I/o Sensors, Inc.

Geosource, Inc.

I/o of Austin, Inc.

Franklin W Mayo

Richard A Johnson

Ben William Jones

Scott T Dupuie

Michael L Abrams

Burton A Devolk

Jeffery C Gannon

Miles A Smither

Matthew W Ip

Mark E Burchfield

Mauricio A Zavaleta

Roger Maher

Raymond K Erickson

Bing F Fung

A high performance method and apparatus for testing a closed loop transducer is disclosed. A test bitstream signal is combined with a .SIGMA..DELTA. feedback bitstream of the transducer to produce a combined bitstream which is converted to a physical feedback to the sensor of the transducer. The .SIGMA..DELTA. bitstream output of the transducer is recorded for later analysis so as to test characteristics of the transducer. The test bitstream signal is preferably an oversampled, pulse density modulated signal. A testing arrangement is provided which is based upon the storage of short-length test patterns which are repetitively accessed to form a continuous test pattern. The test bitstream provided by the method of the invention produces very low noise and low distortion test signals where a repetitive test pattern is equivalent in length to one period of the test signal.

Method and apparatus for generation of test bitstreams and testing of

A method and apparatus for measuring and compensating for stray capacitance of a micro-machined sensor of an accelerometer system is disclosed. Stray capacitance differences between a top plate and a sensing element and between a bottom plate and the sensing element degrade accelerometer performance if not compensated for. Measurement of stray capacitance difference is achieved by operating the accelerometer in two calibration phases and measuring the steady-state output voltage in each of the two phases. In calibration phase 1, no force is applied to the sensor during clock intervals 1-4. In calibration phase 2, a dummy force up is applied and then a dummy force down is applied during those intervals 1-4. The difference in the output voltage of the two calibration phases is representative of the difference in stray capacitance of the sensor. Capacitance is added to the top or bottom plates in an amount proportional to the measured stray capacitance. The procedure is repeated until the voltage difference of the two calibration phases is zeroed, which is indicative that the inherent stray capacitance has been zeroed.

Method and apparatus for calibration of stray capacitance mismatch in a

Apparatus for measuring a characteristic of motion and methods for its manufacture are disclosed in which a sensor structure includes a support structure, and a mass suspended from such support structure by a spring connecting arrangement and electrical devices for measuring displacement of the mass which results from a force applied to the support structure. An apparatus is provided where the mechanical spring constant of the connecting arrangement of the sensor structure is provided to be a high value representative of a strong, stiff spring which resists breaking due to high forces applied to it, and where an electric spring constant is provided to yield a small effective sensor spring constant K.sub.eff =K.sub.m -K.sub.e. Methods are also provided to manufacturing the apparatus by specifying the mechanical spring constant and providing an electric spring constant which will yield a desired effective spring constant which produces a desired characteristic of the sensor structure. Alternatively, the apparatus may be manufactured by specifying the electric spring constant which, with a mechanical spring constant, provides a certain sensor structure characteristic, e.g., natural frequency, and then providing a connecting arrangement characterized by a mechanical spring constant which yields such sensor characteristic. According to another aspect of the invention, the sensing force applied to the mass is adjusted in coordination with the mechanical spring constant and damping factor of the apparatus so that a desired characteristic of the apparatus is achieved.

Apparatus with mechanical and electric springs and method for its

An improved duty cycle controlled filter, wherein a resistance is included in every circuit path that exists between a switch terminal and an amplifier terminal. Such improved filter produces low distortion and has been found to be especially useful in data acquisition circuits of seismic exploration systems.

Electronic filter

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Houston, TX, United States of America

Franklin W Mayo