Low noise, temperature-compensated, electrochemical cell sigma-delta current measurement readout circuit

Abstract

Nanopore ion channels are a promising solution for certain molecular structure analyses. Large arrays of nanopore channels and their associated readout circuits are used in many molecular studies such as DNA sequencing. Readout circuits must meet challenging performance criteria such as low noise operation, low power consumption, in-channel digitization capability, and high linearity. Previously, sigma-delta modulators have been presented to address these criteria; however, their specifications show drifts with temperature. In this paper, an approach is presented to keep modulator performance constant with temperature variations. For this purpose, the sigma-delta modulator's feedforward and feedback branches are modified so that their gain coefficient remains constant over a certain temperature range. With large sensors arrays, solutions employing high bias currents in the feedback paths are not suitable due to power consumption limitations. Here, the design gives the possibility of switching low current levels in the feedback paths without affecting the ENOB. The proposed temperature compensation solution shows good performance when temperature is swept from 27 degrees C to 100 degrees C. Over the mentioned temperature range, the gain and bandwidth of the modulator show a change of less than 0.4%. It is further shown that for a 10 kHz input current signal with an amplitude of 600 pA, the ENOB and power consumption are 12.9 and 4.6 mW, respectively. In the proposed second-order sigma-delta modulator, the feedforward (voltage-to-current converter) and feedback paths are modified so that the transfer function remains independent of temperature. Over a temperature range of 27 degrees C to 100 degrees C, the gain and bandwidth of the modulator show a change of less than 0.4%. image