Oscillator and phase synchronizing circuit

When a direct-current voltage is applied from a power supply, a signal line generates a standing wave having the ¾ wavelength where a starting end of the signal line connected to the power supply is used as a node and a terminating end is used as an antinode. Strips are connected to a ground layer through switches, respectively. The switches switch connection and non-connection of the strips and the ground layer, under the control from a switch controller. By switching the connection and non-connection of the switches, the distance between the signal line and the ground layer is pseudo adjusted and the effective permittivity in a transmission line unit changes. Therefore, the frequency of the standing wave can be adjusted.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-144676, filed on Jun. 17, 2009, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are directed to an oscillator and a phase synchronizing circuit.

BACKGROUND

In recent years, a technology for adjusting an oscillation frequency by an oscillator having an incorporated resonance circuit in a communication system, such as an optical communication system, has been known. According to this technology, a variable capacitative element, such as a capacitor or a diode, is provided in the resonance circuit to control the capacitance of the variable capacitative element. Thereby, a resonance frequency of the resonance circuit is adjusted, which results in changing a frequency (oscillation frequency) of a clock signal output from the oscillator. By using the oscillator, a clock signal having a high frequency of 20 GHz or more can be output, and a recent requirement for increasing a communication speed or apparatus performance can be met.

When a higher oscillation frequency is needed, an oscillator using a standing wave generated in a transmission path, such as a micro strip line, is used. In this oscillator, the length of the transmission path in the oscillator is determined based on an electrical length of the standing wave. That is, the length of the transmission path in the oscillator becomes ¾ of the electrical length of the oscillation frequency, which is the length where the standing wave is generated. If a voltage is applied to the transmission path, the standing wave is generated on the transmission path. Specifically, a standing wave where a traveling wave propagated to a terminating end of the transmission path and a reflected wave reflected on the terminating end of the transmission path are synthesized is generated. As a result, a clock signal that corresponds to the frequency of the standing wave generated in the transmission path is output from the oscillator. In the case of the oscillator using the standing wave, a variable capacitative element is connected to the terminating end of the transmission path, and the oscillation frequency of the oscillator is adjusted by controlling the capacitance of the variable capacitative element.

Such conventional technologies are disclosed in for example Japanese Laid-open Patent Publication Nos. 2008-118550 and 2005-217752, and Jri Lee et al., “A 75-GHz PLL in 90-nm CMOS Technology”, ISSCC 2007/SESSION 23/BROADBAND RF AND RADAR/23.8, pp. 432-433.

In general, the oscillation frequency of the oscillator has a negative correlative relationship with the capacitance of the variable capacitative element. Specifically, if the capacitance of the variable capacitative element decreases, the oscillation frequency of the oscillator increases, and if the capacitance of the variable capacitative element increases, the oscillation frequency of the oscillator decreases. However, since a variable range of the capacitance of one variable capacitative element is restricted, it is considered to provide plural variable capacitative elements and increase the variable range of the capacitance to flexibly adjust the oscillation frequency of the oscillator over a wide band.

However, when the plural variable capacitative elements are provided, a parasitic capacitance of an entire circuit increases as the number of variable capacitative elements increases. As a result, even though the capacitance of each variable capacitative element is controlled to have a minimum value, the capacitance of the entire circuit is increased by only the parasitic capacitance due to the plural variable capacitive elements. For this reason, a sufficiently high oscillation frequency may not be obtained.

In regards to the oscillator using the standing wave, the oscillation frequency becomes a relatively high frequency, but the variable range of the capacitance of the variable capacitative element needs to be restricted to generate the standing wave which may be used in oscillation. That is, in the oscillator using the standing wave, a phase of the traveling wave at the terminating end of the transmission path is changed by controlling the capacitance of the variable capacitative element. However, if a standing wave where surrounding portions of the terminating end of the transmission path are used as antinodes is not generated, the oscillation frequency cannot be obtained. For this reason, in the oscillator using the standing wave, phases in the surrounding portions of the terminating end of the transmission path cannot be freely adjusted, and the capacitance of the variable capacitative element cannot be greatly changed. In the oscillator using the standing wave, it is difficult to flexibly adjust the oscillation frequency over a wide band, because of a restrictive condition due to the phases.

SUMMARY

According to an aspect of an embodiment of the invention, an oscillator includes a signal line that propagates a traveling wave according to application of a power supply voltage and has a length from a voltage applied portion where the power supply voltage is applied to at least one end is odd number times as long as the ¼ wavelength of the propagated traveling wave; a maintaining unit that maintains a standing wave generated in the signal line according to the traveling wave propagated by the signal line; an output unit that outputs a signal having an oscillation frequency using the standing wave maintained by the maintaining unit; a potential changing electrode that includes a facing portion, which faces the signal line in the vicinity of the signal line and of which the potential changes to the ground potential; and a controller that changes the potential of the facing portion included in the potential changing electrode and adjusts the oscillation frequency of the signal output from the output unit.

According to another aspect of an embodiment of the invention, an oscillator includes a signal line which propagates a traveling wave according to application of a power supply voltage and of which the length from a voltage applied portion where the power supply voltage is applied to at least one end is odd number times as long as the ¼ wavelength of the propagated traveling wave; a changing unit that changes effective permittivity corresponding to a propagation speed of the traveling wave in the signal line; and an output unit that outputs a signal having an oscillation frequency using the traveling wave propagated by the signal line, after the effective permittivity is changed by the changing unit.

According to still another aspect of an embodiment of the invention, a phase synchronizing circuit includes an oscillator that outputs a signal having an oscillation frequency according to an input voltage; and a comparator that compares the oscillation frequency of the signal output by the oscillator and a predetermined reference frequency and inputs an input voltage corresponding to a difference between the oscillation frequency and the reference frequency to the oscillator. The oscillator includes a signal line that propagates a traveling wave according to application of a power supply voltage and has a length from a voltage applied portion where the power supply voltage is applied to at least one end is odd number times as long as the ¼ wavelength of the propagated traveling wave; a potential changing electrode that includes a facing portion, which faces the signal line in the vicinity of the signal line and of which the potential changes to the ground potential; a controller that changes the potential of the facing portion included in the potential changing electrode according to the input voltage from the comparator; and an output unit that outputs a signal having an oscillation frequency using the traveling wave propagated by the signal line, after the potential of the facing portion is changed by the control signal from the control unit.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be explained with reference to accompanying drawings. However, the exemplary embodiments are not limitative.

[a] First Embodiment

Configuration of an Oscillator

FIG. 1Aillustrates the configuration of an oscillator according to a first embodiment. The oscillator illustrated inFIG. 1Ahas a voltage controller110, a variable capacitative element120, a transmission line unit130, a switch controller140, a buffer unit150, an output terminal155, and an oscillation inducing unit170.

The voltage controller110controls a voltage that is applied to the variable capacitative element120and changes the capacitance of the variable capacitative element120with respect to a ground.

The variable capacitative element120is an element of which the capacitance changes according to a control voltage applied from the voltage controller110. For example, as the variable capacitative element120, a metal-oxide semiconductor field-effect transistor (MOSFET) is used. A board of the MOSFET is connected to a ground, a source and a drain thereof are connected to the voltage controller110, and a gate thereof is connected to one end of a signal line131in the transmission line unit130. A frequency of a standing wave that is generated in the transmission line unit130changes according to a change in the capacitance of the variable capacitative element120. That is, if the capacitance of the variable capacitative element120changes, the phase shift amount in one end of the signal line131changes and the frequency of the standing wave changes. Specifically, if the capacitance of the variable capacitative element120increases, the frequency of the standing wave decreases, and if the capacitance of the variable capacitative element120decreases, the frequency of the standing wave increases.

In the first embodiment, only one MOSFET is provided as the variable capacitative element120, and the parasitic capacitance that is generated in a circuit is minimally suppressed. Accordingly, the frequency of the standing wave can be prevented from decreasing due to the parasitic capacitance of the circuit. The variable range of the capacitance is narrow in one MOSFET. However, in the first embodiment, even though the capacitance of the variable capacitative element120does not change, an oscillation frequency can be flexibly adjusted. For this reason, in the first embodiment, the capacitance of the variable capacitative element120may be changed to a degree to which the oscillation frequency can be minutely adjusted, and the variable range does not need to be increased.

The transmission line unit130includes the signal line131that is connected to a power supply and a ground layer that is connected to the ground. In the transmission line unit130, a dielectric layer that includes a mixture medium of SiO2and silicon is interposed between the signal line131and the ground layer. When a direct-current voltage Vdc is applied to the signal line131, the transmission line unit130propagates a traveling wave and generates a standing wave. At this time, the transmission line unit130increases or decreases the appearance permittivity of the dielectric layer and changes a frequency of the standing wave over a wide band. Specifically, a frequency f of the standing wave is represented by the following Equation (1), using the light velocity c, the length L of the signal line131, the phase shift amount ΔΦ in one end of the signal line131, and the appearance permittivity Er in the transmission line unit130.

In Equation (1), Er indicates the appearance permittivity in the transmission line unit130, which is an effective permittivity corresponding to the speed of the traveling wave propagated by the transmission line unit130. That is, since the material that is contained in the dielectric layer does not change, the specific permittivity of the dielectric layer that is determined from the unique permittivity of the material does not change. However, the effective permittivity Er corresponding to the propagation speed of the traveling wave can be changed, and the frequency f of the standing wave changes according to a change in the effective permittivity Er. As described above, in the first embodiment, since the variable range of the capacitance of the variable capacitative element120is narrow, the phase shift amount ΔΦ in one end of the signal line131cannot be greatly changed. However, if the effective permittivity Er in the transmission line unit130is mainly changed, the frequency f of the standing wave is adjusted. Specifically, the transmission line unit130has the signal line131, strips132-1to132-n(n is an integer of 1 or more), switches133-1to133-n, and an amplifier136.

