Systems and methods providing a transmitter for transmitting signals in a near-field communication (NFC) frequency band are disclosed. According to embodiments, a transmitter for transmitting signals in a near-field communication frequency band comprises an antenna, a first current source for generating a first current to excite the antenna, a first detector for detecting a first voltage at an output of the first current source, and means for reducing the current output by the first current source if the detected first voltage exceeds a first predefined threshold. An integrated circuit of embodiments may comprise the foregoing transmitter. A transmitter configuration of embodiments, including means for reducing the current, provides for limited distortion in the transmitted signal and reducing the risk of components in the transmitter being damaged.
1. A transmitter for transmitting signals in a near-field communication (NFC) frequency band, the transmitter comprising:
an antenna;
a first current source for generating a first current to excite the antenna;
a first detector for detecting a first voltage at an output of the first current source; and
circuitry for reducing the current output by the first current source if the detected first voltage exceeds a first predefined threshold, wherein the circuitry for reducing the first current output by the first current source comprises a variable amplifier.
2. A transmitter according to claim 1 , wherein the first detector comprises an attenuator and a diode.
3. A transmitter according to claim 1 , further comprising a first load inductor arranged to be charged by the first current output from the first current source and to discharge its stored current into the antenna.
4. A transmitter according to claim 1 , wherein the first predefined threshold is approximately 2V, where V is the voltage at the output of the first current source.
5. A transmitter according to claim 1 , further comprising:
a second current source for generating a second current to excite the antenna;
a second detector for detecting a second voltage at an output of the second current source; and
circuitry for reducing the second current output by the second current source if the detected second voltage exceeds said second predefined threshold.
6. A transmitter according to claim 5 , wherein the first current is substantially equal to the second current.
7. A transmitter according to claim 5 , wherein the first voltage is substantially equal to the second voltage.
8. A transmitter according to claim 5 , wherein the first predefined threshold is substantially equal to the second predefined threshold.
9. A transmitter according to claim 5 , wherein the first current source supplies the first current for a first predetermined duration, and second current source supplied the second current for a second predetermined duration.
10. A transmitter according to claim 9 , wherein the first and second predetermined durations are substantially the same.
11. A transmitter according to claim 10 , wherein the first and second current sources operate alternately.
12. A transmitter according to claim 5 , further comprising a second load inductor arranged to be charged by the second current output from the second current source.
13. A transmitter according to claim 12 , wherein the second load inductor is arranged to discharge its stored current into the antenna.
14. A transmitter according to claim 5 , wherein the second predefined threshold is approximately 2V, where V is the voltage at the output of the second current source.
15. A transmitter according to claim 5 , wherein the first and second currents supplied by the first and second current sources are supplied on alternate half-cycles of a signal to be transmitted by the transmitter.
16. An integrated circuit comprising:
a transmitter for transmitting signals in a near-field communication (NFC) frequency band, the transmitter comprising:
a first current source for generating a first current to excite an antenna;
a first detector for detecting a first voltage at an output of the first current source; and
circuitry for reducing the current output by the first current source if the detected first voltage exceeds a first predefined threshold, wherein the circuitry for reducing the first current output by the first current source comprises a variable amplifier.
17. A transmitter for transmitting signals in a near-field communication (NFC) frequency band, the transmitter comprising:
an antenna;
a first current source for generating a first current to excite the antenna;
a first detector for detecting a first voltage at an output of the first current source; and
circuitry for reducing the current output by the first current source if the detected first voltage exceeds a first predefined threshold, wherein the transmitter further comprises a first load inductor arranged to be charged by the first current output from the first current source and to discharge its stored current into the antenna.
18. A transmitter for transmitting signals in a near-field communication (NFC) frequency band, the transmitter comprising:
an antenna;
a first current source for generating a first current to excite the antenna;
a first detector for detecting a first voltage at an output of the first current source; and
circuitry for reducing the current output by the first current source if the detected first voltage exceeds a first predefined threshold, wherein the transmitter further comprises:
a second current source for generating a second current to excite the antenna;
a second detector for detecting a second voltage at an output of the second current source; and
circuitry for reducing the second current output by the second current source if the detected second voltage exceeds said second predefined threshold.