Analog Devices,inc.

John Memishian

James M Lee

David C Hollocher

Thomas W Kelly

The systems, methods, and devices disclosed herein relate to a bit-per-stage ADC. The bit-per-stage ADC extracts one or more bits at each stage and creates a residue so that succeeding similar or identical stages can extract more bits. The ADC uses a reflected binary output code so that a bit can be extracted by observing the sign (e.g., polarity) of an input. The residue can be generated by rectifying the input, multiplying it by two, and level-shifting it by half the span. The generation of the residue is achieved using capacitors and switches. This causes the ADC to have low power consumption and a small size.

High resolution analog to digital converter

A method of detecting activity with a MEMS accelerometer stores a value of acceleration, then measures acceleration at a later time, calculates a change in acceleration using the measured acceleration and the stored acceleration, and compares the change in acceleration to an activity threshold to detect activity. A method of detecting inactivity uses a similar technique along with a timer. The method of detecting inactivity with a MEMS accelerometer stores an acceleration value, then measures acceleration at a later time, calculates a change in acceleration using the measured acceleration and the stored acceleration, and compares the change in acceleration to an inactivity threshold. If the change in acceleration is less than the inactivity threshold and, if a predetermined period of time has elapsed, then inactivity is detected.

Activity detection in MEMS accelerometers

A method of detecting activity in a MEMS accelerometer captures an acceleration bias, measures acceleration at a predetermined time, calculates a change in acceleration using the measured acceleration and the acceleration bias, and compares the change in acceleration to a threshold to detect activity. A method of detecting inactivity uses a similar technique along with a timer. The method of detecting inactivity in a MEMS accelerometer captures an acceleration bias, measures acceleration at a predetermined time, calculates a change in acceleration using the measured acceleration and the acceleration bias, and compares the change in acceleration to a threshold to detect inactivity. The method further determines if the change in acceleration is less than the threshold and, if so, determines if a predetermined period of time has elapsed to detect inactivity.

One or more fixed sensing electrodes are employed to sense movement of a mass both within the plane of the mass/electrodes and along an axis normal to that plane. In order to measure movement of the mass along the axis normal to the plane, a reference capacitance is measured between the fixed sensing electrode(s) and an underlying conducting plane and a measurement capacitance is measured between the mass and the underlying conducting plane. A value Cv-KCf may be computed, where Cf is the reference capacitance, Cv is the measurement capacitance, and K is a predetermined constant. In accordance with certain embodiments of the invention, a standard one or two axis acceleration sensor that measures movement of the mass within the plane can be used to also measure movement of the mass in the axis normal to the plane.

Multiple axis acceleration sensor

An accelerometer had a movable electrode between two fixed electrodes to form a differential capacitor. Drivers provide AC drive signals to the fixed electrodes. The movable electrode is coupled through reading circuitry to an output terminal. In response to a sensed acceleration, feedback is provided from the output terminal to one or both drivers to null any AC signal on the movable electrode and to keep the electrostatic forces between the movable electrode and each of the fixed electrodes equal.

Feedback circuit for micromachined accelerometer

An accelerometer has a movable electrode between two fixed electrodes to form a differential capacitor. Drivers provide AC drive signals to the fixed electrodes. The movable electrode is coupled through reading circuitry to an output terminal. In response to a sensed acceleration, feedback is provided from the output terminal to one or both drivers to null any AC signal on the movable electrode and to keep the electrostatic forces between the movable electrode and each of the fixed electrodes equal.

In a circuit for use with a micromachined device having a movable mass that forms an inner electrode of a differential capacitor, oppositely phased square waves are applied to two outer electrodes of the differential capacitor. A reset voltage is applied to the inner electrode synchronously with the square waves to stabilize and control the potential on the inner electrode. The signal on the inner electrode is demodulated by sampling during a first half of the square wave and a second half of the square wave between applications of the reset pulse to obtain a voltage that does not contain noise due to the reset switch.

Reset switch for a micromachined device

A micromachined device has first, second, and third electrodes forming a differential capacitor, and first and second drivers for providing clocked signals to the first and second electrodes. The drivers each have supply leads coupled to first and second reference voltage supplies via fixed first and second resistors, and also coupled together with variable resistors for trimming an offset so that electrostatic forces are balanced.

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Weston, MA, United States of America

John Memishian