Autocalibration of the A/D converter within the CMOS type image sensor

A method for initializing a signal sensing apparatus comprising a signal sensing array having N columns of output line for outputting N analog signals, respectively, and a signal processing means having N input lines and N A/D converters for generating N digital signals, each of which corresponds to one of N analog signals, respectively, N being an integer greater than one, the method comprising the steps of:

• (a) during an initialization period prior to generating the N analog signals, coupling a predetermined reference voltage to the outputs of the N A/D converters of the signal processing means such that a compensation value corresponding to each set of A/D converters is obtained at the output of each of the N A/D converters, wherein the compensation value is a binary complement to, the digital signal from the corresponding A/D converter as the reference voltage is applied;
• and
• (b) prior to generating the N analog signals, initializing a counter within each of the N A/D converters with the corresponding compensation value to compensate for the digital output of the corresponding A/D converter, thereby balancing non-uniformity of elements within the signal processing means.

A signal processing means for use in a signal sensor apparatus comprising a signal sensing means having N columns of output lines for outputting N analog signals, respectively, the signal processing means having N input lines for generating N digital signals each of which corresponds to one of the N analog signals, respectively, N being, an integer greater than one wherein the signal processing means comprises:

• N A/D converters each of which includes a counter for generating one of the N digital signals, respectively, wherein, during an initialization period prior to the N digital signals being produced, a predetermined reference voltage is coupled to inputs of the N A/D converters and a compensation value corresponding to each of the N A/D converters is obtained, wherein the compensation value is a binary complement to the digital signal from the corresponding A/D converter as the reference voltage is applied during the initialization period, so that the counter within each of the N A/D converters is initialized with the compensation value to compensate for the digital output of the corresponding A/D converter, thereby balancing non-uniformity of elements within the signal processing means.

In a signal sensing apparatus comprising a signal sensor means having N columns of output lines for outputting N analog signals, respectively, and a signal processing means having N input lines and comprising N A/D converters for generating N digital signals each of which corresponds to one of the N analog signals, respectively, N being an integer greater than one, a method for initializing a counter within a corresponding one of the N A/D converters within the signal processing means in order to minimize non-uniformity of the elements within the signal processing means, the method comprising the steps of:

• (i) during an initialization period prior to generating the N analog signals, coupling a predetermined reference voltage to the outputs of the N A/D converters of the signal processing means such that a compensation value corresponding to each of the N A/D converters is obtained at the output of each set of A/D converters, wherein the compensation value is a binary complement to the digital signal from the corresponding A/D converter as the reference voltage is applied;
• and
• (ii) prior to generating the N analog signals, initializing the counter within each of the N A/D converters with the corresponding compensation value to compensate for the digital output of the corresponding A/D converter, thereby balancing non-uniformity of elements within the signal processing means.