Chemical sensor array with leakage compensation circuit
View Patent ↗To reduce the pixel size to the smallest dimensions and simplest form of operation, a pixel may be formed by using only one ion sensitive field-effect transistor (ISFET). This one-transistor, or 1T, pixel can provide gain by converting the drain current to voltage in the column. Configurable pixels can be created to allow both common source read out as well as source follower read out. A plurality of the 1T pixels may form an array, having a number of rows and a number of columns and a column readout circuit in each column.
1. A device comprising:
an array of chemically-sensitive field-effect transistors (chemFETs) coupled to a plurality of lines; and
a circuit for reading a selected chemFET in the array, the selected chemFET coupled to a first line and a second line in the plurality of lines, the circuit to:
induce a current between the first line and the second line through the selected chemFET to establish a voltage on the second line;
compensate for leakage current through at least one additional chemFET coupled to the second line; and
read the selected chemFET based on the voltage on the second line.
2. The device of claim 1 , wherein the circuit includes a current sink coupled to the second line to compensate for the leakage current.
3. The device of claim 1 , wherein the voltage on the second line indicates an ion-concentration of an analyte solution coupled to the selected chemFET.
4. The device of claim 1 , wherein the circuit includes a pre-charge circuit to pre-charge the second line to a pre-charge voltage level.
5. The device of claim 4 , wherein the pre-charge circuit comprises a switch coupled between the second line and a reference voltage.
6. The device of claim 1 , wherein the circuit includes a sample circuit to sample the voltage level on the second line to read the selected chemFET.
7. The device of claim 6 , wherein the sample circuit includes a sample and hold circuit to hold an analog value of the voltage on the second line, and an analog to digital converter to convert the analog value to a digital value.
8. The device of claim 6 , wherein the sample circuit includes an analog to digital converter to directly convert the voltage on the second line to a digital value.
9. The device of claim 1 , wherein the circuit to compensate for the leakage current establishes a minimum current level on the second line.