Adjustable radio frequency power amplifier and transmitter

• US 6,122,492 A
• Filed: 02/08/1999
• Issued: 09/19/2000
• Est. Priority Date: 02/08/1999
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Sears, Frederick E.
• Primary Examiner(s): Bost, Dwayne D.
• Assistant Examiner(s): Gelin, Jean Alland
• Application Number:
  US09/246,232
• Time in Patent Office: 589 Days
• Field of Search: 455/571, 455/572, 455/127, 455/128, 455/129, 455/103, 455/118, 455/114, 330/10, 330/124 R, 330/146, 330/149
• US Class Current: 455/127.1
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10326 the antenna being of the very-near field type, e.g. capacitive
• CPC Class Codes: H01Q 1/36 Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewithH01Q1/08, H01Q1/14 take precedence
• CPC Class Codes: H01Q 1/50 Structural association of antennas with earthing switches, lead-in devices or lightning protectors
• CPC Class Codes: H03F 1/02 Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
• CPC Class Codes: H03F 3/245 with semiconductor devices only

Abstract

A modulator (104) varies the duty cycle of a waveform to amplitude modulate information for transmission. A push-pull amplifier (106) in accordance with the invention, preferably constructed of CMOS devices, receives the waveform with a varying duty cycle in order to drive an antenna (108) such that a wireless transceiver can become excited by the oscillating waveform and receive the amplitude modulated signal and demodulate it to obtain the transmitted information. The power generated by the push-pull power amplifier (106) is simply increased or decreased by varying the voltage of the power supplied to the power amplifier or by varying the number of devices driving the antenna (108) in parallel.

Claims

1. A radio frequency power amplifier and transmitter for driving an antenna to radiate radio frequency energy, the radio frequency power amplifier and transmitter comprising:

a first plurality of buffers coupled together in parallel, the first plurality of buffers receiving a waveform signal as input and providing a driving signal to the antenna;

a first inverter receiving the waveform signal as an input, the first inverter generating an out-of-phase waveform signal;

a second plurality of buffers coupled together in parallel, the second plurality of buffers receiving the out-of-phase waveform signal from the first inverter as input and providing an out-of-phase driving signal to the antenna; and

wherein the first plurality of buffers and the second plurality of buffers are pushing or pulling responsive to the waveform signal and the out-of-phase waveform signal such that radio frequency energy is radiated by the antenna.

2. The radio frequency power amplifier and transmitter of claim 1, wherein each buffer of the first plurality of buffers and the second plurality of buffers is selectively activated to vary power delivered to the antenna.

3. The radio frequency power amplifier and transmitter of claim 1, wherein the first plurality of buffers and the second plurality of buffers have power supply connections coupled to an adjustable power supply such that a power generated by the radio frequency power amplifier and transmitter is adjustable.

4. The radio frequency power amplifier and transmitter of claim 1, wherein the waveform signal and the out-of-phase waveform signal each have a variable duty cycle and the first plurality of buffers and the second plurality of buffers varies an amplitude of a signal transmitted by the antenna, the amplitude being responsive to the variable duty cycle.

5. The radio frequency power amplifier and transmitter of claim 1, wherein each buffer of the first plurality of buffers and the second plurality of buffers has an input signal and an output signal and each buffer comprises:

a buffer inverter, the buffer inverter inverting the input signal to generate an inverted signal; and

a plurality of additional inverters, the plurality of additional inverters coupled in parallel together and coupled in series to the buffer inverter such that the plurality of additional inverters inverts the inverted signal received from the buffer inverter and produces the output signal.

6. The radio frequency power amplifier and transmitter of claim 5, wherein the buffer inverter and the plurality of additional inverters are CMOS inverters.

7. The radio frequency power amplifier and transmitter of claim 6, wherein each of the CMOS inverters comprises:

a P channel field effect transistor having a gate coupled to an input of the CMOS inverter, a source coupled to an adjustable power supply, and a drain coupled to an output of the CMOS inverter; and

an N channel field effect transistor having a gate coupled to the input of the CMOS inverter, a source coupled to a low level power supply, and a drain coupled to the output of the CMOS inverter.

