Transforming voltage in a voltage controlled oscillator for wireless sensor devices

1. A wireless sensor device comprising a voltage controlled oscillator, the voltage controlled oscillator comprising:

a first inverter comprising a first inverter input node, a third inverter input node, and a first inverter output node;

a second inverter comprising a second inverter input node, a fourth inverter input node, and a second inverter output node; and

a transformer connected between the first inverter and the second inverter, the transformer comprising:

a primary winding portion connected between the first inverter output node and the second inverter output node, connected between the third inverter input node and the fourth inverter input node, and inductively coupled to a first secondary winding portion and a second secondary winding portion;

the first secondary winding portion connected between the primary winding portion and the first inverter input node; and

the second secondary winding portion connected between the primary winding portion and the second inverter input node.

2. The wireless sensor device of claim 1 , wherein the first inverter comprises an n-type MOSFET and a p-type MOSFET, and the second inverter comprises an n-type MOSFET and a p-type MOSFET.

3. The wireless sensor device of claim 1 , wherein the first inverter comprises two n-type MOSFETs and two p-type MOSFETs, and the second inverter comprises two n-type MOSFETs and two p-type MOSFETs.

4. The wireless sensor device of claim 1 , wherein the voltage controlled oscillator comprises a capacitive portion connected between the first inverter and the second inverter.

5. The wireless sensor device of claim 4 , wherein the capacitive portion comprises a digital-controlled capacitor element.

6. The wireless sensor device of claim 5 , wherein the capacitive portion comprises an analog-controlled capacitor element.

7. A voltage controlled oscillator circuit comprising:

a transformer having a primary winding portion connected between a first node and a second node, a first secondary winding portion connected between the first node and a third node, and a second secondary winding portion connected between the second node and a fourth node;

a capacitive portion connected between the first node and the second node;

a first inverter having a first inverter input node connected to the third node, a third inverter input node connected to the first node, and a first inverter output node connected to the second node; and

a second inverter having a second inverter input node connected to the fourth node, a fourth inverter input node connected to the second node, and a second inverter output node connected to the first node.

8. The voltage controlled oscillator of claim 7 , wherein

the first inverter comprises:

a first p-type transistor having a source coupled to a first power supply node, a gate of the first p-type transistor being the first inverter input node; and

a first n-type transistor having a source coupled to a second power supply node, a gate of the first n-type transistor being the third inverter input node, a drain of the first p-type transistor and a drain of the first n-type transistor being connected together as the first inverter output node; and

the second inverter comprises:

a second p-type transistor having a source coupled to the first power supply node, a gate of the second p-type transistor being the second inverter input node; and

a second n-type transistor having a source coupled to the second power supply node, a gate of the second n-type transistor being the fourth inverter input node, a drain of the second p-type transistor and a drain of the second n-type transistor being connected together as the second inverter output node.

9. The voltage controlled oscillator of claim 7 , wherein

the first inverter comprises:

a first p-type transistor having a source coupled to a first power supply node;

a first n-type transistor having a source coupled to a second power supply node, a gate of the first p-type transistor and a gate of the first n-type transistor being connected together as the first inverter input node;

a second p-type transistor having a source coupled to the first power supply node; and

a second n-type transistor having a source coupled to the second power supply node, a gate of the second p-type transistor and a gate of the second n-type transistor being connected together as the third inverter input node, respective drains of the first p-type transistor, the first n-type transistor, the second p-type transistor, and the second n-type transistor being connected together as the first inverter output node; and

the second inverter comprises:

a third p-type transistor having a source coupled to the first power supply node;

a third n-type transistor having a source coupled to the second power supply node, a gate of the third p-type transistor and a gate of the third n-type transistor being connected together as the second input node;

a fourth p-type transistor having a source coupled to the first power supply node; and

a fourth n-type transistor having a source coupled to the second power supply node, a gate of the fourth p-type transistor and a gate of the fourth n-type transistor being connected together as the third inverter input node, respective drains of the third p-type transistor, the third n-type transistor, the fourth p-type transistor, and the fourth n-type transistor being connected together as the second inverter output node.

10. The voltage controlled oscillator of claim 7 , wherein the transformer comprises an autotransformer.

11. The voltage controlled oscillator of claim 7 , wherein the capacitive element comprises a first capacitor bank and a second capacitor bank, the first capacitor bank comprising analog-tunable capacitors, the second capacitor bank comprising discretely-controlled capacitors.

12. A method comprising:

outputting a first voltage from a first inverter to a first node of an inductive-capacitive (LC) tank, the LC tank comprising a capacitive portion and a primary winding portion of a transformer, the capacitive portion being connected between the first node and a second node of the LC tank, the primary winding portion being connected between the first node and the second node;

inputting a second voltage from a third node to a first input node of the first inverter, a first secondary winding portion of the transformer being connected between the second node and the third node; and

inputting a third voltage from the second node to a second input node of the first inverter.

13. The method of claim 12 , wherein the first voltage oscillates.

14. The method of claim 12 , comprising transforming voltage in the transformer between the primary winding portion and the first secondary winding portion.

15. The method of claim 12 further comprising:

outputting a third voltage from a second inverter to the second node; and

inputting a fourth voltage from a fourth node to a second input node of the second inverter, a second secondary winding portion of the transformer being connected between the first node and the fourth node.

16. The method of claim 15 , comprising:

transforming voltage in the transformer between the primary winding portion and the first secondary winding portion; and

transforming voltage in the transformer between the primary winding portion and the second secondary winding portion.

17. The method of claim 15 , wherein the transformer comprises an autotransformer that includes the primary winding portion, the first secondary winding portion and the second secondary winding portion.

18. The method of claim 12 further comprising controlling a resonance frequency of the LC tank by at least one of:

controlling switches in the capacitive portion to selectively couple capacitors to the LC tank; or

tuning analog-tunable capacitors in the capacitive portion.