In an embodiment an analog-to-digital converter circuit has an input for receiving at least a first analog signal level, a ramp generator adapted to provide a ramp signal having a constant and adjustable starting level which splits into a first section which is rising and a second section which is falling concurrently to the first section's rising, wherein the starting level lies within an input range of the analog-to-digital converter circuit, a comparison unit which is coupled by its first input to the input of the analog-to-digital converter circuit and is coupled by its second input in a switchable manner to the ramp generator, a counter which is coupled to a control unit, and the control unit which is coupled to an output of the comparison unit, wherein the control unit is prepared to enable the counter depending on a comparison of the ramp signal with the first analog signal level and to determine a digital value as a function of a count of the counter reached at an intersection point of the ramp signal with at least the first analog signal level.