Patent ID: 7660570

Claim:
A filter circuit for adjusting attenuation of a first signal in response to the power of the first signal without use of an external power source other than the first signal itself, the filter circuit comprising: a first terminal configured to receive the first signal; a first element in electrical communication with said first terminal and configured to pass a portion of the first signal that is above a first frequency without attenuation and configured to cause attenuation to a portion of the first signal that is below the first frequency; a second element in electrical communication with said first terminal and said first element and configured to rectify the first signal; a third element in electrical communication with said second element and configured to cause attenuation to the first signal; and a second terminal in electrical communication with said first element and said third element and configured to output the first signal; wherein the magnitude of said attenuation in said third element is a function of the magnitude of the voltage of the first signal at an input to said third element.