ADIS16354SLASHPCBZ datasheet(12/28 Pages) AD

12 / 28 page

ADIS16354

Rev. 0 | Page 12 of 28

THEORY OF OPERATION

OVERVIEW

The ADIS16354 integrates three orthogonal axes of gyroscope

sensors with three orthogonal axes of accelerometer sensors,

creating the basic six degrees of freedom (6DOF) in a single

package. The accelerometers are oriented along the axis of rota-

tion for each gyroscope. These six sensing elements are held

together by a mechanical structure that provides tight force and

motion coupling. Each sensor’s output signal is sampled using

an ADC, and then the digital data is fed into a proprietary

digital processing circuit. The digital processing circuit applies

the correction tables to each sensor’s output, manages the

input/output function using a simple register structure and

serial interface, and provides many other features that simplify

system-level designs.

GYROSCOPE SENSOR

The core MEMS angular rate sensor (gyroscope) used in the

ADIS16354 operates on the principle of a resonator gyroscope.

Two polysilicon sensing structures each contain a dither frame,

which is electrostatically driven to resonance. This provides the

velocity element required to produce a Coriolis force during

rotation. At two of the outer extremes of each frame, orthogonal

to the dither motion, are movable fingers, which are placed

between fixed fingers to form a capacitive pickoff structure that

senses Coriolis motion. The resulting signal is fed to a series of

gain and demodulation stages that produce the electrical rate

signal output.

ACCELEROMETER SENSOR

The core acceleration sensor used in the ADIS16354 is a surface

micromachined polysilicon structure built on top of the silicon

wafer. Polysilicon springs suspend the structure over the surface

of the wafer and provide a resistance against acceleration forces.

Deflection of the structure is measured using a differential

capacitor that consists of independent fixed plates and central

plates attached to the moving mass. Acceleration deflects the

beam and unbalances the differential capacitor, resulting in a

differential output that is fed to a series of gain and demodula-

tion stages that produce the electrical rate signal output.

FACTORY CALIBRATION

The ADIS16354 provides a factory calibration that simplifies

the process of integrating it into system-level designs. This

calibration provides correction for initial sensor bias and

sensitivity, power supply variation, temperature variation, axial

alignment, and linear acceleration (gyroscopes). An extensive,

three-dimensional characterization provides the basis for

generating correction tables for each individual sensor.

CONTROL REGISTER STRUCTURE

The ADIS16354 provides configuration control to many critical

operating parameters by using a dual-memory register structure.

The volatile SRAM register locations control operation of the

part while the nonvolatile flash memory locations preserve the

configuration settings. Updating a register’s contents only affects

its SRAM location. Preserving the updates in its corresponding

flash memory location requires initiation of the flash update

command. This helps reduce the number of write cycles to the

flash memory and consequently increases the endurance of the

flash memory. During startup and reset-recovery sequences, the

flash memory contents are automatically loaded into the SRAM

AUXILIARY ADC FUNCTION

The auxiliary ADC function integrates a standard 12-bit ADC

into the ADIS16354 to digitize other system-level analog signals.

The output of the ADC can be monitored through the AUX_ADC

approximation converter. The output data is presented in

straight binary format with the full-scale range extending from

0 V to 2.5 V.

Figure 26 shows the equivalent circuit of the analog input struc-

ture of the ADC. The input capacitor (C1) is typically 4 pF and

can be attributed to parasitic package capacitance. The two diodes

provide ESD protection for the analog input. Care must be taken to

ensure that the analog input signals are never outside the range

of −0.3 V to +3.5 V. Signals outside this range causes the diodes

to become forward-biased and to start conducting. The diodes

can handle 10 mA without causing irreversible damage. The

resistor is a lumped component that represents the on resistance

of the switches. The value of this resistance is typically 100 Ω.

Capacitor C2 represents the ADC sampling capacitor and is

typically 16 pF.

VDD

Figure 26. Equivalent Analog Input Circuit

Conversion Phase: Switch Open

Track Phase: Switch Closed

For ac applications, removing high frequency components from

the analog input signal is recommended by the use of a low-pass

filter on the analog input pin.

In applications where harmonic distortion and signal-to-noise

ratios are critical, the analog input must be driven from a low

impedance source. Large source impedances significantly affect

the ac performance of the ADC. This can necessitate the use of

an input buffer amplifier. When no input amplifier is used to drive

the analog input, the source impedance should be limited to

values lower than 1 kΩ.

ADIS16354/PCBZ датащи(PDF) 12 Page - Analog Devices

ADIS16354/PCBZ датащи(HTML) 12 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL