ADXL213 Просмотр технического описания (PDF) - Analog Devices

Номер в каталоге

Компоненты Описание

производитель

ADXL213

Low Cost ±1.2 g Dual Axis Accelerometer

Analog Devices 

ADXL213

THEORY OF OPERATION

PIN 8

XOUT = 80%

YOUT = 50%

PIN 8

XOUT = 50%

YOUT = 20%

TOP VIEW

(Not to Scale)

PIN 8

XOUT = 50%

YOUT = 80%

PIN 8

XOUT = 20%

YOUT = 50%

XOUT = 50%

YOUT = 50%

EARTH'S SURFACE

Figure 21. Output Response vs. Orientation

The ADXL213 is a complete dual axis acceleration measure-

ment system on a single monolithic IC. It contains a polysilicon

surface-micromachined sensor and signal conditioning

circuitry to implement an open-loop acceleration measurement

architecture. The output signals are duty cycle modulated digital

signals proportional to acceleration. The ADXL213 is capable of

measuring both positive and negative accelerations to ±1.2 g.

The accelerometer can measure static acceleration forces such

as gravity, allowing the ADXL213 to be used as a tilt sensor.

The sensor 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 mea-

sured using a differential capacitor that consists of independent

fixed plates and plates attached to the moving mass. The fixed

plates are driven by 180° out-of-phase square waves. Accelera-

tion deflects the beam and unbalances the differential capacitor,

resulting in an output square wave whose amplitude is propor-

tional to acceleration. Phase sensitive demodulation techniques

are then used to rectify the signal and determine the direction

of the acceleration.

The output of the demodulator is amplified and brought off-

chip through a 32 kΩ resistor. At this point, the user can set the

signal bandwidth of the device by adding a capacitor. This

filtering improves measurement resolution and helps prevent

aliasing.

After being low-pass filtered, the duty cycle modulator converts

the analog signals to duty cycle modulated outputs that can be

read by a counter. A single resistor (RSET) sets the period for a

complete cycle. A 0 g acceleration produces a 50% nominal duty

cycle. The acceleration can be determined by measuring the

length of the positive pulse width (t1) and the period (t2). The

nominal transfer function of the ADXL213 is

Acceleration = ((t1/t2) – Zero g Bias)/Sensitivity

Where in the case of the ADXL213

Zero g Bias = 50% nominal

Sensitivity = 30%/g nominal

t2 = RSET/125 MΩ

PERFORMANCE

Rather than using additional temperature compensation

circuitry, innovative design techniques have been used to ensure

that high performance is built in. As a result, there is essentially

no quantization error or nonmonotonic behavior, and

temperature hysteresis is very low (typically less than 10 mg

over the –40°C to +85°C temperature range).

Figure 9 shows the zero g output performance of eight parts (X

and Y axis) over a –40°C to +85°C temperature range.

Figure 12 demonstrates the typical sensitivity shift over

temperature for VS = 5 V. Sensitivity stability is optimized for

VS = 5 V, but is still very good over the specified range; it is

typically better than ±2% over temperature at VS = 3 V.

Rev. 0 | Page 8 of 12

Share Link: