Column ADC
The described embodiments may provide a chemical detection circuit. The chemical detection circuit may comprise a column of chemically-sensitive pixels. Each chemically-sensitive pixel may comprise a chemically-sensitive transistor, and a row selection device. The chemical detection circuit may further comprise a column interface circuit coupled to the column of chemically-sensitive pixels and an analog-to-digital converter (ADC) coupled to the column interface circuit. Each column interface circuit and column-level ADC may be arrayed with other identical circuits and share critical resources such as biasing and voltage references, thereby saving area and power.
1. A method of using a chemically-sensitive sensor device, comprising:
selecting a first tile of an array of pixels, the array of pixels arranged in a plurality of rows and a plurality of columns, each pixel including a chemically-sensitive field effect transistor (chemFET) and a row select transistor;
selecting a first group of first columns and a first group of second columns from a first row of a first quadrant of the first tile array of pixels,
reading out data in parallel for the first group of first columns through a first output buffer of a first output circuit and for the first group of second columns though a second output buffer of a second output circuit; and
repeating sequentially selecting each of a next group of first columns and each of a next group of second columns and sequentially reading out data in parallel for each next group of first columns and each next group of second columns until all first row pixels for the first quadrant have been read.
2. The method of claim 1 , wherein each of the next group of first columns and each of the next group of second columns is selected during a readout time of a previously selected group of first columns and a previously selected group of second columns.
3. The method of claim 2 , wherein reading out data in parallel for the first group of first columns and the first group of second columns further comprises:
digitizing data in parallel through a first column analog-to-digital converter (ADC) for the first group of first columns and through a second column ADC for the first group of second columns;
serializing the digitized data in parallel through a first input/output (I/O) circuit coupled to the first column ADC for the first group of first columns and through a second I/O circuit coupled to the second column ADC for the first group of second columns; and
transmitting the digitized data in parallel through a plurality of first serial link terminals coupled to the first I/O circuit for the first group of first columns and through a plurality of second serial link terminals coupled to the second I/O circuit for the first group of second columns.
4. The method of claim 3 , further comprising sequentially reading out data for each first row of each remaining quadrant in the first tile by repeating the steps for reading the first row of the first quadrant.
5. The method of claim 4 , further comprising sequentially reading out data for each subsequent row of each quadrant by repeating the steps for reading the first row of each quadrant until each pixel of the first tile has been read.
6. The method of claim 3 , wherein the transmitting the digitized data is carried out using low-voltage differential signaling (LVDS) or current mode logic (CML) via an impedance controlled transmission line.
7. The method of claim 1 , wherein reading out data for a chemFET pixel is in response to detecting a signal resulting from a reaction in a reaction chamber capacitively coupled to the chemFET.
8. The method of claim 7 , wherein reading out data for the chemFET pixel is in response to detecting a signal resulting from incorporation of nucleotide during a sequencing reaction.
9. The method of claim 7 , wherein the chemFET is an ISFET pixel, and reading out data is in response hydrogen ion release during incorporation of a nucleotide during a sequencing reaction.