Detecting peaks in a received signal in a near field communications (NFC) device

1. A near field communications (NFC) device, comprising:

an antenna configured to receive a radio frequency (RF) signal inductively coupled onto a magnetic field;

a peak detector configured to determine an envelope of the RF signal;

a regulator configured to adjust the RF signal when the envelope is greater than a reference voltage; and

a demodulator configured to recover information from the adjusted RF signal based upon the envelope.

2. The NFC device of claim 1 , wherein the regulator comprises:

an error amplifier configured to provide an error signal that is indicative of a difference between the envelope and the reference voltage; and

a shunt element configured to adjust its impedance to regulate the RF signal based on the error signal.

3. The NFC device of claim 1 , wherein the RF signal comprises:

a first differential RF signal and a second differential RF signal.

4. The NFC device of claim 3 , wherein the first differential RF signal is a mirror of the second differential RF signal.

5. The NFC device of claim 3 , wherein the peak detector comprises:

a comparator configured to compare the first differential RF signal to the second differential RF signal to provide a comparator output, the comparator output being at a first voltage when the first differential RF signal is greater than the second differential RF signal or at a second voltage when the second differential RF signal is greater than the first differential RF signal.

6. The NFC device of claim 5 , wherein the peak detector further comprises:

a first delay element configured to delay a rising edge of the comparator output when the comparator output is at the first voltage to provide a delayed first differential RF signal; and

a second delay element configured to delay a falling edge of the comparator output when the comparator output is at the second voltage to provide a delayed second differential RF signal.

7. The NFC device of claim 3 , wherein the peak detector comprises:

a first pulse generator configured to provide a first control voltage;

a second pulse generator configured to provide a second control voltage;

a first impedance configured to provide the first differential RF signal when the first control voltage is at a first level; and

a second impedance configured to provide the second differential signal when the second control voltage is at the first level.

8. The NFC device of claim 7 , wherein the first pulse generator and the second pulse generator are configured to refrain from biasing the first impedance and the second impedance into the conductive state simultaneously.

9. The NFC device of claim 3 , wherein the envelope is at the first voltage when the first differential RF signal is greater than the second RF signal or at the second voltage when the second differential RF signal is greater than the first differential RF signal.

10. The NFC device of claim 1 , further comprising:

a clock signal deriver configured to derive a clock signal from the RF signal;

a plurality of delay elements configured to delay the clock signal to provide a delayed clock signal;

an edge detector configured to detect a rising edge of the clock signal as the clock signal propagates through a delay line; and

a phase comparer configured to receive the clock signal and the delayed clock signal and to provide a first control voltage signal to bias an impedance into the conductive state based on the rising edge of the clock signal and a second control voltage signal to bias the impedance into a nonconductive state based on a rising edge of the delayed clock signal.

11. A peak detector for a near field communications (NFC) device, the peak detector comprising:

a clock signal deriver configured to derive a clock signal from a radio frequency (RF) signal;

a plurality of delay elements configured to form a delay line to delay the clock signal to provide a delayed clock signal;

an edge detector configured to detect a rising edge of the clock signal as the clock signal propagates through the delay line; and

a phase comparer configured to receive the clock signal and the delayed clock signal, to provide a first control voltage signal to bias an impedance into a conductive state based on the rising edge for the clock signal and to bias the impedance into a nonconductive state based on a rising edge for the delayed clock signal.

12. The peak detector of claim 11 , wherein each delay element from among the plurality of delay elements is further configured to detect an edge transition of the clock signal at an input and an output of each delay element.

13. The peak detector of claim 12 , wherein the phase comparer is further configured to control the plurality of delay elements to configure each delay element to delay the clock signal for an equal period.

14. The peak detector of claim 11 , wherein the clock signal comprises:

a square wave that includes a first voltage at a first level and a second voltage at a second level, wherein the first voltage is greater than the second voltage.

15. The peak detector of claim 14 , wherein the edge detector is configured to detect the rising edge for the clock signal as the square wave transitions from the first voltage to the second voltage.

16. The peak detector of claim 11 , wherein the edge detector comprises:

a plurality of logic gates, coupled to the plurality of delay elements, each of the plurality of logic gates being configured to provide a corresponding edge detector output from among a plurality of edge detector outputs at a first level when the clock signal is at the rising edge for the clock signal or at a second level when the clock signal is at a falling edge.

17. A method for demodulating by a near field communications (NFC) device, comprising:

receiving, by the NFC device, a radio frequency (RF) signal inductively coupled onto a magnetic field;

determining, by the NFC device, an envelope of the RF signal;

adjusting, by the NFC device, the RF signal when the envelope is greater than a reference voltage; and

recovering, by the NFC device, information from the adjusted RF signal based upon the envelope.

18. The method of claim 17 , wherein the adjusting comprises:

providing, by the NFC device, an error signal that is indicative of a difference between the envelope and the reference voltage; and

regulating, by the NFC device, the RF signal based on the error signal by adjusting an impedance.

19. The method of claim 17 , further comprising:

deriving a clock signal from the RF signal;

delaying the clock signal to provide a delayed clock signal;

detecting a rising edge of the clock signal as the clock signal is being delayed; and

providing a first control voltage signal to bias an impedance into a conductive state based on the rising edge of the clock signal and a second control voltage signal to bias the impedance into a nonconductive state based on a rising edge of the delayed clock signal.

20. The method of claim 19 , wherein the detecting comprises:

providing a plurality of edge detector outputs, each of the plurality of edge detector outputs being at a first level when the clock signal is at the rising edge for the clock signal or at a second level when the delayed clock signal is at the rising edge for the delayed clock signal.