Variable inductor, and oscillator and communication system using the same

• US 20060097811A1
• Filed: 11/08/2005
• Published: 05/11/2006
• Est. Priority Date: 11/09/2004
• Status: Active Grant

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: Renesas Electronics Corporation
• Inventors: Nakamura, Takahiro, Masuda, Toru
• Granted Patent: US 7,902,934 B2
• Time in Patent Office: Days
• US Class Current: 331/167
• CPC Class Codes: H03B 2201/0208 the means being an element with a variable capacitance, e.g. capacitance diode
• CPC Class Codes: H03B 2201/0216 the means being an element with a variable inductance
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1218 the generator being of the balanced type
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1231 the amplifier comprising one or more bipolar transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1253 the transistors being field-effect transistors
• CPC Class Codes: H03B 5/1256 the means comprising a variable inductance
• CPC Class Codes: H03B 5/1293 having means for achieving a desired tuning characteristic, e.g. linearising the frequency characteristic across the tuning voltage range
• CPC Class Codes: H03B 5/1296 the feedback circuit comprising a transformer
• CPC Class Codes: H03H 5/12 with at least one voltage- or current-dependent element
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank

Abstract

There are provided a variable inductor with little degradation in quality factor, and an oscillator and a communication system using the variable inductor. An inductance controller comprising a reactance device with a variable device value, such as, for example, a variable capacitor, is connected to a secondary inductor, magnetically coupled to a primary inductor through mutual inductance. The inductance controller is provided with an inductance control terminal for receiving a control signal for controlling capacitance of the variable capacitor. Inductance of the primary inductor is varied by varying the capacitance by the control signal.

Claims

1. A variable inductor comprising:

a first inductor;

a second inductor magnetically coupled to the first inductor through mutual inductance; and

an inductance controller comprising a reactance device, the inductance controller being connected to the second inductor,

wherein the inductance controller has an inductance control terminal for receiving a control signal for varying a device value of the reactance device, and as a result of variation in the device value of the reactance device, caused by the control signal, inductance of the first inductor varies.

2. The variable inductor according to claim 1, wherein the reactance device is a variable capacitor whose capacitance is varied by the control signal.

3. The variable inductor according to claim 1, wherein the reactance device comprises a plurality of parallel-coupled variable capacitors whose capacitance is varied into large or small by the control signal.

4. The variable inductor according to claim 2, wherein the variable capacitor is a pn-junction capacitor of semiconductor, and the control signal is applied to both ends of the pn-junction capacitor.

5. The variable inductor according to claim 3, wherein each of the plurality of variable capacitors is a pn-junction capacitor of semiconductor, and the control signal is individually applied to both ends of the pn-junction capacitor for every one of the plurality of variable capacitors.

6. The variable inductor according to claim 2, wherein the variable capacitor is a MOS capacitor of a MOS transistor and the control signal is applied between a gate and a source•

drain of the MOS transistor.

7. The variable inductor according to claim 3, wherein each of the plurality of variable capacitors is aMOS capacitor of aMOS transistor and the control signal is individually applied between a gate and a source-drain of the MOS transistor for every one of the plurality of variable capacitors.

8. The variable inductor according to claim 3, wherein each of the plurality of variable capacitors comprises a fixed capacitor and a switch connected in series to the fixed capacitor, opening/closing of the switch is controlled by the control signal individually applied for every one of the plurality of variable capacitors, and each of the plurality of variable capacitors has capacitance that is varied into large or small by the opening/closing of the switch.

9. An oscillator comprising:

a resonator including an inductor and a capacitor connected in parallel; and

a negative conductance generator for generating negative conductance, the negative conductance generator being connected to the resonator,

wherein said oscillator outputs a signal whose frequency is substantially determined by a resonance frequency of the resonator;

wherein the inductor is a variable inductor whose inductance varies,

wherein the resonance frequency of the resonator varies as a result of the variation in the inductance; and

wherein said variable inductor comprising;

a first inductor;

a second inductor magnetically coupled to the first inductor through mutual inductance; and

an inductance controller comprising a reactance device, the inductance controller being connected to the second inductor,

wherein the inductance controller has an inductance control terminal for receiving a control signal for varying a device value of the reactance device, and as a result of variation in the device value of the reactance device, caused by the control signal, inductance of the first inductor varies.

