Near field communications receiver
View Patent ↗The present application relates to a near field communications (NFC) receiver in which a received NFC signal comprising a carrier signal onto which a data signal is modulated is digitised and downconverted, and the digitised and downconverted received signal is filtered to recover a digitised and downconverted version of the carrier signal of the NFC signal. This digitised and downconverted version of the carrier signal is converted into an analogue signal which is then upconverted to generate an estimate of the carrier signal, and this estimate is combined with the received NFC signal to suppress or negate, at least partially, the carrier of the received signal.
1. A near field communications (NFC) receiver, the receiver comprising:
an analogue to digital converter (ADC) for digitising a received NFC signal comprising a carrier modulated with an information signal;
a downconverter for downconverting the digitised signal;
a filter for filtering the downconverted signal to recover a digitised and downconverted version of the carrier;
a digital to analogue converter (DAC) for converting the digitised and downconverted version of the carrier into an analogue signal;
an upconverter for generating, from the analogue signal generated by the DAC, an estimate of the carrier of the received NFC signal; and
a combiner for combining the estimate with the received NFC signal.
2. A NFC receiver according to claim 1 wherein the ADC comprises a delta-sigma ADC.
3. A NFC receiver according to claim 2 wherein the ADC is configured to have a sampling frequency which is four times the frequency of the carrier of the received NFC signal.
4. A NFC receiver according to claim 1 further comprising a signal generator for generating a local signal for use in the downconverter.
5. A NFC receiver according to claim 4 wherein the signal generator is configured to generate a square wave signal.
6. A NFC receiver according to claim 1 wherein the ADC is configured to have zeros in its frequency response at odd integer multiples of the carrier of the received NFC signal.
7. A NFC receiver according to claim 1 wherein the downconverter is configured to downconvert the digitised signal to DC.
8. A NFC receiver according to claim 7 wherein the upconverter is configured to generate an estimate having a frequency equal to that of the carrier of the received NFC signal.
9. A NFC receiver according to claim 4 wherein the upconverter is configured to use the signal generated by the local signal generator.
10. A method of suppressing a carrier in a near field communications (NFC) signal, the method comprising:
receiving an NFC signal comprising a carrier modulated with an information signal;
digitising the received NFC signal;
downconverting the digitised signal;
filtering the downconverted signal to recover a digitised and downconverted version of the carrier;
converting the digitised and downconverted version of the carrier into an analogue signal;
generating, from the analogue signal generated by the DAC, an estimate of the carrier of the received NFC signal; and
combining the estimate with the received NFC signal.
11. A method according to claim 10 wherein digitising the received signal is performed by a delta-sigma ADC.
12. A method according to claim 11 wherein the ADC is configured to have a sampling frequency which is four times the frequency of the carrier of the received NFC signal.
13. A method according to claim 10 further comprising generating a local signal for use in downconverting the digitised signal.
14. A method according to claim 13 wherein the local signal comprises a square wave signal.
15. A method according to claim 10 wherein digitising the received signal comprises attenuating components at odd integer multiples of the carrier of the received NFC signal.
16. A method according to claim 10 wherein the digitised signal is downconverted to DC.
17. A method according to claim 16 wherein the estimate has a frequency equal to that of the carrier of the received NFC signal.
18. A method according to claim 13 wherein the local signal is used in generating the estimate.