Fig 1a shows one type of multi-channel biopotential sensor interface proposed in 4 Each channel has an instrument amplifier IA and programmable gain amplifier PGA and a clock-controlled multiplexer MU

In this paragraph, two types of multi-channel biopotential sensor interfaces are discussed, namely voltage domain-time division multiplexing (VD-TDM) and current domain-time division multiplexing (CD-TDM). The former involves a clock-controlled multiplexer (MUX) that selects a certain signal to drive a shared analog-to-digital converter (ADC), and each channel consists of an instrument amplifier (IA) and programmable gain amplifier (PGA). A simplification proposed in literature involves sharing the IA, buffer, and ADC, but the loading capacitance of the MUX increases exponentially with the number of channels, limiting the number of channels that can be supported. The latter type involves a programmable transconductance gain amplifier (PTGA) that converts voltage signals to current signals, and a transimpedance instrumental amplifier (TIA) that converts current signals back to voltage signals. The output of the PTGA can drive a low impedance load, thus avoiding the problem of loading capacitance of the MUX. However, the theoretical limit of TDM-based multi-channel biopotential interfaces is constrained by the need to ensure signal information integrity for each channel, and the increasing speed of IA leads to higher power consumption for a single channel