8. The radio frequency power amplifier and transmitter of claim 5, wherein the buffer inverter and the plurality of additional inverters have power supply connections coupled to an adjustable power supply such that a power output generated by the radio frequency power amplifier and transmitter is adjustable.

9. The radio frequency power amplifier and transmitter of claim 5, wherein each buffer of the first plurality of buffers and the second plurality of buffers further comprises:

an input protection resistor coupled to an input of the buffer inverter, the input protection resistor receiving the input signal and protecting the input of the buffer inverter from excessive voltage and current;

an output protection resistor coupled to an output of the plurality of additional inverters, the output protection resistor transferring the output signal of each buffer and protecting the output of the plurality of additional inverters from excessive voltage and current; and

a power supply bypass capacitor coupled to a high level power supply of the buffer inverter and the plurality of additional inverters at a first end and a low level power supply at a second end.

10. A radio frequency exciter for exciting and transmitting information to a wireless transceiver, the radio frequency exciter comprising:

an antenna having a first connection at one end and a second connection at an opposite end;

a modulator that generates a carrier signal and varies a duty cycle of the carrier signal in response to the information;

a power amplifier coupled to the modulator and the first and second connection of the antenna, the power amplifier receiving and amplifying the carrier signal responsive to the duty cycle, the power amplifier comprising;

a first plurality of buffers coupled together in parallel, the first plurality of buffers receiving the carrier signal responsive to duty cycle as input and providing a driving signal to the first connection to the antenna;

a first inverter that receives the carrier signal as an input, the first inverter generating an out-of-phase waveform signal;

a second plurality of buffers coupled together in parallel, the second plurality of buffers receiving as input the out-of-phase waveform signal from the first inverter and providing an out-of-phase driving signal to the second connection to the antenna; and

wherein the first plurality of buffers and the second plurality of buffers are pushing or pulling responsive to the carrier signal and the out-of-phase waveform signal such that radio frequency energy is radiated by the antenna.

11. The radio frequency exciter of claim 10 wherein each buffer of the first plurality of buffers and the second plurality of buffers has an input signal and an output signal and each buffer comprises:

a buffer inverter, the buffer inverter inverting the input signal to generate an inverted signal; and

a plurality of additional inverters, the plurality of additional inverters coupled in parallel together and coupled in series to the buffer inverter such that the plurality of additional inverters inverts the inverted signal received from the buffer inverter and produces the output signal.

12. The radio frequency exciter of claim 11, wherein the first inverter, the buffer inverter, and plurality of additional inverters are CMOS inverters.

13. The radio frequency exciter of claim 12, wherein the first inverter, the buffer inverter, and the plurality of additional inverters are CMOS inverters having power supply connections coupled to an adjustable power supply such that a power output generated by the power amplifier is adjustable.

14. A method for amplifying and modulating an oscillating waveform of a carrier signal in order to transmit information to a wireless transceiver, the method comprising the steps of:

(a) generating the oscillating waveform with a duty cycle of approximately fifty percent;

(b) filtering out undesirable harmonics from the oscillating waveform;

(c) varying the duty cycle of the oscillating waveform responsive to information to generate a variable duty cycle oscillating waveform;

(d) amplifying the variable duty cycle oscillating waveform with a CMOS power amplifier to generate an amplified variable duty cycle oscillating waveform; and

(e) driving an antenna with the amplified variable duty cycle oscillating waveform to transmit information to the wireless transceiver.

15. The method of claim 14 for amplifying and modulating a carrier signal in order to transmit information to a passive transceiver, further comprising the step of:

(f) adjusting a voltage of a power supply of the CMOS power amplifier to adjust amplification of the variable duty cycle oscillating waveform.

16. The method of claim 14, wherein the CMOS power amplifier comprises:

a first plurality of CMOS buffers coupled together in parallel, the first plurality of CMOS buffers receiving the variable duty cycle oscillating waveform as input and providing a driving signal to the antenna;

an inverter that inverts the variable duty cycle oscillating waveform to generate an out-of-phase variable duty cycle oscillating waveform; and

a second plurality of buffers coupled together in parallel, the second plurality of buffers receiving the out-of-phase variable duty cycle oscillating waveform as input and providing an out-of-phase driving signal to the antenna.