Near field communicator implementing switched circuit states for demodulation
A near field RF communicator has an inductive coupler to couple inductively to an H field of an RF signal from another near field RF communicator in near field range to provide a received signal, a demodulator coupled to extract any modulation from a source signal representing a received RF signal to provide an extracted modulation signal; and a controller coupled to receive an extracted modulation signal from the demodulator. The demodulator has a sampler to sample the source signal in sampling periods and to compare signal samples with at least one of other signal samples and a clock or reference signal to remove or reject the carrier of the received RF signal and to extract the modulation.
1. A near field communications (NFC) device, comprising:
a demodulator, including a first capacitor and a second capacitor, configured to:
sample a received signal over a first period to provide a first sample, store a first charge on the first capacitor, the stored first charge being related to the first sample and a first reference voltage; and store a second charge on the second capacitor, the stored second charge being related to the first reference voltage and to a second reference voltage in a first sampling configuration; and
sample the received signal over a second period to provide a second sample in a second sampling configuration,
wherein a change in the received signal between the first sample and the second sample causes charge to move from the first capacitor to the second capacitor to provide an output voltage representing the change in the received signal between the first sampling configuration and the second sampling configuration; and
a controller configured to adjust a configuration of the demodulator between the first sampling configuration and the second sampling configuration,
wherein the output voltage is a result of a capacitive charge transfer within the demodulator between the first capacitor and the second capacitor as the demodulator configuration is adjusted between the first sampling configuration and the second sampling configuration.
2. The NFC device of claim 1 , wherein the demodulator comprises:
a voltage detector module configured to provide an output signal representative of the output voltage when the output voltage exceeds a threshold voltage.
3. The NFC device of claim 1 , wherein the first period and the second period are different time periods.
4. The NFC device of claim 2 , wherein the controller is further configured to adjust the threshold voltage based on a modulation protocol of the received signal or a modulation width of the received signal.
5. The NFC device of claim 1 , wherein the demodulator comprises:
a sampler including the first capacitor and the second capacitor.
6. The NFC device of claim 1 , wherein the controller is further configured to switch the demodulator configuration between the first sampling configuration, a non-sampling configuration, and the second sampling configuration.
7. The NFC device of claim 2 , wherein the voltage detector module comprises:
an analog-to-digital converter (ADC), and
wherein the output signal comprises:
a digital signal.
8. A near field communications (NFC) device, comprising:
a demodulator configured to:
sample a received signal for a first sampling period to provide a first sample and store a first charge related to the first sample and a second charge related to a reference voltage in a first configuration, and
sample the received signal for a second sampling period to provide a second sample in a second configuration,
wherein a change in the received signal between the first sample and the second sample causes a capacitive charge transfer of the stored charge to the stored second charge to provide an output voltage representing the change in the received signal between the first configuration and the second configuration,
a controller configured to adjust a configuration of the demodulator from the first configuration to the second configuration.
9. The NFC device of claim 8 , wherein the demodulator comprises:
a voltage detector module configured to provide an output signal representative of the output voltage when the output voltage exceeds a threshold voltage.
10. The NFC device of claim 8 , wherein the first sampling period and the second sampling period are different time periods.
11. The NFC device of claim 9 , wherein the controller is further configured to adjust the threshold voltage based on a modulation protocol of the received signal or a modulation width of the received signal.
12. The NFC device of claim 8 , wherein the demodulator comprises:
a sampler including a first capacitor and a second capacitor,
wherein the first capacitor is configured to store the first charge, and
wherein the second capacitor is configured to store the second charge.
13. The NFC device of claim 8 , wherein the controller is further configured to switch the demodulator configuration between the first configuration, a non-sampling configuration, and the second configuration.
14. The NFC device of claim 9 , wherein the voltage detector module comprises:
an analog-to-digital converter (ADC), and
wherein the output signal comprises:
a digital signal.
15. A near field communications (NFC) device, comprising:
a demodulator, including a first capacitor and second capacitor configured to:
sample a received signal over a first period to provide a first sample, store a first charge on the first capacitor, the stored first charge being related to the first sample and a first reference voltage; and store a second charge on the second capacitor, the stored second charge being related to the first reference voltage and to a second reference voltage in a first sampling configuration; and
sample the received signal over a second period to provide a second sample in a second sampling configuration,
wherein a change in the received signal between the first sample and the second sample causes charge to move from the first capacitor to the second capacitor to provide an output voltage representing the change in the received signal between the first sampling configuration and the second sampling configuration;
provide an output signal representative of the output voltage when the output voltage exceeds a threshold voltage; and
a controller configured to adjust the demodulator configuration between the first sampling configuration and the second sampling configuration,
wherein the output voltage is a result of a capacitive charge transfer within the demodulator between the first capacitor and the second capacitor as the demodulator configuration is adjusted between the first sampling configuration and the second sampling configuration.
16. The NFC device of claim 15 , wherein the demodulator comprises: an analog-to-digital converter (ADC) configured to provide the output signal.
17. The NFC device of claim 15 , wherein the first period and the second period are different time periods.
18. The NFC device of claim 16 , wherein the controller is further configured to adjust the threshold voltage based on a modulation protocol of the received signal or a modulation width of the received signal.
19. The NFC device of claim 15 , wherein the demodulator comprises:
a sampler including the first capacitor and the second capacitor.
20. The NFC device of claim 15 , wherein the controller is further configured to switch the demodulator configuration between the first sampling configuration, a non-sampling configuration, and the second sampling configuration.