Patent ID: 7794584

Claim:
A pH-change sensor, comprising: a first IST-operational-transconductance-amplifier (the “first IOTA”) having: (a) an output (the “first IOTA output”), (b) an ion-sensitive transistor (the “first IST”) having a drain region, and (c) a load transistor (the “first load transistor”) having a source region, a drain region, and a channel region, the channel region electrically connecting the source region and the drain region, wherein the drain region of the first IST is electrically connected to the drain region of the first load transistor; a second IST-operational-transconductance-amplifier (the “second IOTA”) having: (a) an output (the “second IOTA output”), (b) an ion-sensitive transistor (the “second IST”) having a drain region, and (c) a load transistor (the “second load transistor”) having a source region, a drain region and a channel region, the channel region electrically connecting the source region and the drain region, wherein the drain region of the second IST is electrically connected to the drain region of the second load transistor; a differential sensor having: (a) a first input connected to the first IOTA output, (b) a second input connected to the second IOTA output, and (c) an output (the “differential sensor output”), wherein the differential sensor output may be used to provide an indication of a voltage difference between the first input and the second input; wherein the first load transistor provides a drain-to-source resistance (the “first rds”), and the second load transistor provides a drain-to-source resistance (the “second rds”), and the first rds is different from the second rds.