JP4356759B2 - Surface acoustic wave oscillator and frequency variable method thereof - Google Patents

Description

  The present invention relates to a surface acoustic wave oscillator including surface acoustic wave elements having different resonance frequencies and a cross coupling circuit that differentially connects them, and a frequency variable method thereof.

  In a mobile communication device or the like, communication is performed by switching a large number of channels in an assigned use frequency band, so it is necessary to switch to a channel (frequency) designated by a control channel, and a synthesizer using a PLL (Phase Locked Loop) Is used. In this PLL circuit, a voltage controlled oscillator (VCO: Voltage Controlled Oscillator) is usually used, and the oscillation frequency is switched by applying a control voltage. As a conventional example of a VCO that switches the oscillation frequency by applying a control voltage, for example, as shown in FIG. 3 of Patent Document 1, by applying a control voltage to a variable capacitance diode, the capacitance is changed, and a surface acoustic wave (SAW) : Surface Acoustic Wave) There is a method of changing the oscillation frequency by shifting the resonance point of the element.

  However, when a channel is switched within the used frequency band, a high SN ratio (ratio between signal power and noise power) and CN ratio (ratio between carrier power and noise power) are required over all channels in the frequency band. . However, the conventional VCO has a drawback in that it is difficult to keep the SN ratio and CN ratio high with respect to all the frequency bands, and the SN ratio and CN ratio decrease as the frequency change amount increases. Conversely, if the SN ratio and CN ratio are kept high, there is a problem that the frequency variable range becomes narrow. In order to technically solve such a problem, there is a method of using two VCOs and allocating half of the frequency band, but using two VCOs counteracts the miniaturization of communication devices and solves practical problems. It can not be said.

  In order to solve this problem, for example, Patent Document 1 describes a method in which two SAW elements are connected in parallel and are used by switching each.

JP-A-8-213838

  However, Patent Document 1 has a problem that the oscillation frequency output when two SAW elements are switched cannot be continuously switched.

  An object of the present invention is to provide a surface acoustic wave oscillator with a wide band while providing continuity of oscillation frequency, and to provide a frequency variable method capable of adjusting the frequency without complicated control.

  The surface acoustic wave oscillator according to the present invention includes a pair of first active elements and a cross-coupled circuit including a second active element differentially connected to a first output terminal and a second output terminal, and the cross couple Capacitance values change according to the first control voltage applied from the first control terminal, and the first and second surface acoustic wave elements having different resonance frequencies connected in parallel to the mold circuit A first variable capacitance circuit that includes a first variable capacitance element that changes a resonance frequency of the first surface acoustic wave element, and a capacitance value according to a second control voltage applied from a second control terminal And a second variable capacitance circuit that changes a resonance frequency of the second surface acoustic wave element, the second variable capacitance circuit including a second variable capacitance element that changes, wherein the first surface acoustic wave element and the first surface acoustic wave element A variable capacitance circuit, the second surface acoustic wave element, and the second A variable capacitance circuit, is connected, by the cross-coupled circuit, and outputs a combined oscillation output of said first surface acoustic wave element and the second surface acoustic wave element.

  According to the present invention, the first variable capacitance element and the second variable capacitance element are connected to the first and second surface acoustic wave elements having different resonance frequencies connected in parallel to the cross-coupled circuit. The first control voltage or the second control voltage is applied through the first and second surface acoustic wave elements to oscillate. At this time, since the oscillation output in which the first surface acoustic wave element and the second surface acoustic wave element are coupled is output by the cross-coupled circuit, each oscillation frequency can be continuously switched and output. It is possible to output a broad oscillation frequency with continuity.

  The first surface acoustic wave element and the second surface acoustic wave element are stacked on a semiconductor chip including the cross-coupled circuit, the first variable capacitance circuit, and the second variable capacitance circuit. Preferably it is formed.

