逐次比较式ADC采样频率的选取及应用

在设计数据采集系统时,一项重要的任务是选择模数转换器(ADC)的采样频率.根据采样理论,采样频率至少应为输入信号带宽的两倍,实际往往采用更高的采样频率来保证数据采集系统的精度.但当逐次比较式ADC的采样频率过高时,会使其内部采样保持的开关电容充电不充分,从而导致ADC转换误差过大.选择一个合适的采样频率是保证数据采集系统可靠工作的关键.通过建立ADC及前向通道的等效模型及推导,在保证ADC的转换精度下,推出ADC的采样时间与信号放大电路输出阻抗的匹配关系,得到ADC最合适的采样频率.

The selection and application of successive-approximation ADC's sampling frequency

When a data acquisition system is designed, an important task is selecting the sampling frequency of the ADC. According to sampling theory, the sampling frequency should at least for input signal bandwidth two times. The higher sampling frequency is selected in fact for the precision of the data acquisition system. But when the sampling frequency of successive-approximation ADC is too high, the switched capacitor can't be charged properly. And this will result in too big conversion error. An appropriate sampling frequency is the key of the data acquisition system reliable work. This paper sets up the equivalent model of ADC and frontal channel, and determines the relation of the ADC sampling time and the value of the external driving source resistance to provide a desired ADC conversion accuracy, and an appropriate sampling frequency is inferred.