In an apparatus and method for monitoring defects in wafers, a monitoring circuit is fabricated on an area of each one of the wafers. The monitoring circuit includes representative devices that replicate similar devices located in a die area of the wafers. Defects if present in the representative devices contribute to a generation of a noise, thereby causing an imbalance in a differential signal measurable across selected ones of the representative devices. A digitizing circuit that uses a common mode voltage as a reference to measure the imbalance digitizes the differential signal to a digital signal, the digital signal being indicative of the noise generated by the defects. The digital signal is stored over a configurable time interval to form a digital bit stream. The digital bit stream is compared to a reference to determine whether the defeats are within an allowable range.