Patent ID: 7702294

Claim:
A notch filter suitable for attenuating certain frequencies of a radio-frequency signal, said filter comprising: an input for receiving said radio-frequency signal and an output for the output of a portion of said radio-frequency signal; first and second capacitive means; at least one inductor and a negative resistance circuit for compensating the resistive losses of said at least one inductor, said inductor and said first and second capacitive means being placed to produce a resonator; and a control device suitable for controlling said negative resistance circuit, the input impedance of said filter comprising a pole and a zero, wherein said pole depends on said second capacitive means and said zero depends on both said first and second capacitive means, said first and second capacitive means are variable and said control device is operative for controlling said first and second capacitive means, wherein said control device comprises: means for detecting the peak of said portion of signal in output from the filter; an amplitude comparator for comparing the value of the signal in output from the peak detector with a reference signal; and a frequency comparator for comparing the frequency of the portion of signal in output from the filter with a reference frequency, said comparators being operative for sending signals representative of said comparisons to a logic means operative for sending control signals to said first and second capacitive means and to said negative resistance circuit until the amplitude and the frequency of said portion of signal in output from the filter are substantially equal to said reference signal and to said reference frequency.