Improving the sensitivity of a vision chip using the software A-D conversion method

We developed a new method of pixel-level Analog-to-Digital (A-D) conversion for vision chips, removing Fixed Pattern Noise (FPN) at the same time. Vision chips are CMOS image sensors integrating a processing element (PE) and a photodetector (PD) in each pixel. The chip can handle high frame rate images in real time because its processing speed is high due to the parallel processing and also because it does not need high-bandwidth communication. Pixel-level A-D conversion is an essential technology for vision chips because digital operations must be performed in each pixel. The vision chip, which we have developed, contains a programmable PE in each pixel, and it directly controls the behavior of the PD with the use of the software. In our developed method, the chip controls the reference voltage to cancel the FPN by using this feature. We applied this method to our vision chip, and confirmed that the FPN was reduced and the sensitivity improved. We made a test chip including only PDs to solve the problem on the existing vision chip. As a result of applying this method to the test chip, the detectable minimum illuminance improved about 40 times in comparison with applying our existing method.