In order to obtain the best device performance, particular attention must be paid to the proximity analog electronics. A proposed circuit that includes a reference voltage, the sensor decoupling capacitors and output buffers is described in the figure below.
Optimal acceleration measurements are obtained using the differential output (OUTPs-OUTNs). If a single-ended acceleration signal is required, it must be generated from the differential acceleration output in order to remove the common mode noise.
Block Diagram & Schematic
The main blocks that require particular attention are the power supply management, the accelerometer sensor
electronic and the output buffer. The following schematic shows an example of VS1000 implementation.
Recommended Circuit
The accelerometer output is ratio-metric to the power supply voltage and its performance will directly impact the accelerometer bias, scale factor, noise or thermal performance. Therefore, a low-noise, high-stability and low thermal drift power supply is recommended. Key performance should be:
- Output Noise < 1μV/√Hz
- Output temperature coefficient < 10ppm/°C
The power supply can be used as an output signal (VDD_S) in order to compensate any variation on the power supply voltage that will impact the accelerometer signal (ratiometric output).
The electronic circuit within the accelerometer is based on a switched-capacitor architecture clocked at 200 KHz. High-frequency noise or spikes on the power supply will affect the outputs and induce a signal within the device bandwidth.
Accelerometer Sensor
The sensor block is composed of the VS1000 accelerometer and the 3 decoupling capacitors: C1, C2 and C3. These capacitors are mandatory for the proper operation and full performance of the accelerometer. We recommend placing them as close as possible to the VS1000 package on the printed circuit board.
Output Signal Conditioning
The output buffer must be correctly selected in order match the VS1000 output impedance and signal bandwidth. The AD8571 is proposed for the acceleration output (OUTP & OUTN) and the temperature output (TEMP).
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