of the first embodiment described above, and a description thereof is omitted here.

  The resonance circuit 42 of the present embodiment has a configuration similar to that of the above-described resonance circuit 32 of the third embodiment, and is mainly in that the inductor L41 is connected in series between the variable capacitance element circuit 44 and the ground. Different.

  In the resonance circuit 42, one end of the capacitor C41 for high frequency bypass and one end of the inductor L42 are connected to the control voltage input terminal Vc4, the other end of the capacitor C41 is grounded, and the cathode of the varactor diode VD41 is connected to the other end of the inductor L42. is doing. The anode of the varactor diode VD41 is further connected to the cathode of the varactor diode VD42. The anode of the varactor diode VD42 is connected to one end of an inductor L41 that mainly acts as the inductance of the LC resonance circuit. The end is grounded. The variable capacitance element circuit 44 of the present invention is formed by the varactor diodes VD41 and VD42, and the combined capacitance mainly acts as the capacitance of the LC resonance circuit. The cathode of the varactor diode VD41 is connected to a capacitor C43 for coupling to the amplifier circuit 43 and for DC cut.

  Thus, in the present embodiment, one end of the variable capacitance element circuit 44 is connected to the control voltage input terminal Vc4 via the inductor L42, and the other end of the variable capacitance element circuit 44 is grounded via the inductor L41.

  In the present embodiment, since a resistance voltage dividing circuit for reducing the reverse bias voltage applied to the varactor diode is not required, even if the control voltage is input from the control voltage input terminal Vc4, the control voltage input terminal Vc4 is Current does not flow through.

  As a result, the external control voltage circuit connected to the control voltage input terminal Vc4 can reliably prevent the voltage controlled oscillator 41 from oscillating abnormally and the oscillation signal from containing spurious components. Since no resistor is included in 42, generation of thermal noise can be suppressed, and generation of phase noise can be suppressed.

  As described in the above embodiments, the present invention can be applied to LC resonance circuits having various configurations, and although not specifically shown here, the present invention is not limited to an LC resonance circuit but a resonance circuit using another configuration such as a crystal resonator. Is also applicable. The present invention can be implemented by performing voltage division using a variable capacitance element circuit.

It is a circuit diagram which shows the structure of the conventional voltage controlled oscillator. 1 is a circuit diagram showing a configuration of a voltage controlled oscillator according to a first embodiment. FIG. It is a circuit diagram which shows the structure of the voltage controlled oscillator which concerns on 2nd Embodiment. It is a circuit diagram which shows the structure of the voltage controlled oscillator which concerns on 3rd Embodiment. It is a circuit diagram which shows the structure of the voltage controlled oscillator which concerns on 4th Embodiment.

Explanation of symbols

1,11,21,31,41,51-Voltage controlled oscillator 2,12,22,32,42,52-Resonant circuit 3,13,23,33,43,53-Amplifier circuit 14,24,34,44 , 54-Variable capacitance element circuit

Claims (2)

In a voltage controlled oscillator comprising a resonance circuit including a variable capacitance element, and an amplification circuit connected to the resonance circuit, wherein a control voltage input terminal for inputting a control voltage of the variable capacitance element is provided in the resonance circuit.
The resonant circuit includes a variable capacitance element circuit in which a plurality of the variable capacitance elements are connected in series,
A voltage controlled oscillator in which the control voltage is directly applied to the variable capacitance element circuit. The variable capacitance element is a varactor diode;
2. The voltage controlled oscillator according to claim 1, wherein the variable capacitance element circuit is formed by connecting the varactor diodes in series in the same direction.

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