  In this paper, an schema for controlling the oscillation frequency of a
quadrature oscillator is proposed. The method involves controlling the
threshold voltage of the PMOS transistors in the inverter through control of
the bulk bias voltage. Results obtained using HSPICE simulation are presented
in a technology of 0.35{\mu}m, and experimental results using discrete elements
(HEF4007) are also shown. Both sets of experiments show the effectiveness of
the technique.
