Patent ID: 8253616

Claim:
An analog-to-digital converter for generating an output digital value equivalent to the difference between two analog signal values comprising: at least one input for receiving a first analog signal level and a second analog signal level; an input for receiving a ramp signal; a counter which is operable to count in a single direction; a control stage which is arranged to enable the counter based on a comparison of the ramp signal with the first analog signal and the second analog signal; an output for outputting a value accumulated by the counter during a period when it is enabled; wherein the analog-to-digital converter is operable over a conversion cycle using a ramp signal having a single cycle, and wherein the control stage is arranged to: compare the ramp signal with the first analog signal level and to enable the counter when the ramp signal substantially equals the first analog signal level; compare the ramp signal with the second analog signal level and to disable the counter when the ramp signal substantially equals the second analog signal level.