system and circuit design for a capacitive mems gyroscope - Aaltodoc

1.3 Research Contribution 5
1.3 Research Contribution
The research work reported in this thesis was performed by the author and others at
the Electronic Circuit Design Laboratory, Helsinki University of Technology, Espoo,
Finland, in the years 2003-2007. The work has two areas of focus. First, it concen-
trates on the system-level design of a MEMS angular velocity sensor, trying to provide
as general-purpose an analysis as possible of selected aspects. Second, it concentrates
on the integrated implementation and design of the electronics required by the angu-
lar velocity sensor. The research questions that the thesis is intended to answer are
what the fundamental system-level non-idealities are that need to be considered dur-
ing the design of a MEMS angular velocity sensor, and how those non-idealities can
be addressed by the means of circuit design, in particular, by applying digital signal
processing (DSP) methods whenever possible.
More particularly, the work focuses on a system based on a vibratory microgyro-
scope, which operates in the low-pass mode with a moderate resonance gain, and with
an open-loop configuration of the secondary (sense) resonator (i.e. the secondary res-
onator is not controlled by a force feedback). Both resonators are assumed to have a
high quality factor. Furthermore, the gyroscope employs electrostatic excitation and
capacitive detection.
Although some of the effects of high resonance gain and, eventually, mode-matched
operation are mentioned on various occasions, they are not of primary interest. The
same applies to the use of the force feedback as well. A large amount of the system-
level analysis is independent of the actual excitation and detection methods, whereas
the circuit design part of the work concentrates purely on electrostatic excitation and
capacitive detection. Finally, the mechanical design of the sensor element, together
with the sensor packaging, is completely beyond the scope of this work.
Before the system-level design part, the basic properties of a vibratory microgyro-
scope and the related excitation and detection mechanisms are first introduced. This
gives the necessary background information for the rest of the thesis. After this there
follows a detailed analysis of issues related to different non-idealities in synchronous
demodulation, the dynamics of the primary (drive) resonator excitation, the compen-
sation of the mechanical quadrature signal, and the zero-rate output (ZRO).
The electronics design focuses primarily on the design of the sensor readout cir-
cuitry, comprising: continuous-time front-end performing the capacitance-to-voltage
(C/V) conversion, filtering, and signal level normalization; a bandpass ΣΔ analog-to-
digital (A/D) converter, and the required DSP. The other fundamental circuit blocks,
which are a phase-locked loop (PLL) required for clock generation, a high-voltage
(HV) digital-to-analog (D/A) converter, the necessary charge pumps for HV genera-
tion, an analog phase shifter, and the D/A converter (DAC) used to generate the pri-