Injection-locked oscillator

1 . An electronic oscillator circuit comprising:

a tank circuit comprising a first inductive winding and a capacitor; and

an injection circuit comprising a second inductive winding and a current controller;

wherein the injection circuit is not electrically connected to the tank circuit;

wherein the current controller is configured such that when it is in a first state, an injected current flows from the current controller through the second inductive winding;

wherein the current controller is configured such that when it is in a second state, no injected current flows through the second inductive winding; and

wherein the first inductive winding and the second inductive winding are coupled such that the injected current in the second inductive winding of the injection circuit causes a corresponding injected current to be induced in the first inductive winding of the tank circuit;

wherein the current controller is an NMOS transistor, arranged such that the source of the NMOS transistor is connected to ground or other sink of current;

wherein a first terminal and a second terminal of the second inductive winding are connected to a power supply rail or other supply of current; and

wherein a third terminal of the second inductive winding is connected to the drain of the NMOS transistor;

wherein the third terminal is a centre tap of the second inductive winding.

2 . The electronic oscillator circuit of claim 1 , wherein the first inductive winding comprises a first winding part and a second winding part;

wherein the first winding part is connected between a first side of the tank circuit and a central terminal;

wherein the second winding part is connected between a second side of the tank circuit and the central terminal;

wherein the induced current in the first winding part flows from the central terminal towards the first side of the tank circuit; and

wherein the induced current in the second winding part flows from the second side of the tank circuit towards the central terminal.

3 . The electronic oscillator circuit of claim 1 , further comprising a first cross-coupled pair circuit connected to the tank circuit.

4 . The electronic oscillator circuit of claim 3 , wherein the first cross-coupled pair circuit comprises a pair of cross-coupled PMOS transistors, the source of each of the PMOS transistors being connected to a power supply rail or other supply of current.

5 . The electronic oscillator circuit of claim 1 , further comprising a second cross-coupled pair circuit connected to the tank circuit.

6 . The electronic oscillator circuit of claim 5 , wherein the second cross-coupled pair circuit comprises a pair of cross-coupled NMOS transistors, the source of each of the NMOS transistors being connected to ground or other sink of current.

7 . The electronic oscillator circuit of claim 1 , further comprising an injection clock source, wherein the injection clock source is configured to apply a clock signal to the current controller in the injection circuit with a predetermined duty-cycle such that the current controller transitions from the second state to the first state at a frequency set by said duty-cycle.

8 . The electronic oscillator of claim 7 , wherein the injection clock source is configured to cause the current controller to transition from the second state to the first state at a frequency close to, or having a harmonic component close to, the resonant frequency of the tank circuit.

9 . The electronic oscillator of claim 1 , wherein the capacitor and the inductive winding are connected in parallel in the tank circuit.

10 . The electronic oscillator of claim 1 , wherein the capacitor is a variable capacitor.

11 . An electronic oscillator circuit comprising:

a tank circuit comprising an inductor and a capacitor, wherein the inductor and the capacitor each have a first terminal connected to a first side of the tank circuit and a second terminal connected to a second side of the tank circuit;

a PMOS transistor; and

an NMOS transistor;

wherein the PMOS transistor is connected to the first side of the tank circuit;

wherein the NMOS transistor is connected to the second side of the tank circuit;

wherein the PMOS transistor is arranged such that it can act as a current source for the tank circuit;

wherein the NMOS transistor is arranged such that it can act as a current sink for the tank circuit;

wherein the PMOS transistor and the NMOS transistor are configured such that when the PMOS transistor and the NMOS transistor are in a first state, an injected current is introduced into the tank circuit from the PMOS transistor, and flows out of the circuit through the NMOS transistor; and

when the first PMOS transistor and the NMOS transistor are in a second state, no current is injected into the tank circuit.

12 . The electronic oscillator circuit of claim 11 , further comprising a first cross-coupled pair circuit connected to the tank circuit.

13 . The electronic oscillator circuit of claim 12 , wherein the first cross-coupled pair circuit comprises a pair of cross-coupled PMOS transistors, the source of each of the PMOS transistors being connected to a power supply rail or other supply of current.

14 . The electronic oscillator circuit of claim 11 , further comprising a second cross-coupled pair circuit connected to the tank circuit.

15 . The electronic oscillator of claim 14 , wherein the second cross-coupled pair circuit comprises a pair of cross-coupled NMOS transistors, the source of each of the NMOS transistors being connected to ground or other sink of current.

16 . The electronic oscillator circuit of claim 11 , further comprising an injection clock source, wherein the injection clock source is configured to apply a clock signal to the PMOS transistor and the NMOS transistor with a predetermined duty-cycle such that the PMOS transistor and the NMOS transistor transition from the second state to the first state at a frequency set by said duty-cycle of the injection clock source.

17 . The electronic oscillator of claim 16 , wherein the injection clock source is configured to cause the PMOS transistor and the NMOS transistor to transition from the second state to the first state at a frequency close to, or having a harmonic component close to, the resonant frequency of the tank circuit.

18 . The electronic oscillator of claim 11 , wherein the capacitor and inductor are connected in parallel in the tank circuit.

19 . The electronic oscillator of claim 11 , wherein the capacitor is a variable capacitor.

20 . An electronic oscillator circuit comprising:

a tank circuit comprising a first inductive winding and a capacitor; and

an injection circuit comprising a second inductive winding and a current controller;

wherein the injection circuit is not electrically connected to the tank circuit;

wherein the current controller is configured such that when it is in a first state, an injected current flows from the current controller through the second inductive winding;

wherein the current controller is configured such that when it is in a second state, no injected current flows through the second inductive winding; and

wherein the first inductive winding and the second inductive winding are coupled such that the injected current in the second inductive winding of the injection circuit causes a corresponding injected current to be induced in the first inductive winding of the tank circuit;

wherein the current controller is a PMOS transistor, arranged such that the source of the PMOS transistor is connected to a power supply rail or other supply of current;

wherein a first terminal and a second terminal of the second inductive winding are connected to ground or other sink of current; and

wherein a third terminal of the second inductive winding is connected to the drain of the PMOS transistor;

wherein the third terminal is a centre tap of the second inductive winding.

21 . The electronic oscillator circuit of claim 20 , wherein the first inductive winding comprises a first winding part and a second winding part;

wherein the first winding part is connected between a first side of the tank circuit and a central terminal;

wherein the second winding part is connected between a second side of the tank circuit and the central terminal;

wherein the induced current in the first winding part flows from the central terminal towards the first side of the tank circuit; and

wherein the induced current in the second winding part flows from the second side of the tank circuit towards the central terminal.