Telepowered contactless card

1. A method, comprising:

receiving, by an antenna couplable to an electronic device, an amplitude-modulated analog signal associated with an electromagnetic field generated by an external device, the electromagnetic field having intervals with minimal levels;

generating a demodulated signal based on the amplitude-modulated analog signal, the demodulated signal comprising a rectified, filtered, and demodulated signal of the amplitude-modulated analog signal;

generating a binary signal based on the demodulated signal;

determining a maximum amplitude value of the electromagnetic field before a pause based on the binary signal; and

coupling a resistance to the antenna during the pause, a value of the resistance being based on the maximum amplitude value.

2. The method of claim 1 , wherein the coupling comprises coupling the resistance to the antenna in response to a change in the binary signal from a first state to a second state.

3. The method of claim 2 , further comprising decoupling the resistance from the antenna in response to a change in the binary signal from the second state to the first state.

4. The method of claim 2 , further comprising decoupling the resistance from the antenna in response to a completion of a constant duration after coupling the resistance to the antenna.

5. The method of claim 1 , further comprising:

converting the demodulated signal to a first digital signal;

generating a second digital signal based on the first digital signal, the second digital signal being equal to the first digital signal with a delay;

generating a third digital signal, the third digital signal having a constant digital value in response to the binary signal being in a first state, the third digital signal having a digital value equal to a value of the second digital signal in response to the binary signal changing from the first state to a second state; and

converting the third digital signal to the value of the resistance.

6. An electronic device, comprising:

a first circuit configured to generate a demodulated signal based on an amplitude-modulated analog signal, the demodulated signal comprising a rectified, filtered, and demodulated signal of the amplitude-modulated analog signal, the amplitude-modulated analog signal associated with an electromagnetic field generated by an external device and received by an antenna couplable to the electronic device, the electromagnetic field having intervals with minimal levels;

a second circuit configured to generate a binary signal based on the demodulated signal; and

a third circuit configured to couple a resistance to the antenna during a pause, a value of the resistance being based on a maximum amplitude value of the electromagnetic field before the pause, the maximum amplitude value being determined based on the binary signal.

7. The electronic device of claim 6 , wherein the third circuit is configured to couple the resistance to the antenna in response to a change in the binary signal from a first state to a second state.

8. The electronic device of claim 7 , wherein the third circuit is configured to decouple the resistance from the antenna in response to a change in the binary signal from the second state to the first state.

9. The electronic device of claim 7 , wherein the third circuit is configured to decouple the resistance from the antenna in response to a completion of a constant duration after coupling the resistance to the antenna.

10. The electronic device of claim 6 , wherein the third circuit comprises:

an analog-to-digital converter (ADC) configured to convert the demodulated signal to a first digital signal;

a fourth circuit configured to generate a second digital signal based on the first digital signal, the second digital signal being equal to the first digital signal with a delay;

a fifth circuit configured to generate a third digital signal, the third digital signal having a constant digital value in response to the binary signal being in a first state, the third digital signal having a digital value equal to a value of the second digital signal in response to the binary signal changing from the first state to a second state; and

a resistive digital-to-analog converter (DAC) configured to convert the third digital signal to the value of the resistance.

11. The electronic device of claim 10 , wherein the ADC is clocked by a first clock signal, and wherein the fourth circuit comprises a flip-flop circuit clocked by a second clock signal, a frequency of the second clock signal being a sub-multiple of a frequency of the first clock signal.

12. The electronic device of claim 10 , wherein the fifth circuit comprises:

a flip-flop circuit clocked by an inverse of a second binary signal, the flip-flop circuit configured to receive the second digital signal; and

AND-type logic gates, each AND-type logic gate configured to:

output a different bit of bits of the third digital signal,

receive the second binary signal at a first input, and

receive an output of a different flip-flop of the flip-flop circuit at a second input.

13. The electronic device of claim 12 , wherein the second binary signal is equal to the binary signal.

14. The electronic device of claim 12 , wherein each rising edge of the second binary signal is simultaneous with a corresponding falling edge of the binary signal, and wherein each falling edge of the second binary signal follows a rising edge of the second binary signal, the rising edge of the second binary signal preceding each falling edge of the second binary signal by a constant duration.

15. A contactless read card, comprising:

an antenna configured to receive an amplitude-modulated analog signal associated with an electromagnetic field generated by an external device, the electromagnetic field having intervals with minimal levels;

a first circuit coupled to the antenna, the first circuit configured to generate a demodulated signal based on the amplitude-modulated analog signal, the demodulated signal comprising a rectified, filtered, and demodulated signal of the amplitude-modulated analog signal;

a second circuit configured to generate a binary signal based on the demodulated signal; and

a third circuit configured to couple a resistance to the antenna during a pause, a value of the resistance being based on a maximum amplitude value of the electromagnetic field before the pause, the maximum amplitude value being determined based on the binary signal.

16. The contactless read card of claim 15 , wherein the third circuit is configured to couple the resistance to the antenna in response to a change in the binary signal from a first state to a second state.

17. The contactless read card of claim 16 , wherein the third circuit is configured to decouple the resistance from the antenna in response to a change in the binary signal from the second state to the first state.

18. The contactless read card of claim 16 , wherein the third circuit is configured to decouple the resistance from the antenna in response to a completion of a constant duration after coupling the resistance to the antenna.

19. The contactless read card of claim 16 , wherein the third circuit comprises:

an analog-to-digital converter (ADC) configured to convert the demodulated signal to a first digital signal;

a fourth circuit configured to generate a second digital signal based on the first digital signal, the second digital signal being equal to the first digital signal with a delay;

a fifth circuit configured to generate a third digital signal, the third digital signal having a constant digital value in response to the binary signal being in a first state, the third digital signal having a digital value equal to a value of the second digital signal in response to the binary signal changing from the first state to a second state; and

a resistive digital-to-analog converter (DAC) configured to convert the third digital signal to the value of the resistance.

20. The contactless read card of claim 19 , wherein the ADC is clocked by a first clock signal, and wherein the fourth circuit comprises a flip-flop circuit clocked by a second clock signal, a frequency of the second clock signal being a sub-multiple of a frequency of the first clock signal.