  According to this configuration, since the two surface acoustic wave elements formed on the semiconductor chip (integrated circuit) substrate are provided in parallel, the area of the surface acoustic wave elements for about two is sufficient. Therefore, it is possible to reduce the size while suppressing an increase in area.

  The surface acoustic wave oscillator frequency variable method of the present invention is a cross-coupled type including a pair of first active elements and second active elements differentially connected to a first output terminal and a second output terminal. A first surface acoustic wave device and a second surface acoustic wave device having different resonance frequencies connected in parallel to the circuit, the cross-coupled circuit, and a first control voltage applied from a first control terminal A first variable capacitance circuit including a first variable capacitance element whose capacitance value changes in response to the resonance frequency of the first surface acoustic wave element, and a second control applied from a second control terminal. A second variable capacitance circuit that includes a second variable capacitance circuit that changes a capacitance value according to a voltage and changes a resonance frequency of the second surface acoustic wave device, and the first surface acoustic wave device. And the first variable capacitance circuit, the second elastic surface An element is connected to the second variable capacitance circuit, and the cross-coupled circuit outputs a combined oscillation output of the first surface acoustic wave element and the second surface acoustic wave element. A method of varying a frequency of a surface acoustic wave oscillator, wherein the first surface acoustic wave element and the second surface acoustic wave element are changed by changing voltage values of the first control voltage and the second control voltage. The oscillation frequency is changed.

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 first value corresponding to the capacitance value. The resonance frequency of the surface acoustic wave element changes almost continuously. In addition, the capacitance value (capacitor capacitance) of the second variable capacitance element is changed by changing the second control voltage applied to the second control terminal, and the second surface acoustic wave element corresponding to the capacitance value. The resonance frequency changes continuously.
Since the first surface acoustic wave element and the second surface acoustic wave element have different resonance frequencies and are connected in parallel to the cross-coupling circuit, the first surface acoustic wave element and the second surface acoustic wave element The surface acoustic wave element can be broadened in the oscillation frequency, and the oscillation frequency can be changed with continuity.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 4 show the configuration, operation, and frequency variable method of the surface acoustic wave oscillator according to the present embodiment, and FIGS. 5 to 18 show the configuration of the surface acoustic wave oscillator according to a modification of the embodiment. ing.
(Embodiment)

  First, a 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 a configuration of a surface acoustic wave oscillator according to an embodiment of the present invention.

  In FIG. 1, a surface acoustic wave oscillator 1 includes a cross-coupled circuit 10, a current mirror circuit 11, a first output terminal OUT 1 serving as a first output terminal, and an output terminal OUT 2 serving as a second output terminal. A SAW resonator 20 as a surface acoustic wave element, a SAW resonator 30 as a second surface acoustic wave element, and a first variable capacitance circuit 100 connected to a control terminal Vcont1, which is a first control terminal, The second variable capacitance circuit 200 is connected to a control terminal Vcont2 that is a second control terminal.

  The cross-coupled circuit 10 includes a pair of first active elements Nch transistor N1 (hereinafter simply referred to as transistor N1) and a second active element Nch that are differentially connected to the output terminal OUT1 and the output terminal OUT2. The transistor N2 (hereinafter simply referred to as transistor N2) is connected to a current mirror circuit 11 and a constant current source 40 including Pch transistors P1 and P2 (hereinafter simply referred to as transistors P1 and P2).

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

  The variable capacitance circuit 100 includes a varicap diode 50 that is a first variable capacitance element. The varicap diode 50 has a cathode terminal connected to the control terminal Vcont1 and an anode terminal connected to the ground potential line GND.

  The variable capacitance circuit 200 includes a varicap diode 60 that is a second variable capacitance element. The varicap diode 60 has a cathode terminal connected to the control terminal Vcont2 and an anode terminal connected to the ground potential line GND.

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

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

  Note that the resonance frequencies of the SAW resonator 20 and the SAW resonator 30 are set to be slightly different.

