Ground switching load modulation for high frequency band radio frequency identification transponders

This research work focuses on the front-end circuit design of high frequency (HF) band radio frequency identification (RFID) transponders. Specifically, the research investigates effective communication schemes for passive HF band RFID transponders to send data back to the reader. A new ground switching load modulation scheme is proposed. It allows passive HF transponders to communicate with the reader in the strong field more effectively using simple RF clamping circuits for over voltage protection, compared with traditional resistive and capacitive load modulation schemes. Also presented is a ground isolation doubler rectifier to isolate the side effects of the parasitic diodes in the clamping circuits, thus, enabling passive HF transponders to extract power more efficiently in the weak field. As a result, the proposed front-end circuit topology enables passive HF transponders to work in a very wide range of magnetic field strength, therefore improves the transponder's operational range.;The proposed circuit topology is implemented and fabricated in a TSMC 0.35-microm CMOS double-poly mixed signal N-well process. The ground switching load modulation is measured using the standard industry testing procedure and achieved 30 mV modulation depths across the field strength from 0.15 A/m to 7.5 A/m. The fabricated chip further includes the low power data demodulator, bias and power-on-reset (POR) circuits with 1.5 microA current consumption. An RF regulator is also explored to regulate the RF envelope down so that the transponder is sensitive to the data envelope change especially when the modulation index is as low as 10%. A new peak envelope demodulation scheme is also proposed for fast rate data detection at 848 bits/s. Working together with the RF regulator, the ground switching modulator achieves a modulation depth of 50 mV at a field strength of 2.15 A/m while a 1.5 K resistive load modulator achieve achieves a depth of 10mV at a weaker field strength of 0.52 A/m.