Design of CMOS VCO and Combiner used in RF Transmitter for Wireless sensors

Abstract:
This paper describes a transmitter circuit based on CMOS standard technology. It operates with the 863–870 MHz European band for Wireless Sensor applications. The proposed transmitter combines a BFSK modulator which uses the Frequency Hopping Spread Spectrum (FHSS) and it is designed for short range wireless applications, an up conversion mixer and a power amplifier. In this paper, two important blocs are presented and discussed: a Voltage Controlled ring Oscillator (VCO) and a new Combiner architecture for direct conversion transmitter based on CMOS inverters only. The oscillation frequency of the VCO is controlled by a voltage VCTRL. Simulation results of the proposed VCO show that power consumption, at desired oscillation frequency and under a supply voltage of 3.3 V, is only 7.48 mW and the phase noise is lower than - 126 dBc/Hz at 10 MHz offset frequency. The combiner operates with transconductance cells and a typical application of subtractor is presented to illustrate the circuit capabilities. Index Terms — Wireless sensor, CMOS technology, direct conversion transmitter, Ring VCO, CMOS inverter, Combiner.