In the field of Factory Automation (FA), process control, and Supervisory Control and Data Acquisition (SCADA), an analog data acquisition system using isolation transformers is commonly used to measure and record analog signals through isolated inputs. In order to improve the input precision of the acquisition system, circuit techniques and a design method of the analog frontend circuit with the signal transformers are proposed in this paper. A circuit technique to compensate for the droop of the pulse signal due to the characteristics of the signal transformer is employed. Also, a numerical analysis of a non-linear circuit equation, which represents a behavior of the core saturation of the signal transformer, is performed in order to determine the parameters of the circuit. Using a small signal transformer, dedicatedly developed for this acquisition system, the performance of the precision achieved for the linearity error is experimentally confirmed within +0.0204%/-0.0215%.