Weak Inversion ISFETs for ultra-low power biochemical sensing and real-time analysis

A novel pH sensor input stage is presented using the ISFET biased in the weak inversion region so that current levels are of the order of nanoamps. Translinear current mode circuit techniques are introduced as a way of mathematically manipulating chemical/biochemical signals coded as weak inversion current. The circuit presented is an example of application of these concepts and yields a linear relation between drain current and hydrogen ion concentration valid over 4 decades. The first-order temperature dependence of these circuits is greatly reduced from that of their voltage mode counterparts. The paper demonstrates an important and necessary step towards Chemical VLSI.