10. The oscillator according to claim 9, wherein the reactance device is a variable capacitor whose capacitance is varied by the control signal.

11. The oscillator according to claim 9, wherein the reactance device comprises a plurality of parallel-coupled variable capacitors whose capacitance is varied into large or small by the control signal.

12. The oscillator according to claim 9, wherein the capacitor is a variable capacitor whose capacitance varies and the resonance frequency of the resonator varies as a result of the variation in the capacitance.

13. The oscillator according to claim 9, wherein a first capacitor is connected between an input terminal of a transistor and a grounded terminal of the transistor, a second capacitor is connected between an output electrode of the transistor and the grounded electrode, and the variable inductor is connected between the output electrode and the grounded electrode;

wherein the negative conductance generator is formed between the output electrode and the grounded electrode.

14. The oscillator according to claim 13, wherein two units of the oscillators are connected to each other so as to act as a differential oscillator.

15. The oscillator according to claim 12, wherein the negative conductance generator comprises two units of transistors, an input terminal of one of the transistors being mutually connected to an output terminal of the other transistor while respective grounded terminals of both the transistors are connected with each other, and a constant current source being connected to a node connecting the respective grounded terminals.

16. A communication system comprising:

a low-noise amplifier for amplifying a receive signal received by an antenna;

a mixer for converting a frequency of an output signal of the low-noise amplifier;

an oscillator for generating a local oscillator signal for conversion of the frequency, and outputting the local oscillator signal to the mixer;

a demodulator for taking out a receive base band signal from an output signal of the mixer;

a modulator for modulating a transmit base band signal and outputting two signals orthogonal in phase to each other;

an orthogonal modulator for modulating the two signals orthogonal in phase to each other by use of the local oscillator signal outputted by the oscillator to thereby output an orthogonal modulation signal;

a power amplifier for amplifying the orthogonal modulation signal; and

a switch for supplying the receive signal received from the antenna to the low-noise amplifier at the time of receiving and supplying the orthogonal modulation signal outputted by the power amplifier to the antenna at the time of transmitting,

wherein said oscillator comprising;

a resonator including an inductor and a capacitor connected in parallel; and

a negative conductance generator for generating negative conductance, the negative conductance generator being connected to the resonator,

wherein said oscillator outputs a signal whose frequency is substantially determined by a resonance frequency of the resonator;

wherein the inductor is a variable inductor whose inductance varies,

wherein the resonance frequency of the resonator varies as a result of the variation in the inductance; and

wherein said variable inductor comprising;

a first inductor;

a second inductor magnetically coupled to the first inductor through mutual inductance; and

an inductance controller comprising a reactance device, the inductance controller being connected to the second inductor,

wherein the inductance controller has an inductance control terminal for receiving a control signal for varying a device value of the reactance device, and as a result of variation in the device value of the reactance device, caused by the control signal, inductance of the first inductor varies.

17. The communication system according to claim 16, wherein the reactance device is a variable capacitor whose capacitance is varied by the control signal.

18. The communication system according to claim 16, wherein the reactance device comprises a plurality of parallel-coupled variable capacitors whose capacitance is varied into large or small by the control signal.

19. The communication system according to claim 16, wherein the capacitor is a variable capacitor whose capacitance varies and the resonance frequency of the resonator varies as a result of the variation in the capacitance.

20. The communication system according to claim 16, wherein a transmitting and receiving circuit comprising the low-noise amplifier, the mixer, the oscillator, the demodulator, the modulator and the orthogonal modulator is made up as a semiconductor device.