The analog-to-digital converters (ADCs) have been widely used in the applications of such as precision metrology, motion control, position, and pose estimation, whose phase–frequency characteristic usually brings in an inevitable influence. In order to ensure the performance of these applications, the phase–frequency characteristic of ADCs has to be definitely determined before they are used. In this letter, a new sine approximation-based comparison measurement method is presented, which accurately determines this characteristic by utilizing the linear frequency modulation signal with high carrier frequency and narrow bandwidth instead of the sinusoidal signal. Experimental results demonstrate that the presented method is able to obtain the satisfactory accuracy for the phase–frequency characteristic of general ADCs and promote the improvement of their applications.