Current readout circuit using two-stage amplification method for 64-channel CNT arrays

In this paper, a readout circuit with a novel two-stage amplification method is presented for current sensing of 64-channel CNT(carbon nanotube) arrays. Key blocks of the proposed readout circuit consist of a transimpedance amplifier (TIA) block and an 11-bit SAR-ADC. In whole sensing sequence, the TIA block converts sensing currents of 64-channel CNT sensors into corresponding voltage levels through 64 active input current mirrors (AICMs) and a shared variable gain amplifier (VGA). This amplification method uses only one VGA requiring a high power consumption and large area for passive elements. Therefore, the proposed two-stage amplification method can be designed with small area and low power. Also, the output of the VGA is digitalized using the SAR-ADC with adaptive resolutions based on lower bit skipping algorithm according to an input voltage level for low power operation. The readout circuit is designed with the area of 0.173 mm² in 0.13 μm CMOS technology. The power consumption is measured about 73.06 μW at the conversion rate of 640 S/s.