| Compared with old models,modern automobile has much more swithes and buttons.Not only its quantity is increasing greatly,it also need to be installed easily on the control panel of automobile. In addition, it must have cost benefit in order to take place of airproof switches. One popular method is to use CapSense technology.CapSense chip intergrates 4 main blocks: capacitive sensor interface, relaxation oscillator, PWM and counter. Capacitive sensor tests the existence of human finger. Relaxation oscillator tests the capacitance variation of capacitive sensor. PWM and counter measure the period of relaxation oscillator output, by which the capacitance variation of sensor can be calculated. Counter output is connected with host computer through serial ports, transfer the data of finger position to all kinds of system control function.The primary work in this thesis is listed as follow:1. Considering both cost and performance demand, we select capacitive sense technology. Realize the low cost, easy operation and good endurance of switchs.2. The work principle and design of PWM is analyzed detailly.The use of△-Σmodulation makes the circuit have the invariable operation frequency. The design of folded operational amplifiers, high speed comparator, non-overlap control clock and CMOS swiths makes the PWM have good sample speed,slew rate and accuracy.3. Digital function block is built in the chip, realizing the design of mix signal IC. It will implement the harmony chip and host computer interaction.According to the simulation and test result, CapSence has a good linearity and accuracy from 2.4Vto 5.5V and -40℃to 120℃. The cost and design difficuilty is much lower which is a beneficial for both the manufacturer and customer.
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