Polar transmitter using multi-phase buck converter
A polar transmitter for an RFID reader and a system using the polar transmitter are disclosed. An RFID system according to at least some embodiments of the invention includes a polar transmitter, a receiver to receive responses from RFID tags, and a coupler connected to the polar transmitter, the receiver and one or more antennas. In at least some embodiments, the polar transmitter of the RFID system includes an envelope amplifier with a multi-phase buck converter to provide an envelope signal and a phase modulator connected to a power amplifier to phase modulate the power amplifier using a phase signal. In at least some embodiments, the polar transmitter of the RFID system transmits OPR-ASK signals to reduce AM modulation depth and provide a continuous phase signal for the phase modulator.
1. A radio frequency identification (RFID) system comprising:
a receiver to receive responses from RFID tags; and
a polar transmitter, the polar transmitter further comprising:
a power amplifier to produce a transmitter output signal; and
an envelope amplifier connected to the power amplifier to supply an envelope signal to the power amplifier, the envelope amplifier further comprising a multi-phase buck converter.
2. The RFID system of claim 1 further comprising a coupler connected to the polar transmitter and the receiver to pass the transmitter output signal to one or more antennas and to pass the responses to the receiver.
3. The RFID system of claim 1 wherein the receiver and the polar transmitter are separated.
4. The RFID system of claim 1 further comprising a phase modulating digital frequency synthesizer connected to the power amplifier to phase modulate the power amplifier using a phase signal.
5. The RFID system of claim 1 further comprising a digital-to-analog converter connected to the power amplifier to provide bias modulation.
6. The RFID system of claim 1 further comprising a digital-to-analog converter connected to a voltage-controlled amplifier to provide drive level modulation.
7. The RFID system of claim 1 wherein the envelope amplifier further comprises:
a switch mode power supply; and
a linear regulator connected to the switch mode power supply.
8. The RFID system of claim 7 wherein the switch mode power supply and the linear regulator are connected in parallel.
9. The RFID system of claim 7 wherein the switch mode power supply and the linear regulator are connected in series.
10. A method of operating a transmitter for a radio frequency identification (RFID) system, the method comprising:
producing, using a processor, a sampled data envelope amplifier signal and a sampled data phase signal;
providing, using the processor, the sampled data envelope amplifier signal to an envelope amplifier including a multi-phase buck converter;
supplying, using the processor, an envelope signal from the envelope amplifier to a power amplifier; and
phase modulating, using the processor, the power amplifier using the sampled data phase signal to produce a transmitter output signal from the envelope signal.
11. The method of claim 10 wherein the phase modulating of the power amplifier further comprises shifting the phase using the sampled data phase signal.
12. The method of claim 10 wherein the phase modulating of the power amplifier further comprises using a digital frequency synthesizer.
13. The method according to claim 10 further comprising using a first digital-to-analog converter (DAC) to provide bias modulation to the power amplifier and using a second DAC to provide drive level modulation to the power amplifier.
14. The method according to claim 10 wherein the transmitter output signal is produced using offset phase reversal amplitude shift keying (OPR-ASK).
15. Apparatus for radio frequency identification (RFID) comprising:
means for producing a sampled data envelope amplifier signal and a sampled data phase signal;
means for providing the sampled data envelope amplifier signal to an envelope amplifier including a multi-phase buck converter;
means for supplying an envelope signal from the envelope amplifier to a power amplifier; and
means for phase modulating the power amplifier using the sampled data phase signal to produce a transmitter output signal from the envelope signal.
16. The apparatus of claim 15 further comprising means for receiving a response from an RFID tag.
17. A non-transitory storage medium that includes instructions that are executable by a processor for causing the processor to perform operations related to a radio frequency identification (RFID) system, the operations comprising:
producing a sampled data envelope amplifier signal and a sampled data phase signal;
providing the sampled data envelope amplifier signal to an envelope amplifier including a multi-phase buck converter;
supplying an envelope signal from the envelope amplifier to a power amplifier; and
phase modulating the power amplifier using the sampled data phase signal to produce a transmitter output signal from the envelope signal.
18. The non-transitory storage medium of claim 17 wherein the phase modulating of the power amplifier further comprises using a phase modulating frequency synthesizer.
19. The non-transitory storage medium of claim 17 wherein the operations further comprise using a first digital-to-analog converter (DAC) to provide bias modulation to the power amplifier and using a second DAC to provide drive level modulation to the power amplifier.
20. The non-transitory storage medium according to claim 17 wherein the transmitter output signal is produced using offset phase reversal amplitude shift keying (OPR-ASK).