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

Next, the operation of the surface acoustic wave oscillator will be described with reference to the drawings.
2 and 3 are graphs for explaining the operation of the surface acoustic wave oscillator. The graph of FIG. 2 illustrates the case where the same voltage (that is, the first control voltage = the second control voltage) is applied to the first control terminal and the second control terminal of the surface acoustic wave oscillator while being changed. ing. FIG. 3 is an enlarged view of the horizontal axis of FIG.

  The horizontal axis represents frequency (MHz), the left vertical axis represents reflection coefficient (S11: dB), and the right vertical axis represents phase characteristics (phase: ω). The plurality of graphs of the reflection coefficient S11 and the phase characteristic (Phase) shown in the figure represent the cases where the first control voltage and the second control voltage are changed, respectively. The intersection with the point at which the reflection coefficient S11 is 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 of 315.05 MHz to 315.10 MHZ. That is, the frequency can be continuously varied within this range.

  FIG. 4 is a graph showing the relationship between the capacitance values (capacitor capacities) of the varicap diodes 50 and 60 of the surface acoustic wave oscillator according to this embodiment and the frequency. That is, the frequency change in FIGS. 2 and 3 is plotted, and shows that the surface acoustic wave oscillator can continuously vary the frequency from about 315.05 to 315.10 MHz.

  As shown in FIG. 4, the frequency changes corresponding to the capacitor capacity. Specifically, f1 = 315.105 MHz is output in the vicinity of 1 pF, and f7 = 315.05 MHz is output at 30 pF, and the frequency changes in a non-linear continuity during this period. Therefore, by changing each of the first control voltage and the second control voltage, the capacitor capacity of the varicap diodes 50 and 60 can be changed and adjusted to the desired output frequencies of the SAW resonators 20 and 30, respectively. . Note that the frequencies f1 to f7 shown in FIG. 4 coincide with the frequencies f1 to f7 shown in FIG.

  In the above-described embodiment, the case where the voltages applied to the control terminal Vcont1 and the control terminal Vcont2 are the same has been described. However, by controlling the voltages with different voltages, it is possible to set the frequency to be further subdivided. In addition, a wider band can be achieved.

  Therefore, according to the present embodiment, the SAW resonators 20 and 30 having different resonance frequencies connected in parallel to the cross-coupled circuit 10 are connected to the first control voltage and the second voltage via the varicap diodes 50 and 60, respectively. The control voltage is applied. By changing the applied voltage of the first control voltage and the second control voltage, the capacitance of the varicap diodes 50 and 60 is changed to oscillate the SAW resonators 20 and 30 at a desired oscillation frequency. At this time, since the oscillation output in which the SAW resonator 20 and the SAW resonator 30 are coupled is output by the cross-coupled circuit, each oscillation frequency is continuously switched and output. It can be varied with continuity.

  The SAW resonators 20 and 30 are stacked on a semiconductor chip substrate including the cross-coupled circuit 10, the first variable capacitance circuit 100, and the second variable capacitance circuit 200. According to such a configuration, the surface acoustic wave oscillator 1 needs only the area of two surface acoustic wave elements (SAW resonators 20 and 30), and the size can be reduced while suppressing the increase in area.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be implemented in various forms without departing from the spirit of the present invention. Hereinafter, a modification of the circuit configuration will be described. 1 and 5 to 9 illustrate the case where the varicap diode is an NMOS type, and FIGS. 10 to 14 illustrate the case where the varicap diode is a PMOS type.
(Modification 1)

  FIG. 5 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to Modification 1 of the present invention. In the first modification, the surface acoustic wave oscillator 1 is connected to the cross-coupled circuit 10 (between the transistor N1 and the transistor P1) and the output terminal OUT1 with respect to the above-described embodiment (see FIG. 1). The difference is that a capacitor C2 is connected between the cross-coupled circuit 10 (between the transistor N2 and the transistor P2) and the output terminal OUT2.