The signal line131is a transmission path of which one end is connected to a power supply to supply a direct-current voltage Vdc and the other end is connected to the variable capacitative element120and the buffer unit150. In the description below, one end of the signal line131that is connected to the power supply is referred to as a “starting end” and the other end of the signal line131that is connected to the variable capacitative element120and the buffer unit150is referred to as a “terminating end”. The length of the signal line131from the starting end to the terminating end is ¾ of the wavelength of the traveling wave used in oscillation. For this reason, if the direct-current voltage Vdc is applied from the power supply, the signal line131generates a standing wave having the ¾ wavelength, in which the starting end where the direct-current voltage Vdc is applied is used as a node and the terminating end is used as an antinode. At this time, the frequency f of the standing wave that is generated by the signal line131is inversely proportional to a square root of the effective permittivity Er in the transmission line unit130, as illustrated in Equation (1). Accordingly, if the effective permittivity Er in the transmission line unit130increases, the frequency f of the standing wave decreases, and if the effective permittivity Er in the transmission line unit130decreases, the frequency f of the standing wave increases.

The dielectric layer that includes a mixture medium of SiO2and silicon is formed between the signal line131and the ground layer, and the strips132-1to132-nand the switches133-1to133-nare disposed in the dielectric layer. The mixture medium, the strips132-1to132-n, and the switches133-1to133-nform the dielectric layer as a whole and change the effective permittivity Er in the transmission line unit130. The specific configuration of the transmission line unit130will be described in detail below.

Each of the strips132-1to132-nis composed of an elongated plate-shaped electrode that is formed of a conductor, such as a metal, and are arranged in parallel along the signal line131such that the strips do not contact the signal line131. The strips132-1to132-nare connected to the ground layer through the switches133-1to133-n, respectively. Accordingly, if the switches133-1to133-nconnect the strips132-1to132-nand the ground layer, the potential of the strips132-1to132-nthat are disposed in the vicinity of the signal line131changes to the ground potential.

The switches133-1to133-nswitch connection and non-connection of the strips132-1to132-nand the ground layer, respectively, under the control from the switch controller140. As the switches133-1to133-n, for example, MOSFETs are used. If the switches133-1to133-nconnect the strips132-1to132-nand the ground layer, the signal line131becomes pseudo close to the ground layer. That is, if the connection and the non-connection of the switches133-1to133-nare switched, the distance between the signal line131and the ground layer is pseudo adjusted. Even though the material forming the dielectric layer between the signal line131and the ground layer does not change, the effective permittivity Er that corresponds to the propagation speed of the traveling wave can be changed.

Specifically, if the number of connected switches133-1to133-nincreases, it can be assumed that the signal line131and the ground layer become close to each other. Since the propagation speed of the traveling wave becomes slow, it can be assumed that the effective permittivity Er in the transmission line unit130increases. If the number of connected switches133-1to133-ndecreases, it can be assumed that the signal line131and the ground layer become away from each other. Since the propagation speed of the traveling wave becomes fast, it can be assumed that the effective permittivity Er in the transmission line unit130decreases. As illustrated in Equation (1), if the effective permittivity Er in the transmission line unit130changes, the frequency f of the standing wave also changes. That is, the effective permittivity Er can be changed by switching the connection and non-connection of the switches133-1to133-n, and the frequency f of the standing wave that is generated in the signal line131can be adjusted.

The amplifier136maintains the standing wave that is generated in the signal line131. That is, the amplifier136amplifies the standing wave that is generated in the signal line131and prevents attenuation, and maintains oscillation in the signal line131. Specifically, the amplifier136is connected to the position of the ¼ wavelength from the starting end of the signal line131and the position of the predetermined distance ΔL from the terminating end of the signal line131, and causes the amplitudes of the standing waves at the two connection positions to have the same magnitudes to be inverted to each other. Essentially, the amplifier136associates the amplitudes at the position of the ¼ wavelength from the starting end of the signal line131and the position of the terminating end of the signal line131where the antinodes of the standing waves are formed. However, since the delay is generated until the amplitude at the connection position of the amplifier136arrives at the amplifier136, in the first embodiment, the delay is compensated for by shifting the connection position of the amplifier136by the predetermined distance ΔL from the terminating end of the signal line131. Thereby, the amplitudes of the standing waves at the position of the ¼ wavelength from the starting end of the signal line131and the amplitude of the standing wave at the position of the terminating end of the signal line131always have the same magnitudes to be inverted to each other, respectively.

The connection position of the amplifier136is not limited to the example ofFIG. 1A, and the arbitrary connection position may be used, as long as the arbitrary connection position is the connection position that considers the delay generated until the amplitude of the standing wave at the connection position arrives at the amplifier136. For example, the signal line131may be curved such that the portion of the ¼ wavelength from the starting end of the signal line131and the terminating end of the signal line131come close to each other, and the two points which are close to each other may be set to the connection positions of the amplifier136, thereby negligibly decreasing the delay generated until the amplitude of the standing wave arrives at the amplifier136.

Examples of the specific configuration of the amplifier136are illustrated inFIG. 1B to 1E. Types of the amplifier136include an inverter type where two inverters are combined, a phase adjustment type where a phase of an input voltage is adjusted, an NMOS (Negative-channel Metal Oxide Semiconductor) type where two NMOS inverters are combined, and a CMOS (Complementary Metal Oxide Semiconductor) type where two CMOS inverters are combined. The amplifier136illustrated inFIGS. 1B to 1Einputs voltages V1and V2of the signal line131at all of the connection positions as inputs and maintains the oscillation in state where phases of the voltages V1and V2are opposite to each other.

The switch controller140controls switching of the connection and non-connection of each of the switches133-1to133-n. Specifically, when the oscillation frequency of the oscillator is increased, the switch controller140decreases the number of connected switches133-1to133-n. When the oscillation frequency of the oscillator is decreased, the switch controller140increases the number of connected switches133-1to133-n.

The buffer unit150has a buffering circuit, and excludes an influence from the side of the output terminal155with respect to the circuit such as the variable capacitative element120and the transmission line unit130and stably operates the circuit including the variable capacitative element120and the transmission line unit130. Specifically, the buffer unit150includes a MOSFET, and a gate of the MOSFET is connected to the terminating end of the transmission line unit130, a source thereof is connected to a power supply supplying a power supply voltage Vdd through a resistor element, and a drain thereof is connected to a ground. For this reason, if the standing wave having the frequency f is generated in the transmission line unit130, the source and the drain become a conductive state with a cycle corresponding to the frequency f, and the buffer unit150outputs a clock signal having the frequency f to the output terminal155.

When the oscillator starts, the oscillation inducing unit170discharge electricity to the transmission line unit130and induces a traveling wave in the signal line131. Specifically, the oscillation inducing unit170has a switch171that is provided between a terminal of the power supply voltage Vdd and the terminating end of the signal line131. When the oscillator starts, the switch171temporarily connects the terminal of the power supply voltage Vdd and the terminating end of the signal line131and induces a traveling wave in the signal line131. The time when the switch171is closed and the terminal of the power supply voltage Vdd and the terminating end of the signal line131are connected to each other is determined according to the capacitance of the variable capacitative element120.

Configuration of the Transmission Line Unit

FIG. 2is a perspective view illustrating the configuration of the transmission line unit130according to the first embodiment. As illustrated inFIG. 2, the transmission line unit130is configured by interposing a dielectric layer134between the signal line131and a ground layer135, and the strips132-1to132-nand the switches133-1to133-n(not illustrated) are provided in the dielectric layer134. The dielectric layer134is mainly formed of a mixture medium of SiO2and silicon, and has the configuration where the strips132-1to132-nand the switches133-1to133-nare fixed in the mixture medium. The dielectric layer134functions as one dielectric body as a whole. The ground layer135is connected to a ground and the potential thereof is always maintained at the ground potential.

The strips132-1to132-nare disposed at an equivalent interval along the signal line131in the vicinity of the signal line131. InFIG. 2, it is assumed that one end of the signal line131at the lower left of the figure is a starting end connected to the power supply applying the direct-current voltage Vdc and the other end of the signal line131at the upper right of the figure is a terminating end connected to the buffer unit150. That is, it is assumed that a propagation direction of the traveling wave of the signal line131is a direction toward the strip132-nfrom the strip132-1. The strips132-1to132-nare connected to switches131-1to131-nthrough connection portions132a, respectively.

In the transmission line unit130that has the above configuration, when the direct-current voltage Vdc is applied to the signal line131and a traveling wave whose wavelength λ is 2 mm and the frequency f is 52 GHz is propagated, a distribution of electric field strength in the vicinity of the signal line131is as illustrated inFIG. 3. That is, the electric field strength is distributed in a waveform-like shape corresponding to the ¾ wavelength based on the signal line131. This waveform is a waveform of a standing wave where positions of the zero wavelength and the ½ wavelength from the end of the signal line131at the side of the strip132-1are used as nodes and positions of the ¼ wavelength and the ¾ wavelength from the end of the signal line131at the side of the strip132-1are used as antinodes. In the antinodes of the standing wave, the electric field strength becomes 150 kV/m or more. As such, if the length of the signal line131is set to ¾ of the wavelength λ, the standing wave is generated in the signal line131.

Since the terminating end of the signal line131becomes the antinode of the standing wave and oscillates, the oscillator can output a clock signal having an oscillation frequency, using the standing wave. As illustrated in Equation (1), since the frequency f of the standing wave depends on the effective permittivity Er in the transmission line unit130, the frequency f of the standing wave can be adjusted by changing the effective permittivity Er in the transmission line unit130. As a result, even though the capacitance of the variable capacitative element120is not changed, the oscillation frequency of the oscillator can be changed.

Next, the configuration of the transmission line unit130will be specifically described with reference toFIGS. 4 and 5.FIGS. 4 and 5simply illustrate the strips132-1to132-nand the switches133-1to133-nas the strip132and the switch133.

FIG. 4is a schematic plan view illustrating the configuration of the transmission line unit130according to the first embodiment. As illustrated inFIG. 4, the transmission line unit130has the signal line131of which the length Len is 1.5 mm and the width w is 0.07 mm and plural strips132of which the transverse width Ls is 0.075 mm and the longitudinal width ws is 0.12 mm. The strips132face the signal line131and are arranged at equivalent intervals ss of 0.12 mm. In each strip132, the connection portion132athat is connected to the switch133is provided. The configuration illustrated inFIG. 4is only an example of the specific configuration of the transmission line unit130according to the first embodiment, and dimensions of the signal line131and the strip132are not limited to dimensions illustrated inFIG. 4.

