Passive transponder with a charging circuit
In one embodiment, a passive transponder comprising a first circuit comprising a first attenuator, the first circuit configured to receive a first signal from at least one base station and coupled to a first node, a first rectifier coupled to the first node, the first rectifier configured in a forward direction to charge a first capacitor, and the first capacitor coupled to the first rectifier, the first capacitor configured to receive a charge from the attenuator sufficient for powering the passive transponder.
1. A system comprising:
a first resonant circuit including a first coil and a first resonant capacitor interconnected by a first node;
a second resonant circuit including a second coil and a second resonant capacitor interconnected by a second node;
a third resonant circuit including a third coil and a third resonant capacitor interconnected by a third node;
a passive transponder coupled to the first, second and third resonant circuits, the passive transponder including:
a first attenuator coupled to the first resonant circuit, the first attenuator operable to adjust a first bandwidth of the first resonant circuit;
a second attenuator coupled to the second resonant circuit, the second attenuator operable to adjust a second bandwidth of the second resonant circuit;
a third attenuator coupled to the third resonant circuit, the third attenuator operable to adjust a third bandwidth of the third resonant circuit; and
a control circuit operable to control the first, second and third attenuators.
2. The system of claim 1 , further comprising:
a supply voltage capacitor coupled to the first, second and third nodes and to the control circuit, the supply voltage capacitor operable to provide a supply voltage at least to the control circuit.
3. The system of claim 2 , further comprises:
a first rectifier coupled to the first node and the supply voltage capacitor;
a second rectifier coupled to the second node and the supply voltage capacitor; and
a third rectifier coupled to the third node and the supply voltage capacitor.
4. The system of claim 3 , wherein the supply voltage capacitor is charged by the first, second and third attenuators through the first, second and third rectifiers, respectively.
5. The system of claim 1 , further comprising:
a first load modulation element coupled to the first node and the control circuit;
a second load modulation element coupled to the second node and the control circuit; and
a third load modulation element coupled to the third node and the control circuit.
6. The system of claim 5 , wherein at least one of the first, second or third load modulation elements includes a switch in series with a Zener diode, where the switch is controlled by the control circuit.
7. The system of claim 1 , further comprising:
a radio frequency receiver coupled to the control circuit and to the first, second and third resonant circuits.
8. The system of claim 7 , further comprising:
a microprocessor coupled to the control circuit and the radio frequency receiver.
9. The system of claim 8 , wherein the microprocessor is coupled to a battery.
10. The system of claim 1 , wherein the system is a passive entry system and the control circuit is an immobilization unit.
11. The system of claim 1 , wherein the control circuit is configured to sequentially utilize the first, second and third resonant circuits.
12. The system of claim 1 , wherein the first, second and third coils are coupled in parallel with the first, second and third resonant capacitors, respectively.
13. The system of claim 1 , wherein at least one of the first, second or third attenuators includes a switch coupled in series with a resistor.
14. The system of claim 1 , wherein at least one of the first, second or third resonant circuits has a resonant frequency in a range of about 20 kHz to about 30 MHz.
15. The system of claim 1 , wherein a resonant frequency of at least two of the first, second or third resonant circuits is about the same.
16. The system of claim 1 , wherein at least one of the first, second or third resonant circuits has a Q-factor that is greater than or equal to 5.
17. The system of claim 1 , wherein at least two of the first, second or third coils are aligned orthogonally.
18. The system of claim 1 , wherein the control circuit is operable to read modulated signals from the first, second and third resonant circuits.
19. The system of claim 3 , wherein at least one of the first, second or third rectifier is a diode.
20. The system of claim 13 , wherein the switch is controlled by the control circuit.