Consumer-electronic (CE) gyroscopes have recently enjoyed broad deployment in high-volume applications, largely due to intuitive user interfaces in smart phones and video game controllers. For their continued expansion into more demanding CE applications, a further reduction of their noise, offset drift, and power dissipation, especially in the emerging always-on category, is mandatory. To be viable, solutions to these conflicting requirements must overcome the challenges of low cost and ever-shrinking package size. This paper describes one such solution with special emphasis on offset drift reduction. The system presented here discards the standard practice of electrically cancelling the quadrature error, and instead combines information derived from continuously monitoring the quadrature error together with a single-point temperature calibration to reduce offset drift. This paper presents the architecture and circuits used to realize a 3-axis open-loop gyroscope with a one-sigma TCO of 0.0065°/s/K. Figure 27.3.1 illustrates a fundamental mechanism of offset drift in an open-loop vibratory gyroscope.A suspended mass is driven into a steady state oscillation in a drive axis. Under rotation, some of the kinetic energy in the drive oscillation couples onto a sense axis. Manufacturing imperfections also cause some of the drive oscillation to appear directly in the sense axis independent of rotation, a stress-sensitive coupling referred to as the quadrature error. Due to their modulation by the drive velocity and displacement respectively, the desired angular-rate and the unwanted quadrature-error signals are orthogonal, which, in principle, allows their discrimination via synchronous demodulation. However, the phase delay through the sense axis introduces a skew between the modulated signals and the demodulation clock, which allows a portion of the quadrature error to appear as an angular-rate signal at the output. For high yield, the magnitude of the acceptable worst-case quadrature error can exceed the full-scale angular rate by over 20dB, simultaneously placing a heavy burden on the dynamic range of the readout circuitry and very tight bounds on the phase error. To ease the dynamic range burden on the readout circuitry, state-of-theart CE gyroscopes electrically cancel the quadrature error at the input of the sense channel capacitance-to-voltage (C/V) converter [1, 2]. However, besides the noise penalty that the cancelation signal injection incurs, the inevitable phase mismatch between the quadrature error and the cancellation signal can even exacerbate the offset drift problem.The sensing element used in this work operates far below the sense resonance frequency, where the phase delay through the sense axis is inversely proportional to the quality factor of the sense resonance. While the quality factor varies with process and temperature, its temperature dependence when normalized to its value at a reference temperature is known and quite stable over process. This implies that the phase delay is φ≅φ(T 0 )G(T 0 ,...