Since each strip132is disposed to face the signal line131, the potential of each strip132becomes the ground potential, and the distance between the signal line131and the ground layer can be pseudo shortened. If the signal line131becomes close to the ground layer, it can be assumed that the effective permittivity Er in the transmission line unit130increases. As a result, a value of a denominator of the right side of Equation (1) increases and the frequency f of the standing wave that is generated in the signal line131decreases. Accordingly, if the number of strips132whose potential becomes the ground potential is increased or decreased, the frequency f of the standing wave can be adjusted and the oscillation frequency of the oscillator can be adjusted.

FIG. 5is a schematic lateral view illustrating the configuration of the transmission line unit130according to the first embodiment. As illustrated inFIG. 5, the transmission line unit130has a layered structure, and the signal line131, a SiO2layer134a, a silicon layer134b, and the ground layer135are formed from an upper side of the figure. The SiO2layer134aand the silicon layer134bform the dielectric layer134.

The signal line131is formed on a surface of the transmission line unit130, and the distance h from the ground layer135to the signal line131is 0.25 mm. The SiO2layer134ais an insulating layer made of SiO2where the strips132are fixed, and the distance hs from the ground layer135to the strip132is 0.1 mm. Accordingly, the distance hv from the strip132to the signal line131becomes 0.15 mm. The SiO2layer134aalso includes a gate133aof a MOSFET to form the switch133. The gate133ais connected to the switch controller140.

The silicon layer134bis a semiconductor layer that includes a source133band a drain133cof the MOSFET to form the switch133. Although not illustrated inFIG. 5, the source133bof the switch133is connected to the ground layer135. The drain133cof the switch133is connected to the strip132. When the transmission line unit130has a layered structure illustrated inFIG. 5, the transmission line unit130can be formed using a standard CMOS process and the oscillator can be easily manufactured.

The material SiO2constituting the SiO2layer134aand the silicon constituting the silicon layer134bare materials that have the fixed specific permittivity. Accordingly, if the specific permittivity of SiO2is defined as ∈r (SiO2) and the specific permittivity of the silicon is defined as ∈r (Si) and the height of the SiO2layer134ais defined as h (SiO2) and the height of the silicon layer134bis defined as h (Si) as illustrated inFIG. 5, the specific permittivity ∈r of the dielectric layer134is represented by the following Equation (2).

The effective permittivity Er in the transmission line unit130is represented by the following Equation (3), using the total number n of switches133, the number k of connected switches133, the specific permittivity ∈r of the dielectric layer134, the distance h between the signal line131and the ground layer135, and the distance hv between the signal line131and the strip132. However, each of A and B is a constant that is determined according to the specific permittivity ∈r of the dielectric layer134.

As can be seen from Equation (3), even when a ratio between the width w of the signal line131and a variable z is not more than 1 or more than 1, if the variable z increases, the effective permittivity Er decreases. The variable z indicates the effective distance between the signal line131and the ground layer135according to the number of connected switches133. If the number of connected switches133decreases, the variable z increases. Accordingly, if the number of connected switches133is reduced from Equation (3), it can be confirmed that the effective permittivity Er decreases. If the effective permittivity Er decreases, the frequency f of the standing wave that is generated in the transmission line unit130increases.

As such, the transmission line unit130according to the first embodiment switches connection and non-connection of the switches133, increases and decreases the number of connected switches133, changes the effective permittivity Er, and may adjust the frequency f of the standing wave. As a result, even though the variable range of the variable capacitative element120is narrow, the oscillation frequency that is output from the buffer unit150to the output terminal155can be flexibly adjusted over a wide band.

Configuration of the Switch

FIG. 6illustrates an example of the configuration of the switch133according to the first embodiment. The switch133illustrated inFIG. 6has the gate133a, the source133b, the drain133c, and a via133d. As described above, the gate133ais connected to the switch controller140. If a gate voltage is applied from the switch controller140, the gate133acauses the source133band the drain133cto become a conductive state. That is, if the gate voltage is applied, the gate133acauses the switch133to become a connection state and causes the potential of the drain133cto be matched with the potential of the source133b. While the gate voltage is not applied from the switch controller140, the gate133acauses the switch133to become a non-connection state and does not cause the potential of the drain133cto be matched with the potential of the source133b.

The source133bis connected to the ground layer135, and transmits the ground potential to the drain133cwhen the switch133is in a connection state. The drain133cis connected to the strip132through the via133d, and the potential thereof becomes the ground potential when the switch133is in a connection state. The via133dcauses the drain133cand the connection portion132aof the strip132to be connected, and causes the potential of the strip132to be matched with the ground potential of the drain133cwhen the switch133is in a connection state.

In the switch133that has the above configuration, if the gate voltage is applied from the switch controller140to the gate133a, the source133band the drain133cbecomes a conductive state and the potential of the strip132that is connected to the drain133cbecomes the ground potential. That is, if the switch133becomes a connection state by the control from the switch controller140, the potential of each of the ground layer135, the source133b, the drain133c, the via133d, and the strip132becomes the ground potential, and the distance between the signal line131and the ground layer135becomes pseudo shortened. Thereby, the effective permittivity Er in the transmission line unit130changes and the frequency f of the standing wave that is generated in the transmission line unit130is adjusted.

Operation of the Oscillator

Next, the operation of the oscillator having the transmission line unit130configured in the above way will be described. If the direct-current voltage Vdc is applied from the power supply to the starting end of the signal line131, the standing wave having the frequency f according to the capacitance of the variable capacitative element120and the effective permittivity Er in the transmission line unit130is generated in the signal line131. At this time, the effective permittivity Er in the transmission line unit130is adjusted by switching the connection and non-connection of the switches133-1to133-nby the switch controller140.

Specifically, the potential of the strips132-1to132-nthat correspond to the switches133-1to133-nbecoming a connection state by the switch controller140becomes the ground potential. For this reason, if the number of connected switches133-1to133-nincreases, the signal line131and the ground layer135become pseudo close to each other. As a result, the propagation speed of the traveling wave that is propagated along the signal line131by application of the direct-current voltage Vdc decreases, it can be assumed that the effective permittivity Er increases, and the frequency f of the standing wave decreases.

In contrast, if the number of connected switches133-1to133-ndecreases, the signal line131and the ground layer135become pseudo far away from each other. As a result, the propagation speed of the traveling wave that is propagated along the signal line131by application of the direct-current voltage Vdc increases, it can be assumed that the effective permittivity Er decreases, and the frequency f of the standing wave increases.

The capacitance of the variable capacitative element120is adjusted by a control voltage applied from the voltage controller110to the variable capacitative element120. In the first embodiment, however, the variable range of the capacitance of the variable capacitative element120is narrow, and only minute adjustment of the frequency f of the standing wave is performed by minutely changing the phase shift amount ΔΦ. As such, even though the variable range of the capacitance of the variable capacitative element120is narrow, since the variable range of the effective permittivity Er in the transmission line unit130is wide in the first embodiment, a control range of the frequency f can be widened.

As described above, since the standing wave where the frequency f is adjusted has an antinode at the terminating end of the signal line131connected to the buffer unit150, a clock signal that corresponds to the frequency f of the standing wave is output to the output terminal155by the buffer unit150.

Switching Operation of the Switch

Next, a specific example of the switching operation of the switch133according to the first embodiment will be described.FIG. 7illustrates a specific example of the switching operation of switches133-1to133-9when nine strips132-1to132-9are arranged with respect to the signal line131. InFIG. 7, an upper part illustrates a waveform of the standing wave that is generated in the signal line131and a lower part illustrates the switches133-1to133-9that become a connection state according to the magnitude of the frequency f. That is, if the switches133-1to133-9that are illustrated by circles (“O”) inFIG. 7are made to become a connection state, the potential of the corresponding strips132-1to132-9becomes the ground potential and the magnitude of the frequency f of the standing wave changes.

Specifically, if the number of connected switches decreases, the frequency f of the standing wave increases, and if the number of connected switches increases, the frequency f of the standing wave decreases.FIG. 7illustrates the case where the connection and non-connection of the switches133-1to133-9are switched such that the connected switches are equally disposed. For example, when only one switch is made to become a connection state, the switch133-5that corresponds to the strip132-5disposed at the center becomes a connection state and the remaining eight switches become a non-connection state.

When the two switches are made to become a connection state, the switch133-5and the switch133-7become a connection state and the remaining seven switches become a non-connection state. In this case, the switch133-7is selected as the second switch because the strip132-7is disposed in the vicinity of a node163of the standing wave. That is, when the potential of the strips (for example, strips132-4and132-9) that are disposed at the antinodes of the standing wave becomes the ground potential, the relatively large parasitic capacitance is generated and energy loss is generated. Meanwhile, when the potential of the strips (for example, strips132-1and132-7) that are disposed at the nodes of the standing wave becomes the ground potential, the parasitic capacitance can be prevented from being generated. For this reason, when the switches are connected, if the switches becoming a connection state are not equally disposed, the switches becoming a connection state are determined in consideration of the waveform of the standing wave.

When the three switches are made to become a connection state, the switches133-5,133-7, and133-3become a connection state and the remaining six switches become a non-connection state. The strip132-3is relatively close to an antinode162of the standing wave. However, at a stage where the two switches are made to become a connection state, since the switch133-7has become a connection state, the switch133-3that is disposed at the position symmetrical to the position of the switch133-7becomes a connection state.

As such, if the switches133-1to133-9are switched such that the connected switches are equally disposed, the entire signal line131becomes equally close to the ground layer135. For this reason, the frequency f of the standing wave that is generated in the signal line131can be accurately adjusted by securely changing the effective permittivity Er of the signal line131.

Similar to the above examples, when the four switches are made to become a connection state, the switch133-1that corresponds to the strip132-1close to a node161of the standing wave newly becomes a connection state. When the five switches are made to become a connection state, the switch133-9that is disposed at the position symmetrical to the position of the switch133-1which is already connected becomes a connection state. When the six switches are made to become a connection state, the switch133-6that corresponds to the strip132-6close to the node163of the standing wave becomes a connection state.

InFIG. 7, when the number of connected switches increases, the connected switches are made to continuously become a connection state. However, when the number of connected switches changes, which switch is made to become a connection state may be arbitrarily determined. For example, when the number of connected switches increases from 1 to 2, a state of the switch133-5which is already connected may be switched to a non-connection state and states of the switches133-3and133-7may be then switched to connection states. In this way, the connected switches can always be equally disposed. Instead of equality of the arrangement of the connected switches, a sequence may be considered. For example, the switches may become a connection state sequentially from the switches corresponding to the strips close to the nodes161and163of the standing wave.

