Micro-silicon Capacitive Acceleration Sensor Single-chip Test Circuit Design, The Relaxation Oscillator

Silicon sensors are the tendency of the development of sensors. With the development of technology, MEMS( Micro-Electro-Mechanical Systems ) have became more and more attractive. This paper aims at designing a relaxation oscillator which is used in the readout circuits for silicon capacitive accelerometers with CMOS process.In this paper, we introduce the methods to test the tiny capacitors and analyse the principle of relaxation oscillator used in the readout circuits for silicon capacitive accelerometers. To form a complete relaxation oscillator, we design the current source,the switch,the control logic and the comparator. At last, we test the output of the oscillator.The current source plays an important part in the performance of the oscillator. With the help of the voltage reference, we design a constant current source which does not vary with the temperature,the voltage source and the process.To reduce the effect of the comparator's delay, we use the high-speed comparator, whose delay is about 4.5ns.The temperature performance of the relaxation oscillator is too bad. So we analyse the temperature impact on the output frequency and a new temperature compensation method is introduced to get better temperature performance. It can improve the temperature performance easily without increasing the cost and the consumption of the area. This method also can be used in other situation where the relaxation oscillator is applied to get better temperature performance.Because popular simulative tools can not test the output jitter of the oscillator, so with the help of the previous research, we estimate the jitter of the oscillator.The simulative result shows that the relaxation oscillator can work in the range from - 40°C to 85°C ,the temperature coefficient of it is about 60 ppm /°C and the output jitter is about 6.37ns.