Adapting filter to detected interference level
A receiver uses a sigma delta ADC ( 126 ) and an adaptable digital filter ( 132 ). Detector circuitry detects information about unwanted parts of the signal from an oversampled digital signal, before the filtering, and feeds forward the detected information to the filter, to adapt the filter. By feeding forward the detection information, rather than feeding back an output of the filter, the adaptation can respond much more quickly to rapid changes in the unwanted interference. This enables reduced filtering to save power when interference is low, without risking a sudden increase in interference causing an avalanche of errors before the filter can be adapted correctly. The filter receives the oversampled digital signal combines decimation and channel filtering in one stage.
1. A circuit comprising an analogue to digital converter ADC for converting an input signal to a digital signal, an adaptable digital filter for filtering the digital signal, a detector for detecting information about an unwanted part of the input signal, from the input signal or from the digital signal before the filter, the detector comprising circuitry for determining a frequency of the unwanted part, and means for feeding forward the detected information to the filter, the filter being arranged to adapt according to the information, the analogue to digital converter ADC comprising a noise shaping circuit, and the detector being arranged to use an output of the noise shaping circuit.
2. The circuit of claim 1 , the input signal comprising multiple channels, and the digital filter comprising a channel filter for selecting a desired channel.
3. The circuit of claim 2 , the analogue to digital converter ADC comprising a sigma delta ADC having a modulator for outputting an oversampled digital signal, and a decimator.
4. The circuit of claim 3 , the digital filter being arranged to receive the oversampled digital signal and combine the ADC decimator operation and the channel filter operation.
5. The circuit of claim 3 , the detector being arranged to detect the unwanted part of the signal from the oversampled digital signal.
6. The circuit of claim 5 , the detector being arranged to detect a frequency that a number of sequences appear in the oversampled digital signal, corresponding to the unwanted part.
7. The circuit of claim 1 , the adaptable digital filter being arranged to adapt any of filter order, filter coefficients, and quantisation level.
8. The circuit of claim 1 , the noise shaping circuit comprising two or more series coupled integrator stages, outputs of two or more of the stages being coupled to the detector.
9. The circuit of claim 8 , the detector comprising circuitry for combining the outputs of the two or more stages so as to give more weight to a preceding one of the stages.
10. An integrated circuit having the circuit of claim 1 .
11. A mobile battery powered device having the circuit of claim 1 .
12. A circuit comprising an analogue to digital converter ADC for converting an input signal to a digital signal, an adaptable digital filter for filtering the digital signal, a detector for detecting information about an unwanted part of the input signal, from the input signal or from the digital signal before the filter, and means for feeding forward the detected information to the filter, the filter being arranged to adapt according to the information, the analogue to digital converter ADC comprising a noise shaping circuit, and the detector being arranged to use an output of the noise shaping circuit, the input signal comprising multiple channels, and the digital filter comprising a channel filter for selecting a desired channel, the analogue to digital converter ADC comprising a sigma delta ADC having a modulator for outputting an oversampled digital signal, and a decimator, the detector being arranged to detect the unwanted part of the signal from the oversampled digital signal, the detector being arranged to detect a frequency that a number of sequences appear in the oversampled digital signal, corresponding to the unwanted part.
13. The circuit of claim 12 , the digital filter being arranged to receive the oversampled digital signal and combine the ADC decimator operation and the channel filter operation.
14. The circuit of claim 12 , the detector comprising circuitry for determining information about wanted and unwanted parts of the input signal, and the digital filter being adaptable according to a comparison of the information about the wanted and unwanted parts.
15. The circuit of claim 14 , the digital filter being arranged to carry out a reduced amount of processing when the comparison indicates a strong signal, than when the comparison indicates a weaker signal.
16. A circuit comprising an analogue to digital converter ADC for converting an input signal to a digital signal, an adaptable digital filter for filtering the digital signal, a detector for detecting information about an unwanted part of the input signal, from the input signal or from the digital signal before the filter, means for feeding forward the detected information to the filter, the filter being arranged to adapt according to the information, the analogue to digital converter ADC comprising a noise shaping circuit, and the detector being arranged to use an output of the noise shaping circuit, the noise shaping circuit comprising two or more series coupled integrator stages, outputs of two or more of the stages being coupled to the detector.
17. The circuit of claim 16 , the detector comprising circuitry for combining the outputs of the two or more stages so as to give more weight to a preceding one of the stages.
18. The circuit of claim 16 , further comprising circuitry arranged to demodulate a signal operable according to the information.
19. The circuit of claim 16 , the detector comprising circuitry for determining a frequency of the unwanted part.
20. The circuit of claim 16 , the input signal comprising multiple channels, and the digital filter comprising a channel filter for selecting a desired channel.