As such, if the switch133is switched and the number of switches133in a connection state is changed, as illustrated by a solid line ofFIG. 8, impedance of the signal line131increases or decreases in a range of variance Δz based on 50Ω. Likewise, as illustrated by a broken line ofFIG. 8, the effective permittivity Er in the transmission line unit130changes from a minimum value Er (low) to a maximum value Er (high). Accordingly, if a frequency fo corresponding to the effective permittivity Er(o) of when the switches133whose number is half the existing number of switches become a connection state is set as a central frequency, the frequency f of the standing wave can be adjusted according to a change in the effective permittivity Er due to an increase and decrease in the number of connected switches133.

In the first embodiment, the capacitance of the variable capacitative element120may also change. For this reason, if a control voltage Vcont that is applied from the voltage controller110to the variable capacitative element120is changed, the frequency f of the standing wave can be minutely adjusted, even though the number of connected switches133is fixed. For example, as illustrated inFIG. 9, if the control voltage Vcont increases, the frequency f of the standing wave increases, even though the number of connected switches133does not change. InFIG. 9, plural curved lines illustrate changes in the frequency f when the number of connected switches133is different, and the lower curved lines of the figure illustrate changes in the frequency f when the number of connected switches133is large. Accordingly, if the switches133are switched and the control voltage Vcont is changed, the frequency f of the standing wave can be adjusted with the wide control width illustrated inFIG. 9.

As such, according to the first embodiment, the strips that are connected to the ground layer through the switches are disposed in the vicinity of the signal line, and the signal line and the ground layer are made to become pseudo close to or away from each other by switching the connection and non-connection of the switches. Thereby, the effective permittivity that corresponds to the propagation speed of the traveling wave propagated along the signal line changes. As a result, the frequency of the standing wave that is generated in the signal line can be changed, and the oscillation frequency of the oscillator can be flexibly adjusted over a wide band. Since the plural capacitative elements are not needed to adjust the oscillation frequency, the parasitic capacitance can be prevented from being generated, and a clock signal having an oscillation frequency of a sufficiently high frequency band can be output.

In the first embodiment, the plural strips132are arranged along the signal line131at an equivalent interval, but the arrangement of the strips132is not limited thereto. For example, as illustrated inFIG. 10, intervals between the plural strips132may not be equal.FIG. 10illustrates the configuration where plural strips132are disposed to be closer to a node of the standing wave generated in the signal line131than an antinode thereof. That is, in the sequence close to the node of the standing wave, intervals ss1, ss2, ss3, and ss4between the strips132satisfy a relationship of the following Equation (4).
ss1<ss2<ss3<ss4  (4)

In this way, generation of the parasitic capacitance in the antinode of the standing wave and generation of the energy loss due to the generation of the parasitic capacitance can be decreased, and the frequency f of the standing wave can be efficiently adjusted. Similarly, since the antinode of the standing wave is formed even in the terminating end of the signal line131that is connected to the buffer unit150, the strips132may not be disposed in the vicinity of the terminating end of the signal line131.

[b] Second Embodiment

In a second embodiment, semiconductor strips that have the functions of the strips and the switches in the first embodiment are disposed in the vicinity of the signal line, the effective permittivity of the signal line is changed, and the oscillation frequency is flexibly adjusted.

Since the configuration of the oscillator according to the second embodiment is almost the same as the configuration (refer toFIG. 1A) of the oscillator according to the first embodiment, the description is not repeated here. In the second embodiment, the configuration of the transmission line unit130is different from the configuration of the transmission line unit in the first embodiment.

Configuration of the Transmission Line Unit

FIG. 11is a perspective view illustrating the configuration of the transmission line unit130according to the second embodiment. InFIG. 11, the same components as those ofFIG. 2are denoted by the same reference numerals and the description thereof is not repeated here. As illustrated inFIG. 11, the transmission line unit130is configured by interposing the dielectric layer134between the signal line131and the ground layer135, and semiconductor strips201-1to201-nare provided in the dielectric layer134.

The semiconductor strips201-1to201-nare composed of semiconductors, such as MOSFETs, and are arranged along the signal line131such that the semiconductor strips do not contact the signal line131. Specifically, a drain of each of the semiconductor strips201-1to201-nfaces the signal line131and a gate thereof is connected to the switch controller140. Although not illustrated inFIG. 11, a source of each of the semiconductor strips201-1to201-nis connected to the ground layer135. Accordingly, if a gate voltage is applied from the switch controller140to the gate of each of the semiconductor strips201-1to201-n, the potential of the drain that faces the signal line131becomes the ground potential. As such, it can be assumed that the semiconductor strips201-1to201-nin the second embodiment are electrodes where the strips132-1to132-nand the switches133-1to133-nin the first embodiment are integrated with each other.

FIG. 12is a schematic plan view illustrating the configuration of the transmission line unit130according to the second embodiment. As illustrated inFIG. 12, the transmission line unit130has the signal line131and the semiconductor strips201-1to201-n. Each of the semiconductor strips201-1to201-nhas a gate201a, a source201b, and a drain201c. The drain201cof each of the semiconductor strips201-1to201-nfaces the signal line131and the source201bthereof is connected to the ground layer135. The gate201ais connected to the switch controller140and is applied with the gate voltage, if necessary. The configuration of the semiconductor strip201-1when viewed from an X direction ofFIG. 12will be described in detail below with reference toFIG. 14.

In the second embodiment, since the source201bof each of the semiconductor strips201-1to201-nis connected to the ground layer135, the gate voltage is applied to the gate201aand the source201band the drain201cbecome a conductive state, and the potential of the drain201cbecomes the ground potential. Since the drain201cfaces the signal line131, if the potential of the drain201cbecomes the ground potential, the distance between the signal line131and the ground layer135can be pseudo shortened. If the signal line131becomes close to the ground layer135, it can be assumed that the effective permittivity Er in the transmission line unit130increases. As a result, the frequency f of the standing wave that is generated in the signal line131decreases. Accordingly, if the gate voltage is applied and the number of semiconductor strips201-1to201-nbecoming a conductive state is increased or decreased, the frequency f of the standing wave can be adjusted and the oscillation frequency of the oscillator can be adjusted.

FIG. 13is a schematic lateral view illustrating the configuration of the transmission line unit130according to the second embodiment. InFIG. 13, the same components as those ofFIG. 5are denoted by the same reference numerals and the description thereof is not repeated here. As illustrated inFIG. 13, the transmission line unit130has the same layered structure as that ofFIG. 5, and the SiO2layer134aincludes the gate201aof a semiconductor strip201. The gate201ais connected to the switch controller140.

The silicon layer134bis a semiconductor layer that includes the source201band the drain201cof the semiconductor strip201. Although not illustrated inFIG. 13, the source201bof the semiconductor strip201is connected to the ground layer135. The drain201cthat becomes a conductive state with the source201bby applying the gate voltage to the gate201afaces the signal line131. As such, if the strips that are disposed in the vicinity of the signal line131are composed of the semiconductor strips201, the effective permittivity Er can be changed even though the conductor strips are not disposed in the vicinity of the signal line131, and the parasitic capacitance can be prevented from increasing due to the arrangement of the conductors in the vicinity of the signal line131.

FIG. 14illustrates an example of the configuration of the semiconductor strip201-1when viewed from the X direction ofFIG. 12. As illustrated above, the gate201ais connected to the switch controller140. If the gate voltage is applied from the switch controller140to the gate201a, the gate201acauses the source201band the drain201cto become a conductive state. That is, if the gate voltage is applied to the gate201a, the gate201acauses the potential of the drain201cto be matched with the potential of the source201b.

The source201bis connected to the ground layer135. If the gate voltage is applied to the gate201a, the source201btransmits the ground potential to the drain201c. The drain201cextends long in a direction away from the source201b, and an extended portion faces the signal line131. When the gate voltage is applied to the gate201a, the potential of the drain201cbecomes the ground potential. In the second embodiment, since the drain201cis formed to extend longer than the source201b, the gate201aand the source201bcan be provided at positions away from the signal line131, while the signal line131and the drain201care made to face each other. Thereby, the transmission line unit130that includes the signal line131and the semiconductor strip201can be easily manufactured. However, if the drain201cfaces the signal line131, the drain201cdoes not need to be formed in a shape different from a shape of the source201b.

In the semiconductor strip201that is configured in the above way, if the gate voltage is applied from the switch controller140to the gate201a, the source201band the drain201cbecome a conductive state and the potential of the drain201cbecomes the ground potential. That is, if the semiconductor strip201becomes a conductive state by the control from the switch controller140, the potential of each of the ground layer135, the source201b, and the drain201cbecomes the ground potential, and the distance between the signal line131and the ground layer135becomes pseudo shortened. Thereby, the effective permittivity Er in the transmission line unit130changes and the frequency f of the standing wave that is generated in the transmission line unit130is adjusted.

Operation of the Oscillator

Next, the operation of the oscillator having the transmission line unit130configured in the above way will be described. If the direct-current voltage Vdc is applied from the power supply to the starting end of the signal line131, the standing wave having the frequency f according to the capacitance of the variable capacitative element120and the effective permittivity Er in the transmission line unit130is generated in the signal line131. At this time, the effective permittivity Er in the transmission line unit130is adjusted by switching the conduction and non-conduction of the semiconductor strips201-1to201-nby the switch controller140.

Specifically, the potential of the drain201cof each of the semiconductor strips201-1to201-nthat become a conductive state by the switch controller140becomes the ground potential. If the number of semiconductor strips201-1to201-nbecoming a conductive state increases, the signal line131and the ground layer135become pseudo close to each other. As a result, the propagation speed of the traveling wave that is propagated along the signal line131by application of the direct-current voltage Vdc decreases, it can be assumed that the effective permittivity Er increases, and the frequency f of the standing wave decreases.

In contrast, if the number of semiconductor strips201-1to201-nbecoming a conductive state decreases, the signal line131and the ground layer135become pseudo far away from each other. As a result, the propagation speed of the traveling wave that is propagated along the signal line131by application of the direct-current voltage Vdc increases, it can be assumed that the effective permittivity Er decreases, and the frequency f of the standing wave increases.

