Cmosis has introduced an image sensor concept yielding low dark noise and using dual gain readout to increase the dynamic range above 89.5dB. The new approach offers substantial advantages for numerous image processing tasks in scientific, diagnostic and security applications.
The Cmosis image sensor concept is based on a special pixel type, for which the dynamic range is increased by two distinct techniques. Most significant is its very low dark noise of less than 3.4e- at a full well capacity of 100ke-. Equally important is that the integration of the image charge takes place simultaneously at a low and a high amplification setting. The dual gain readout results in two different images. They are read out sequentially and combined externally into one final image, for which the dynamic range extends to more than 89.5dB.
The image capture array based on this pixel type offers an electronic rolling shutter, for which lines can be selected and read out via the columns. Due to the twofold readout of each pixel, the sensor has twice the number of column amplifiers than columns. Their amplification factors are programmable at 1x to 16x. This yields a broad range of optical sensitivity.
Several multiplexers are provided to select the proper column and transfer the analogue signals to a three-stage output circuit, which consists of an amplifier for correlated double sampling at 1x, 2x or 4x and programmable offset, limiter and output driver. Therefore, analogue-to-digital conversion can be done off-chip while programmable amplification and offset can adapt the sensor IC to different A/D converters.
Since the basic circuitry of this image sensor provides no on-chip runtime control, the pixel array is completely controlled externally. It comes with a serial interface that allows the setting of several internal registers for parameter selection.
Cmosis has developed a demonstration version of the sensor: the CLN1000 (Cmosis Low Noise 1,000K pixel). The sample unit features a 1 Megapixel array (1,024 x 1,024) laid out as a 10 x 10µm grid. Two amplifier paths (a total of 2,048) per pixel column (total of 1,024) minimise readout noise. Four analogue output channels of 16 MSPS each, which can be combined via a 4:1 multiplexer to a 64 MSPS output, are driven by four 512:1 multiplexers and output stages. Maximum frame rate of this configuration is 20fps. The CLN1000 sample is housed in a JLCC-84. It consumes about 300 to 350mW of power.
Based on this 1 Megapixel sample unit, Cmosis will design and implement a number of future sensor products for specific applications. Among the manifold uses of the dual gain readout sensor concept are scene monitoring and analysis, medical diagnostics, astronomy, microscopy and spectroscopy, industrial image processing, X-ray radiography, as well as luminescence- and fluorescence-based applications.
