Experimental investigations were carried out in order to identify the portable device requirements for in-vitro muscle tissue monitoring over time. Based on these investigations, specifications for the measurement system were defined considering the type and amplitude of excitation signals (500 mV), frequency range (1 kHz 10 MHz) and impedance range (10 Omega-4 k Omega). For these requirements, a portable device structure is proposed based on the magnitude ratio and phase difference detection using a gain phase detector. To fulfill the requirements of the gain phase detector circuit's inputs, an interface circuit is proposed with an error lower than 0.09% from 2 m V up to 200 mV.