A 24-channel implantable neural recording based on time and frequency-division multiplexing

This paper presents a novel approach to encapsulate prerecorded neural signals in implantable neural recording microsystems. We have increased the number of channels and the reconstructed neural signal quality in the receiver by combining time-division-multiplexing (TDM) and frequency-division-multiplexing (FDM) method. Reducing the number of channels in each TDM module is the fundamental advantage of this method that leads to reduced crosstalk noise. We evaluate some possible configurations and propose an optimized system that has less power dissipation and area occupation than other configurations. A 24-channel implantable neural recording based on the optimized system is designed in both system and circuit level. In this system, first, channels are divided into three 8-channel groups then after multiplexing in the time domain, they are combined together by FDM method. Finally, a frequency modulator wirelessly transmits neural signals to an external setup. In addition, we adjust local carrier frequencies and the bandwidth of TDM to synchronize detection without transmitting pilot carrier. To justify the system operation, using 0.18 μm CMOS technology, we design the system in circuit level. The designed circuit consumes a power of 1.39 mW at a supply voltage of 1.8 V. This leads to a power consumption of 58 μW per channel.