Microelectromechanical system resonator-based oscillator

1. A device, comprising:

a microelectromechanical system (MEMS) resonator having terminals; and

an oscillator circuit coupled to the MEMS resonator, the oscillator circuit including:

a first transistor having a first control terminal-, a first current terminal and a second current terminal;

a second transistor having a second control terminal, a third current terminal and a fourth current terminal;

a resonator coupling network configured to:

inductively couple the MEMS resonator terminals to the first current terminal and to the third current terminal; and

couple the first current terminal to the third current terminal;

a control terminal coupling network configured to:

couple the first control terminal to the second control terminal; and

reduce a voltage swing at the first and second transistor control terminals relative to a voltage swing at the first and third current terminals; and

a second terminal coupling network configured to couple the second current terminal to the fourth current terminal, wherein the second terminal coupling network has a resonant frequency approximately equal to a resonant frequency of the MEMS resonator.

2. The device of claim 1 , wherein the oscillator circuit includes a control terminal bias network configured to provide a programmable bias voltage to the control terminal coupling network.

3. The device of claim 2 , wherein the control terminal bias network includes:

a third transistor having a third control terminal configured to receive a first voltage indicating a first portion of a digital code, a fifth current terminal coupled to a supply voltage terminal, and a sixth current terminal coupled to a bias voltage terminal; and

a fourth transistor having a fourth control terminal configured to receive a second voltage indicating a second portion of the digital code, a seventh current terminal coupled to the bias voltage terminal, and an eighth current terminal coupled to a ground terminal;

wherein a voltage at the bias voltage terminal is the programmable bias voltage.

4. The device of claim 1 , wherein the resonator coupling network is a transformer including:

a primary coil coupled to the first current terminal and to the third current terminal; and

a secondary coil coupled to the MEMS resonator terminals.

5. The device of claim 4 , wherein the primary coil is coupled to a supply voltage terminal, the first current terminal is a positive output terminal, and the third current terminal is a negative output terminal.

6. The device of claim 4 , wherein the transformer is an autotransformer, the primary coil of the autotransformer has a number of turns (n) and the secondary coil is a subset of the primary coil having a number of turns (m).

7. The device of claim 4 , wherein the transformer includes a tertiary coil and the control terminal coupling network includes the tertiary coil coupled to the first control terminal and to the second control terminal.

8. The device of claim 1 , wherein the control terminal coupling network includes:

a first capacitor coupled to the first control terminal and to a ground terminal;

a second capacitor coupled to the second control terminal and to a ground terminal;

a first cross-coupled capacitor coupled to the first control terminal and to the third current terminal; and

a second cross-coupled capacitor coupled to the second control terminal and to the first current terminal.

9. The device of claim 1 , wherein the second terminal coupling network includes a series inductor-capacitor circuit coupled to the second current terminal and to the fourth current terminal.

10. The device of claim 9 , wherein the series inductor-capacitor circuit includes:

a first capacitor coupled to the second current terminal;

an inductor coupled to the first capacitor; and

a second capacitor coupled to the inductor and to the fourth current terminal;

wherein the second terminal coupling network includes a first resistor coupled to the second current terminal and to a ground terminal and a second resistor coupled to the fourth current terminal and to the ground terminal.

11. The device of claim 1 , wherein each of the first and second transistors is a bipolar junction transistor, each of the first and second control terminals is a base, each of the first and third current terminals is a collector, and each of the second and fourth current terminals is an emitter.

12. A device, comprising:

a microelectromechanical system (MEMS) resonator having a first MEMS terminal and a second MEMS terminal; and

an oscillator circuit coupled to the MEMS resonator, the oscillator circuit including:

a first transistor having a first control terminal, a first current terminal and a second current terminal;

a second transistor having a second control terminal, a third current terminal and a fourth current terminal;

a transformer including a primary coil coupled to the first current terminal and the third current terminal, and a secondary coil coupled to the first and second MEMS terminals;

a control terminal coupling network coupled between the first and second control terminals; and

a second terminal coupling network coupled between the second and fourth current terminals, the second terminal coupling network comprising a first capacitor, an inductor and a second capacitor coupled in series between the second and fourth current terminals.

13. The device of claim 12 , wherein the control terminal coupling network includes:

a third capacitor coupled to the first control terminal and to a ground terminal;

a fourth capacitor coupled to the second control terminal and to a ground terminal;

a first cross-coupled capacitor coupled to the first control terminal and to the third current terminal; and

a second cross-coupled capacitor coupled to the second control terminal and to the first current terminal.

14. The device of claim 12 , wherein the control terminal coupling network includes a tertiary coil of the transformer.

15. The device of claim 12 , wherein the oscillator circuit includes a control terminal bias network configured to provide a programmable bias voltage to the control terminal coupling network.

16. The device of claim 15 , wherein the control terminal bias network includes:

a third transistor having a third control terminal configured to receive a first voltage indicating a first portion of a digital code, a fifth current terminal coupled to a supply voltage terminal, and a sixth current terminal coupled to a bias voltage terminal; and

a fourth transistor having a fourth control terminal configured to receive a second voltage indicating a second portion of the digital code, a seventh current terminal coupled to the bias voltage terminal, and an eighth current terminal coupled to a ground terminal;

wherein a voltage at the bias voltage terminal is the programmable bias voltage.

17. The device of claim 12 , wherein the primary coil is coupled to a supply voltage terminal, the first current terminal is a positive output terminal, and the third current terminal is a negative output terminal.

18. The device of claim 12 , wherein the transformer is an autotransformer, the primary coil of the autotransformer has a number of turns (n) and the secondary coil is a subset of the primary coil having a number of turns (m).

19. A device, comprising:

a microelectromechanical system (MEMS) resonator having a first MEMS terminal and a second MEMS terminal; and

an oscillator circuit coupled to the MEMS resonator, the oscillator circuit including:

a first transistor having a first control terminal, a first current terminal and a second current terminal;

a second transistor having a second control terminal, a third current terminal and a fourth current terminal; and

a coupling network configured to couple the second current terminal to the fourth current terminal, wherein the coupling network has a resonant frequency approximately equal to a resonant frequency of the MEMS resonator; and

a transformer including:

a primary coil coupled to the first control terminal and to the second control terminal;

a secondary coil coupled to the first MEMS terminal and the second MEMS terminal; and

a tertiary coil coupled to the first control terminal and the second control terminal.

20. The device of claim 19 , wherein the oscillator circuit includes a control terminal bias network configured to provide a programmable bias voltage to the tertiary coil.

21. The device of claim 20 , wherein the control terminal bias network includes:

a third transistor having a third control terminal configured to receive a first voltage indicating a first portion of a digital code, a fifth current terminal coupled to a supply voltage terminal, and a sixth current terminal coupled to a bias voltage terminal; and

a fourth transistor having a fourth control terminal configured to receive a second voltage indicating a second portion of the digital code, a seventh current terminal coupled to the bias voltage terminal, and an eighth current terminal coupled to a ground terminal;

wherein a voltage at the bias voltage terminal is the programmable bias voltage.