Abstract: An RF system using PR-ASK with orthogonal offset is disclosed. In some embodiments, the system includes a PR-ASK signal generator and an orthogonal offset generator. The PR-ASK signal generator can produce a signal representing a sequence of symbols, for example, RFID symbols. The orthogonal offset generator can shift the PR-ASK signal trajectory away from the origin while maintaining the time domain requirements for an RFID signal, such as waveform edge rise and fall times. In some embodiments stored waveforms incorporating the controlled orthogonal offset are used to synthesize a sequence of symbols. The stored waveforms may also include nonlinear and/or linear predistortion to reduce computational complexity. The waveforms can be represented in Cartesian coordinates for use in a direct conversion transmitter or polar coordinates for use in a polar modulation transmitter. An RFID system can also include a receiver to receive incoming RFID signals.

Abstract: A waveform synthesis technique for radio frequency identification (RFID) transmitters and an RFID system making us of the technique are disclosed. The RFID transmitter in example embodiments synthesizes a continuous transmitter waveform from a symbol alphabet without Nyquist or interpolation filters. High spectral occupancy waveforms are achieved which include the ability to do both linear and nonlinear predistortion with no increase in computational load once the signal set has been adapted to compensate for linear and nonlinear distortion in the transmitter analog circuitry. A polarity generator can be used to impart the required polarity to each waveform. The RFID transmitter can be employed in RFID readers to reduce the computational requirements of the digital signal processor (DSP).

Abstract: A passively coupled RFID receiver is disclosed. The apparatus according to embodiments of the invention can reduce the cost of the RFID reader while significantly improving the linearity of the reader's receiver. An example system for reading RFID tags includes an active mixer passively connected to an antenna port to convert an incoming signal to a baseband signal. The baseband signal passes through a receive path, which may include other elements, and is ultimately provided to a processor that decodes the baseband signal. In some embodiments a complete RFID system making use of the passively coupled receiver includes an RFID transmitter that sends an RF carrier signal to cause the RFID tag to produce the incoming signal. In some embodiments a TX-RX coupler is connected to the transmitter, the receiver, and the antenna port, wherein the active mixer is passively connected to the antenna port through a receive port.

Abstract: A radio frequency (RF) metal detector and an electronic article surveillance (EAS) system are disclosed. The RF metal detector in example embodiments transmits an RF signal. A receiver measures the power and phase of the signal as reflected from metallic objects in an interrogation zone. The RF metal detector can be deployed in a combined system that performs multiple functions. For example, the RF metal detector can be integrated with an EAS system that also sends RFID commands and receives RFID responses. In some embodiments the metal detector can discriminate between moving metal objects and stationary metal objects, and/or discriminate between objects in the interrogation zone and objects outside the interrogation zone. An antenna or antennas can be connected in a mono-static or bi-static configuration and the phase and power signals can be either DC-coupled or AC-coupled into the system through a mixer.