Interferometric fiber optic gyroscopes (IFOGs) are used for sensing inertial rotation. High performance IFOGs are typically setup in a closed loop configuration in order to improve scale factor stability, scale factor linearity, and dynamic range. However, voltage dependent bias errors (VDBEs), such as electrical cross-coupling, polarization, back scatter, and electronic pick up, can cause the loop to become less stable at certain rotation rates. A particular problem is when attempting to sense a rotation rate near zero. Typically, the loop settles to a point where the VDBEs cancel the input rate causing the sensor output signal to be zero over a finite input range. This range is known as the “dead band”, “dead zone”, or “region of instability”.
To mitigate the effect of dead band, dead band error suppression modulation, also referred to as Feedback Spread Spectrum Modulation (FSSM), can be used. FSSM is typically implemented as a phase jump in the feedback signal with random amplitude and a fixed frequency. FSSM (also referred to herein as “jumping the phase step”) is described in more detail in U.S. Pat. No. 6,744,519, which is hereby incorporated herein by reference. The result of FSSM is that VDBEs are averaged over the full feedback voltage range, reducing the likelihood of entering into dead band. Since FSSM works by averaging the VDBEs over the full feedback voltage range, the angle random walk (ARW) resulting from VDBEs decreases as the frequency of the phase jumps increases.
In conventional implementations, however, there are other error sources affecting the angle random walk (ARW) that increase as the frequency of phase jumping (also referred to herein as the “FSSM frequency”) increases. These error sources are related to losses of phase information during the phase jump and when data is rejected due to the presence of the phase jump. Because there is a noise source that decreases with the frequency of phase jumping and one that increases with the frequency of phase jumping, optimization is performed on a unit-by-unit (individual) basis to determine the FSSM frequency for the unit that provides the least noise. This unit-by-unit optimization is a cost driver during initial unit testing. Additionally, if the dead band errors and/or phase loss errors are large enough; the noise performance of the sensor will be compromised leading to degraded performance.