CN101145758A - Surface acoustic wave oscillator and its frequency changing method - Google Patents

Abstract

The invention provides a surface acoustic wave oscillator. Broadband is achieved while maintaining the continuity of the oscillation frequency. The surface acoustic wave oscillator (1) has; a cross-coupling type circuit (10), which is differentially connected to an output terminal (OUT1) and an output terminal (OUT2); SAW resonators (20, 30), which are connected to the cross-coupling type circuit ( 10) connected in parallel and having different resonant frequencies; a variable capacitance circuit (100) including a variable capacitance diode (50) whose capacitance value changes according to a first control voltage applied from an output terminal (OUT1), and the variable capacitance The circuit (100) changes the resonance frequency of the SAW resonator (20); and the variable capacitance circuit (200) includes a variable capacitance diode ( 60), and the variable capacitance circuit (200) changes the resonant frequency of the SAW resonator (30), the SAW resonator (20) is connected to the variable capacitance circuit (100), and the SAW resonator (30) is connected to the variable capacitance The circuit (200) is connected, and the cross-coupling circuit (10) is used to output the oscillation output of the coupling between the SAW resonator (20) and the SAW resonator (30).

Description

Surface acoustic wave oscillator and its frequency changing method

technical field

The present invention relates to a surface acoustic wave oscillator comprising surface acoustic wave elements having different resonant frequencies and a cross-coupled circuit differentially connecting these surface acoustic wave elements, and a method for changing the frequency thereof.

Background technique

In mobile communication devices, etc., it is necessary to switch to the channel (frequency) specified by the control channel due to the switching of multiple channels in the allocated frequency band for communication. ring) synthesizer. A voltage controlled oscillator (VCO: Voltage Controlled Oscillator) is usually used in this PLL circuit to provide a control voltage to switch the oscillation frequency. As a conventional example of a VCO that switches the oscillation frequency by supplying a control voltage, there is a method in which, for example, as shown in FIG. (SAW: Surface Acoustic Wave) The resonance point of the element moves to change the oscillation frequency.

However, in the case of using intra-band switching channels, it is required to have high SN ratio (ratio of signal power to noise power) and CN ratio (ratio of carrier power to noise power) in all channels of the band. However, in the conventional VCO described above, it is difficult to ensure high SN ratio and CN ratio for all channels in the frequency band, and there is a disadvantage that the SN ratio or CN ratio decreases when the amount of frequency variation increases. Conversely, when securing a high SN ratio and CN ratio, there is a problem of narrowing the frequency variable range. In order to technically solve this problem, there is a method of using two VCOs to allocate half of the frequency band. However, using two VCOs violates the miniaturization of the communication device and does not practically solve the problem.

In order to solve this problem, for example, Patent Document 1 describes a method of connecting two SAW elements in parallel and switching and using the two SAW elements.

[Patent Document 1] Japanese Patent Application Laid-Open No. 8-213838

However, in Patent Document 1, there is a problem that the oscillation frequencies output when the two SAW elements are switched cannot be continuously switched.

Contents of the invention

It is an object of the present invention to provide a frequency changing method capable of widening the bandwidth of a surface acoustic wave oscillator while having continuity of oscillation frequency and adjusting the frequency without complicated controls.

The surface acoustic wave oscillator of the present invention has: a cross-coupled circuit including a pair of first active element and second active element differentially connected to the first output terminal and the second output terminal; the first surface acoustic wave element and a second surface acoustic wave element having different resonant frequencies and connected in parallel to the cross-coupled circuit; a first variable capacitance circuit comprising a first variable capacitance element and changing the resonant frequency of the first surface acoustic wave element, The capacitance value of the first variable capacitance element changes according to the first control voltage applied from the first control terminal; and a second variable capacitance circuit including the second variable capacitance element and making the above-mentioned second surface acoustic wave element The resonant frequency of the variable capacitance element changes, the capacitance value of the second variable capacitance element changes according to the second control voltage applied from the second control terminal, the first surface acoustic wave element is connected to the first variable capacitance circuit, and the second The surface acoustic wave element is connected to the second variable capacitance circuit; and the coupled oscillation output of the first surface acoustic wave element and the second surface acoustic wave element is output using the cross-coupled circuit.

