Low-Power QPSK Transmitter Based on an Injection-Locked Power Amplifier

Abstract

An injection-locked frequency divider was used as a quadrature phase-shift keying (QPSK) modulator by exploiting the property that a polarity flip of the injected signal results in a phase shift of 90 degrees at the output. Furthermore, the power amplifier was integrated with the divider by adding a transformer to couple to the antenna. Combining these two ideas resulted in a high-efficiency, high-bandwidth QPSK transmitter, capable of operating at up to 120 Mbit/s and delivering 1.3 m W output power with a system efficiency of 38 %.