T. Northemann

Drive and sense interface for gyroscopes based on bandpass sigma-delta modulators

This paper demonstrates a MEMS gyroscope system with extensive use of sigma-delta (ΣΔ) modulation in both, primary and secondary modes. The primary loop has a bandpass ΣΔ-digital-to-analog converter (DAC) driving the primary mass into resonance, which is implemented on a field programmable gate array (FPGA). With this strategy of shifting the primary oscillation control into the digital domain, the analog circuit complexity is enormously reduced. A continuous-time (CT) fourth-order micro-electro-mechanical ΣΔ Modulator (ΣΔM) incorporating the secondary resonator is used to convert the Coriolis rate signal into a bit stream. This ΣΔM is implemented on PCB performing an in-band noise (IBN) below −60 dBFS.

Modulated electro-mechanical continuous-time lowpass sigma-delta-modulator for micromachined gyroscopes

In this paper a novel system concept is presented for the implementation of lowpass sigma-delta (ΣΔ) modulators for micromachined gyroscopes. Within the electro-mechanical ΣΔ-modulator two modulation-stages are implemented, reducing the sampling frequency compared to bandpass- and conventional lowpass modulators by a factor of 4 and 100, respectively. By implementing two modulation-stages in the loop the frequency characteristic of the mechanical sensor is changed, thus it is possible to model the mechanical sensor as filter with lowpass-characteristic in the band of interest. Therefore the complete system functions with only one relevant frequency, namely the primary resonance frequency of the mechanical sensor. This concept enables the design of a continuous-time (CT) interface with an extremely low sampling frequency, hence the power dissipation is reduced enormously. A systematic design approach of this architecture is presented and simulation results are shown and discussed.

Low-Power, Continuous-Time Sigma-Delta Interface for Micromachined Gyroscopes Employing a Sub-Nyquist-Sampling Technique

In this paper a novel system concept for the implementation of low-power readout electronics for micromachined gyroscopes is described. The main innovation is a modified Chopper Stabilization (CHS) technique in a SigmaDelta loop based on an undersampling process. It enables the design of a full Continuous-Time (CT) SigmaDelta interface dissipating less power than its Discrete-Time (DT) counterpart without additional hardware effort for a flicker noise suppression. Further a systematic design approach for an interface employing this method and an architecture enabling this procedure is presented.

Phase-locked drive loop with amplitude regulation based on phase-shifting for gyroscopes

This paper presents a phase-locked drive loop for gyroscopes with an amplitude regulation based on phase-shifting. Instead of regulating the AC or DC value of the driving stage in order to maintain a constant primary oscillation, this concept introduces a tunable phase delay into the driving loop. Compared to conventional amplitude regulation this concept is advantageous, since the high voltages of the driving stage can be set to a constant value and do not have to be adjusted. This reduces the complexity of the analog circuitry enormously and eases the use of higher driving voltages. Additionally this concept provides a sampling frequency for a sigma-delta modulator readout interface.

An amplitude regulation for gyroscope drive loops based on phase-shifting

To achieve high quality measurements with micro gyroscopes it is essential to maintain a primary oscillation with a constant amplitude for a reliable detection of angular rotations with the Coriolis effect. This paper presents a self-oscillation drive loop for gyroscopes with a new amplitude regulation based on phase shifting. Instead of regulating the driving stage in order to control the oscillation amplitude of the primary mass to a constant value, this concept introduces a variable phase delay between the velocity of the primary mass and driving force in a self-oscillation drive loop. A Schmitt trigger with a tunable hysteresis is used to generate the necessary phase delay. Compared to conventional amplitude regulation this concept is beneficial, since the high voltages of the driving stage can be set to a constant value and do not have to be adjusted. As a result the analog circuit complexity is enormously reduced. Simulation results show the principle of maintaining the sensor deflection by a phase shifting element.

Controlling the primary mode of gyroscopes with a phase-based amplitude regulation

This paper presents the circuit implementation of an amplitude regulation for the primary mode of gyroscopes based on phase-shifting. Instead of regulating the AC or DC value of the driving stage in order to maintain a constant primary oscillation, this concept introduces a tunable phase delay into the driving loop. The high voltages of the driving stage can be set to a constant value and do not have to be adjusted. The driving stage can be realized with a set of simple switches applying two fixed voltages to the gyroscope for actuation. This reduces the complexity of the circuitry enormously. Measurements reveal that the frequency is held constant with a sigma of 1Hz and the amplitude regulation is within 0.6% of the defined value.