OOK/NCP-FSK Modulator based on Coupled Open-Closed-Loop VCOs

In this paper a simple FSK/OOK modulator based on a proposed CMOS coupled voltage controlled oscillators is presented. In FSK mode the circuit is a non-continuous phase FSK (NCPFSK) which exhibits a relatively low phase discontinuity at the frequency transition times. The proposed modulator is built from CMOS inverters. The circuit is self biased and the frequency of oscillations can be easily shifted by opening and closing the open loop of each oscillators. Regarding technology, the modulator, which uses any active inductor, is able to operate at high frequency and provides digital output with suitable phase noise. Simulation result from typical parameters of a 0.35 mum CMOS Process is given. The circuit functioning has been also acted from measurements completed from prototypes fabricated with HFE4069 from Philips Semiconductor [1].