Further, the SAW resonator 20 and the variable capacitance circuit 100 are connected in series between the output terminal OUT1 and the ground potential line GND, and the SAW resonator 30 variable capacitance circuit 200 is connected between the output terminal OUT2 and the ground potential line GND. Are connected in series. Even if it is such a structure, the effect similar to embodiment mentioned above is acquired.
(Modification 2)

  FIG. 6 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to the second modification of the present invention. In Modification 2, the surface acoustic wave oscillator 1 includes a capacitor C1 connected between the variable capacitance circuit 100 (varicap diode 50) and the output terminal OUT1, and between the variable capacitance circuit 200 (varicap diode 60) and the output terminal OUT2. Is connected to a capacitor C2.

Further, 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 variable capacitance circuit 200 and the SAW resonator 30 are connected in series in this order. As shown in FIG. 6, even if the left and right are asymmetrical with respect to the cross-coupled circuit 10, the same effects as those of the above-described embodiment can be obtained.
Note that only one of the capacitors C1 and C2 may be used.
(Modification 3)

FIG. 7 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to the third modification of the present invention. In Modification 3, the surface acoustic wave oscillator 1 includes a SAW resonator 20 and a variable capacitance circuit 100 connected in series between the output terminal OUT1 and VDD, and a SAW resonator 30 and a variable capacitance between the output terminal OUT2 and VDD. The circuit 200 is connected in series. The configuration of the cross-coupled circuit 10 is the same as that of the above-described embodiment (see FIG. 1).
(Modification 4)

FIG. 8 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to Modification 4 of the present invention. The modification 4 is characterized in that capacitors C1 and C2 are added to the above-described modification 3 (see FIG. 7). As shown in FIG. 8, the surface acoustic wave oscillator 1 includes a capacitor C1, a SAW resonator 20, and a variable capacitance circuit 100 connected in series between a 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 cross-coupled circuit 10 (between the transistor N2 and the transistor P2) and VDD.
(Modification 5)

FIG. 9 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to the fifth modification of the present invention. In the modified example 5, the arrangement positions of the capacitors C1 and C2 added to the modified example 4 (see FIG. 8) described above are changed. 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, the capacitor C2, the SAW resonator 30, and the variable capacitance circuit 200 are connected in series between the output terminal OUT2 and VDD.
(Modification 6)

  FIG. 10 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to Modification 6 of the present invention. In the sixth modification, the cross-coupled circuit 10 shown in FIGS. 1 and 5 to 9 is replaced with a cross-coupled circuit 12 in which the first active element and the second active element are configured by Pch transistors. The cross-coupled circuit 12 includes a pair of first active elements Pch transistor Px1 (hereinafter simply referred to as transistor Px1) and a second active element Pch that are differentially connected to the output terminal OUT1 and the output terminal OUT2. The transistor Px2 (hereinafter simply referred to as the transistor Px2) is connected to the current mirror circuit 13 including the Nch transistors Nx1 and Nx2 (hereinafter simply referred to as the transistors Nx1 and Nx2) and the constant current source 40. Has been. The transistor Nx1 has a source terminal connected to the ground potential line GND, and a gate terminal and a drain terminal connected to the output terminal OUT1.

The transistor Nx2 has a source terminal connected to the ground potential line GND, a gate terminal connected to the output terminal OUT1, and a drain terminal connected to the output terminal OUT2. The transistor Px1 has a source terminal connected to VDD via the constant current source 40, a gate terminal connected to the output terminal OUT2, and a drain terminal connected to the output terminal OUT1. The transistor Px2 has a source terminal connected to VDD via the constant current source 40, a gate terminal connected to the output terminal OUT1, and a drain terminal connected to the output terminal OUT2.
Further, the varicap diodes 50 and 60 used in the modified example 6 are PMOS diodes.
(Modification 7)

FIG. 11 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to Modification 7 of the present invention. The modification 7 is characterized in that capacitors C1 and C2 are added to the above-described modification 6 (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 an output terminal OUT1 and a ground potential line GND, and 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)

