A second-order sigma-delta pixel sensor for X-ray applications

X-ray sensor applications in general need a high resolution, a high SNR, a low FPN and a low power consumption. Digital pixels with an ADC integrated in each pixel can satisfy not only aforementioned requirements but also a fast frame rate. Nyquist ADCs, however, have a large area to be implemented and thus need a sophisticated circuit design in order to operate properly. In the other hand, a sigma-delta ADC does not require a complicated circuit design and consumes a small area. Therefore, a second-order sigma-delta ADCs in each X-ray log pixel is chosen due to its low power consumption, high resolution and high frame rate. The designed X-ray array has a dimension of 10×20 with a pixel size of 100μm and the measured power consumption of each sigma-delta pixel is less than 700nW.