A PLL based WSN transmitter and I/Q LO signal generator at 430–435 MHz

Abstract

A fully integrated Phase-Locked Loop (PLL) based transmitter and I/Q Local Oscillating (LO) signal generator used for half-duplex Wireless Sensor Networks (WSN) transceivers is proposed. Instead of one 430---435 MHz PLL for frequency synthesizing, a 1.72---1.74 GHz PLL is designed together with a 1/4 frequency divider. Then the chip area of the inductors in the Voltage-Controlled Oscillator (VCO) is decreased to about 1/16, and I/Q dual-path LO signals can be obtained without additional power consumption. A Gray-code controlled prescaler is proposed to avoid the glitches and uncertain states, and then the frequency dividing accuracy is improved by 17%. A Gauss Frequency Shift Keying (GFSK) transmitter with a pipeline modulator is proposed, the 1st and 2nd Adjacent Channel Power Ratio (ACPR) are ?19.9 and ?20.7 dBc, respectively. A mathematical spur model of 1/4 frequency dividers is built here, and then a low-spur 1/4 frequency divider composed of our proposed improved Current Mode Logic (CML) latches is designed. The testing results show that the reference spurs are ?61.2 dBc@20 MHz and ?57.7 dBc@40 MHz at the output of the PLL, and ?70.5 dBc@20 MHz and ?66.6 dBc@40 MHz at the output of our 1/4 divider. With 2.6-mW power consumption, our proposed 1/4 frequency divider has a phase-noise contribution of only 0.5 dBc/Hz@500 kHz and 0.2 dBc/Hz@1 MHz.