CMOS VCO WITH IMPLICIT COMMON-MODE RESONANCE

• US 20160373058A1
• Filed: 08/10/2015
• Published: 12/22/2016
• Est. Priority Date: 06/22/2015
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: MURPHY, David Patrick, Darabi, Hooman
• Granted Patent: US 9,742,353 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H03B 2200/009 Reduction of phase noise
• 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 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1265 switched capacitors
• CPC Class Codes: H03B 5/1271 the frequency being controlled by a control current, i.e. current controlled oscillators
• CPC Class Codes: H03B 5/1278 the parameter being an amplitude of a signal, e.g. maintaining a constant output amplitude over the frequency range
• CPC Class Codes: H03B 5/1284 the parameter being another frequency, e.g. a harmonic of the oscillating frequency
• CPC Class Codes: H03B 5/1296 the feedback circuit comprising a transformer
• CPC Class Codes: H04B 1/40 Circuits

Abstract

A circuit for an oscillator with common-mode resonance includes a first oscillator circuit and a second oscillator circuit coupled to the first oscillator circuit. Each of the first oscillator circuit or the second oscillator circuit includes a tank circuit, a cross-coupled transistor pair, and one or more capacitors. The tank circuit is formed by coupling a first inductor with a pair of first capacitors. The cross-coupled transistor pair is coupled to the tank circuit, and one or more second capacitors are coupled to the tank circuit and the cross-coupled transistor pair. Each of the first oscillator circuit or the second oscillator circuit allows tuning of a respective common mode (CM) resonance frequency (F_cm) to be at twice a respective differential resonance frequency (F_D).

DM_——ITS 62683970-1.093986 0453

Claims

1. A circuit for an oscillator with common-mode resonance, the circuit comprising:

a first oscillator circuit comprising a first cross-coupled transistor pair; and

a second oscillator circuit comprising a second cross-coupled transistor pair coupled to the first oscillator circuit via a joint tank circuit,

wherein at least one of the first oscillator circuit or the second oscillator circuit the joint tank circuit comprises;

a differential inductor including first and second pair of nodes, each of the first and second pair of nodes coupled with a pair of first capacitors to ground potential; and

a pair of second capacitors, one capacitor of the pair of second capacitors being coupled to between the first pair of nodes of the differential inductor that is coupled to drain nodes the first cross-coupled transistor pair, and another capacitor of the pair of second capacitors being coupled between the second pair of nodes of the differential inductor that is coupled to drain nodes the second cross-coupled transistor pair.

2. The circuit of claim 1, wherein the first and the second oscillator circuits are similar except for transistor types of the first and second cross-coupled transistor pairs, wherein the first cross-coupled transistor pair comprises NMOS transistors, and wherein the second cross-coupled transistor pair comprises PMOS transistors.

3. The circuit of claim 2, wherein:

the first and the second oscillator circuits comprise a single differential-inductor oscillator,

the single differential-inductor oscillator comprises a voltage-controlled oscillator (VCO), and

the single differential-inductor oscillator is configured to allow tuning of a respective common mode resonance frequency (F_CM) to be at twice a respective differential resonance frequency (F_D) by adjusting a ratio of capacitance values of the pair of the first and second capacitors.

4. The circuit of claim 1, wherein the differential inductor comprises a coupled inductor pair that is realized as a spiral inductor having an inner loop that is smaller than an outer loop.

5. The circuit of claim 1, wherein the first pair of capacitors is realized by a differential switch capacitance circuit comprising a plurality of differential switch capacitance unit cells.

6. The circuit of claim 5, wherein at least some of the plurality of differential switch capacitance unit cells are realized by two capacitors and a variable capacitance associated with a deep N-well device, having inherent junction diodes, that is biased by using high impedance supplies.

7. The circuit of claim 1, wherein the pair of second capacitors are realized by a CM capacitance tuning circuit comprising a plurality of CM capacitance tuning unit cells, and wherein at least some of the plurality of CM capacitance tuning unit cells are realized by two capacitors having a common node coupled through a switch to ground potential.

8. The circuit of claim 1, wherein the at least one of the first oscillator circuit or the second oscillator circuit is configured to allow tuning of a respective F_CM independent of a respective F_D, and wherein the at least one of the first oscillator circuit or the second oscillator circuit is configured to allow maximizing a value of a CM impedance at the respective F_CM.

9. The circuit of claim 1, wherein the oscillator with common-mode resonance is configured to achieve the same phase noise performance as one of the first oscillator circuit or the second oscillator circuit, and wherein the first and second cross-coupled transistor pair comprises thin-oxide devices.

10. The circuit of claim 1, wherein at least one of the first oscillator circuit or the second oscillator circuit is configured to maximize values of phase noise per unit power for multiple frequency offsets at a point that corresponds to an optimum ratio of capacitance values of the first and second capacitors, wherein the multiple frequency offsets are measured from a resonance frequency of a single differential-inductor oscillator, and wherein the optimum ratio of capacitance values of the pair of first and second capacitors corresponds to a respective F_CM being twice a respective F_D.

11. A method for providing an oscillator with common-mode resonance, the method comprising:

providing a first oscillator circuit comprising a first cross-coupled transistor pair and a second oscillator circuit comprising a second cross-coupled transistor pair; and

coupling the first oscillator circuit to the second oscillator circuit via a joint tank circuit,

wherein providing the joint tank circuit comprises;

providing a differential inductor including first and second pair of nodes, each of the first and second pair of nodes coupled via a pair of first capacitors to ground potential;

coupling one capacitor of a pair of second capacitors between the first pair of nodes of the differential inductor that is coupled to drain nodes of the first cross-coupled transistor pair, and another capacitor of the pair of second capacitors being coupled between the second pair of nodes of the differential inductor that is coupled to drain nodes the second cross-coupled transistor pair.

12. The method of claim 11, wherein providing the first and the second oscillator circuits comprises providing similar circuitry except for transistor types of the first and second cross-coupled transistor pair, and further comprising:

providing the first oscillator circuit with the first cross-coupled transistor pair comprising NMOS transistors; and

providing the second oscillator circuit with the second cross-coupled transistor pair comprising PMOS transistors.

13. The method of claim 12, wherein:

providing the first and the second oscillators comprise providing a single differential-inductor oscillator,

providing the single differential-inductor oscillator comprises a voltage-controlled oscillator (VCO), and

the method further comprises configuring the single differential-inductor to allow tuning of a respective F_CM to be at twice a respective F_D by adjusting a ratio of capacitance values of the pairs of the first and second capacitors.

14. The method of claim 11, wherein the differential inductor comprises a coupled inductor pair that is realized as a spiral inductor having an inner loop that is smaller than an outer loop.

15. The method of claim 14, further comprising:

implementing the first pair of capacitors by a differential switch capacitance circuit comprising a plurality of differential switch capacitance unit cells; and

implementing at least some of the plurality of differential switch capacitance unit cells by coupling two capacitors and a variable capacitance associated with a deep N-well device with inherent junction diodes, and biasing the deep N-well device by using high impedance supplies.

16. The method of claim 11, further comprising implementing the pair of second capacitors by a CM capacitance tuning circuit comprising a plurality of CM capacitance tuning unit cells, and realizing at least some of the plurality of CM capacitance tuning unit cells by two capacitors having a common node coupled through a switch to ground potential.

17. The method of claim 11, further comprising:

configuring at least one of the first oscillator circuit or the second oscillator circuit to allow tuning of a respective F_CM independent of a respective F_D; and

configuring the at least one of the first oscillator circuit or the second oscillator circuit to maximize a value of a CM impedance at the respective F_CM.

18. The method of claim 11, further comprising configuring at least one of the first oscillator circuit or the second oscillator circuit to maximize values of phase noise per unit power for multiple frequency offsets at a point that corresponds to an optimum ratio of capacitance values of the pair of the first and second capacitors, wherein the multiple frequency offsets are measured from a resonance frequency of the at least one of the first oscillator circuit or the second oscillator circuit, and wherein the optimum ratio of capacitance values of the pair of the first and second capacitors corresponds to a respective F_CM being twice a respective F_D.

19. The method of claim 11, further comprising:

configuring an oscillator with common-mode resonance to achieve the same phase noise performance as one of the first oscillator circuit or the second oscillator circuit; and

implementing the first and second cross-coupled transistor pairs using thin-oxide devices.

20. A communication device comprising:

a radio-frequency (RF) transceiver comprising one or more local oscillators,

the one or more local oscillators comprising at least one oscillator with common-mode resonance, wherein the at least one oscillator with common-mode resonance comprises;

a first oscillator circuit comprising a first cross-coupled transistor pair; and

a second oscillator circuit comprising a second cross-coupled transistor pair coupled to the first oscillator circuit via a joint tank circuit,

wherein the joint tank circuit comprises;

a differential inductor including first and second pair of nodes, each of the first and second pair of nodes coupled via a pair of first capacitors to ground potential; and

a pair of second capacitors, one capacitor of the pair of second capacitors being coupled between the first pair of nodes of the differential inductor that is coupled to drain nodes the first cross-coupled transistor pair, and another capacitor of the pair of second capacitors being coupled between the second pair of nodes of the differential inductor that is coupled to drain nodes the second cross-coupled transistor pair.