Instantaneous Frequency Measurement (IFM) Devices are the essential parts of any ESM, ELINT, and RWR receiver. Analog IFMs have been used for several decades. However, these Devices are bulky, complex and expensive. Nowadays, there is a great interest in developing a wide band, high dynamic range, and accurate Digital IFMs. One Digital IFM that has suitably reached all these requirements is mono-bit zero-crossing IFM, made by some different producers at present. In this paper, the Performance of mono-bit digital Instantaneous Frequency Measurement (IFM) Device is analyzed. This analysis includes quantization error, thermal noise, clock jitter, comparator bias and also "Pulse-on-Pulse" occurrence. The error limits due to all these factors are computed and analyzed, and a unified approach to the system design is presented.