FIG. 12 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to Modification 8 of the present invention. The modification 8 is characterized in that the arrangement of the capacitors C1 and C2 added to the above-described modification 7 (see FIG. 11) is changed. As shown in FIG. 12, the surface acoustic wave oscillator 1 includes a capacitor C1, a SAW resonator 20, and a variable capacitance circuit 100 between a cross-coupled circuit 12 (between the transistor Px1 and the transistor Nx1) and the ground potential line GND. The capacitor C2, the SAW resonator 30, and the variable capacitance circuit 200 are connected in series between the cross-coupled circuit 12 (between the transistor Px2 and the transistor Nx2) and the ground potential line GND.
(Modification 9)

  FIG. 13 is a circuit diagram showing a 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 the above-described modification 6 (see FIG. 10), and the arrangement of the variable capacitance circuits 100 and 200 is changed. As shown in FIG. 13, the surface acoustic wave oscillator 1 includes a variable capacitance circuit 100 and a SAW resonator 20 connected in series between a cross-coupled circuit 12 (between the transistor Nx1 and the transistor Px1) and a ground potential line GND. A SAW resonator 20 and a 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 Nx2 and the transistor Px2) and the ground potential line GND, and between the ground potential line GND and the output terminal OUT2. A SAW resonator 30 and a capacitor C2 are connected in series.
(Modification 10)

  FIG. 14 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to Modification 10 of the present invention. The modification 10 is characterized in that two varicap diodes are added to the variable capacitance circuits 100 and 200 of the modification 9 (see FIG. 13) described above. Capacitors C1 and C2 are not used. As shown in FIG. 14, the surface acoustic wave oscillator 1 includes a variable capacitance circuit 101 (varicap diodes 51 and 50) and a SAW between a cross-coupled circuit 12 (between the transistor Nx1 and the transistor Px1) and the ground potential line GND. The resonator 20 is connected in series, and the control terminal Vcont 1 is connected between the varicap diodes 51 and 50. The varicap diodes 50 and 51 are connected in series between the output terminal OUT1 and the cross-coupled circuit 12.

  On the other hand, the variable capacitance circuit 201 (varicap diodes 61 and 60) and the 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 diodes 61 and 60. The varicap diodes 60 and 61 are connected in series between the output terminal OUT2 and the cross-coupled circuit 12.

  Even if it is a structure like the modification 1-the modification 10 (refer FIGS. 5-14) demonstrated above, the surface acoustic wave oscillator 1 is the same as that of embodiment (refer FIGS. 1-4) mentioned above. It is possible to achieve various effects.

10 to 14, the configuration using the PMOS type varicap diode has been described. However, in the circuit configuration using the NMOS type varicap diode shown in FIGS. 7 to 9, the NMOS type is changed to the PMOS type varicap. A circuit configuration may be used instead of a diode (not shown).
(Modification 11)

  Next, Modification 11 of the present invention will be described with reference to the drawings. The modification 11 is characterized in that the first embodiment and the modifications 1 to 10 described above are connected in parallel to the SAW resonator and the variable capacitance circuit connected in series. ing. Note that a configuration using an NMOS type as the varicap diode will be described as an example.

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

  The variable capacitance circuit 103 includes a varicap diode 50 and a capacitor C1. The varicap diode 50 has a cathode terminal connected to the control terminal Vcont1 and an anode terminal connected to the ground potential line GND. The capacitor C1 has one terminal connected to the control terminal Vcont1 (varicap diode 50) and the other terminal connected to the output terminal OUT1.

The variable capacitance circuit 203 includes a varicap diode 60 and a capacitor C2. The varicap diode 60 has a cathode terminal connected to the control terminal Vcont2 and an anode terminal connected to the ground potential line GND. The capacitor C2 has one terminal connected to the control terminal Vcont2 (varicap diode 60) and the other terminal connected to the output terminal OUT2.
The SAW resonator 20 has one terminal connected to the output terminal OUT1 and the other terminal connected to the ground potential line GND.