According to the present invention, the first control voltage or the second control voltage is applied via the first variable capacitance element and the second variable capacitance element to the first surface acoustic wave element and the second surface acoustic wave element having different resonant frequencies connected in parallel with the cross-coupled circuit. The surface acoustic wave element oscillates the first surface acoustic wave element and the second surface acoustic wave element. In this case, since the coupled oscillation output of the first surface acoustic wave element and the second surface acoustic wave element is output using a cross-coupled circuit, each oscillation frequency can be continuously switched and output, and a broadband oscillation frequency can be continuously output.

Preferably, the first surface acoustic wave element and the second surface acoustic wave element are laminated on a semiconductor chip including the cross-coupled circuit, the first variable capacitance circuit, and the second variable capacitance circuit.

According to this structure, since the two surface acoustic wave elements stacked on the substrate of the semiconductor chip (integrated circuit) are arranged side by side, the area of approximately two surface acoustic wave elements is sufficient, and the increase in area can be suppressed and miniaturization can be achieved.

And, the method for changing the frequency of a surface acoustic wave oscillator according to the present invention, wherein the surface acoustic wave oscillator has: a cross-coupled circuit including a pair of first active elements differentially connected to a first output terminal and a second output terminal and a second active element; a first surface acoustic wave element and a second surface acoustic wave element having different resonant frequencies and connected in parallel to the above-mentioned cross-coupled circuit; a first variable capacitance circuit including a first variable capacitance element and changing the resonant frequency of the first surface acoustic wave element, the capacitance value of the first variable capacitance element is changed according to the first control voltage applied from the first control terminal; and the second variable capacitance circuit includes the first 2 variable capacitance elements and changing the resonant frequency of the second surface acoustic wave element, the capacitance value of the second variable capacitance element changes according to the second control voltage applied from the second control terminal, and the first surface acoustic wave element Connected to the above-mentioned first variable capacitance circuit, the above-mentioned second surface acoustic wave element is connected to the above-mentioned second variable capacitance circuit; use the above-mentioned cross-coupled circuit to output the phase coupling between the above-mentioned first surface acoustic wave element and the above-mentioned second surface acoustic wave element The frequency changing method of the surface acoustic wave oscillator changes the oscillation frequencies of the first surface acoustic wave element and the second surface acoustic wave element by changing the voltage values of the first control voltage and the second control voltage.

According to the present invention, the capacitance value (capacitor capacitance) of the first variable capacitance element is changed by changing the first control voltage applied to the first control terminal, and the resonance frequency of the first surface acoustic wave element is approximately change continuously. Then, by changing the second control voltage applied to the second control terminal, the capacitance value (capacitor capacitance) of the second variable capacitance element is changed, and the resonance frequency of the second surface acoustic wave element is continuously changed according to the capacitance value. .

Furthermore, since the first surface acoustic wave element and the second surface acoustic wave element have mutually different resonance frequencies and are connected in parallel to the cross-coupled circuit, widening of the oscillation frequency of the first surface acoustic wave element and the second surface acoustic wave element can be achieved, Moreover, the oscillation frequency can be continuously changed.

Description of drawings

FIG. 1 is a circuit diagram showing the structure of a surface acoustic wave oscillator according to an embodiment of the present invention.

FIG. 2 is a graph illustrating the operation of the surface acoustic wave oscillator according to the embodiment of the present invention.

FIG. 3 is an enlarged view on the horizontal axis of FIG. 2 .

FIG. 4 is a graph showing the relationship between capacitor capacitance and frequency according to the embodiment of the present invention.

5 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 1 of the present invention.

6 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 2 of the present invention.

7 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 3 of the present invention.

8 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 4 of the present invention.

9 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 5 of the present invention.

10 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 6 of the present invention.

11 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 7 of the present invention.

12 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 8 of the present invention.

13 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 9 of the present invention.

14 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 10 of the present invention.

15 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 11 of the present invention.

16 is a graph showing the relationship between capacitor capacitance and frequency in Modification 11 of the present invention.

FIG. 17 is a graph illustrating the operation of a surface acoustic wave oscillator according to Modification 11 of the present invention.

18 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 12 of the present invention.

Label description

1: surface acoustic wave oscillator; 10: cross-coupled circuit; 11: current mirror circuit; 20, 30: SAW resonator 40: constant current source; 50, 60: varactor diode; 100, 200: variable capacitance circuit .

