Ramp signal calibration apparatus and method and image sensor including the ramp signal calibration apparatus

摘要

Provided are a ramp signal calibration apparatus and method and image sensor including the apparatus. The apparatus includes: an analog-to-digital converter (ADC) including a trimmable transistor having a gain value that varies according to stored data, and configured to receive a ramp signal in a state where the gain value is a first gain value, and to output first and second output signals; a subtractor configured to calculate a difference between the first and second output signals; a digital comparator configured to compare the difference with a reference value and to determine whether a slope of the ramp signal has changed; and a counter configured to change the stored data based on whether the slope of the ramp signal has changed, wherein when the counter changes the data, the first gain value of the trimmable transistor is changed to a second gain value according to the changed data.

主权项

1. A ramp signal calibration apparatus comprising:
an analog-to-digital converter (ADC) comprising a trimmable transistor having a gain value that varies according to stored data, the ADC configured to receive a ramp signal in a state where the gain value is set to a first gain value, and to output a first output signal and a second output signal based on the received ramp signal; a subtractor configured to calculate a difference between the first output signal and the second output signal; a digital comparator configured to compare the calculated difference with a reference value and to determine whether a slope of the ramp signal has changed based on a result of the comparing; and a counter configured to change the stored data based on the determining of whether the slope of the ramp signal has changed; wherein when the counter changes the stored data, the first gain value of the trimmable transistor is changed to a second gain value according to the changed data, wherein the trimmable transistor comprises a reference transistor, N metal oxide semiconductor (MOS) transistors, and N switches connected in parallel, and each of the N switches is disposed on a side of each of the N MOS transistors, respectively, and the N switches are turned on or off according to the data, and wherein the ramp signal comprises a coarse ramp signal and a fine ramp signal, the first output signal comprises an output of the fine ramp signal, which corresponds to a first level of the coarse ramp signal, and the second output signal comprises an output of the fine ramp signal, which corresponds to a second level of the coarse ramp signal, and a difference between the second level and the first level corresponds to a least significant bit (LSB) of the coarse ramp signal.