In the second embodiment, switching of the conduction and non-conduction of the semiconductor strips201-1to201-ncan be performed in the same sequence as switching of the connection and non-connection of the switches133-1to133-nin the first embodiment. That is, in the sequence where the arrangement of the semiconductor strips in a conductive state is equalized, the switch controller140applies the gate voltage to the gate201aof the semiconductor strips201-1to201-n. At this time, the switch controller140applies the gate voltage preferentially to the gate201aof each of the semiconductor strips close to the node of the standing wave.

The capacitance of the variable capacitative element120is adjusted by a control voltage applied from the voltage controller110to the variable capacitative element120. In the second embodiment, however, the variable range of the capacitance of the variable capacitative element120is narrow, and only minute adjustment of the frequency f of the standing wave is performed by minutely changing the phase shift amount ΔΦ. As such, even though the variable range of the capacitance of the variable capacitative element120is narrow, since the variable range of the effective permittivity Er in the transmission line unit130is wide in the second embodiment, a control range of the frequency f can be widened.

As described above, since the waveform of the standing wave where the frequency f is adjusted has an antinode at the terminating end of the signal line131connected to the buffer unit150, a clock signal that corresponds to the frequency f of the standing wave is output to the output terminal155by the buffer unit150.

As such, according to the second embodiment, the semiconductor strips where the sources are connected to the ground layer are disposed such that the drains face the signal line, and the signal line and the ground layer are made to become pseudo close to or away from each other by switching the conduction and non-conduction of the semiconductor strips. Thereby, the effective permittivity that corresponds to the propagation speed of the traveling wave propagated along the signal line changes. As a result, the frequency of the standing wave that is generated in the signal line can be changed, and the oscillation frequency of the oscillator can be flexibly adjusted over a wide band. Since a lot of capacitative elements are not needed to adjust the oscillation frequency, the parasitic capacitance can be prevented from being generated, and a clock signal having an oscillation frequency of a sufficiently high frequency band can be output. Since the strips disposed in the vicinity of the signal line are not the conductors but the semiconductors, the parasitic capacitance can be prevented from increasing due to the arrangement of the conductors.

In a third embodiment, in an oscillator that has two signal lines connected by a clamp circuit, the strips are disposed in the vicinity of each of the signal lines and a sufficiently high oscillation frequency can be flexibly adjusted over a wide band.

Configuration of the Oscillator

FIG. 15illustrates the configuration of the oscillator according to the third embodiment. The oscillator illustrated inFIG. 15has a voltage controller310, a variable capacitative element320, transmission line units330and340, a clamp unit350, a switch controller360, buffer units370and380, and output terminals375and385.

The voltage controller310controls a voltage that is applied to the variable capacitative element320and changes the capacitance of the variable capacitative element320.

The variable capacitative element320is an element of which the capacitance changes according to the control voltage applied from the voltage controller310. As the variable capacitative element320, for example, a capacitor is used. A phase of the standing wave at the terminating ends of the transmission line units330and340is shifted according to the capacitance of the variable capacitative element320. Accordingly, if the capacitance of the variable capacitative element320increases or decreases, the phase shift amount at the terminating ends of signal lines331and341of the transmission line units330and340changes and the frequency of the standing wave changes. However, if the capacitance of the variable capacitative element320greatly increases or decreases, the phase shift amount at the terminating ends of the signal lines331and341excessively increases and the oscillation is not generated at the terminating ends of the signal lines331and341. Accordingly, the capacitance of the variable capacitative element320cannot be greatly increased or decreased, and the frequency of the standing wave cannot be flexibly adjusted by only adjusting the control voltage by the voltage controller310.

The transmission line units330and340include the signal lines331and341that are connected to a constant current source Is and the ground layer, respectively. In the transmission line units330and340, a dielectric layer that includes a mixture medium of SiO2and silicon is interposed between the signal lines331and341and the ground layer. When a power supply voltage is applied from the constant current source Is, the transmission line units330and340propagate a traveling wave and generate a standing wave. That is, each of the transmission line units330and340has almost the same configuration as that of the transmission line unit130according to the first embodiment.

The transmission line units330and340generate standing waves where phases are inverted. Each of the transmission line units330and340increases or decreases the effective permittivity and changes the frequency of the standing wave over a wide range. Specifically, a frequency f of the standing wave is represented by Equation (1) in the first embodiment, using the light velocity c, the lengths L of the signal lines331and341, the phase shift amounts ΔΦ at the terminating ends of the signal lines331and341, and the effective permittivity Er.

As described above, in the third embodiment, the phase shift amounts ΔΦ at the terminating ends of the signal lines331and341cannot be increased by greatly increasing or decreasing the capacitance of the variable capacitative element320. For this reason, the frequency f of the standing wave is adjusted by changing the effective permittivity Er of the transmission line units330and340. Specifically, the transmission line unit330has the signal line331, strips332-1to332-n, and switches333-1to333-n. The transmission line unit340has the signal line341, strips342-1to342-n, and switches343-1to343-n.

The signal lines331and341are transmission paths of which starting ends are connected to the constant current source Is and terminating ends are connected to the variable capacitative element320and the buffer units370and380. The lengths of the signal lines331and341from the starting ends to the terminating ends are ¾ of the wavelength of the traveling wave used in oscillation. For this reason, if the power supply voltage is applied from the constant current source Is to the signal lines331and341, the signal lines331and341generate standing waves having the ¾ wavelength where the starting ends connected to the constant current source Is are used as nodes and the terminating ends are used as antinodes. However, the phases of the standing waves at the terminating ends of the signal lines331and341are shifted by the phase shift amount ΔΦ by the capacitance of the variable capacitative element320. The frequency f of the standing wave that is generated by the signal lines331and341is inversely proportional to a square root of the effective permittivity Er in the transmission line units330and340, as illustrated in Equation (1). Accordingly, if the effective permittivity Er increases, the frequency f of the standing wave decreases, and if the effective permittivity Er decreases, the frequency f of the standing wave increases.

Each of the strips332-1to332-nand342-1to342-nis composed of an elongated plate-shaped electrode that is formed of a conductor, such as a metal, and are arranged along the signal lines331and341such that the strips do not contact the signal lines331and341. The strips332-1to332-nand342-1to342-nare connected to the ground layer through the switches333-1to333-nand343-1to343-n, respectively. Accordingly, if the switches333-1to333-nand343-1to343-nconnect the strips332-1to332-nand342-1to342-nand the ground layer, the potential of the strips332-1to332-nand342-1to342-nthat are disposed in the vicinity of the signal lines331and341becomes the ground potential.

The switches333-1to333-nand343-1to343-nswitch connection and non-connection of the strips332-1to332-nand342-1to342-nand the ground layer, respectively, under the control from the switch controller360. As the switches333-1to333-nand343-1to343-n, for example, MOSFETs are used. If the switches333-1to333-nand343-1to343-nconnect the strips332-1to332-nand342-1to342-nand the ground layer, the signal lines331and341become pseudo close to the ground. That is, if the connection and the non-connection of the switches333-1to333-nand343-1to343-nare switched, the distance between the signal lines331and341and the ground layer is pseudo adjusted. The effective permittivity Er in the transmission line units330and340can be changed.

Specifically, if the number of connected switches333-1to333-nand343-1to343-nincreases, it can be assumed that the signal lines331and341and the ground layer become close to each other. Since the propagation speed of the traveling wave becomes slow, it can be assumed that the effective permittivity Er increases. If the number of connected switches333-1to333-nand343-1to343-ndecreases, it can be assumed that the signal lines331and341and the ground layer become away from each other. Since the propagation speed of the traveling wave becomes fast, it can be assumed that the effective permittivity Er decreases. Therefore, as illustrated in Equation (4), the frequency of the standing wave changes inversely proportional to the square root of the effective permittivity Er. That is, the frequency of the standing wave can be adjusted by switching the connection and non-connection of the switches333-1to333-nand343-1to343-n.

The clamp unit350is connected to a position of the ¼ wavelength from the starting ends of the signal lines331and341and associates the amplitudes of the standing waves generated in the signal lines331and341with each other. That is, the clamp unit350causes the amplitude of the standing wave generated in the signal line331and the amplitude of the standing wave generated in the signal line341to become the amplitudes having the same magnitude to be inverted to each other. Accordingly, if the amplitude at the position of the signal line331where the clamp unit350is connected is positive, the clamp unit350causes the amplitude at the position of the signal line341where the clamp unit350is connected to be negative and causes the magnitudes of the two amplitudes to be equal to each other.

The switch controller360controls switching of the connection and non-connection of each of the switches333-1to333-nand343-1to343-n. Specifically, the switch controller360simultaneously switches the switches333-1to333-nand343-1to343-ncorresponding to each other from a connection state to a non-connection state or from the non-connection state to the connection state. When the oscillation frequency of the oscillator is increased, the switch controller360decreases the number of connected switches333-1to333-nand343-1to343-n. When the oscillation frequency of the oscillator is decreased, the switch controller360increases the number of connected switches333-1to333-nand343-1to343-n.

Each of the buffer units370and380has a buffering circuit, and excludes an influence from the side of the output terminals375and385with respect to the circuit such as the variable capacitative element320and the transmission line units330and340and stably operates the circuit including the variable capacitative element320and the transmission line units330and340. That is, the buffer units370and380have the same configuration as that of the buffer unit150in the first embodiment, and output the clock signals corresponding to the frequency f of the standing wave to the output terminals375and385, respectively. However, the outputs from the buffer units370and380are inverted to each other.

FIGS. 16A and 16Billustrate the configuration of two clamp units350of NMOS and CMOS types, as configuration examples of the clamp unit350according to the third embodiment.

The clamp unit350of the NMOS type is configured by combining NMOS inverters. Specifically, the clamp unit350of the NMOS type includes two MOSFETs351and352that are connected symmetrical to each other. That is, a source of the MOSFET352is connected to a gate of the MOSFET351and a source of the MOSFET351is connected to a gate of the MOSFET352. In addition, drains of the two MOSFETs351and352are connected to a ground.

Meanwhile, the clamp unit350of the CMOS type is configured by combining CMOS inverters. Specifically, the clamp unit350of the CMOS type includes two MOSFETs353and354in addition to the two MOSFETs351and352. That is, a source of the MOSFET354is inversely connected to a gate of the MOSFET353and a source of the MOSFET353is inversely connected to a gate of the MOSFET354. In addition, drains of the two MOSFETs353and354are connected to a power supply.