Detailed ways

Embodiments of the present invention will be described below with reference to the drawings.

1 to 4 show the structure, operation, and frequency changing method of the surface acoustic wave oscillator of this embodiment, and FIGS. 5 to 18 show the structure of a surface acoustic wave oscillator according to a modified example of this embodiment.

(implementation mode)

First, the configuration of a surface acoustic wave oscillator according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing the structure of a surface acoustic wave oscillator according to an embodiment of the present invention.

In FIG. 1 , a surface acoustic wave oscillator 1 is composed of a cross-coupled circuit 10 and a current mirror circuit 11 connected to an output terminal OUT1 as a first output terminal and an output terminal OUT2 as a second output terminal; The SAW resonator 20 as the first surface acoustic wave element; the SAW resonator 30 as the second surface acoustic wave element; the first variable capacitance circuit 100 connected to the first control terminal, that is, the control terminal Vcontl; The second variable capacitance circuit 200 connected to the control terminal Vcont2.

The cross-coupled circuit 10 includes a pair of Nch transistor N1 (hereinafter simply referred to as transistor N1) which is a first active element and a pair of Nch transistor N2 (hereinafter simply referred to as transistor N1) which is a second active element and which are differentially connected to an output terminal OUT1 and an output terminal OUT2. It is composed of a transistor N2 for short), and is connected to a current mirror circuit 11 composed of Pch transistors P1 and P2 (hereinafter simply represented as transistors P1 and P2 ) and a constant current source 40 .

The source terminal of the transistor P1 is connected to the power supply line VDD (hereinafter simply referred to as VDD), and the gate terminal and the drain terminal thereof are connected to the output terminal OUT1. The source terminal of the transistor P2 is connected to VDD, the gate terminal thereof is connected to the output terminal OUT1 , and the drain terminal thereof is connected to the output terminal OUT2 . In addition, the source terminal of the transistor N1 is connected to the ground potential line GND via the constant current source 40 , the gate terminal is connected to the output terminal OUT2 , and the drain terminal is connected to the output terminal OUT1 . The source terminal of the transistor N2 is connected to the ground potential line GND via the constant current source 40 , the gate terminal is connected to the output terminal OUT1 , and the drain terminal is connected to the output terminal OUT2 .

The variable capacitance circuit 100 has a varactor diode 50 which is a first variable capacitance element. The cathode terminal of the varactor diode 50 is connected to the control terminal Vcont1, and the anode terminal thereof is connected to the ground potential line GND.

The variable capacitance circuit 200 has a varactor diode 60 as a second variable capacitance element. The cathode terminal of the varactor diode 60 is connected to the control terminal Vcont2, and the anode terminal thereof is connected to the ground potential line GND.

In the SAW resonator 20 , a piezoelectric thin film and excitation electrodes are stacked on a semiconductor chip substrate, and one terminal is connected to the output terminal OUT1 , and the other terminal is connected to the cathode terminal of the varactor diode 50 of the variable capacitance circuit 100 . That is, the SAW resonator 20 and the varactor diode 50 are connected in series between the ground potential line GND and the output terminal OUT1 (the cross-coupled circuit 10 ).

In the SAW resonator 30 , a piezoelectric thin film and excitation electrodes are stacked on a semiconductor chip substrate, and one terminal is connected to the output terminal OUT2 , and the other terminal is connected to the cathode terminal of the variable capacitance diode 60 of the variable capacitance circuit 200 . That is, the SAW resonator 30 and the varactor diode 60 are connected in series between the ground potential line GND and the output terminal OUT2 (cross-coupled circuit 10 ).

In addition, the resonance frequencies of SAW resonator 20 and SAW resonator 30 are set to be slightly different.

As shown in FIG. 1, in the surface acoustic wave oscillator 1, between the output terminal OUT1 and the output terminal OUT2 of the cross-coupled circuit 10, the SAW resonator 20 and the variable capacitance circuit 100 are connected to the ground potential line GND, and the variable capacitance The circuit 200 and the SAW resonator 30 are connected to the ground potential line GND. Therefore, with respect to the cross-coupled circuit 10 , the SAW resonator 20 and the variable capacitance circuit 100 , and the SAW resonator 30 and the variable capacitance circuit 200 are connected in parallel.

