Ordered electromagnetic interference cancellation
View Patent ↗Progressive cancellation of electromagnetic interference (EMI) is achieved by establishing a canceller stage processing order in a receiver feed circuit. Such a processing order may be one that progressively narrows an interference analysis bandwidth around desired target signal and optimizes gain-bandwidth characteristics of a cancellation loop in each canceller stage accordingly. A cancellation signal generated by each canceller stage is adaptively controlled without disturbing the stability of the cancellation loop. By doing so, the residual interference-to-noise ratio at each adaptive canceller stage is optimized independently from the closed cancellation loop control of the other canceller stages resulting in improved interference cancellation in the receiver feed circuit.
1. An apparatus comprising:
an interference reference circuit configured to provide an interference reference signal indicative of electromagnetic interference impinging on a target signal;
a plurality of canceller stages configured to generate respective cancellation signals from respective reference signals provided thereto, the canceller stages configured to evaluate the reference signals over respective analysis bandwidths, each of the analysis bandwidths encompassing a frequency band of the target signal by an amount other than that of other of the canceller stages;
a receiver feed circuit coupled to the canceller stages and configured to apply the cancellation signals to an incoming signal comprising the target signal as impinged upon by the electromagnetic interference in a prescribed processing order in a receiver processing path, the application of the cancellation signals in the receiver processing path generating residue signals therein, the receiver feed circuit being constructed to provide each of the residue signals from one canceller stage to another in accordance with the processing order of the receiver processing path, the canceller stages being coupled to the receiver feed circuit such that an initial one of the reference signals evaluated in the processing order is the interference reference signal; and
a receiver coupled to the receiver feed circuit and configured to generate a data signal from a final one of the residue signals in the receiver processing path.
2. The apparatus of claim 1 , wherein the canceller stages are coupled to the receiver feed circuit in a progressively narrowing analysis bandwidth order to define therewith the prescribed order in which the cancellation signals are applied in the receiver processing path.
3. The apparatus of claim 2 , wherein the canceller stages comprise respective control circuits and are coupled to the receiver feed circuit to form respective closed control loops having a gain bandwidth product establishing stability therein, bandwidth and gain in the gain bandwidth product being variable within the corresponding analysis bandwidths.
4. The apparatus of claim 3 , wherein the control loop gains increase in the processing order with narrowing analysis bandwidths in the processing order.
5. The apparatus of claim 4 , wherein each of the control circuits comprises:
an error detector configured to generate an error signal from the reference signal and a corresponding one of the residue signals;
a variable-gain/variable-bandwidth integrator coupled to the error detector and configured to integrate the error signal within the analysis bandwidth of the canceller stage; and
a controller coupled to the integrator and configured to generate the cancellation signal in accordance with the integrated error signal.
6. The apparatus of claim 5 further comprising:
a processor configured to adjust the control loop gains of the integrators to minimize the error signal in the corresponding analysis bandwidth and to adjust the control loop bandwidths in accordance with the adjusted gains to maintain the respective gain bandwidth products.
7. The apparatus of claim 4 , wherein the receiver feed circuit includes a one or more tapping couplers and one or more injection couplers connected in series one to another in alternating order, the canceller stages being coupled to the tap ports and the injection ports in such that the respective residue signals generated at the cancellers are provided to both the canceller stage that generated the residue signal and the canceller stage next in the processing order.
8. The apparatus of claim 4 , wherein the canceller stages are coupled to the interference reference circuit such that all of the reference signals are the interference reference signal.
9. The apparatus of claim 4 , wherein the canceller stages are connected in cascade such that the cancellation signal of each of the canceller stages is provided as the reference signal to a next canceller stage in the processing order.
10. An apparatus comprising:
a reference antenna configured to intercept an interference signal;
a receiving antenna configured to intercept a target signal in the presence of the interference signal;
a receiver feed circuit coupled to the receiving antenna and including a plurality of series-connected signal couplers;
a plurality of canceller stages coupled to the signal couplers and configured to define a prescribed processing order that progressively cancels the interference signal from an incoming signal comprising the interference signal and the target signal, each of the canceller stages extracting a residue signal from one of the signal couplers and injecting a cancellation signal into another of the signal couplers, the cancellation signal being generated from the residual signal analyzed over a corresponding analysis bandwidth encompassing a frequency band of the target signal by an amount other than that of other of the canceller stages; and
a receiver configured to generate a data signal from the residue signal of one of the canceller stages nearest thereto in the processing order.
11. The apparatus of claim 10 , wherein the canceller stages are coupled to the receiver feed circuit in a progressively narrowing analysis bandwidth order to define therewith the prescribed order in which the cancellation signals are applied in the receiver processing path.
12. The apparatus of claim 11 , wherein the canceller stages comprise respective control circuits and are coupled to the receiver feed circuit to form respective closed control loops having a gain bandwidth product establishing stability therein, bandwidth and gain in the gain bandwidth product being variable within the corresponding analysis bandwidths.
13. The apparatus of claim 12 , wherein each of the control circuits comprises:
an error detector configured to generate an error signal from a reference signal and a corresponding one of the residue signals;
a variable-gain/variable-bandwidth integrator coupled to the error detector and configured to integrate the error signal within the analysis bandwidth of the canceller stage; and
a controller coupled to the integrator and configured to generate the cancellation signal in accordance with the integrated error signal.
14. The apparatus of claim 13 further comprising:
a processor configured to adjust the control loop gains of the integrators to minimize the error signal in the corresponding analysis bandwidth and to adjust the control loop bandwidths in accordance with the adjusted gains to maintain the respective gain bandwidth products.
15. The apparatus of claim 13 , wherein the canceller stages are coupled to the reference antenna such that the reference signal of the canceller stages is the interference signal.
16. The apparatus of claim 13 , wherein the canceller stages are connected in cascade such that the cancellation signal of each of the canceller stages is provided as the reference signal to a next canceller stage in the processing order.
17. A method comprising:
configuring gain-bandwidth products for stable operation in respective control loops of respective canceller stages in an interference cancellation system;
progressively attenuating interference in a target signal in a processing order defined by interconnection of the canceller stages;
modifying gain in each of the control loops to maintain a minimum error between a corresponding residue signal and a corresponding reference signal indicative of the interference; and
modifying the bandwidth in the control loops based on the modified gain in each of the control loops to maintain the gain-bandwidth products for stable operation.
18. The method of claim 17 , further comprising:
generating the residue signal at each of the canceller stages from the target signal having the interference therein attenuated by the canceller stages preceding in the processing order.
19. The method of claim 18 , wherein progressively attenuating interference comprises:
generating cancellation signals at each of the canceller stages per a progressively narrowing analysis bandwidth order as the processing order;
applying the cancellation signals to the residue signal at each of the canceller stages.
20. The method of claim 19 further comprising:
integrating the error between the residue signal and the reference signal within the analysis bandwidth and at the gain of the corresponding one of the canceller stages.