The extreme sensitivity of nano electro mechanical system (NEMS) to atomic scale physical variations has led to the breakthrough development of NEMS-based mass spectrometry systems capable of measuring a single molecule [1]. Parallel sensing using thousands of devices will help to circumvent the small effective sensing area while opening new perspectives for applications that require spatial mapping. While the development of NEMS CMOS co-integration technology [2] is of paramount importance to achieve high density sensor arrays (>,1000 devices), the readout circuitry capable of tracking NEMS resonator frequency shifts is still the limiting factor for the very large scale integration of individually addressed sensors. Moreover, in order to resolve the mass and position of an adsorbed analyte, single particle mass sensing applications require to track simultaneously and in real time at least two modes of the resonators. This requirement adds complexity to the design of the overall system. To respond to the size, power consumption and resolution constraints linked to NEMS array measurement, we propose a compact heterodyne self-oscillator analog front-end IC which performs 1ms simultaneous dual-mode frequency tracking compatible with a 'pixel-based' readout scheme. We report less than 1mA power consumption with a 300zg mass resolution for 26000?m2 size. © 2017 IEEE.