LC oscillator with wide tuning range and low phase noise

• US 20030227340A1
• Filed: 05/23/2003
• Published: 12/11/2003
• Est. Priority Date: 06/10/2002
• Status: Active Grant

• Current Assignee: GCT Semiconductor Incorporated
• Original Assignee: GCT Semiconductor Incorporated
• Inventors: Lee, Jeong-Woo, Lee, Kyeongho, Park, Joonbae, Koo, Yido
• Granted Patent: US 6,876,266 B2
• Time in Patent Office: Days
• US Class Current: 331/177R
• CPC Class Codes: H03B 2201/025 the means being an electronic switch for switching in or out oscillator elements
• 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 5/1265 switched capacitors
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop

Abstract

A voltage-controlled oscillator including an active oscillator circuit, an inductor, and capacitive circuits is disclosed. The capacitive circuits are selectively turned on and off to control the frequency of the voltage-controlled oscillator. Particularly, the inductor and the capacitors in the capacitive circuits form LC circuits that provide feedback to the active oscillator circuit. To avoid damage to the switches in the capacitive circuits, the capacitive circuits further comprise resistors. The resistors can be configured in several different ways so that the voltage-controlled oscillator can have a high degree of reliability, and a wide tuning range with constant phase noise performance.

Claims

1. A system comprising:

at least one adjusting circuit operably coupled to an oscillator, wherein the adjusting circuit comprises;

a resistor;

a reactive element; and

a first switch, wherein the first switch is in series with the reactive element and couples and decouples the reactive element to an output of the oscillator, and wherein the resistor provides a bias voltage to the reactive element so that the reactive element has a bias voltage when the first switch is open.

2. The system of claim 1, wherein the reactive element is a capacitor.

3. The system of claim 1, further comprising:

a second switch, wherein the second switch couples and decouples the resistor to the bias voltage when the first switch decouples the reactive element and decouples the resistor from the bias voltage when the first switch couples the reactive element.

4. The system of claim 1, wherein the bias voltage is at least one of a voltage generated from a resistor divider, a ground voltage, a supply voltage, and a common mode voltage of the oscillator output.

5. The system of claim 4, wherein the bias voltage from the resistor divider ranges from a ground voltage to a supply voltage.

6. The system of claim 1, wherein the resistor is sized so that the bias voltage can be constantly coupled to the resistor and so that the bias voltage does not substantially change the operating characteristics of the adjusting circuit when the first switch is closed.

7. The system of claim 1, wherein the first switch is a semiconductor device.

8. The system of claim 3, wherein the first switch is a transistor and the second switch is a transistor that is smaller than the first switch.

9. The system of claim 1, further comprising a plurality of adjusting circuits.

10. The system of claim 9, wherein each reactive element in each of the plurality of adjusting circuits is a capacitor, and wherein the capacitance of each capacitor is the same.

11. The system of claim 1, wherein the system is at least one of an active oscillator circuit, a PLL, a receiver, a transmitter, a transceiver, a wireless communication device, a base station, and a mobile unit.

12. An apparatus comprising:

an active oscillator, wherein the active oscillator comprises a first output node and a second output node;

an inductor, wherein the inductor couples the first output node and the second output node; and

at least one capacitive circuit coupled to either the first output node or the second output node, each capacitive circuit comprising;

a capacitor;

a resistor; and

a first switch, wherein the resistor provides a bias voltage to the capacitor when the first switch is open and wherein the first switch is in series with the capacitor and couples and decouples the capacitor to the output of the oscillator.

13. The apparatus of claim 12, wherein the capacitor couples the first switch to either the first or second output node, the first switch couples the capacitor to a ground voltage level, and the resistor is coupled to the capacitor and first switch at a common node of the capacitor and first switch.

14. The apparatus of claim 12, wherein the bias voltage is at least one of a voltage generated from a resistor divider, a ground voltage, a supply voltage, and a common mode voltage of the oscillator output.

15. The apparatus of claim 12, wherein the at least one capacitive circuit comprises a second switch and the second switch couples and decouples the resistor to the bias voltage.

16. The apparatus of claim 15, wherein the second switch and resistor are in series, and wherein the bias voltage is a common mode voltage of the oscillator output.

17. The apparatus of claim 15, wherein the at least one capacitive circuit is configured such that:

if the first switch is open then the second switch is closed; and

if the first switch is closed then the second switch is open.

18. The apparatus of claim 12, wherein the apparatus is at least one of a PLL, a receiver, a transmitter, a transceiver, a wireless communication device, a base station, and a mobile unit.

19. A method for adjusting an oscillator, the method comprising:

providing a bias voltage via a resistor to a reactive element so that the reactive element has a bias voltage when a first switch is open; and

using the first switch to couple and decouple the reactive element from the oscillator, thereby adjusting the frequency of the oscillator.

20. The method of claim 19, further comprising:

coupling the resistor to the bias voltage via a second switch when the first switch decouples the reactive element; and

decoupling the resistor from the bias voltage via the second switch when the first switch couples the reactive element.