Patent ID: 7586385

Claim:
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.