A device for gain calibration of an analog-to-digital converter (ADC) residue amplifier includes a digital-to analog converter (DAC) configured to convert a digital signal to an analog signal. The DAC includes a calibration capacitor that can be used in the gain calibration of the ADC residue amplifier. A flash ADC, including a plurality of comparators and an additional comparator, generates the digital signal. The additional comparator provides a threshold voltage approximately in a middle point of a nominal subrange. The nominal subrange comprises a portion of a voltage range corresponding to threshold voltages of two adjacent comparators of the plurality of comparators.