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Model-Based Design for Embedded Systems- P73

Model-Based Design for Embedded Systems- P73: This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. | 706 Model-Based Designfor Embedded Systems 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 2.5 m 2.0 m 1.5 m 1.0 m 0.5 m 0.0 m 0.5 m -1.0 m -1.5 m -2.0 m -2.5 m 0.0 m 10.0 m 20.0 m 30.0 m 40.0 m 50.0 m 60.0 m 70.0 m 80.0 m 90.0 m 100.0 m110.0 m Time s FIGURE 21.7 Simulation of the accelerometer behavioral model. The mathematical model describes the accelerometer as a mass-spring system. It applies the Newton s second law which also deals with the damping force. Again the constants used have been obtained through experimental measurement and known physical values. This model shows the possibilities of VHDL-AMS of solving differential equations. 21.5.2 Output Circuitry The output circuitry of the accelerometer can be treated separately in two parts. The first one is the signal conditioning circuitry based on Chopper stabilization CHS so it amplifies the signal and eliminates the noise. The second part consists of a sample and hold SH device and an ADC and makes possible the connection of the sensor to a digital device. The entire system scheme can be seen in Figure 21.8. First we address the signal conditioning circuitry. The operation principle in CHS is to avoid low level noise by moving the signal to higher frequencies and restoring it to its original frequency once amplified. The output voltage of the accelerometer reaches the first modulator so it is transferred to the frequency imposed by the oscillator. The next step is to amplify the signal and pass through a band-pass filter in order to eliminate undesirable signals. Smart Sensors Modeling Using VHDL-AMS 707 FIGURE 21.8 Accelerometer output circuitry. Finally the second modulator and the low-pass filter restore the original frequency signal. The signal conditioning circuitry is composed of two modulators input output which are controlled by an oscillator signal a preamplification a band-pass filter an oscillator a low-pass filter 40 dB decade and 10 kHz Butterworth filter and a frequency divider. .