Frequency agile filter using a digital filter and bandstop filtering
View Patent ↗The present invention is a hybrid RF-digital signal processor-based filter for multiband radio architectures systems capable of spectrum re-farming and software defined radios. It performs low-loss frequency agile multiple notch filtering at RF where a large dynamic range exists at a filter input between signals in a stopband and passband. It is a frequency dependent signal attenuation apparatus having two paths connected together by directional couplers. The first path comprising a component such as a delay component or duplexer. The second path comprising a bandstop filter connected to a down converter, a digital filter, and an up converter. At the output of a power amplifier, the invention can be used to attenuate spurs, or noise within bands with strict emission constraints. At the input of a low noise amplifier, the invention can be used to attenuate blockers and transmitter noise outside of the receiver passband.
1. A frequency dependent signal attenuation apparatus, comprising:
an input signal receiver coupled to a first directional coupler, which splits the input signals into a first signal path and a second signal path;
a bandstop filter coupled to the first signal path, said bandstop filter provides its output signal to a first RF/Analog frequency down converter, the first RF/Analog frequency down converter having one or more down converter mixers coupled to a first filter and an analog to digital converter, and said one or more down converter mixers being controlled by a local frequency oscillator signal;
a second filter coupled to the one or more down converter mixers in the first RF/Analog frequency down converter through the first filter and analog to digital converter in the first RF/Analog frequency down converter;
a second RF/Analog frequency up converter coupled to the second filter, which has one or more up converter mixers coupled to the second filter through a third filter and a digital to analog converter, each of said one or more up converter mixers being controlled by a local frequency oscillator signal, said second RF/Analog frequency up converter provides its output signal to a second directional coupler that also receives a second signal along the second path from the first directional coupler, said signal from the first directional coupler passes through a component before being received at the second directional coupler; and
a signal output provided by the second directional coupler that includes recombined signals that have passed through the first and second paths, said signal from said first signal path attenuates the signal from the second signal path at the second directional coupler.
2. The apparatus of claim 1 , wherein said second filter is a reconfigurable discrete-time filter.
3. The apparatus of claim 1 , wherein said bandstop filter is a notch filter.
4. The apparatus of claim 3 , wherein said notch filter is tunable.
5. The apparatus of claim 1 , wherein said second filter is a programmable digital filter.
6. The apparatus of claim 1 , wherein the frequency down converter mixers are frequency agile.
7. The apparatus of claim 1 , wherein the frequency up converter mixers are frequency agile.
8. The apparatus of claim 1 , further including a circuit that exhibits negative group delay over frequencies where attenuation is desired that is placed on the first path.
9. The apparatus of claim 1 , wherein said bandstop filter is tunable.
10. A frequency dependent signal attenuation apparatus, comprising:
an input signal receiver coupled to a first directional coupler, which splits the input signals into a first signal path and a second signal path;
a bandstop filter coupled to the first signal path, said bandstop filter providing its output signal to a first RF/Analog frequency down converter, the first RF/Analog frequency down converter having one or more down converter mixers coupled to a first filter and an analog to digital converter, and said one or more down converter mixers being controlled by a local frequency oscillator signal;
a second filter coupled to one or more down converter mixers in the first RF/Analog frequency down converter through the first filter and analog to digital converter in the first RF/Analog frequency down converter;
a second RF/Analog frequency up converter coupled to the second filter, which has one or more up converter mixers coupled to the second filter through a third filter and a digital to analog converter, each of said one or more up converter mixers being controlled by a local frequency oscillator signal, said second RF/Analog frequency up converter providing its output signal to a second directional coupler that also receives a second signal along the second path from the first directional coupler, said signal from the first directional coupler passes through a component element before being received at the second directional coupler, a signal output provided by the second directional coupler that includes recombined signals that have passed through the first and second paths; and
a third directional coupler coupled to the second directional coupler, which provides a signal to a third RF/Analog frequency down converter, said down converter providing a signal to a controller that provides a feedback control signal to the second filter.
11. The apparatus of claim 10 , wherein said second filter is a reconfigurable discrete-time filter.
12. The apparatus of claim 10 , wherein said bandstop filter is a notch filter.
13. The apparatus of claim 12 , wherein said notch filter is tunable.
14. The apparatus of claim 10 , wherein said second filter is a programmable digital filter.
15. The apparatus of claim 10 , wherein the frequency down converter mixers are frequency agile.
16. The apparatus of claim 10 , wherein the frequency up converter mixers are frequency agile.
17. The apparatus of claim 10 , further including a circuit that exhibits negative group delay over frequencies where attenuation is desired that is placed on the first path.
18. The apparatus of claim 10 , wherein said bandstop filter is tunable.
19. A method of providing a frequency dependent attenuated signal comprising the steps of:
receiving an input signal at a first directional coupler;
splitting the input signal at the first directional coupler into a first signal path and a second signal path;
receiving a signal along the first signal path at a bandstop filter where signal along said first signal path is filtered;
providing a signal from the bandstop filter to a first RF/Analog frequency down converter, the first RF/Analog frequency down converter processing the received signal with one or more analog to digital converters, one or more down converter mixers and a first filter,
providing an output signal from the first RF/Analog frequency down converter to a second filter, which processes and filters the signal provided on the first signal path;
receiving the output of the second filter at a second RF/Analog frequency up converter, which processes the signal in one or more digital to analog converters, one or more up converter mixers, and a third filter;
providing the signal from the second RF/Analog frequency up converter to a second directional coupler; and
combining at the second directional coupler the output of the bandstop filter with a signal from the first directional coupler that passes through a component before being received at the second directional coupler, said combined signal produced at the output of the second directional coupler is said signal from said first signal path attenuated by the signal from said second signal path.
20. The method of claim 19 further comprising the steps of;
providing the combined signal produced at the output of the second directional coupler to a third directional coupler, which provides a signal to a third RF/Analog frequency down converter; and
providing a feedback signal from the third RF/Analog frequency down converter to a controller that provides a feedback control signal to the second filter.
21. The method of claim 20 further comprising the step of:
providing an output signal from the third directional coupler.
22. The method of claim 19 wherein said second filter is a reconfigurable discrete-time filter.
23. The method of claim 19 wherein said second filter is a programmable digital filter.