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參數(shù)資料
| 型號： | ADXL311 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Low Cost, Ultracompact 【2 g Dual-Axis Accelerometer |
| 中文描述： | 低成本，超小型【2克雙軸加速度計 |
| 文件頁數(shù)： | 7/12頁 |
| 文件大?。?/td> | 419K |
| 代理商： | ADXL311 |
ADXL311
THEORY OF OPERATION
The ADXL311 is a complete, dual-axis acceleration measure-
ment system on a single monolithic IC. It contains a polysilicon
surface-micromachined sensor and signal conditioning cir-
cuitry to implement an open-loop acceleration measurement
architecture. The output signals are analog voltage proportional
to acceleration. The ADXL311 is capable of measuring both
positive and negative accelerations to at least ±2 g The acceler-
ometer can measure static acceleration forces, such as gravity,
allowing it 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 meas-
ured using a differential capacitor that consists of independent
fixed plates and central plates attached to the moving mass. The
fixed plates are driven by 180° out of phase square waves. Accel-
eration will deflect the beam and unbalance the differential
capacitor, resulting in an output square wave whose amplitude is
proportional 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 k 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.
Applications
POWER SUPPLY DECOUPLING
For most applications, a single 0.1 μF capacitor, CDC, will ade-
quately decouple the accelerometer from noise on the power
supply. However, in some cases, particularly where noise is pre-
sent at the 100 kHz internal clock frequency (or any harmonic
thereof), noise on the supply may cause interference on the
ADXL311 output. If additional decoupling is needed, a 100
(or smaller) resistor or ferrite beads may be inserted in the sup-
ply line of the ADXL311. Additionally, a larger bulk bypass
capacitor (in the 1 μF to 4.7 μF range) may be added in parallel
to CDC.
SETTING THE BANDWIDTH USING C
X
AND C
Y
The ADXL311 has provisions for bandlimiting the X
OUT
and
Y
OUT
pins. Capacitors must be added at these pins to implement
low-pass filtering for antialiasing and noise reduction. The
equation for the 3 dB bandwidth is
(
dB
F
32
2
/
3
–
)
(
)
(
)
Y
X,
C
×
π
=
kΩ
or, more simply
(
)
Y
X,
dB
3
–
C
/
F
F
5
μ
=
The tolerance of the internal resistor (R
FILT
) can vary typically as
much as ±15% of its nominal value of 32 k; thus, the band-
width will vary accordingly. A minimum capacitance of 1000 pF
for C
X
and C
Y
is required in all cases.
Table 4. Filter Capacitor Selection, C
X
and C
Y
Bandwidth
10 Hz
50 Hz
100 Hz
200 Hz
500 Hz
5 kHz
Capacitor (μF)
0.47
0.10
0.05
0.027
0.01
0.001
SELF TEST
The ST pin controls the self-test feature. When this pin is set to
V
DD
, an electrostatic force is exerted on the beam of the acceler-
ometer. The resulting movement of the beam allows the user to
test if the accelerometer is functional. The typical change in
output will be 270 mg(corresponding to 45 mV). This pin may
be left open circuit or connected to common in normal use.
R
BIAS
SELECTION
A bias resistor (R
BIAS
) must always be used. If no resistor is pre-
sent, the ADXL311 may appear to work but will suffer degraded
noise performance. The value of the resistor used is not critical.
Any value from 50 k to 2 M can be used. Using a 2 M
resistor rather than a 50 k will save roughly 25 μA of supply
current.
Design Trade-Offs for Selecting Filter
Characteristics: The Noise/BW Trade-Off
The accelerometer bandwidth selected will ultimately determine
the measurement resolution (smallest detectable acceleration).
Filtering can be used to lower the noise floor, which improves
the resolution of the accelerometer. Resolution is dependent on
the analog filter bandwidth at X
OUT
and Y
OUT
.
The output of the ADXL311 has a typical bandwidth of 5 kHz.
The user must filter the signal at this point to limit aliasing
errors. The analog bandwidth must be no more than half the
A/D sampling frequency to minimize aliasing. The analog
bandwidth may be further decreased to reduce noise and
improve resolution.
The ADXL311 noise has the characteristics of white Gaussian
noise that contributes equally at all frequencies and is described
in terms of μg/√Hz, i.e., the noise is proportional to the square
Rev. A | Page 7 of 12
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| ADXL312ACPZ | 功能描述:IC ACCEL SPI/I2C 3AX 32LFCSP RoHS:是 類別:傳感器，轉換器 >> 加速計 系列:- 標準包裝:1 系列:SCA1000 軸:X，Y 加速范圍:±1.7g 靈敏度:1.2V/g 電源電壓:4.75 V ~ 5.25 V 輸出類型:數(shù)字 帶寬:50±30Hz 接口:SPI 安裝類型:表面貼裝 封裝/外殼:12-SMD 供應商設備封裝:12-SMD 其它名稱:551-1007-1 |
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