Circuits and methods for flicker noise upconversion minimization in an oscillator

• US 9,559,702 B1
• Filed: 09/30/2014
• Issued: 01/31/2017
• Est. Priority Date: 09/30/2013
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Manetakis, Konstantinos
• Primary Examiner(s): Tan, Richard
• Application Number:
  US14/503,173
• Time in Patent Office: 854 Days
• Field of Search: 331/117.R, 331/117.FE, 331/108.A, 331/167
• US Class Current: 1/1
• CPC Class Codes: H03B 2201/0208 the means being an element with a variable capacitance, e.g. capacitance diode
• CPC Class Codes: H03B 5/00 Generation of oscillations using amplifier with regenerative feedback from output to input H03B9/00, H03B15/00 take precedence
• CPC Class Codes: H03B 5/08 with frequency-determining element comprising lumped inductance and capacitance
• CPC Class Codes: H03B 5/12 active element in amplifier being semiconductor device H03B5/14 takes precedence
• 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: H03L 7/00 Automatic control of frequency or phase; Synchronisation

Abstract

A circuit comprises an oscillator including a differential tank circuit, an oscillator carrier, and an active device. A phase difference between the oscillator carrier and a device current of the active device is adjusted to reduce upconversion of flicker noise of the oscillator. The circuit includes a common-mode reactance circuit configured to provide an intentionally introduced common-mode inductance, common-mode capacitance, or both, The common-mode reactance circuit is configured to adjust at common-mode impedance of the oscillator. A method comprises adjusting a phase difference between an oscillator carrier of an oscillator and a device current of an active device of the oscillator. The adjusted phase difference is selected to reduce upconversion of flicker noise generated in the oscillator. Adjusting the phase difference includes adjusting a common-mode impedance of the oscillator.

Claims

1. A circuit comprising:

an oscillator to output an oscillator carrier, the oscillator including a differential tank circuit, an active device, and a common-mode reactance circuit,

wherein the differential tank circuit includes a first variable capacitor and a second variable capacitor each coupled to a common-mode port of the differential tank circuit,

wherein the common-mode reactance circuit includes a common-mode variable capacitor coupled to the common-mode port of the differential tank circuit,

wherein a phase difference between a voltage of the oscillator carrier and a device current of the active device is adjusted to reduce upconversion of flicker noise of the oscillator,

wherein adjusting the phase difference to reduce upconversion of the flicker noise is performed by adjusting, using the common-mode reactance circuit, a common-mode impedance of the oscillator to generate, at a second harmonic of a frequency of the oscillator carrier and according to an imaginary part of the common-mode impedance, a phase shift of a common mode current that is substantially equal to a negative of a phase shift of a differential mode current in the active device, the second harmonic being a frequency twice the frequency of the oscillator carrier, and

wherein adjusting the common-mode impedance includes adjusting the common-mode impedance to have the imaginary part substantially equal to a value Z_i at the second harmonic of the frequency of the oscillator carrier, the value Z_i being determined by;

2. The circuit of claim 1, wherein the adjusted phase difference is substantially zero.

3. The circuit of claim 1, wherein the common-mode reactance circuit includes an active circuit connected to the common-mode port of the differential tank circuit.

4. The circuit of claim 1, wherein the common-mode variable capacitor is connected between the common-mode port of the differential tank circuit and ground.

5. The circuit of claim 1, wherein the oscillator is a current-biased oscillator.

6. The circuit of claim 1, wherein the oscillator is a voltage-biased oscillator.

7. The circuit of claim 1, wherein the circuit is provided in an integrated circuit.

8. A method comprising:

adjusting a phase difference between a voltage of an oscillator carrier generated by an oscillator and a device current of an active device of the oscillator,

wherein the adjusted phase difference is selected to reduce upconversion of flicker noise generated in the oscillator,

wherein adjusting the phase difference to reduce upconversion of the flicker noise includes adjusting, using a common-mode reactance circuit, a common-mode impedance of the oscillator to generate, at a second harmonic of a frequency of the oscillator carrier and according to an imaginary part of the common-mode impedance, a phase shift of a common mode current that is substantially equal to a negative of a phase shift of a differential mode current in the active device, the second harmonic being a frequency twice the frequency of the oscillator carrier,

wherein the oscillator includes a differential tank circuit including a first variable capacitor and a second variable capacitor each coupled to a common mode port of the differential tank circuit,

wherein the common-mode reactance circuit includes a common-mode variable capacitor coupled to the common mode port of the differential tank circuit, and

wherein adjusting the common-mode impedance includes adjusting the common-mode impedance to have the imaginary part substantially equal to a value Z_i at the second harmonic of the frequency of the oscillator carrier, the value Z_i being determined by;

9. The method of claim 8, wherein adjusting the phase difference includes minimizing the phase difference.

10. The method of claim 8, wherein adjusting the phase difference includes adjusting a common-mode resonance frequency of the oscillator to be slightly above the second harmonic.