freescale powerpoint template - nxp semiconductors · 2016. 3. 12. · a gyro senses rotation...

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• State-of-the-art review

− Introduction

− Performance metrics

− Application

− Operating Principles

• Conclusions and Questions

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An accelerometer sense straight line motion

(linear motion)

Measured in m/s2 or “g”

A Gyro senses rotation “angular rate”

Measured in deg/s

Earth rotation: 0.004o/s

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rc VmF 2

dc VmF

2

A fictional force on a moving object when

observed on a rotating frame. The Coriolis force

scales with the angular velocity of the frame.

Angular rate (), drive motion (Vd) and Coriolis

force (Fc) are always located on there axes

orthogonal to each other.

This is where the confusion might begin. We

called XY gyro with the sensing direction is in Z-

axis while Z gyro with sensing direction in XY

direction ….

Input angular

rate ()

Coriolis

Force

Drive

Motion

Input

Rotation

Drive

Velocity

Coriolis

Force

Coriolis Force

X (Fc)

Z ()

Y (Vd)

Coriolis force causes

spiral motion in

Hurricanes

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• Three types of Gyros:

− Spinning Mass (Gimbal) -tilting produces precession

Impractical in MEMS

− Optical – measure time differences in laser paths

Very expensive, but also the best performance

− Vibrating – based on Coriolis effect

The most common

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• Four main components:

− Proof mass

− Elastic springs

− Drive (actuation) system

− Sensing method

• Proof mass is put into

oscillation (x-axis)

• Sensitive to angular rotation

in the z-axis

• Induced Coriolis acceleration

(y- axis)

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• DAU – Drive actuation unit, DMU – Drive measurement unit

• Goal is to maintain an oscillation with large and constant amplitude to provide enough Coriolis force for sensing the angular rate

• Comb drive is natural choice for DAU and DMU

- Capable of large travel range with linear force

• A high Q system is preferred (vacuum package)

- Close looped and positive feedback system with amplitude control (AGC) to enable oscillation

- Two port differential drive (push/pull) often used

- Travel amplitude is magnified by Q-factor (4000 – 20,000) times at resonance

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• SMU – sense measurement unit, FFU – force feedback unit

• Goal is to convert Coriolis force into sense displacement, into a different capacitance change

- Sense displacement is also an oscillatory motion!

- Coriolis force will mix (amplitude-modulate) the angular rate (low frequency) with drive velocity (high frequency carrier)

- Demodulation is require to extract the angular rate information from

• Capacitive sensing similar to accelerometer in terms of MEMS structure

- Gap closing parallel plate electrodes

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• Major challenge for gyroscope design, major offset error source

• Key contributor: manufacturing imperfection causes the principle axis (drive and sense motion) to rotate – Anisoelasticity coupling, cause the drive motion to “leak” into sense direction

• Quadrature is often very large (due to the large travel amplitude)

• Quadrature is 90o out of phase for Coriolis force. Demodulation will help eliminate quad error from the device output. But the detrimental effects are

- Large quad error cause ASIC front end to statue

- Small phase error cause quad error to leak into ZRO

- Noise – phase noise translates into output noise

• However, a small phase error will cause quad error to leak into ZRO.

• QCU – quadrature compensation unit

- Different techniques to compensate/cancel quad error

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• Mode match (drive frequency = sense frequency)

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Off-vertical Ion impact from the DRIE plasma produce asymmetrically tilted etched. This has been the major contributor to quadrature error in X and Y-axis gyroscope with out-of-plane detection mode

Even a small etch angle (0.1o) can cause quad error as large as 10,000dps)

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Governed by noise Drifting over

time/temperature

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• Operating range (Full scale range)

• Bias (Zero rate output – ZRO) or Offset − Angle Random Walk (white noise)

− Bias Instability (o/hr) (1/f, flicker noise)

− Rate Random Walk (1/f2 noise)

− TCO

• Scale factor (sensitivity) − Accuracy (trim error, scale factor stability)

− Linearity

− Cross-axis

− TCS

• Noise, resolution

• Turn on time

• Linear/angular vibration/acoustic sensitivity

• Shock resistance (1/g, 1/gxg)

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• The Allan Variance (AVAR) is a method of analyzing a time sequence to pull out the intrinsic noise in the system as a function of the averaging time.

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• Human Transportation

• Image Stabilization (camera, camcorders)

• Mobile devices (smart phone, tablet)

− Personal navigation system

− Location based services

− Mobile content navigation

− Game, dead-reckoning, gesture recognition

• Smart TV (remote)

• Gaming (3D tracking of gaming gestrure)

• Sports

• Health monitoring, RC toys, Shoes…

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• Segway Scooter

−Uses five MEMS gyroscopes for

tilt and rotation detection.

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• High Demo of key

functionality

• ODR, FS, HPF,

• Sample Time,

Data logger

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Features Function Benefits

Complete Portfolio

Freescale provides all sensing technologies and

associated algorithms based on broad sensing

portfolio such as pressure, touch, gyroscope,

magnetics, temperature, ambient light sensing,

and others.

Modularize the basic sensor configuration and

control functions

Manages sensor data acquisition depending on

function

Compatible with Proven

9-Axis solutions

Supported with libraries and adapters for

FXLC95000CL accelerometer is the 32-bit ColdFire

V1 processor

Provides added features and complete

resources to help you develop for your

application quickly and easily

Selectable Full Scale

Range +/-1600, 800, 400, and 200 dps

Configurable maximum angular velocity that the

gyro can read allows for multiple use cases

to be addressed with a single device.

Intelligent FIFO Buffer 192 byte FIFO buffer with circular and trigger

operating modes

Power Management Fast turn on time

Configurable power saving modes and auto-

wake/sleep capability allows the FXAS21000 to

become a part of the power management

decision to achieve optimal current consumption

Connectivity Communication protocols: I2C/SPI

I2C for both Normal and Fast Modes

Communication between master and slave ports

Flexible configuration options for easy design

ISF Enablement

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Xtrinsic ISF Gyro Adapters available

Sensor Adapter Board for

Demonstration

FXCL950000 tools for

Sensor Hub and gyro applications

9-Axis DIP for Prototyping

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DIP95000-9AXIS-H FXLC9500 9-axis adapter DIP

• Includes FAS21000 and FXOS87000 on DIP

• Works with the FXLC95000 Intelligent sensing EVK

• Available Q4’13 at www.freescale.com/gyro

FRDM-FXS-MULTI Xtrinsic Shield board

• Includes:

• MPL3115A2 – 20-115 kPa Digital Absolute Pressure Sensor

• MMA8652 – 3-Axis 12bit Accelerometer in 2x2mm DFN

• FXAS21000 - 3-Axis gyroscope

• FXOS8700 – 6-Axis ecompass sensor

• FXLS8471 – 3-Axis 14-bit Accelerometer with SPI

• MMA955x - 32-Bit 16K Flash CPU and 3-axis Accelerometer

• MAG3110 – 3-Axis magnetometer

• Available Q4’13 at www.freescale.com/gyro

Relevant Application Notes:

Application Notes will be posted in Q4

EcoSystem

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