An innovative readout channel, based on analog amplitude modulation (AM) of the signals recorded by each electrode, is developed for high-density CMOS-based MEAs. This new readout method enables the design of a low-noise amplification stage while still reading the extracellular activity sensed by the whole array. Hence, the circuit architecture provides an efficient solution to the major limitation of high-density active MEAs related to the real-time transmission of every electrode input. CMOS implementation of the readout channel is presented. Each pixel contains a double-balanced CMOS mixer having a size of 26.5 x 26.5 um2. It is shown that in the case where signals from five different pixels are simultaneously recorded, the dominant noise source of the system is the noise generated in the two-stage operational amplifier. Furthermore, the maximum number of pixels which can be contained in a single readout channel is limited by the thermal noise of each pixel which sums up at the amplifier input node. A maximum limit of 20 pixels is estimated.