Wideband Digitally Controlled Injection-Locked Oscillator

• US 20160099720A1
• Filed: 10/03/2015
• Published: 04/07/2016
• Est. Priority Date: 10/03/2014
• Status: Active Grant

• Current Assignee: Short Circuit Technologies Llc
• Original Assignee: Short Circuit Technologies Llc
• Inventors: Staszewski, Robert Bogdan, Bashir, Imran
• Granted Patent: US 10,008,980 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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 5/1218 the generator being of the balanced type
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/124 the means comprising a voltage dependent capacitance
• CPC Class Codes: H03B 5/1265 switched capacitors
• CPC Class Codes: H03B 5/1281 the parameter being the amount of feedback
• CPC Class Codes: H03B 5/1293 having means for achieving a desired tuning characteristic, e.g. linearising the frequency characteristic across the tuning voltage range
• CPC Class Codes: H03B 5/1296 the feedback circuit comprising a transformer
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03L 7/081 provided with an additional controlled phase shifter H03L7/0998 takes precedence
• CPC Class Codes: H03L 7/0991 the oscillator being a digital oscillator, e.g. composed of a fixed oscillator followed by a variable frequency divider H03L7/0995 takes precedence; fixed oscillators with means for selecting among various phases H03L7/0814
• CPC Class Codes: H03L 7/1976 using a phase accumulator for controlling the counter or frequency divider

Abstract

A novel and useful digitally controlled injection-locked RF oscillator with an auxiliary loop. The oscillator is injection locked to a time delayed version of its own resonating voltage (or its second harmonic) and its frequency is modulated by manipulating the phase and amplitude of injected current. The oscillator achieves a narrow modulation tuning range and fine step size of an LC tank based digitally controlled oscillator (DCO). The DCO first gets tuned to its center frequency by means of a conventional switched capacitor array. Frequency modulation is then achieved via a novel method of digitally controlling the phase and amplitude of injected current into the LC tank generated from its own resonating voltage. A very linear deviation from the center frequency is achieved with a much lower gain resulting in a very fine resolution DCO step size and high linearity without needing to resort to oversampled noise shaped dithering.

Claims

1. A frequency modulator circuit, comprising:

a frequency oscillator incorporating a tank circuit and operative to generate a resonating waveform;

a delay circuit coupled to said frequency oscillator and operative to generate a delayed version of said resonating waveform;

a feedback loop coupled to said frequency oscillator and said delay circuit, said feedback loop operative to inject said delayed resonating waveform back into said tank circuit; and

wherein said modulator circuit frequency is determined by a duration said resonating waveform is delayed by said delay circuit.

2. The oscillator circuit according to claim 1, wherein said resonating frequency of said frequency generator is controlled by a tunable element in said tank circuit.

3. The oscillator circuit according to claim 1, wherein said delay circuit comprises two paths with approximate 90 degree phase shift.

4. The oscillator circuit according to claim 1, wherein said delayed resonating waveform comprise current.

5. A method of generating an oscillating signal, comprising:

generating a resonating waveform utilizing an LC tank circuit;

delaying said resonating waveform to generate a delayed version of said resonating waveform therefrom;

injecting said delayed version of said resonating waveform into said tank circuit to modify the frequency of said resonating waveform; and

wherein the oscillator signal frequency is determined by the time said resonating waveform is delayed.

6. The method according to claim 5, wherein the frequency of said oscillating signal is controlled by a tunable element in said tank circuit.

7. The method according to claim 5, wherein said delaying comprises generating two signals phase separated by approximately 90 degrees.

8. The method according to claim 5, further comprising converting the resonating waveform to a square wave clock for input to a phase generator.

9. An oscillator circuit, comprising:

a digitally controlled oscillator (DCO) incorporating an LC tank circuit and operative to generate a resonating waveform;

a phase generator for operative to generate a coarse delayed version of said resonating waveform;

a digital phase rotator (DPR) circuit operative to generate a fine delayed version of said resonating waveform by interpolating said coarse delayed version of said resonating waveform;

a feedback loop coupled to said digitally controlled oscillator and said digital phase rotator circuit, said feedback loop operative to inject said fine delayed version of said resonating waveform back into said tank circuit; and

wherein said oscillator circuit frequency is determined by the duration said resonating waveform is delayed by said phase generator and said digital phase rotator circuit.

10. The oscillator circuit according to claim 9, wherein said resonating frequency of said digitally controlled oscillator is controlled by a tunable element in said tank circuit.

11. The oscillator circuit according to claim 10, wherein said tunable element comprises a tunable capacitor.

12. The oscillator circuit according to claim 9, further comprising a oscillator buffer operative to convert the output of said digitally controlled oscillator to a square wave clock for input to said phase generator.

13. The oscillator circuit according to claim 9, wherein said phase generator is operative to generate first and second output clocks having an approximately quadrature phase relationship.

14. The oscillator circuit according to claim 9, wherein said digital phase rotator circuit is operative to interpolate between first and second output clocks generated by said phase generator so as to generate first and second synchronous current pulses which are summed and injected back into said LC tank circuit for determining the frequency of oscillation of said oscillator circuit.

15. The oscillator circuit according to claim 9, wherein said digital phase rotator circuit comprises first and second interleaved current steering digital to analog converters (DACs) having mutually exclusive selection of current sources.

16. The oscillator circuit according to claim 9, wherein said coarse delayed version of said resonating waveform is doubled in frequency compared to said fine delayed version of said resonating waveform.