RF power extracting circuit and related techniques

1. A far-field power extraction circuit comprising:

an antenna comprising:

an inductive loop;

two impedance inverters each coupled to the inductive loop; and

two resonant loops each coupled to a respective one of the two impedance inverters, the antenna configured to receive an electromagnetic signal, said antenna having a resonant frequency and configured to subsequently match an antenna impedance with a remainder of the far-field power extraction circuit at the resonant frequency; and

a multi-stage rectifier coupled to the antenna, the multi-stage rectifier adapted to receive an electromagnetic signal from the antenna and in response thereto, to produce a direct current (DC) voltage at a rectifier output, the multi-stage rectifier comprising N stages, where N >1,

wherein the multi-stage rectifier comprises at least one circuit element having a nonlinear capacitance characteristic and at least one inductor between each of the rectifier stages.

2. The circuit of claim 1 wherein each of the two resonant loops has a perimeter substantially equal to one-half wavelength at the resonant frequency.

3. The circuit of claim 1 wherein a first rectifier stage of the N rectifier stages includes four transistors.

4. The circuit of claim 3 wherein the four transistors comprise two p-type metal-oxide-semiconductor (PMOS) transistors.

5. The circuit of claim 4 wherein the four transistors comprise two n-type metal-oxide-semiconductor (NMOS) transistors.

6. The circuit of claim 3 wherein the four transistors comprises a floating gate transistor.

7. The circuit of claim 1 wherein the antenna is provided having a size and shape such that it is resonant at a frequency of about 900 MHz.

8. The circuit of claim 1 , further comprising a feedback tuning network coupled between the antenna and a terminal of the rectifier at which a voltage is generated.