Next, the operation of the surface acoustic wave oscillator will be described with reference to the drawings.

2 and 3 are diagrams explaining the action of a surface acoustic wave oscillator. The graph in FIG. 2 exemplifies a case where the same voltage (namely, first control voltage=second control voltage) is applied to the first control terminal and the second control terminal of the surface acoustic wave oscillator while changing the same voltage. FIG. 3 is an enlarged view on the horizontal axis of FIG. 2 .

The horizontal axis represents frequency (MHz), the left vertical axis represents reflection coefficient (S11: dB), and the right vertical axis represents phase characteristic (phase: ω). The plurality of graphs of the reflection coefficient S11 and the phase characteristic (Phase) shown in the figure respectively show when the first control voltage and the second control voltage are changed. The intersection with the point where the reflection coefficient S11 becomes the lowest when the phase characteristic ω=0 corresponds to the output frequency. As shown in FIGS. 2 and 3 , in the graph of the reflection coefficient S11 , the reflection coefficient S11 decreases in a wide range from 315.05 MHz to 315.10 MHz. That is, it means that the frequency can be continuously changed within this range.

FIG. 4 is a graph showing the relationship between the capacitance value (capacitor capacitance) and the frequency of the varactor diodes 50 and 60 of the surface acoustic wave oscillator according to the present embodiment. That is, the figure depicts the frequency variation in FIGS. 2 and 3, showing that the surface acoustic wave oscillator can continuously vary the frequency between about 315.05-315.10 MHz.

As shown in Fig. 4, the frequency varies corresponding to the capacitance of the capacitor. Specifically, f1 = 315.105 MHz is output around 1 pF, f7 = 315.055 MHz is output at 30 pF, and the frequency continuously changes nonlinearly between them. Therefore, by changing the first control voltage and the second control voltage respectively, the capacitance of the capacitors of the varactor diodes 50 and 60 is changed, and the respective desired output frequencies of the SAW resonators 20 and 30 can be adjusted. In addition, frequencies f1 to f7 shown in FIG. 4 coincide with frequencies f1 to f7 shown in FIG. 3 .

In addition, in the above-mentioned present embodiment, the case where the voltage applied to the control terminal Vcont1 and the control terminal Vcont2 is the same has been described, however, by controlling with different voltages respectively, it is possible to set a finer frequency, And achieve broadband.

Therefore, according to the present embodiment, the first control voltage and the second control voltage are applied to the SAW resonators 20 and 30 connected in parallel to the cross-coupled circuit 10 and having different resonance frequencies through the varactor diodes 50 and 60 , respectively. By changing the applied voltage of the first control voltage and the second control voltage, the capacitor capacitance of the varactor diodes 50 and 60 is changed, and the SAW resonators 20 and 30 are oscillated at a desired oscillation frequency. At this time, since the cross-coupled circuit is used to output the coupled oscillation output of the SAW resonator 20 and the SAW resonator 30 , each oscillation frequency can be continuously switched and output to achieve broadband and continuously change the oscillation frequency.

Furthermore, the SAW resonators 20 and 30 are configured to be stacked on a substrate of a semiconductor chip including the cross-coupled circuit 10 , the first variable capacitance circuit 100 , and the second variable capacitance circuit 200 . According to this configuration, the surface acoustic wave oscillator 1 only needs to have the area of two surface acoustic wave elements (SAW resonators 20 and 30 ), and it is possible to suppress an increase in the area and achieve miniaturization.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, It can implement in various forms in the range which does not deviate from the summary of this invention. Hereinafter, modification examples of the circuit configuration will be described. In addition, FIGS. 1 and 5 to 9 illustrate the case where the varactor diode is an NMOS type, and FIGS. 10 to 14 illustrate the case where the varactor diode is a PMOS type.

(Modification 1)

5 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 1 of the present invention. Modification 1 is different from the above-mentioned embodiment (see FIG. 1 ) in that the surface acoustic wave oscillator 1 has a capacitor C1 connected between the cross-coupled circuit 10 (between the transistor N1 and the transistor P1 ) and the output terminal OUT1. A capacitor C2 is connected between the type circuit 10 (between the transistor N2 and the transistor P2 ) and the output terminal OUT2.

