Notch filter and apparatus for receiving and transmitting radio-frequency signals incorporating same
View Patent ↗A notch filter suitable for attenuating certain frequencies of a radio-frequency signal includes an input for receiving the radio-frequency signal and an output for the output of a portion of the radio-frequency signal, first and second capacitive means, at least one inductor and a negative resistance circuit suitable for compensating the resistive losses of said at least one inductor. The inductor and the first and second capacitive means are placed to produce a resonator and the filter comprises a control device suitable for controlling the negative resistance circuit. The input impedance of the filter comprises a pole and a zero, with the pole depending on the second capacitive means and the zero depending on both the first and second capacitive means. The first and second capacitive means are variable and the control device is suitable for controlling the first and second capacitive means.
1. A notch filter comprising:
an input/output terminal;
first and second variable capacitor circuits coupled to the input/output terminal, and having an intermediate node;
a variable gain transconductance amplifier having an input coupled to the intermediate node, and an output;
a peak detector having an input coupled to the output of the transconductance amplifier, and an output;
a first comparator having a first input coupled to the output of the peak detector, a second input for receiving a reference voltage, and an output;
a second comparator having a first input coupled to the output of the transconductance amplifier, a second input for receiving a reference frequency, and an output; and
a control circuit having inputs coupled to the output of the first comparator and the second comparator, and outputs for controlling the first and second variable capacitor circuits and the transconductance amplifier.
2. The notch filter of claim 1 wherein the first variable capacitor circuit comprises a switchable capacitor array.
3. The notch filter of claim 1 wherein the second variable capacitor circuit comprises a switchable capacitor array.
4. The notch filter of claim 1 wherein the variable gain transconductance amplifier comprises a transconductance amplifier coupled to an error amplifier.
5. The notch filter of claim 1 wherein the variable gain transconductance amplifier comprises a DAC.
6. The notch filter of claim 1 wherein the first comparator comprises a voltage comparator.
7. The notch filter of claim 1 wherein the second comparator comprises a frequency comparator.
8. The notch filter of claim 1 further comprising an inductor in parallel with the second variable capacitor circuit.
9. The notch filter of claim 1 further comprising a resistor in series with the first variable capacitor circuit.
10. The notch filter of claim 1 further comprising a resistor in parallel with the second variable capacitor circuit.
11. A notch filter comprising:
first, second, and third terminals;
a first variable capacitor circuit coupled between the first and second terminals;
a second variable capacitor circuit coupled between the second terminal and ground;
a variable gain transconductance circuit coupled between the second and third terminals;
a peak detector coupled to the variable gain transconductance circuit;
a first comparator coupled to the peak detector;
a second comparator coupled to the variable gain transconductance circuit; and
a control circuit coupled to the first comparator and second comparator for controlling the first and second variable capacitor circuits and the variable transconductance circuit.
12. The notch filter of claim 11 wherein the first variable capacitor circuit comprises a switchable capacitor array.
13. The notch filter of claim 11 wherein the second variable capacitor circuit comprises a switchable capacitor array.
14. The notch filter of claim 11 wherein the variable gain transconductance circuit comprises a transconductance amplifier coupled to an error amplifier.
15. The notch filter of claim 11 wherein the variable gain transconductance amplifier comprises a DAC.
16. The notch filter of claim 11 wherein the first comparator comprises a voltage comparator.
17. The notch filter of claim 11 wherein the second comparator comprises a frequency comparator.
18. The notch filter of claim 11 further comprising an inductor in parallel with the second variable capacitor circuit.
19. The notch filter of claim 11 further comprising a resistor in series with the first variable capacitor circuit.
20. The notch filter of claim 11 further comprising a resistor in parallel with the second variable capacitor circuit.