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The present paper proposes an analog front-end (AFE) circuit, including only one low-noise amplifier with chopping techniques and one high-pass sigma-delta modulator (HPSDM), which can be applied as a sensing circuit for electroencephalogram or electrocorticogram (ECoG) signal acquisition systems. The low-noise amplifier, which has a close-loop gain of 20 V/V and CMRR of 109.6 dB, is implemented by a differential difference amplifier with feedback pseudo-resistors and capacitors. The HPSDM is implemented in a feed-forward architecture with an order of 3, an oversampling ratio of 128, and a 1-bit quantizer under a sampling frequency of 51.2 kHz. The TSMC 0.18 μm 1P6M CMOS process is used in the entire AFE circuit with a supply voltage of 1.2 V and power consumption of 28.7 μW. Within the maximum range of ECoG signals, the simulated SNR and SFDR of the entire AFE circuits are 70.8 and 73 dB, respectively.