Furthermore, the SAW resonator 20 and the variable capacitance circuit 100 are sequentially connected in series between the output terminal OUT1 and the ground potential line GND, and the SAW resonator 30 and the variable capacitance circuit are sequentially connected in series between the output terminal OUT2 and the ground potential line GND. Capacitive circuit 200. Even with such a structure, the same effect as that of the above-mentioned embodiment can be obtained.

(Modification 2)

6 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 2 of the present invention. In Modification 2, in the surface acoustic wave oscillator 1, a capacitor C1 is connected between the variable capacitance circuit 100 (varicap diode 50) and the output terminal OUT1, and a capacitor C1 is connected between the variable capacitance circuit 100 (varicap diode 60) and the output terminal OUT2. A capacitor C2 is connected between them.

Furthermore, the capacitor C1, the SAW resonator 20, and the variable capacitance circuit 100 are sequentially connected in series between the output terminal OUT1 and the ground potential line GND, and on the other hand, are sequentially connected in series between the output terminal OUT2 and the ground potential line GND. Capacitor C2 , variable capacitance circuit 200 and SAW resonator 30 . As shown in FIG. 6 , even if a left-right asymmetric structure is adopted with respect to the cross-coupled circuit 10 , the same effects as those of the above-described embodiment can be obtained.

In addition, only one of the capacitors C1 and C2 may be used.

(Modification 3)

7 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 3 of the present invention. Modification 3 is characterized in that in the surface acoustic wave oscillator 1, the SAW resonator 20 and the variable capacitance circuit 100 are connected in series between the output terminal OUT1 and VDD, and the SAW resonator 30 and the variable capacitance circuit are connected in series between the output terminal OUT2 and VDD. Variable capacitance circuit 200. The configuration of the cross-coupled circuit 10 is the same as that of the above-mentioned embodiment (see FIG. 1 ).

(Modification 4)

8 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 4 of the present invention. Modification 4 is characterized in that capacitors C1 and C2 are added to Modification 3 described above (see FIG. 7 ). As shown in FIG. 8, the surface acoustic wave oscillator 1 connects a capacitor C1, a SAW resonator 20, and a variable capacitance circuit 100 in series between the cross-coupled circuit 10 (between the transistor N1 and the transistor P1) and VDD. A capacitor C2, a SAW resonator 30, and a variable capacitance circuit 200 are connected in series between the circuit 10 (between the transistor N2 and the transistor P2) and VDD.

(Modification 5)

9 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 5 of the present invention. Modification 5 changes the arrangement positions of capacitors C1 and C2 added to Modification 4 (see FIG. 8 ). As shown in FIG. 9 , in the surface acoustic wave oscillator 1 , a capacitor C1 is connected between the SAW resonator 20 and the output terminal OUT1 , and a capacitor C2 is connected between the SAW resonator 30 and the output terminal OUT2 . Therefore, the capacitor C1, the SAW resonator 20, and the variable capacitance circuit 100 are connected in series between the output terminal OUT1 and VDD. On the other hand, capacitor C2, SAW resonator 30, and variable capacitance circuit 200 are connected in series between output terminal OUT2 and VDD.

(Modification 6)

10 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 6 of the present invention. In Modification 6, the cross-coupled circuit 10 shown in FIGS. 1 and 5 to 9 is a cross-coupled circuit 12 in which the first active element and the second active element are formed of Pch transistors. The cross-coupled circuit 12 includes a pair of Pch transistor P×1 (hereinafter simply referred to as transistor P×1) as a first active element and a Pch transistor P×1 as a second active element that are differentially connected to output terminal OUT1 and output terminal OUT2. Transistor P×2 (hereinafter simply referred to as transistor Px2), and this cross-coupled circuit 12 is configured with Nch transistors N×1 and N×2 (hereinafter simply referred to as transistors N×1 and N×2). The current mirror circuit 13 is connected to a constant current source 40 . The source terminal of the transistor N×1 is connected to the ground potential line GND, and the gate terminal and the drain terminal thereof are connected to the output terminal OUT1.

The source terminal of the transistor N×2 is connected to the ground potential line GND, the gate terminal thereof is connected to the output terminal OUT1 , and the drain terminal thereof is connected to the output terminal OUT2 . The source terminal of the transistor P×1 is connected to VDD via the constant current source 40 , the gate terminal is connected to the output terminal OUT2 , and the drain terminal is connected to the output terminal OUT1 . The source terminal of the transistor P×2 is connected to VDD via the constant current source 40 , the gate terminal is connected to the output terminal OUT1 , and the drain terminal is connected to the output terminal OUT2 .

Furthermore, the varactor diodes 50 and 60 used in Modification 6 are PMOS type diodes.

(Modification 7)

11 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 7 of the present invention. Modification 7 is characterized in that capacitors C1 and C2 are added to the modification 6 described above (see FIG. 10 ). As shown in FIG. 11, in the surface acoustic wave oscillator 1, a capacitor C1, a SAW resonator 20, and a variable capacitance circuit 100 are connected in series between the output terminal OUT1 and the ground potential line GND, and between the output terminal OUT2 and the ground potential line GND. The capacitor C2, the SAW resonator 30, and the variable capacitance circuit 200 are connected in series.

(Modification 8)

12 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 8 of the present invention. Modification 8 is characterized in that the arrangement of capacitors C1 and C2 added to Modification 7 (see FIG. 11 ) described above is changed. As shown in FIG. 12, in the surface acoustic wave oscillator 1, a capacitor C1, a SAW resonator 20, and a variable In the capacitance circuit 100, a capacitor C2, a SAW resonator 30, and a variable capacitance circuit 200 are connected in series between the cross-coupled circuit 12 (between the transistor P×2 and the transistor N×2) and the ground potential line GND.

(Modification 9)

13 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 9 of the present invention. Modification 9 is characterized in that capacitors C1 and C2 are added to Modification 6 (see FIG. 10 ) described above, and the arrangement of variable capacitance circuits 100 and 200 is changed. As shown in FIG. 13, in the surface acoustic wave oscillator 1, a variable capacitance circuit 100 and a SAW resonator 20 are connected in series between the cross-coupled circuit 12 (between the transistor N×1 and the transistor Px1) and the ground potential line GND. The SAW resonator 20 and the capacitor C1 are connected in series between the ground potential line GND and the output terminal OUT1 .

On the other hand, the variable capacitance circuit 200 and the SAW resonator 30 are connected in series between the cross-coupled circuit 12 (between the transistor N×2 and the transistor P×2) and the ground potential line GND. The SAW resonator 30 and the capacitor C2 are connected in series between the output terminal OUT2.

(Modification 10)

14 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 10 of the present invention. Modification 10 is characterized in that two varactor diodes are added to each of the variable capacitance circuits 100 and 200 of Modification 9 (see FIG. 13 ). In addition, capacitors C1 and C2 are not used. As shown in FIG. 14, in the surface acoustic wave oscillator 1, a variable capacitance circuit 101 (variable capacitance diode 51 , 50) and the SAW resonator 20, and the control terminal Vcont1 is connected between the varactor diodes 51 and 51. Furthermore, varactor diodes 50 and 51 are connected in series between the output terminal OUT1 and the cross-coupled circuit 12 .

On the other hand, a variable capacitance circuit 201 (varicap diodes 61, 60) and a SAW resonator 30 are connected in series between the cross-coupled circuit 12 (between the transistor Nx2 and the transistor Px2) and the ground potential line GND, A control terminal Vcont2 is connected between the varactor diodes 61 and 60 . Furthermore, varactor diodes 60 and 61 are connected in series between the output terminal OUT2 and the cross-coupled circuit 12 .

The surface acoustic wave oscillator 1 can achieve the same effects as those of the above-mentioned embodiment (see FIGS. 1 to 4 ) even with the configurations of Modifications 1 to 10 (see FIGS. 5 to 14 ) described above.

In addition, in Fig. 10 to Fig. 14, the structure using the PMOS type varactor diode has been described. However, in the circuit structure using the NMOS type varactor diode shown in Fig. 7 to Fig. 9, it is also possible to configure the A circuit structure of a varactor diode replaced by an NMOS type with a PMOS type (illustration omitted).

(Modification 11)

Next, Modification 11 of the present invention will be described with reference to the drawings. Compared with Embodiment 1 and Modifications 1 to 10 described above, in which the SAW resonator and the variable capacitance circuit are connected in series, Modification 11 has the following characteristics: the SAW resonator and the variable capacitance circuit are connected in parallel. . In addition, an NMOS type structure is used as an example of a varactor diode for description.