  The SAW resonator 30 has one terminal connected to the output terminal OUT2 and the other terminal connected to the ground potential line GND.

  Therefore, as shown in FIG. 15, the surface acoustic wave oscillator 1 includes a cross-coupled circuit 10, a variable capacitance circuit 103, a SAW resonator 20, and a cross-coupled circuit 10, a variable capacitance circuit 203 and a SAW resonator 30 in parallel. Connected to and configured.

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 the capacitor capacity and the frequency according to the eleventh modification. In FIG. 16, the voltages applied to the control terminal Vcont1 and the control terminal Vcont2 are changed, and the SAW resonators 20 and 30 when the capacitor capacities of the varicap diodes 50 and 60 change corresponding to the magnitudes of the voltage values. It represents the change in frequency. As shown in FIG. 16, the frequency changes corresponding to the capacitor capacity. Specifically, f1 = 315.052 MHz is output in the vicinity of 0 pF, and f7 = 315.034 MHz is output in 30 pF, and the frequency (shown as f2 to f6 in the figure) changes with continuity therebetween. Therefore, by changing the voltage values of the first control voltage and the second control voltage, the capacitance of the varicap diodes 50 and 60 is changed, and the SAW resonators 20 and 30 are adjusted to desired output frequencies. Can do.

  FIG. 17 is a graph illustrating the operation of the surface acoustic wave oscillator according to the eleventh modification. In addition, the graph of FIG. 17 illustrates the case where the same voltage (that is, the first control voltage = the second control voltage) is applied to the control terminal Vcont1 and the control terminal Vcont2 of the surface acoustic wave oscillator 1 while being changed. Yes. The plurality of graphs of the reflection coefficient (S11) and the phase characteristic (Phase) shown in the figure represent the cases where the first control voltage and the second control voltage are changed, respectively. As shown in FIG. 17, in the graph of the reflection coefficient (S11), a gain is obtained in a wide range of 314.97 MHz to 315.09 MHz.

  Since the intersection when the reflection coefficient S11 becomes the lowest when the phase characteristic ω = 0 corresponds to the output frequency, the frequencies f1 to f7 (f4, f5, and f6 are omitted for the sake of illustration) are obtained. It is done. The frequencies f1 to f7 correspond to the frequencies f1 to f7 shown in FIG. Accordingly, the output frequency can be varied between f1 and f7 with continuity.

  Even in the configuration in which the SAW resonator and the variable capacitance circuit are connected in parallel as in the above-described modification example 11, the frequency sensitivity with respect to the change in the capacitor capacitance is slightly lower than that in the configuration in which the SAW resonator is connected in series. It is possible to change the frequency and realize a wider band.

In the above-described modification 11, the case where the voltages applied to the control terminal Vcont1 and the control terminal Vcont2 are the same has been described. However, by controlling each of the voltages with different voltages, further subdivided frequencies and widebands are set. Can do.
(Modification 12)

Next, a surface acoustic wave oscillator according to Modification 12 of the invention will be described with reference to the drawings. The modification 12 is characterized in that two varicap diodes are added to the variable capacitance circuit and capacitors C1 and C2 are deleted from the above-described modification 11 (see FIG. 15). .
FIG. 18 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to Modification 12. In FIG. 18, the surface acoustic wave oscillator 1 includes a cross-coupled circuit 10, a variable capacitance circuit 104, a SAW resonator 20, and a cross-coupled circuit 10, a variable capacitance circuit 204, and a SAW resonator 30 connected in parallel. ing.

  The variable capacitance circuit 104 is configured by connecting varicap diodes 51 and 50 in series between the output terminal OUT1 and the ground potential line GND, and connecting a control terminal Vcont1 between the varicap diode 51 and the varicap diode 50. .

