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ADXL212AEZ Datenblatt(PDF) 9 Page - Analog Devices |
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ADXL212AEZ Datenblatt(HTML) 9 Page - Analog Devices |
9 / 12 page ADXL212 Rev. 0 | Page 9 of 12 THEORY OF OPERATION EARTH'S SURFACE TOP VIEW (Not to Scale) PIN 8 XOUT = 50% YOUT = 62.5% XOUT = 50% YOUT = 50% PIN 8 XOUT = 50% YOUT = 37.5% PIN 8 XOUT = 62.5% YOUT = 50% PIN 8 XOUT = 37.5% YOUT = 50% Figure 20. Output Response vs. Orientation The ADXL212 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 archi- tecture. The output signals are duty cycle modulated digital signals proportional to the acceleration. The ADXL212 is capable of measuring both positive and negative accelerations to ±2 g. The accelerometer can measure static acceleration forces such as gravity, allowing the ADXL212 to be used as a tilt sensor. The sensor is a surface-micromachined polysilicon structure built on top of a 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 plates attached to the moving mass. The fixed plates are driven by 180° out-of-phase square waves. Acceleration deflects the beam and unbalances the differential capacitor, resulting in an output square wave with an amplitude that is proportional to acceleration. Phase sensitive demodulation tech- niques are 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 which 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 analog signals are converted to duty cycle modulated outputs that can be read by a counter. A single resistor (RSET) sets the period for a complete cycle (t2) according to the following equation: t2 (nominal) = RSET/125 MΩ 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 ADXL212 is Acceleration = ((t1/t2) − Zero g Bias)/Sensitivity where: Zero g Bias = 50% nominal. Sensitivity = 12.5%/g nominal. PERFORMANCE High performance is built into the device through innovative design techniques rather than by using additional temperature compensation circuitry. As a result, there is essentially no quantiza- tion 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 10 shows the zero g output performance of eight parts (x-axis and y-axis) over a –40°C to +85°C temperature range. Figure 13 demonstrates the typical sensitivity shift over temper- ature for VS = 5 V. Sensitivity stability is optimized for VS = 5 V but remains very good over the specified range; it is typically better than ±2% over temperature at VS = 3 V. |
Ähnliche Teilenummer - ADXL212AEZ |
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Ähnliche Beschreibung - ADXL212AEZ |
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