15 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 11 of the present invention. In FIG. 15 , the surface acoustic wave oscillator 1 is composed of the following: a cross-coupled circuit 10 having an output terminal OUT1 and an output terminal OUT2; a SAW resonator 20; a SAW resonator 30; a variable capacitor connected to the control terminal Vcont1 circuit 103; and a variable capacitance circuit 203 connected to the control terminal Vcont2.

The variable capacitance circuit 103 has a variable capacitance diode 50 and a capacitor C1. The cathode terminal of the varactor diode 50 is connected to the control terminal Vcont1, and the anode terminal thereof is connected to the ground potential line GND. One terminal of the capacitor C1 is connected to the control terminal Vcont1 (varactor diode 50 ), and the other terminal thereof is connected to the output terminal OUT1 .

The variable capacitance circuit 203 has a variable capacitance diode 60 and a capacitor C2. The cathode terminal of the varactor diode 60 is connected to the control terminal Vcont2, and the anode terminal thereof is connected to the ground potential line GND. One terminal of the capacitor C2 is connected to the control terminal Vcont2 (varactor diode 60 ), and the other terminal thereof is connected to the output terminal OUT2 .

In addition, one terminal of the SAW resonator 20 is connected to the output terminal OUT1, and the other terminal thereof is connected to the ground potential line GND.

One terminal of the SAW resonator 30 is connected to the output terminal OUT2, and the other terminal is connected to the ground potential line GND.

Therefore, as shown in FIG. 15, the surface acoustic wave oscillator 1 is configured such that the cross-coupled circuit 10, the variable capacitance circuit 103, and the SAW resonator 20 are connected in parallel, and the cross-coupled circuit 10, the variable capacitance circuit 203, and the SAW resonator 20 are connected in parallel. Resonators 30 are connected in parallel.

Next, the operation of the surface acoustic wave oscillator according to Modification 11 will be described with reference to the drawings. FIG. 16 is a graph showing the relationship between capacitor capacitance and frequency in Modification 11. FIG. In FIG. 16 , the SAW resonators 20 and 30 are shown when the voltage applied to the control terminal Vcont1 and the control terminal Vcont2 is changed, and the capacitor capacitance of the varactor diodes 50 and 60 is changed according to the magnitude of the voltage value. frequency changes. As shown in FIG. 16, the frequency varies corresponding to the capacitance of the capacitor. Specifically, f1 = 315.052 MHz is output around 0 pF, f7 = 315.034 MHz is output at 30 pF, and the frequency (shown by f2 to f6 in the figure) changes continuously between them. Therefore, by changing the respective voltage values of the first control voltage and the second control voltage, the capacitor capacitances of the varactor diodes 50 and 60 are changed, and the respective desired output frequencies of the SAW resonators 20 and 30 can be adjusted.

FIG. 17 is a graph illustrating the operation of the surface acoustic wave oscillator of Modification 11. FIG. In addition, the graph of FIG. 17 exemplifies a case where the same voltage (namely, first control voltage=second control voltage) is applied to control terminal Vcont1 and control terminal Vcont2 of surface acoustic wave oscillator 1 while being varied. The plurality of graphs of the reflection coefficient ( S11 ) and the phase characteristic (Phase) shown in the figure respectively show when the first control voltage and the second control voltage are changed. As shown in FIG. 17, in the graph of the reflection coefficient (S11), gain is obtained in a wide range from 314.97 MHz to 315.09 MHz.

Furthermore, since the intersection point at which the reflection coefficient S11 becomes the lowest when the phase characteristic ω=0 corresponds to the output frequency, frequencies f1 to f7 are obtained (f4, f5, and f6 are not shown for convenience). The frequencies f1 to f7 correspond to the frequencies f1 to f7 shown in FIG. 16 . Therefore, the output frequency can be continuously changed between fl ~ f7.

Even in the configuration in which the SAW resonator and the variable capacitance circuit are connected in parallel as shown in Modification 11 above, although the frequency sensitivity to the change in capacitor capacitance is slightly lower than the configuration in which the capacitor is connected in series, it is possible to make the output The frequency can be changed continuously to realize broadband.