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

  Also in the configuration of the modification 12, the same effect as that of the modification 11 described above can be obtained.

  In the modification examples 11 and 12, the configuration using the NMOS type varicap diode has been described as an example, but a PMOS type varicap diode can also be used.

1 is a circuit diagram showing a configuration of a surface acoustic wave oscillator according to an embodiment of the present invention. The graph explaining the effect | action of the surface acoustic wave oscillator which concerns on embodiment of this invention. The horizontal axis enlarged view of FIG. The graph which shows the relationship between the capacitor | condenser capacity | capacitance which concerns on embodiment of this invention, and a frequency. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 1 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 2 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 3 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 4 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 5 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 6 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 7 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 8 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 9 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 10 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 11 of this invention. The graph which shows the relationship between the capacitor | condenser capacity | capacitance which concerns on the modification 11 of this invention, and a frequency. The graph explaining the effect | action of the surface acoustic wave oscillator which concerns on the modification 11 of this invention. The circuit diagram which shows the structure of the surface acoustic wave oscillator which concerns on the modification 12 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave oscillator, 10 ... Cross couple type circuit, 11 ... Current mirror circuit, 20, 30 ... SAW resonator, 40 ... Constant current source, 50, 60 ... Varicap diode, 100, 200 ... Variable capacity circuit.

Claims (3)

A cross-coupled circuit including a pair of a first active element and a second active element differentially connected to the first output terminal and the second output terminal;
A first surface acoustic wave element and a second surface acoustic wave element connected in parallel to the cross-coupled circuit;
A first variable capacitance circuit that includes a first variable capacitance element whose capacitance value changes in accordance with a first control voltage applied from a first control terminal, and changes a resonance frequency of the first surface acoustic wave element. When,
A second variable capacitance circuit including a second variable capacitance element whose capacitance value changes in accordance with a second control voltage applied from the second control terminal, and changes a resonance frequency of the second surface acoustic wave element. When,
Have
The first surface acoustic wave element and the first variable capacitance circuit, the second surface acoustic wave element and the second variable capacitance circuit are connected,
The resonance frequency of the first surface acoustic wave element and the resonance frequency of the second surface acoustic wave element are such that the combined oscillation output of the first surface acoustic wave element and the second surface acoustic wave element is A surface acoustic wave oscillator characterized by being slightly different so as to be output by a cross-coupled circuit . The surface acoustic wave oscillator according to claim 1,
The first surface acoustic wave element and the second surface acoustic wave element are stacked on a semiconductor chip including the cross-coupled circuit, the first variable capacitance circuit, and the second variable capacitance circuit. A surface acoustic wave oscillator characterized by being formed. A cross-coupled circuit including a first output terminal and a second pair of first which is differentially connected to the output terminal of the active element and a second active element, first is connected in parallel to the cross-coupled circuit Including the first surface acoustic wave element, the second surface acoustic wave element, and the first variable capacitance element whose capacitance value changes according to the first control voltage applied from the first control terminal. A first variable capacitance circuit that changes a resonance frequency of the surface acoustic wave element; and a second variable capacitance circuit that changes a capacitance value in accordance with a second control voltage applied from a second control terminal. A second variable capacitance circuit that changes a resonance frequency of the second surface acoustic wave element, the first surface acoustic wave element, the first variable capacitance circuit, and the second surface acoustic wave element. said second variable capacitance circuit, is connected, the first surface acoustic wave The resonance frequency of the child and the resonance frequency of the second surface acoustic wave element are such that the oscillation output coupled with the first surface acoustic wave element and the second surface acoustic wave element is output by the cross-coupled circuit. A method of varying the frequency of a slightly different surface acoustic wave oscillator,
An elasticity characterized by changing the oscillation frequency of the first surface acoustic wave element and the second surface acoustic wave element by changing voltage values of the first control voltage and the second control voltage. A method of varying the frequency of a surface wave oscillator.

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