A CMOS Power Amplifier With Integrated-Passive-Device Spiral-Shaped Directional Coupler for Mobile UHF RFID Reader

A CMOS power amplifier (PA) with a compact spiral-shaped directional coupler for a mobile UHF RF identification (RFID) reader is proposed here, and its output power combiner and the directional coupler are implemented using an integrated passive device process. The two-chip solution not only enables a CMOS PA to be highly efficient, but also allows the directional coupler and the power combiner to be mounted in a compact standard package. A polar transmitter is implemented using the CMOS PA with the directional coupler to verify the operation of the proposed configuration for a UHF RFID reader. Measurements indicate that the CMOS PA with the directional coupler transmits 27.3 dBm of output with 44.6% of power-added efficiency and that the implemented polar transmitter satisfies the required UHF RFID reader specifications.