A temperature stabilized CMOS VCO

Abstract

The established method of frequency drift compensation in voltage controlled oscillators (VCOs) resulting from temperature variance involves modulation of control voltage using a non-linear voltage internally generated. An innovative frequency drift compensation scheme for a VCO, based on amplitude control, is described in this paper. Two peak detectors are used to generate voltages representing positive and negative peaks of the sinusoidal driving an error amplifier. The amplifier output controls the delivery of transconductance accessible to the oscillator, thereby keeping the oscillation amplitude steady. Frequency stability has improved to 16 ppm/°C from an uncompensated value of 189 ppm/°C and is applicable where frequency stability requirements are not stringent, such as HS-USB and S-ATA. The temperature stabilized VCO at 2.4 GHz center frequency is prototyped using CMOS technology from ams AG (formerly austriamicrosystems AG). The result obtained from this study indicates that better frequency stability may be achievable if the traditional compensation scheme is preceded by amplitude control.