GYROSCOPE

A vibrating structure gyroscope (30) comprises a resonant structure (10) arranged to vibrate under stimulation from a primary drive electrode. A drive system is arranged to vibrate the vibrating structure at a resonance frequency. An automatic gain control unit (34) varies an amplitude of a primary drive signal (PD). A controller (44) operates the gyroscope (30) such that in a first mode of operation, the automatic gain control unit (34) varies an amplitude of the drive signal (PD) between an operating range defined by upper and lower bounds. The controller (44) may also operate the gyroscope (30) in a second mode operation, in which the automatic gain control unit (34) sets the amplitude of the drive signal (PD) to a predetermined level outside of the operating range. When the gyroscope (3) is operated in the second mode of operation, the controller (44) measures an amplitude of a primary sense signal (PP) after a predetermined time period, determines an oscillation cycle count during said predetermined time period, and determines a quality-factor of the gyroscope (30) from said measured amplitude and oscillation cycle count.