Enrico Chiesa

Interface for MEMS-based rotational accelerometer for HDD applications with 2.5 rad/s/sup 2/ resolution and digital output

A 0.6 /spl mu/m BiCMOS interface for microelectromechanical systems (MEMS) based rotational accelerometers is presented. It is housed in an inexpensive standard SO-24 plastic package with a capacitive rotational accelerometer sensor produced using MEMS technology. This sensitive interface chip includes the analog-to-digital conversion, filtering, and interface functions. The analog-to-digital conversion is realized through a single-bit electromechanical /spl Sigma/-/spl Delta/ loop able to detect capacitive unbalancing as low as 50 aF (50/spl times/10/sup -18/ F). The produced bitstream is then processed by a digital chain and made available through a standard 3.3 V (5 V tolerant) three-wire serial bus. The signal bandwidth is about 800 Hz, the sensitivity is 2.5 rad/s/sup 2/, with a full-scale sinewave of 200 rad/s/sup 2/ and a signal-to-noise ratio peak of 38 dB over 30-800 Hz. Through the serial bus, it is also possible to program device characteristics including gain, offset, filter performance, and phase delay. The complete sensor is used in a feed-forward compensation scheme to cancel external disturbances acting on computer hard-disk drives so as to steadily keep the read-write heads on track: this allows greater track densities and better speed performance.

A Low-g 3 Axis Accelerometer for Emerging Automotive Applications

A 30 µg/sqrt(Hz) resolution MEMS based low-g 3-axis accelerometers targeted for emerging automotive application is presented. The device is composed by 2-dice in a single package: the sensing element and the processing IC. The sensing element is realized with an epitaxial micro-machining process (ThELMA™) while the IC uses a 0.5 μm BICMOS process. The IC amplifier is able to detect capacitive changes as low as 10 aF (10·10−18 F) and the device is able to provide both an analog and a digital output. Moreover it has very good linearity and very low cross talk between the sensing axes thanks to a design that fits very well the ST micro-machining process ThELMA. Finally, the proposed interface accelerometer is factory-trimmed to ensure repeatable performance without production-line adjustments in the end product