为了给软件定义仪器中的数字化前端的设计和选择提供依据，提出了ADC等效分辨率的概念。结合过采样技术和香农限带高斯白噪声信道的容量公式推导出了等效分辨率的公式，并以测量心电信号为例，采样速率为400 SPS、ADC参考电压为2.5 V时，选用等效分辨率为26位的ADC。经实例证明，等效分辨率为ADC的性能评估和软件定义仪器中的数字化前端的选择提供了一个重要参数，也为选择软件定义仪器提供了一个简明的指标，有着一定的指导意义。 Abstract:  In order to provide the basis of the digital front design and selection of the software defined instrument，a concept of equivalent resolution ADC was advised. Equivalent resolution formula was deduced，combined with sample technology and Shannon limit with gaussian white noise channel capacity. And an ECG measuring example was given，which sampling rate was 400SPS，ADC reference voltage was 2.5V，the 26 rates AD equivalent resolution was selected. It was proved that equivalent resolution had provided an important parameter for evaluation the performance of ADC and selecting the digital front during the software defined instruments，but also a concise index and certain significance.