Low Phase-Noise Oscillator

• US 20080143446A1
• Filed: 12/17/2007
• Published: 06/19/2008
• Est. Priority Date: 12/15/2006
• Status: Active Grant

• Current Assignee: Alan N. Willson, Jr.
• Original Assignee: Alan Neil Willson, Chih-Wei Yao
• Inventors: Willson, Alan Neil, Yao, Chih-Wei
• Granted Patent: US 7,847,650 B2
• Time in Patent Office: Days
• US Class Current: 331/45
• CPC Class Codes: H03B 2200/0074 Locking of an oscillator by injecting an input signal directly into the oscillator
• CPC Class Codes: H03B 27/00 Generation of oscillations providing a plurality of outputs of the same frequency but differing in phase, other than merely two anti-phase outputs
• CPC Class Codes: H03B 5/1212 the amplifier comprising a pair of transistors, wherein an output terminal of each being connected to an input terminal of the other, e.g. a cross coupled pair
• 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 5/1253 the transistors being field-effect transistors
• CPC Class Codes: H03L 7/24 using a reference signal directly applied to the generator

Abstract

A tail-tank coupling technique combines two complementary differential LC-VCOs to form a quadrature LC-VCO. The technique reduces phase noise by providing additional energy storage for noise redistribution and by cancelling noise injected by transistors when they operate in the triode region. The resulting noise factor is close to the theoretical minimum 1+γ, similar to a differential LC-VCO driven by an ideal noiseless current source. However, its figure-of-merit is higher, due to the absence of voltage head-room being consumed by a current source. The optimal ratio of tail-tank capacitor to main-tank capacitor for minimizing phase noise is approximately 0.5. The method can be extended to combine any even number of LC tanks resonating at f_o and 2f_o to form an integrated oscillator producing quadrature phase at frequency f_osc and differential output at 2f_osc.

Claims

1. A differential oscillator comprising:

a PMOS cross-coupled pair comprising a first PMOS cross-coupled pair drain node, a second PMOS cross-coupled pair drain node, and a PMOS cross-coupled pair merged source node;

an NMOS cross-coupled pair comprising a first NMOS cross-coupled pair drain node, a second NMOS cross-coupled pair drain node, and an NMOS cross-coupled pair merged source node;

a first LC resonator with a first terminal and a second terminal, wherein said first terminal is connected to said first PMOS cross-coupled pair drain node and said first NMOS cross-coupled pair drain node, and said second terminal is connected to said second PMOS cross-coupled pair drain node and said second NMOS cross-coupled pair drain node;

a second LC resonator with a third terminal and a fourth terminal, wherein said third terminal is connected to said PMOS cross-coupled pair merged source node, and said fourth terminal is connected to a voltage source; and

a third LC resonator with a fifth terminal and a sixth terminal, wherein said fifth terminal is connected to said NMOS cross-coupled pair merged source node, and said sixth terminal is connected to ground or a voltage source.

2. The differential oscillator of claim 1, wherein the resonating frequency of at least one of said second LC resonator and said third LC resonator is approximately twice the resonating frequency of said first LC resonator.

3. The differential oscillator of claim 1, wherein the ratio between at least one of the capacitances of said second LC resonator and said third LC resonator to the capacitance of said first LC resonator is approximately 0.5.

4. A quadrature oscillator comprising:

a first differential oscillator comprising a first LC resonator and a first cross-coupled pair with a first merged node;

a second differential oscillator comprising a second LC resonator and a second cross-coupled pair with a second merged node; and

a third LC resonator connecting between said first merged node and said second merged node, wherein third LC resonator is comprised of a first inductor with a first terminal and a second terminal, said first terminal is connected to said first merged node and said second terminal is connected to said second merged node.

5. The quadrature oscillator of claim 4, further comprising of a second inductor having a third terminal and a fourth terminal, wherein said third terminal is connected to a center-tap of said first inductor, and said fourth terminal is connected to a ground or a voltage source.

6. The quadrature oscillator of claim 4, wherein the resonating frequency of said third LC resonator is approximately twice the resonating frequency of at least one of said first LC resonator and said second LC resonator.

7. The quadrature oscillator of claim 4, wherein the ratio between the capacitance of said third LC resonator to the capacitance of at least one of said first LC resonator and said second LC resonator is approximately 0.5.

8. The quadrature oscillator of claim 5, further comprising:

a third cross-coupled pair and a third merged node within said first differential oscillator;

a fourth cross-coupled pair and a fourth merged node within said second differential oscillator;

a fourth LC resonator connecting between said third merged node and said fourth merged node, wherein said fourth LC resonator is comprised of a third inductor with a fifth terminal and sixth terminal, said fifth terminal is connected to said third merged node and said sixth terminal is connected to said fourth merged node; and

a fourth inductor with a seventh terminal and a eighth terminal, wherein said seventh terminal is connected to a center-tap of said third inductor, and said eighth terminal is connected to ground or a voltage source.

9. The quadrature oscillator of claim 8, wherein the resonating frequency of at least one of said third LC resonator and fourth LC resonator is approximately twice the resonating frequency of at least one of said first LC resonator and said second LC resonator.

10. The quadrature oscillator of claim 8, wherein the ratio between the capacitance of at least one of said third LC resonator and said fourth LC resonator to the capacitance of at least one of said first LC resonator and said second LC resonator is approximately 0.5.

11. A differential oscillator comprising:

a PNP cross-coupled pair comprising a first PNP cross-coupled pair first collector node, a second PNP cross-coupled pair collector node, and a PNP cross-coupled pair merged emitter node;

an NPN cross-coupled pair comprising a first NPN cross-coupled pair collector node, a second NPN cross-coupled pair collector node, and an NPN cross-coupled pair merged emitter node;

a first LC resonator with a first terminal and a second terminal, wherein said first terminal is connected to said first PNP cross-coupled pair first collector node and said first NPN cross-coupled pair collector node, and said second terminal is connected to said second PNP cross-coupled pair collector node and said second NPN cross-coupled pair collector node;

a second LC resonator with a third terminal and a fourth terminal, wherein said third terminal is connected to said PNP cross-coupled pair merged emitter node, and said fourth terminal is connected to a voltage source; and

a third LC resonator with a fifth terminal and a sixth terminal, wherein said fifth terminal is connected to said NPN cross-coupled pair merged emitter node, and said sixth terminal is connected to ground or a voltage source.

12. The differential oscillator of claim 11, wherein the resonating frequency of at least one of said second LC resonator and said third LC resonator is approximately twice the resonating frequency of said first LC resonator.

13. The differential oscillator of claim 11, wherein the ratio between at least one of the capacitances of said second LC resonator and said third LC resonator to the capacitance of said first LC resonator is approximately 0.5.