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.