A polar transmitter architecture with digital switching amplifier for UHF RFID applications

With amplitude shift keying (ASK) modulation and signal envelope rising falling edge slope requirements, the efficiency of UHF RFID system can be improved by using polar transmitter architecture than using linear power amplifiers. In this work, to ensure maximum integration and meet EPC Class-1 Generation-2 specification, an all digital polar transmitter is proposed and verified by transient signal analysis and random pattern simulation. The timing and signal quality constraints of the digital polar transmitter circuits are extracted. Due to the use of RF frequency low pass sigma delta modulation, the system can be designed in pure digital process without on-chip inductive components. Compared to the 31% theoretical efficiency by using class-A linear power amplifier, a minimum 77% theoretical efficiency can be achieved in this proposed digital RFID system.