A direct down-conversion receiver for coherent extraction of digital baseband signals using the injection locked oscillators

Abstract

In today’s digital wireless communications direct down-conversion receiver is becoming a favorite choice due to its overall simplicity and low cost. However, carrier recovery of the received digitally modulated RF signal for clear IQ signal extraction at high symbol rates is not so simple. Until now, phase-locked loop (PLL) and/or direct-digital synthesizers (DDS) or combination of both have been used for better performance but at the expense of high complexity or cost. In this paper for the first time we propose a direct downconversion receiver that uses an injection-locked oscillator (ILO) for carrier recovery and frequency synthesizing. The results are shown for carrier recovery of a 2.1GHz 20Msps 8PSK signal and coherent demodulation of a 2.78GHz 160Msps QPSK signal. The receiver presented is of low-cost and low-complexity and applicable to any kind of digitally modulated signals reception. It can be used in many wireless applications as WiMax, RFID and sensor networks.