Mark Lemkin

A three-axis micromachined accelerometer with a CMOS position-sense interface and digital offset-trim electronics

This paper describes a three-axis accelerometer implemented in a surface-micromachining technology with integrated CMOS. The accelerometer measures changes in a capacitive half-bridge to detect deflections of a proof mass, which result from acceleration input. The half-bridge is connected to a fully differential position-sense interface, the output of which is used for one-bit force feedback. By enclosing the proof mass in a one-bit feedback loop, simultaneous force balancing and analog-to-digital conversion are achieved. On-chip digital offset-trim electronics enable compensation of random offset in the electronic interface. Analytical performance calculations are shown to accurately model device behaviour. The fabricated single-chip accelerometer measures 4/spl times/4 mm/sup 2/, draws 27 mA from a 5-V supply, and has a dynamic range of 84, 81, and 70 dB along the x-, y-, and z-axes, respectively.

A monolithic surface micromachined accelerometer with digital output

A surface micromachined accelerometer with on-chip electronics realized in a 3 /spl mu/m BiCMOS technology is described. The sensing element consists of a thin film of polysilicon that is deposited after fabrication of the electronic circuitry. Acceleration is measured by capacitively sensing sub-angstrom displacements of a mechanical proof-mass weighing 0.5 /spl mu/grams. The sensor uses force-feedback and achieves a resolution of 1.6 mg//spl radic/(Hz) (1 g=9.8 m/s/sup 2/). The limitations arising from the small size and mass of the sensing element and means for improvement are discussed. The small active die area of less than 3 mm/sup 2/ including the sensor along with the possibility to combine several different sensors on a single chip make this approach particularly attractive for applications demanding very small form factors.

A 3-axis force balanced accelerometer using a single proof-mass

This paper presents a new method for wideband force balancing a proof-mass in multiple axes simultaneously. Capacitive position sense and force feedback are accomplished using the same air-gap capacitors through time multiplexing. Proof of concept is experimentally demonstrated with a single-mass monolithic surface micromachined 3-axis accelerometer.

A 3-axis surface micromachined /spl Sigma//spl Delta/ accelerometer

A monolithic 3-axis surface micromachined accelerometer with capacitive sense and feedback circuitry uses three separate proof masses to measure acceleration. Each proof mass has its own set of interface circuitry, all of which are coordinated by an on-chip master clock. By including x-, y-, and z-axis sensors on one chip, this accelerometer provides a single-chip solution for measuring three ofthe six degrees of freedom needed in an inertial measurement unit. The sensor chip is implemented in 2 /spl mu/m CMOS technology.

Velocity estimation from widely spaced encoder pulses

It is often necessary to estimate the velocity of mechanical systems from the output of a digital encoder. Due to cost and/or noise problems, there maybe no direct velocity measurement available on such systems. Velocity reversal and sparseness of encoder signals are not handled well by traditional estimators. This paper proposes a transition logic based switching algorithm and an asynchronous multirate Luenberger observer based estimator to reduce these problems.

A micromachined fully differential lateral accelerometer

A monolithic surface micromachined lateral accelerometer with on-chip A/D converter is described. The device features a fully differential capacitive interface between the sensing element and on-chip electronics to minimize the systematic offset and errors due to switch charge injection. The common centroid layout of the sensor interface reduces cross-axis sensitivity and susceptibility to angular accelerations. The measured noise-floor of the device is 500 /spl mu/g//spl radic/(Hz) and the fullscale range is /spl plusmn/3.5 g(1 g=9.8m/sec/sup 2/).

A design and implementation methodology for real time control of mechanical systems

Real time software forms the core of mechatronic systems. It provides the medium for implementation of far more complex decision making than had been possible with previous technologies. This paper describes a methodology for the design of real time software for control and for its portable implementation. In addition to automated generation of engineering documentation, the method provides for production of diagnostic audit trail information and a means for comparative performance evaluation.

Using a hydraulically balanced beam system in control education

This paper discusses a low cost solution to teaching controls in the laboratory through the use ofa novel balance beam. The balance beam provides a vehicle to study many aspects of both control implementation and control algorithms. Due to the complexity of the system, a full semester of laboratory exercises is provided for even advanced students. The flexibility of the system provides challenging exercises for different levels of education. A low overall cost translates to accessibility to more schools. The ability to achieve good tracking performance with a simple cascaded loop controller makes this an ideal tool for teaching controls in a laboratory setting.

Using a hydraulically balanced beam as a case study in control implementation for control education

This paper discusses a low cost solution to teaching controls in the laboratory through the use of a novel balance beam. The balance beam provides a vehicle to address many problems of control implementation as well as control algorithms. Due to the complexity of the system a full semester of laboratory exercises is provided for even advanced students. The flexibility of the system provides challenging exercises for different levels of education. A low overall cost translates to accessibility to more schools.