A Novel Frequency Readout Method and Circuit for Navigation-Grade Vibrating Beam Accelerometers

Vibrating beam accelerometers (VBAs) have significant application potential in navigation guidance. This article proposed a novel high-precision frequency readout method and integrated CMOS circuit implementation for VBAs, and technologies, including sigma-delta modulation, up-sample and split, data synchronization, and nonlinearity correction, are employed in the method, which is analyzed in detail in this article. The method offers the advantages of low quantization noise, enough range, fixed output rate, and high linearity. Other force-frequency sensors could also benefit from this method but note that its noise suppression is most effective when the output rate is much lower than the frequency under test. The method is implemented by a CMOS circuit and integrated with an oscillator circuit, which makes a full-function single-package VBA possible. Static, shock, random vibration, and centrifugal tests of the frequency readout circuit and VBA were performed. Test results show that the frequency quantization noise is less than $10 \mu $ Hz/ $\surd $ Hz at 1 Hz, and can support $0.1 \mu \text{g}$ noise output. They also show that the vibration rectification error (VRE) is lower than 0.5 mg at 8 $\text{g}_{\text {rms}}$ and that the 20 g full range nonlinearity is 16 ppm.