The invention includes a successive approximation register, a digital-to-analog converter, a comparator and a control stage. The control stage initially sets the successive approximation register to a first digital value. The digital-to-analog converter converts the digital value stored in the successive approximation register to an analog value. The comparator compares the converted digital value with an analog input value. The control stage restricts subsequent analog-to-digital conversion for the analog input value to a search interval above or below the first digital value depending on whether the analog input value is greater or lower than the converted analog value of the first digital value.