If the clamp unit350is configured using the MOSFETs351to354, two voltages V1and V2that are input to the clamp unit350are clamped to the same voltage. Accordingly, if the clamp unit350is connected to the signal lines331and341, the amplitudes of the standing waves that are generated in the signal lines331and341can be adjusted to have the same magnitude.

Operation of the Oscillator

Next, the operation of the oscillator that is configured in the above way will be described. If the power supply voltage is applied from the constant current source Is to the signal lines331and341, the standing wave having the frequency f according to the phase shift amount ΔΦ and the effective permittivity Er is generated in the signal lines331and341. At this time, the phase shift amount ΔΦ is determined according to the capacitance of the variable capacitative element320and controlled by the voltage controller310. The effective permittivity Er is adjusted by switching the connection and non-connection of the switches333-1to333-nand343-1to343-nby the switch controller360.

Specifically, the potential of the strips332-1to332-nthat correspond to the switches333-1to333-nbecoming a connection state by the switch controller360in the transmission line unit330becomes the ground potential. For this reason, if the number of connected switches333-1to333-nincreases, the signal line331and the ground layer become pseudo close to each other. As a result, the propagation speed of the traveling wave that is propagated along the signal line331by application of the power supply voltage decreases, and it can be assumed that the effective permittivity Er increases. As the effective permittivity Er increases, the frequency f of the standing wave decreases.

Meanwhile, in the transmission line unit340, the switches343-1to343-nthat are symmetrical to the connected switches333-1to333-nbecome a connection state by the switch controller360, and the potential of the corresponding strips342-1to342-nbecomes the ground potential. If the number of connected switches343-1to343-nincreases, the signal line341and the ground layer become pseudo close to each other. As a result, the propagation speed of the traveling wave that is propagated along the signal line341by application of the voltage decreases, and it can be assumed that the effective permittivity Er increases. As the effective permittivity Er increases, the frequency f of the standing wave decreases. However, since the signal line341is connected to the signal line331through the clamp unit350, if the standing wave generated in the signal line341is compared with the standing wave generated in the signal line331, the magnitudes of the amplitudes are the same, but phases are inverted.

In contrast, if the number of connected switches333-1to333-nand343-1to343-ndecreases, the signal lines331and341and the ground layer become pseudo far away from each other. As a result, the propagation speed of the traveling wave that is propagated along the signal lines331and341by application of the power supply voltage increases, and it can be assumed that the effective permittivity Er decreases. As the effective permittivity Er decreases, the frequency f of the standing waves that are generated in the signal lines331and341increases.

Switching of the connection and non-connection of the switches333-1to333-nand343-1to343-ncan be performed in the same sequence as that of the first embodiment. That is, in the sequence where the arrangement of the connected switches is equalized, the switch controller360switches the switches333-1to333-nand343-1to343-n. At this time, the switch controller360causes the switches corresponding to the strips close to the node of the standing wave to become preferentially a connection state.

The capacitance of the variable capacitative element320is adjusted by a control voltage applied from the voltage controller310to the variable capacitative element320. In the third embodiment, however, as described above, since the phase shift amount ΔΦ cannot be greatly increased or decreased, the variable range of the capacitance of the variable capacitative element320is narrow. As such, even when the variable range of the capacitance of the variable capacitative element320is narrow and the phase shift amount ΔΦ is not greatly increased or decreased, in the third embodiment, the variable range of the effective permittivity Er is wide. Therefore, the control range of the frequency f can be widened.

As described above, since the waveform of the standing wave where the frequency f is adjusted has antinodes at the terminating ends of the signal lines331and341, a clock signal that corresponds to the frequency f of the standing wave is output to the output terminals375and385by the buffer units370and380.

Specific Example of Adjustment of an Oscillation Frequency

FIG. 17illustrates a specific example of an oscillation frequency of the oscillator according to the third embodiment. In this case, it is assumed that the transmission line units330and340include eleven switches333-1to333-11and343-1to343-11, respectively.

As illustrated inFIG. 17, in the transmission line units330and340, when all of the switches are in a non-connection state, the delay of the traveling wave that is propagated along the signal lines331and341is 8.9 ps. Since the switches are not connected, the effective permittivity Er does not change. Accordingly, even though the frequency band is at both 25 GHz and 40 GHz, the frequency f of the standing wave does not change.

In contrast, when the five switches among the eleven switches are in a connection state, the propagation speed of the traveling wave that is propagated along the signal lines331and341decreases and the delay becomes 9.3 ps. From this, it can be assumed that the effective permittivity Er increases by 7%. As a result, at the frequency band of 25 GHz, the frequency f decreases by 1.8 GHz. At the frequency band of 40 GHz, the frequency f decreases by 2.8 GHz.

When all of the switches are in a connection state, the delay of the traveling wave becomes 9.6 ps, and it can be assumed that the effective permittivity Er increases by 14%. As a result, at the frequency band of 25 GHz, the frequency f decreases by 3.6 GHz. At the frequency band of 40 GHz, the frequency f decreases by 5.7 GHz.

Accordingly, if the oscillation frequency of when the number of connected switches is five is set as the central frequency, by switching the connection and non-connection of the switches, the oscillation frequency can be increased or decreased by about 1.8 GHz at the frequency band of 25 GHz and can be increased or decreased by about 2.8 GHz at the frequency band of 40 GHz. That is, the oscillation frequency of the sufficiently high frequency band can be flexibly adjusted over a wide band.

As such, according to the third embodiment, in the oscillator where the clock signal having the oscillation frequency of the high frequency band can be output using the two signal lines, the strips that are connected to the ground layer through the switches are disposed in the vicinity of each of the signal lines. By switching the connection and non-connection of the switches, the signal lines and the ground layer are made to become pseudo close to or away from each other. Thereby, the effective permittivity that corresponds to the propagation speed of the traveling wave propagated along the signal lines changes. As a result, the frequency of the standing wave that is generated in the signal lines can be changed, and the oscillation frequency of the high frequency band can be flexibly adjusted over a wide band.

In the third embodiment, the two transmission line units330and340having the same configuration are provided. However, portions that are common to the transmission line units330and340may be integrated and the size of the oscillator may be decreased. Specifically, a modification of the oscillator according to the third embodiment is illustrated inFIG. 18. InFIG. 18, the same components as those ofFIG. 15are denoted by the same reference numerals.

In an oscillator illustrated inFIG. 18, facing strips391-1to391-nare provided over both the signal lines331and341. The strips391-1to391-nare connected to the ground layer through switches392-1to392-n, respectively. Accordingly, if the switches392-1to392-nconnect the strips391-1to391-nand the ground layer, the potential of the strips391-1to391-nthat are disposed in the vicinity of the signal lines331and341becomes the ground potential.

The switches392-1to392-nswitch the connection and non-connection of the strips391-1to391-nand the ground layer, under the control of the switch controller360. As the switches392-1to392-n, for example, MOSFETs are used. If the switches392-1to392-nconnect the strips391-1to391-nand the ground layer, the signal lines331and341become pseudo close to the ground. That is, if the connection and the non-connection of the switches392-1to392-nare switched, the distance between the signal lines331and341and the ground layer is pseudo adjusted. The effective permittivity Er in the transmission line units that include the signal lines331and341can be changed.

FIG. 19is a perspective view illustrating the configuration of the transmission line unit in the oscillator illustrated inFIG. 18. As illustrated inFIG. 19, the transmission line unit is configured by interposing a dielectric layer393between the signal lines331and341and a ground layer394, and the strips391-1to391-nand the switches392-1to392-n(not illustrated) are provided in the dielectric layer393. The dielectric layer393is mainly formed of a mixture medium of SiO2and silicon, and has the configuration where the strips391-1to391-nand the switches392-1to392-nare fixed in the mixture medium. The dielectric layer393functions as one dielectric body as a whole. The ground layer394is connected to a ground and the potential thereof is always maintained at the ground potential.

The strips391-1to391-nface over both the signal lines331and341and are disposed at an equivalent interval. InFIG. 19, it is assumed that one end of each of the signal lines331and341at the lower left of the figure is a starting end connected to the constant current source Is and the other end of each of the signal lines331and341at the upper right of the figure is a terminating end connected to the buffer units370and380. That is, it is assumed that a propagation direction of the traveling wave of the signal lines331and341is a direction toward the strip391-nfrom the strip391-1. The strips391-1to391-nare connected to the switches392-1to392-n(not illustrated), respectively.

As such, in the transmission line unit illustrated inFIG. 19, the strips and the switches are not provided with respect to each of the signal lines331and341, but the strips391-1to391-nand the switches392-1to392-nthat are common to the signal lines are provided. For this reason, the size of the transmission line unit can be decreased and the size of the oscillator can be decreased.

For example, as illustrated inFIG. 20, the clamp unit350may be provided to be closer to the buffer units370and380than the terminating ends of signal lines331aand341a. In this case, the length of each of the signal lines331aand341afrom the starting end to the terminating end can be set to ¼ of the wavelength of the traveling wave used in oscillation, and the size of the oscillator can be decreased. That is, the lengths of the signal lines331and341illustrated inFIG. 18are set to ¾ of the wavelength of the traveling wave. However, the lengths of the signal lines331aand341aillustrated inFIG. 20are set to ¼ of the wavelength of the traveling wave, which results in decreasing the size of the entire oscillator. By shortening the signal lines331aand341a, the clamp unit350associates the amplitudes at two points on extended lines of the signal lines331aand341awith each other. Thereby, the oscillation frequency of the high frequency band can be flexibly adjusted over a wide band and the size of the oscillator can be decreased.

In a fourth embodiment, in an oscillator that has a signal line of which both ends become antinodes of a standing wave and an auxiliary signal line having an arc shape, the strips are disposed in the vicinity of the signal lines and an oscillation frequency of the oscillator having a small size is flexibly adjusted over a wide band.

Configuration of the Oscillator

FIG. 21illustrates the configuration of the oscillator according to the fourth embodiment. The oscillator illustrated inFIG. 21has transmission line units410and420, buffer units430and440, and output terminals435and445.