In Modification 11, the case where the same voltage is applied to the control terminal Vcont1 and the control terminal Vcont2 has been described. However, by controlling with different voltages, finer frequency and bandwidth can be set.

(Modification 12)

Next, a surface acoustic wave oscillator according to Modification 12 of the present invention will be described with reference to the drawings. Modification 12 is characterized in that, as with the above-mentioned modification 11 (see FIG. 15 ), two varactor diodes are added to each of the varactor circuits, and capacitors C1 and C2 are eliminated.

FIG. 18 is a circuit diagram showing the configuration of a surface acoustic wave oscillator according to Modification 12. FIG. In FIG. 18, the surface acoustic wave oscillator 1 is configured such that the cross-coupled circuit 10, the variable capacitance circuit 104, and the SAW resonator 20 are connected in parallel, and the cross-coupled circuit 10, the variable capacitance circuit 204, and the SAW resonator 30 are connected in parallel. connected in parallel.

The variable capacitance circuit 104 is configured such that varactor diodes 51 and 50 are connected in series between the output terminal OUT1 and the ground potential line GND, and a control terminal Vcont1 is connected between the varactor diode 51 and the varactor diode 50 .

On the other hand, the variable capacitance circuit 204 is configured such that the variable capacitance diodes 61 and 60 are connected in series between the output terminal OUT2 and the ground potential line GND, and the control terminal Vcont2 is connected between the variable capacitance diode 61 and the variable capacitance diode 60 . .

Also in the configuration of the twelfth modification, the same effects as those of the eleventh modification described above can be obtained.

In Modification 11 and Modification 12, a structure using an NMOS-type varactor diode was exemplified and described, but a PMOS-type varactor diode can also be used.

Claims (3)

1. A surface acoustic wave oscillator, characterized in that, the surface acoustic wave oscillator has: a cross-coupled circuit comprising a pair of a first active element and a second active element differentially connected to a first output terminal and a second output terminal; a first surface acoustic wave element and a second surface acoustic wave element having different resonant frequencies and connected in parallel to the above-mentioned cross-coupled circuit; A first variable capacitance circuit, which includes a first variable capacitance element and changes the resonant frequency of the first surface acoustic wave element, the capacitance value of the first variable capacitance element is controlled by a first control applied from a first control terminal. voltage changes; and A second variable capacitance circuit that includes a second variable capacitance element and changes the resonant frequency of the second surface acoustic wave element, wherein the capacitance value of the second variable capacitance element is controlled by a second control applied from a second control terminal. voltage varies, The first surface acoustic wave element is connected to the first variable capacitance circuit, and the second surface acoustic wave element is connected to the second variable capacitance circuit; A coupled oscillation output of the first surface acoustic wave element and the second surface acoustic wave element is output using the cross-coupled circuit. 2. The surface acoustic wave oscillating circuit according to claim 1, wherein the first surface acoustic wave element and the second surface acoustic wave element are stacked and formed on a semiconductor chip, and the semiconductor chip includes the cross-coupled circuit, the A first variable capacitance circuit and the above-mentioned second variable capacitance circuit. 3. A method for changing the frequency of a surface acoustic wave oscillator comprising: a cross-coupled circuit comprising a pair of first active elements and a first active element differentially connected to a first output terminal and a second output terminal. 2 active elements; a first surface acoustic wave element and a second surface acoustic wave element having different resonant frequencies and connected in parallel with the above-mentioned cross-coupling type circuit; a first variable capacitance circuit including the first variable capacitance element and using The resonant frequency of the first surface acoustic wave element changes, the capacitance value of the first variable capacitance element changes according to the first control voltage applied from the first control terminal; and the second variable capacitance circuit includes a second variable capacitance circuit. variable capacitance element and change the resonant frequency of the second surface acoustic wave element, the capacitance value of the second variable capacitance element changes according to the second control voltage applied from the second control terminal, The first surface acoustic wave element is connected to the first variable capacitance circuit, and the second surface acoustic wave element is connected to the second variable capacitance circuit; the cross-coupled circuit is used to output the first surface acoustic wave element and the second The phase-coupled oscillation output of the surface acoustic wave element, It is characterized in that, The frequency changing method of the surface acoustic wave oscillator changes the oscillation frequencies of the first surface acoustic wave element and the second surface acoustic wave element by changing the voltage values of the first control voltage and the second control voltage.

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