Method and apparatus for varying an impedance

• US 20080116990A1
• Filed: 11/18/2006
• Published: 05/22/2008
• Est. Priority Date: 11/18/2006
• Status: Active Grant

• Current Assignee: Rfmicron, Inc.
• Original Assignee: Rfmicron, Inc.
• Inventors: Rokhsaz, Shahriar
• Granted Patent: US 7,586,385 B2
• Time in Patent Office: Days
• US Class Current: 333/32
• CPC Class Codes: H03H 7/40 Automatic matching of load impedance to source impedance
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03J 3/20 of single resonant circuit by varying inductance only or capacitance only

Abstract

A method and apparatus for dynamically varying the impedance of a tank circuit whereby, over time, the response of the circuit to a received signal is maximized.

Claims

1. A method for dynamically varying the impedance of a tank circuit comprising an inductor and a capacitor, the capacitance of which can be varied in a selected one of first and second directions, the method comprising the steps of:

(1) selecting one of said first and second directions;

(2) capturing a current response of the circuit to a received signal;

(3) varying the capacitor in said selected direction;

(4) comparing the captured response to the current response;

(5) if the comparison made in step 4 indicates that the current response is weaker than the captured response, selecting the other of said directions; and

(6) returning to step 2.

2. The method of claim 1 wherein the first direction is selected to increase the capacitance of the variable capacitor, and the second direction is selected to decrease the capacitance of the variable capacitor.

3. The method of claim 1 wherein step 1 is further characterized as:

(1) selecting, at random, one of said first and second directions.

4. The method of claim 1 wherein step 1 is further characterized as:

(1) selecting a predetermined one of said first and second directions.

5. The method of claim 1 wherein step 6 is further characterized as:

(6) if the comparison made in step 4 indicates that the difference between the current response and the captured response is greater than a predetermined minimum, returning to step 2.

6. The method of claim 1 wherein step 6 is further characterized as:

(6) if the comparison made in step 4 indicates that the difference between the current response and the captured response is greater than a predetermined minimum, selectively returning to step 2.

7. A tuning circuit for dynamically varying the impedance of a tank circuit comprising an inductor and a capacitor, the capacitance of which can be varied in a selected one of first and second directions, the tuning circuit comprising:

a reference voltage generator, coupled to the tank circuit, to produce a reference voltage proportional to the response of the tank circuit to a received signal;

a differentiator, coupled to the generator, to determine a polarity of the change in the reference voltage between a first point in time and a second point in time;

a direction selector, coupled to the differentiator, to select one of said first and second directions in response to said polarity; and

a ramp generator, coupled to the selector and to the capacitor, to selectively vary the capacitance of said capacitor in said selected direction.

8. The circuit of claim 7B01 wherein the first direction is selected to increase the capacitance of the variable capacitor, and the second direction is selected to decrease the capacitance of the variable capacitor.

9. The circuit of claim 7B01 wherein the direction selector is adapted to select, at random, one of said first and second directions prior to said second point in time.

10. The circuit of claim 9B03 wherein the direction selector is adapted to select the other of said first and second directions in response to a negative polarity.

11. The circuit of claim 7B01 wherein the direction selector is adapted to select a predetermined one of said first and second directions prior to said second point in time.

12. The circuit of claim 11B05 wherein the direction selector is adapted to select the other of said first and second directions in response to a negative polarity.

13. The circuit of claim 7B01 wherein the voltage generator comprises:

a rectifier, coupled to the tank circuit; and

a low pass filter, coupled to the rectifier.

14. The circuit of claim 7B01 wherein the differentiator comprises:

a sample-and-hold, coupled to the voltage generator, to sample the reference voltage at said first point in time; and

a comparator, having a first input coupled to the sample-and-hold, and a second input coupled to the voltage generator.

15. The circuit of claim 7B01 wherein the direction selector comprises:

a toggle, coupled to the differentiator, to toggle between said first and second directions in response to a negative polarity.

16. The circuit of claim 7B01 wherein the ramp generator comprises:

a shift register, coupled to the direction selector.

17. The circuit of claim 7B01 wherein the voltage generator comprises:

a non-linear transfer circuit, coupled to the tank circuit.

18. A tuning circuit for dynamically varying the impedance of a tank circuit comprising an inductor and a capacitor, the capacitance of which can be varied in a selected one of first and second directions, the tuning circuit comprising:

a reference voltage generator, coupled to the tank circuit, to produce a reference voltage proportional to the response of the tank circuit to a received signal, wherein the voltage generator comprises;

a rectifier, coupled to the tank circuit; and

a low pass filter, coupled to the rectifier;

a differentiator, coupled to the generator, to determine a polarity of the change in the reference voltage between a first point in time and a second point in time, wherein the differentiator comprises;

a sample-and-hold, coupled to the voltage generator, to sample the reference voltage at said first point in time; and

a comparator, having a first input coupled to the sample-and-hold, and a second input coupled to the voltage generator;

a direction selector, coupled to the differentiator, to select one of said first and second directions in response to said polarity, wherein the direction selector comprises;

a toggle, coupled to the differentiator, to toggle between said first and second directions in response to a negative polarity; and

a ramp generator, coupled to the selector and to the capacitor, to selectively vary the capacitance of said capacitor in said selected direction, wherein the ramp generator comprises;

a shift register, coupled to the direction selector.