The transmission line unit410includes a signal line411that is connected to the constant current source and a ground layer. In the transmission line unit410, a dielectric layer that includes a mixture medium of SiO2and silicon is interposed between the signal line411and the ground layer. When a power supply voltage is applied from the constant current source, the transmission line unit410propagates a traveling wave and generates a standing wave that has the half wavelength. That is, the transmission line unit410generates a standing wave where both ends of the signal line411become antinodes. Specifically, the transmission line unit410has the signal line411and strips412-1to412-n.

Both ends of the signal line411are connected to the buffer units430and440, respectively, and a central portion thereof is connected to the constant current source. The length of the signal line411is ½ of the wavelength of the traveling wave used in oscillation. Accordingly, the lengths from a connection portion of the signal line411with the constant current source to both ends are equal to the ¼ wavelength. For this reason, if the power supply voltage is applied from the constant current source, the signal line411generates a standing wave having the ½ wavelength where the central portion connected to the constant current source is used as a node and both ends are set as the antinodes.

The strips412-1to412-nare connected to the ground layer through switches (not illustrated), respectively, and are arranged along the signal line411such that the strips do not contact the signal line411. Accordingly, if the switches (not illustrated) connect the strips412-1to412-nand the ground layer, the potential of the strips412-1to412-nthat are disposed in the vicinity of the signal line411becomes the ground potential.

As such, the configuration of the transmission line unit410according to the fourth embodiment is the same as that of the transmission line unit130according to the first embodiment, except that the power supply is connected to the central portion of the signal line411and the power supply voltage is applied, and the length of the signal line411is the ½ wavelength.

The transmission line unit420is an auxiliary transmission line unit that is provided to remove an extra frequency component generated in the transmission line unit410. Specifically, the transmission line unit420has a signal line421and strips422-1to422-n.

The signal line421is curved in an arc shape and a central portion thereof is connected to a ground. The length of the signal line421is ½ of the wavelength of the traveling wave, similar to the signal line411. The signal line421is disposed such that the signal lines411and421form a line-symmetric shape with respect to a central line connecting the central portion of the signal line411and the central portion of the signal line421. That is, the central portion of the signal line411and the central portion of the signal line421face each other.

The strips422-1to422-nare connected to the ground through switches (not illustrated), respectively, and are arranged along the signal line421such that the strips do not contact the signal line421. Accordingly, if the switches (not illustrated) connect the strips422-1to422-nand the ground, the potential of the strips422-1to422-nthat are disposed in the vicinity of the signal line421becomes the ground potential.

Each of the buffer units430and440has a buffering circuit, and excludes an influence from the side of the output terminals435and445with respect to the circuit such as the transmission line units410and420and stably operates the circuit including the transmission line units410and420. That is, the buffer units430and440have the same configuration as that of the buffer unit150in the first embodiment, and output the clock signals corresponding to the frequency of the standing wave to the output terminals435and445, respectively. However, the outputs from the buffer units430and440are inverted to each other.

FIG. 22illustrates the configuration of the transmission line unit420according to the fourth embodiment. As illustrated inFIG. 22, the signal line421is formed to be curved, such that the length from both ends to the central portion is ¼ of the wavelength of the traveling wave and the distance between both ends is ¼ of the wavelength of the traveling wave. As described above, since the length of the signal line411is also ½ of the wavelength of the traveling wave, the length of the signal line is short as compared with the oscillator in the first embodiment. As a result, the sizes of the transmission line units410and420can be decreased and a mounting area of the oscillator can be decreased.

Operation of the Oscillator

Next, the operation of the oscillator that has the above configuration will be described. If the power supply voltage is applied from the constant current source to the central portion of the signal line411, a standing wave having the ½ wavelength is generated in the signal line411. At this time, since the signal line421is disposed in the vicinity of the signal line411, extra frequency components, such as second harmonics or third harmonics, which are generated in the signal line411, are removed. The effective permittivity in the transmission line unit410is adjusted by selectively adjusting the potential of the strips412-1to412-nto the ground potential. That is, the strips412-1to412-nare connected to the switches (not illustrated). If the switches become a connection state, the potential of the corresponding strips412-1to412-nbecomes the ground potential.

If the number of connected switches increases, the signal line411and the ground layer become pseudo close to each other, and it can be assumed that the effective permittivity increases. As a result, the frequency of the standing wave that is generated in the signal line411decreases. In contrast, if the number of connected switches decreases, the signal line411and the ground layer become pseudo far away from each other, and it can be assumed that the effective permittivity decreases. As a result, the frequency of the standing wave that is generated in the signal line411increases.

When the switches are switched and the potential of the strips412-1to412-nis adjusted to the ground potential, the switches (not illustrated) are switched even in the transmission line unit420, and the potential of the corresponding strips422-1to422-nalso becomes the ground potential.

As such, the waveform of the standing wave where the frequency is adjusted has the antinodes at both ends of the signal line411. Therefore, the clock signal having the frequency of the standing wave is output to the output terminals435and445by the buffer units430and440.

As such, according to the fourth embodiment, in the small oscillator using the signal line that has the length corresponding to ½ of the wavelength, the strips that are connected to the ground layer through the switches are disposed in the vicinity of the signal lines. If the connection and non-connection of the switches are switched, the signal lines and the ground layer are made to become pseudo close to or away from each other. Thereby, the effective permittivity that corresponds to the propagation speed of the traveling wave propagated along the signal lines changes. As a result, the frequency of the standing wave that is generated in the signal lines can be changed, and the oscillation frequency of the small oscillator can be flexibly adjusted over a wide band.

In the fourth embodiment, the transmission line units410and420are separately provided. However, similar to the modification of the third embodiment, portions that are common to the transmission line units410and420may be integrated and the size of the oscillator may be decreased. That is, the strips412-1to412-nof the transmission line unit410and the strips422-1to422-nof the transmission line unit420that correspond to each other may be integrated, and the integrated strips may be connected to the ground layer through the switches.

In the second to fourth embodiments, the interval between the plural strips or the plural semiconductor strips is not described, but the strips or the semiconductor strips may be disposed in an arbitrary type. That is, in the second to fourth embodiments, similar to the first embodiment, the plural strips or the plural semiconductor strips may be disposed at an equivalent interval. The plural strips or the plural semiconductor strips may be disposed to be closer to the nodes of the standing wave than the antinodes of the standing wave.

The length of the signal line is set to ¾ of the wavelength of the traveling wave in the first to third embodiments, and the length of the signal line is set to ½ of the wavelength of the traveling wave in the fourth embodiment. Theses lengths are set to form the antinodes of the standing wave in the ends of the signal lines and oscillate the ends of the signal lines. Accordingly, if the antinodes of the standing wave are formed in the ends of the signal lines, the lengths of the signal lines are not limited to the above lengths. Specifically, if the length from the position of the signal line where the power supply voltage is applied to the oscillating end is odd number times as long as the ¼ wavelength, the antinodes of the standing wave are formed in the ends of the signal lines, and the oscillator can output the clock signal having the oscillation frequency.

The oscillators according to the first to fourth embodiments can be used in a phase locked loop (PLL) circuit to match an output frequency with a predetermined reference frequency and synchronize phases.FIG. 23is a block diagram illustrating the configuration of the PLL circuit. The PLL circuit illustrated inFIG. 23has a phase comparator10, a low-pass filter20, a voltage controlled oscillator (VCO)30, and a divider40.

The phase comparator10compares the reference frequency and a frequency output from the divider40and outputs a voltage signal corresponding to a phase difference to the low-pass filter20. The low-pass filter20removes an alternating-current component of the voltage signal and outputs a direct-current component of the voltage signal to the VCO30.

The VCO30includes an oscillator that adjusts an oscillation frequency according to an applied voltage, and outputs a signal having an output frequency according to a direct-current component of the voltage signal that is output from the low-pass filter20. That is, the VCO30includes the oscillator according to the first to fourth embodiments. The VCO30switches connection and non-connection of the switches according to the direct-current component of the voltage signal output from the low-pass filter20or switches conduction and non-conduction of the semiconductor strips, and flexibly adjusts an output frequency. Thereby, a signal having an output frequency according to the direct-current component of the voltage signal is reliably output from the VCO30.

The divider40divides the output frequency from the VCO30and feeds a division result back to the phase comparator10.

As such, if the oscillator according to the first to fourth embodiment is used in the PLL circuit, the oscillation frequency can be flexibly adjusted in the VCO30. Accordingly, the PLL circuit can output a signal having an output frequency that is accurately matched with the reference frequency.

According to one aspect of the oscillator and the phase synchronizing circuit disclosed herein, an oscillation frequency can be flexibly adjusted over a wide band, at a sufficiently high frequency band.

In a fifth embodiment (FIG. 24), an oscillator that has a pair of signal lines connected by a clamp circuit, the strips are disposed in the vicinity of each of the signal lines and a sufficiently high oscillation frequency can be flexibly adjusted over a wide band.

Configuration of the Oscillator

FIG. 24illustrates the configuration of the oscillator according to the fifth embodiment. The oscillator illustrated inFIG. 24has a voltage controller310, a variable capacitative element320, transmission line units505gand505h, electrodes (505d-1,505d-2, . . . ,505d-n), a bias voltage generation circuit504, a clamp unit350, switches333-1to333-nand343-1to343-n, a switch controller360, buffer units370and380, and output terminals375and385.

The voltage controller310, the variable capacitative element320, the clamp unit350, the switch controller360, the buffer units370and380, and the output terminals375and385of the fifth embodiment are implemented on an on-chip circuit501on semiconductor.

The transmission line units502and503are on an off-chip circuit505implemented on thin-film material or ferro-electric material.

The configuration of the voltage controller310is almost the same as the configuration (refer toFIGS. 16A,16B) of the oscillator according to the third embodiment, the description is not repeated here.

The configuration of the variable capacitative element320is almost the same as the configuration of the variable capacitative according to the third embodiment, the description is not repeated here.

The bias voltage generation circuit504generates the bias voltage potentials, Vbias, which are connected to switches.

The transmission line units502and503include the signal lines505gand505hthat are connected to a constant current source Is and the ground layer, respectively. The transmission line units502and503are embedded inside a thin film layer that includes a mixture medium of thin film material and coating material which is of dielectric constant equal to or higher than 3. When a power supply voltage is applied from the constant current source Is, the transmission line units502and503propagate a traveling wave and generate a standing wave. That is, each of the transmission line units505gand505hhas almost the same configuration as that of the transmission line units330and340according to the third embodiment.

