Method and apparatus for varying an impedance
First Claim
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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.
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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.
64 Citations
18 Claims
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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:
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(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. - View Dependent Claims (2, 3, 4, 5, 6)
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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:
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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. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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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:
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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.
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Specification