LC resonance circuit and voltage-controlled oscillation circuit

• US 20020014925A1
• Filed: 03/19/2001
• Published: 02/07/2002
• Est. Priority Date: 07/26/2000
• Status: Active Grant

• Current Assignee: LAPIS Semiconductor Co., Ltd. (ROHM Co., Ltd.)
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Ochiai, Toshiyuki
• Granted Patent: US 6,509,805 B2
• Time in Patent Office: Days
• US Class Current: 331/117FE
• 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 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1265 switched capacitors

Abstract

A control voltage Vin that has been input is sequentially reduced at NMOS'"'"'s 11₁˜11₃ constituting means for voltage reduction. The individual voltages resulting from the voltage reduction are applied to control electrodes of MOS varactors 21₁˜21₃ constituting voltage-controlled variable-capacitance elements which are connected in parallel and, thus, the capacitance values of the individual MOS varactors 21₁˜21₃ are determined. An LC resonance circuit constituted of the MOS varactors 21₁˜21₃ and a coil 22 resonates at a specific frequency, NMOS'"'"'s 23 and 24 constituting means for switching engage in on/off operation and oscillation occurs at an oscillation frequency corresponding to the voltage Vin resulting in an oscillation signal output through output terminals 3 and 4. Thus, an LC resonance circuit that allows the rate at which the capacitance values of the voltage-controlled variable-capacitance elements change to be set freely in correspondence to the particulars of design and a high-performance voltage-controlled oscillation circuit (VCO) that employs this LC resonance circuit and enables good control are provided.

Claims

1. An LC resonance circuit comprising;

a coil connected between a first node and a second node;

n (n is a positive integer equal to or larger than 2) variable-capacitance elements, each having a control electrode and connected in parallel between said first node and said second node with the capacitance value thereof caused to change in correspondence to a variable voltage applied to said control electrode; and

m (m is a positive integer equal to or larger than 1) means for voltage reduction, each of which is connected to an input terminal at which a control voltage is input and provides a voltage achieved by lowering the control voltage so said control electrode of one of said n variable-capacitance elements or one of (n−

1) variable-capacitance elements.

2. An LC resonance circuit according to claim 1, wherein:

said variable-capacitance elements are each constituted of a MOS varactor.

3. An LC resonance circuit according to claim 1, wherein:

said variable-capacitance elements are each constituted of a P/N junction type varactor.

4. An LC resonance circuit according to claim 1, wherein:

said means for voltage reduction are each constituted of a MOS transistor that operates by using a forward voltage reduction occurring between a drain electrode and a source electrode in a diode connection achieved by shorting a gate electrode and said drain electrode.

5. An LC resonance circuit according to claim 1, wherein:

said means for voltage reduction are each constituted of a diode that operates by using a forward voltage reduction occurring between a drain electrode and a source electrode in a diode connection achieved by shorting a gate electrode and said drain electrode.

6. An LC resonance circuit according to claim 1, wherein:

said means for voltage reduction are each constituted of a diode that operates by using a reverse breakdown voltage occurring between a drain electrode and a source electrode in a diode connection achieved by shorting a gate electrode and said drain electrode.

7. A voltage-controlled oscillation circuit having an LC resonance circuit, comprising;

a coil connected between a first node and a second node;

n (n is a positive integer equal to or larger than 2) variable-capacitance elements, each having a control electrode and connected in parallel between said first node and said second node with the capacitance value thereof caused to change in correspondence to a variable voltage applied to said control electrode; and

m (m is a positive integer equal to or larger than

     1) means for voltage reduction, each of which is connected to an input terminal at which a control voltage is input and provides a voltage achieved by lowering the control voltage so said control electrode of one of said n variable-capacitance elements or one of (n−

1) variable-capacitance elements.

8. A voltage-controlled oscillation circuit according to claim 7, wherein:

said variable-capacitance elements are each constituted of a MOS varactor.

9. A voltage-controlled oscillation circuit according to claim 7, wherein:

said variable-capacitance elements are each constituted of a P/N junction type varactor.

10. A voltage-controlled oscillation circuit according to claim 7, wherein:

said means for voltage reduction are each constituted of a MOS transistor that operates by using a forward voltage reduction occurring between a drain electrode and a source electrode in a diode connection achieved by shorting a gate electrode and said drain electrode.

11. A voltage-controlled oscillation circuit according to claim 7, wherein:

said means for voltage reduction are each constituted of a diode that operates by using a forward voltage reduction occurring between a drain electrode and a source electrode in a diode connection achieved by shorting a gate electrode and said drain electrode.

12. A voltage-controlled oscillation circuit according to claim 7, wherein:

said means for voltage reduction are each constituted of a diode that operates by using a reverse breakdown voltage occurring between a drain electrode and a source electrode in a diode connection achieved by shorting a gate electrode and said drain electrode.