The transmission line units505gand505hgenerate standing waves where phases are inverted. Each of the electrodes (505d-1,505d-2, . . . ,505d-n) and (505i-1,505i-2, . . . ,505i-n) increases or decreases the effective permittivity and changes the frequency of the standing wave over a wide range. The value of the frequency f of the standing wave is almost the same as represented by Equation (1) in the first embodiment, and the description is not repeated here.

As described above, in the fifth embodiment, the phase shift amounts ΔΦ at the terminating ends of the signal lines331and341cannot be increased by greatly increasing or decreasing the capacitance of the variable capacitative element320. For this reason, the frequency f of the standing wave is adjusted by changing the effective permittivity Er of the transmission line units502and503. Specifically, the transmission line unit502has the signal line505h, strips505d-1to505d-n, and switches333-1to333-n. The transmission line unit503has the signal line505g, strips505i-1to505i-n, and switches333-1to333-n.

The signal lines505gand505hare transmission paths of which starting ends are connected to the constant current source Is and terminating ends are connected to the variable capacitative element320and the buffer units370and380. The lengths of the signal lines331and341from the starting ends to the terminating ends are ¾ of the wavelength of the traveling wave used in oscillation. For this reason, if the power supply voltage is applied from the constant current source Is to the signal lines505gand505h, the signal lines505gand505hgenerate standing waves having the ¾ wavelength where the starting ends connected to the constant current source Is are used as nodes and the terminating ends are used as antinodes. On the other hand, the phases of the standing waves at the terminating ends of the signal lines505gand505hare almost the same as explained in the transmission line units330and340in the third embodiment, as illustrated in Equation (1), and the description is not repeated here.

Each of the strips505d-1to505d-nand505i-1to505i-nis composed of an elongated plate-shaped electrode that is formed of a conductor, such as a metal, and are arranged along the signal lines502and503such that the strips do not contact the signal lines505gand505h. The strips505d-1to505d-nand505i-1to505i-nare connected to the bias voltage through the switches333-1to333-nand343-1to343-n, respectively. Accordingly, if the switches333-1to333-nand343-1to343-nconnect the strips505d-1to505d-nand505i-1to505i-nand the bias voltage, the potential of the strips505d-1to505d-nand505i-1to505i-nthat are disposed in the vicinity of the signal lines505gand505hbecomes the bias voltage potential Vbias.

The switches333-1to333-nand343-1to343-nswitch connection and non-connection of the strips505d-1to505d-nand505i-1to505i-nand the bias voltage, respectively, under the control from the switch controller360. As the switches333-1to333-nand343-1to343-n, for example, MOSFETs are used. If the switches333-1to333-nand343-1to343-nconnect the strips332-1to332-nand342-1to342-nand the bias voltage, the dielectric permittivity of the thin film or ferro-electric material in the thin film layer at the vicinity of signal lines505gand505hchanges. That is, if the connection and the non-connection of the switches333-1to333-nand343-1to343-nare switched, the effective permittivity Er in the transmission line units502and503can be changed.

Specifically, if the number of connected switches333-1to333-nand343-1to343-nincreases, it can be assumed that the electrical transmission distances of signal lines505gand505hincrease. Since the propagation speed of the traveling wave becomes slow, it can be assumed that the effective permittivity Er increases. If the number of connected switches333-1to333-nand343-1to343-ndecreases, it can be assumed that electrical transmission distances of the signal lines331and341decrease. Since the propagation speed of the traveling wave becomes fast, it can be assumed that the effective permittivity Er decreases. Therefore, as represented by Equation (4), the frequency of the standing wave changes inversely proportional to the square root of the effective permittivity Er. That is, the frequency of the standing wave can be adjusted by switching the connection and non-connection of the switches333-1to333-nand343-1to343-n.

The configuration of the clamp unit350is almost the same as described in the clamp unit of the third embodiment. It is connected to a position of the ¼ wavelength from the starting ends of the signal lines505gand505hand associates the amplitudes of the standing waves generated in the signal lines505gand505hwith each other. That is, the clamp unit350causes the amplitude of the standing wave generated in the signal line505gand the amplitude of the standing wave generated in the signal line505hto become the amplitudes having the same magnitude to be inverted to each other. Accordingly, if the amplitude at the position of the signal line505gwhere the clamp unit350is connected is positive, the clamp unit350causes the amplitude at the position of the signal line505hwhere the clamp unit350is connected to be negative and causes the magnitudes of the two amplitudes to be equal to each other.

The configuration of the switch controller360is almost the same as described in the third embodiment, and the description is not repeated here.

Each of the buffer units370and380has a buffering circuit. And, the configuration and function of the buffer units370and380are almost the same as those described in the third embodiment (FIGS. 16A and 16B), and the description is not repeated here.

Operation of the Oscillator

Next, the operation of the oscillator that is configured in the above way will be described. If the power supply voltage is applied from the constant current source Is to the signal lines505gand505h, the standing wave having the frequency f according to the phase shift amount ΔΦ and the effective permittivity Er is generated in the signal lines505gand505h. At this time, the phase shift amount ΔΦ is determined according to the capacitance of the variable capacitative element320and controlled by the voltage controller310. The effective permittivity Er is adjusted by switching the connection and non-connection of the switches333-1to333-nand343-1to343-nby the switch controller360.

Specifically, the potential of the strips505d-1to505d-nthat correspond to the switches333-1to333-nbecoming a connection state by the switch controller360in the transmission line unit330becomes the bias voltage potential. For this reason, if the number of connected switches333-1to333-nincreases, the potential at the vicinity of signal line505gbecome Vbias. As a result, the propagation speed of the traveling wave that is propagated along the signal line505gby application of the power supply voltage decreases, and it can be assumed that the effective permittivity Er increases. As the effective permittivity Er increases, the frequency f of the standing wave decreases.

Meanwhile, in the transmission line unit503, the electrodes505i-1to505i-nthat are symmetrical to the connected switches333-1to333-nbecome a connection state by the switch controller360, and the potential of the corresponding strips342-1to342-nbecomes the bias voltage potential. If the number of connected switches343-1to343-nincreases, the potential at the vicinity of signal line505hbecome Vbias. As a result, the propagation speed of the traveling wave that is propagated along the signal line505hby application of the voltage decreases, and it can be assumed that the effective permittivity Er increases. As the effective permittivity Er increases, the frequency f of the standing wave decreases. However, since the signal line505his connected to the signal line505gthrough the clamp unit350, if the standing wave generated in the signal line503is compared with the standing wave generated in the signal line502, the magnitudes of the amplitudes are the same, but phases are inverted.

In contrast, if the number of connected switches333-1to333-ndecreases, the potential at the vicinity of signal lines505gand505gbecome close to the default voltage value, that is ground voltage. As a result, the propagation speed of the traveling wave that is propagated along the signal lines505gand505hby application of the power supply voltage increases, and it can be assumed that the effective permittivity Er decreases. As the effective permittivity Er decreases, the frequency f of the standing waves that are generated in the signal lines505gand505hincreases.

Switching of the connection and non-connection of the switches333-1to333-nand343-1to343-ncan be performed in the same sequence as that of the first embodiment or the third embodiment. The sequence of switching is almost the same as described in the first embodiment and the third embodiment, and the description is not repeated here.

The capacitance of the variable capacitative element320is adjusted by a control voltage applied from the voltage controller310to the variable capacitative element320. In the fifth embodiment, however, as described above, since the dielectric permittivity of the thin film material or ferro-electric material in the thin film layer can be adjusted and the phase shift amount ΔΦ cannot be greatly increased or decreased, the variable range of the capacitance of the variable capacitative element320is narrow. As such, even when the variable range of the capacitance of the variable capacitative element320is narrow and the phase shift amount ΔΦ is not greatly increased or decreased, in the fifth embodiment, the variable range of the effective permittivity Er is wide. Therefore, the control range of the frequency f can be widened.

FIG. 25is a schematic plan view illustrating the configuration of the transmission line units505gand505haccording to the fifth embodiment. As illustrated inFIG. 25, one side of the signal line505gand505hare connected to the current source Is. The electrodes505i-1to505i-nare located at outermost sides of the signal lines505gand505h. The signal lines505gand505hare connected to the clamp unit350through vias506ato506f.

FIG. 26is a schematic lateral view illustrating the configuration of the transmission line unit502according to the fifth embodiment. As illustrated in the upper part ofFIG. 26, the transmission line unit502has a layered structure, and the signal line505g, a thin film layer, and a coating layer in the off-chip circuit. The thin film layer521and the coating layer522form the off-chip layer520.

As illustrated in the lower part ofFIG. 26, switches133-1to133-nare implemented in the SiO2layer534a, a silicon layer534b, and the ground layer535at the lowermost side of the figure.

The configuration of the MOSFETs formed in the on-chip circuit is almost the same as that described in the first embodiment, and is not described here. There are vias which connect the signal pads505c,506c, etc. to the metal electrodes on the surface of the on-chip circuit, such that they can be connected to the off-chip circuit.

The on-chip electrodes and off-chip electrodes are connected through solder bumps540-1to540-n.

The bias voltage generation circuit generates bias voltages which range from a negative voltage to a voltage which is equal to or larger than 20 V.

Configuration of the Switch

The left part ofFIG. 27illustrates an example of the configuration of the switch133according to the fifth embodiment. The configuration of the MOSFETs formed in the on-chip circuit is almost the same as that described in the first embodiment, and is not described here.

The left part ofFIG. 27illustrates an example of a connection between off-chip transmission signal line505gand the on-chip clamp circuit350according to the fifth embodiment.

The on-chip circuit at the lower parts ofFIGS. 26 and 27can be formed using a standard CMOS process.

Meanwhile, the off-chip circuit at the upper parts ofFIGS. 26 and 27can be easily manufactured on thin-film technology.

As a result, the whole circuit can be manufactured on nowadays technologies.

FIG. 28is a table of chemical names, formula and dielectric constants of several examples of thin film material to be used in the off-chip circuit.

FIG. 29is a table of chemical names, formula and dielectric constants of several examples of ferro-electric material to be used in the off-chip circuit.

Meanwhile, when the metal strips are connected to the bias voltage, they change the effective dielectric constant of the space under signal line. Since material of high dielectric thin film material can be selected, size of off-chip circuit can further be reduced.