差动电容传感器直接数字变换方法与实现

Method and Implementation for Direct Digital Converter of Differential Capacitive Sensor

为了使差动电容传感器与数字仪器间建立数据连接,设计了新型直接数字变换器。变换器采用双斜式变换原理,可实现差动电容传感器差与和之比值的数字输出,给出了原理性电路及测试结果。分析表明:寄生电容、开关泄漏电流和比较器偏置电压等因素对变换过程的影响可以忽略。新型变换技术所获得的高精度和良好的线性只取决于参考电压源而与传感器变换过程参数无关。试验结果显示,对于标称值为10 pF的差动电容传感器,在整个测量范围内,最大线性误差小于0.05%。

To connect a differential capacitive sensor to a digital instrumentation system, a novel direct digital converter was designed. The proposed converter can obtain digital output directly from a differential capacitive sensor and incorporating the dual slope topology and subtraction and add ratio operation, a prototype unit was built and tested. The analysis shows the stray capaci- tance switch leakage currents and comparator offset have a negligible effect on the output. The proposed technique promises high accuracy and linearity since the output is dependent only on a single dc reference voltage other than the sensor transduction param- eter. The practice test results show for a typical differential capacitive sensor with a nominal capacitance value of 10 pF, over the entire range of measurement,with a maximum error of less than ±0.05%.