End of communication detection
An apparatus for detecting the end of a communication is disclosed. The apparatus includes an interface circuit for receiving an encoded signal and a carrier signal recovery circuit coupled to an output of the interface circuit. The carrier signal recovery circuit is configured to output a carrier signal of the encoded signal and a second signal that is out of phase with the carrier signal. The apparatus also includes a decoding circuit configured to decode the encoded signal as a function of both the encoded signal and the carrier signal output by the carrier signal recovery circuit. The apparatus also includes a detection circuit configured to detect an indication of an end of a communication in the encoded signal as a function of both the encoded signal and the second signal.
1. An apparatus, comprising:
an interface circuit for receiving an encoded signal;
a carrier signal recovery circuit coupled to an output of the interface circuit and configured and arranged to
determine and output a carrier signal of the encoded signal, and
generate and output a second signal that is out of phase with the carrier signal;
a decoding circuit, coupled to the output of the interface circuit and to the carrier signal recovery circuit, configured and arranged to decode the encoded signal as a function of the encoded signal and the carrier signal output by the carrier signal recovery circuit; and
a detection circuit, coupled to the output of the interface circuit and to the carrier signal recovery circuit, configured and arranged to detect an indication of an end of a communication in the encoded signal as a function of the encoded signal and the second signal.
2. The apparatus of claim 1 , wherein the second signal is 90 degrees out of phase with the carrier signal.
3. The apparatus of claim 1 , wherein:
the apparatus is an RF powered apparatus, and
the interface circuit includes
a loop antenna,
a power supply coupled to the loop antenna and configured and arranged to generate a power supply voltage from electro-magnetic signals received by the loop antenna, and
a differential amplifier having a first input coupled to a first end of the loop antenna, a second input coupled to a second end of the loop antenna, and an output coupled to the output of the interface circuit.
4. The apparatus of claim 1 , wherein the detection circuit includes a flip-flop having an input terminal connected to receive the second signal from the carrier signal recovery circuit and having a clock terminal connected to receive the encoded signal from the interface circuit.
5. The apparatus of claim 1 , wherein the detection circuit includes a flip-flop having an input terminal connected to receive the encoded signal from the interface circuit and having a clock terminal connected to receive the second signal from the carrier signal recovery circuit.
6. The apparatus of claim 5 , wherein the detection circuit further includes a logical inverter circuit having an input coupled to an output of the flip-flop and an output coupled to an output of the detection circuit.
7. The apparatus of claim 1 , wherein the carrier signal recovery circuit includes a phase-locked-loop (PLL) circuit.
8. The apparatus of claim 7 , wherein the carrier signal recovery circuit further includes a frequency divider coupled to an output of the PLL circuit.
9. The apparatus of claim 1 , wherein the decoding circuit includes a time-to-digital converter.
10. The apparatus of claim 1 , wherein the encoded signal is a phase-shift-key (PSK) encoded signal.
11. A method, comprising:
determining a carrier signal of an encoded signal;
phase shifting the carrier signal to produce a second signal that is out of phase with the carrier signal;
decoding the encoded signal as a function of the encoded signal and the carrier signal; and
detecting whether or not the encoded signal includes an indication of an end of a communication in the encoded signal by comparing the second signal with the encoded signal.
12. The method of claim 11 , wherein the second signal is 90 degrees out of phase with the carrier signal.
13. The method of claim 11 , wherein the comparing includes determining a value of the second signal in response to a rising edge of the encoded signal.
14. The method of claim 11 , wherein the comparing includes determining a value of the encoded signal in response to a rising edge of the second signal.
15. The method of claim 11 , wherein the comparing includes providing the second signal to an input terminal of a flip-flop and providing the encoded signal to an clock terminal of the flip-flop.
16. The method of claim 11 , further comprising:
in response to the second signal having a first value at a time in which a rising edge of the encoded signal is detected, signaling that the indication of an end of a communication is not received; and
in response to the second signal having a second value at a time in which a rising edge of the encoded signal is detected, signaling that the indication that an end of a communication is received.
17. The method of claim 11 , wherein the encoded signal is a phase-shift-key (PSK) encoded signal.
18. A near-field communication device, comprising:
an interface circuit including,
a loop antenna for receiving an encoded signal; and
a power supply coupled to the loop antenna and configured and arranged to generate a power supply voltage from the encoded signal received by the loop antenna;
a carrier signal recovery circuit powered by the power supply voltage, coupled to receive the encoded signal from an output of the interface circuit, and configured and arranged to
determine and output a carrier signal of the encoded signal, and
generate and output a second signal that is 90 degrees out of phase with the carrier signal;
a decoding circuit, powered by the power supply voltage, coupled to the output of the interface circuit and to the carrier signal recovery circuit, and configured and arranged to decode the encoded signal as a function of the encoded signal and the carrier signal output by the carrier signal recovery circuit; and
a detection circuit, powered by the power supply voltage, coupled to the output of the interface circuit and to the carrier signal recovery circuit, configured and arranged to detect an indication of an end of a communication in the encoded signal as a function of the encoded signal and the second signal.
19. The near-field communication device of claim 18 , wherein:
the encoded signal is a phase-shift-key (PSK) encoded signal; and
the detection circuit includes a flip-flop having an input terminal connected to receive the second signal from the carrier signal recovery circuit and having an clock terminal connected to receive the encoded signal from the interface circuit.
20. The near-field communication device of claim 18 , wherein:
the encoded signal is a phase-shift-key (PSK) encoded signal; and
the detection circuit includes
a flip-flop having an input terminal connected to receive the encoded signal from the interface circuit and having an clock terminal connected to receive the second signal from the carrier signal recovery circuit, and
a logical inverter circuit having an input coupled to an output of the flip-flop and an output coupled to an output of the detection circuit.