Series-parallel scan

There exists a wide variety of approaches to the use of charge transfer devices in infrared focal planes. We shall discuss five high packing density, high quantum efficiency, approaches appropriate for series-parallel scan 1) IR sensitive CCD, 2) ctirect injection hybrid, 3) direct injection extrinsic silicon, 4) accumulation mode extrinsic silicon, and 5) infrared sensitive CID with silicon CCD signal processing. The reader is referred to a review article by Steckl et al. for a comprehensive discussion of a number of other approaches not discussed here which include indirect injection pyroelectric detectors and Schottky barrier photoemissive injection [6.1]. Three approaches in our list of five do not require... 

Fig. 6.5. Modulation transfer function (MTF) as a function of Ne where N is the total number of elementary transfers and E is the transfer inefficiency per elementary transfer. The curves are drawn for different spatial frequencies [/ is the Nyquist frequency (JJ2) ] and different array con-iigurations. The solid curves are for a staring array and the dashed curves for an array which uses series-parallel scan with TDl...

With mechanical scanning of the image across the focal plane, the detectors will experience a time varying signal due to structure in the image. The maximum signal frequency of interest for a TDI series-parallel scan system will be the same as for a parallel scan focal plane if both use the same number of interlace steps and do not segment the focal plane. For l/30s frame times and TV compatible... 

SERIES PARALLEL SCAN InSb CID FOCAL PLANE ARRAY... 

Fig. 6.14. Series-parallel scan IR CID. Infrared sensitive IR CID modules are completely read out more than once a dwell time through a preamplifier into a silicon CCD signal processor. In the signal processor TDI is performed and then th% individual lines of imagery are ac coupled and multiplexed. Only the CID module itself is fabricated from IR sensitive material...

One implementation of the series-parallel scanned CID is shown in Fig. 6.14. In this case one preamplifier is used per CID chip. The CID xy readout is used in... 

Fig. 6.17. Series-parallel scan IR CID with one preamplifier per column. All the columns are read out simultaneously. This lowers the readout speed and avoids the column select switches shown in Fig. 6.13...

If correlated double sampling is not used, besides background noise the most important source of noise for the series-parallel scan CID is likely to be kTC noise. If this is the case then the maximum signal frequency for which we can design the device to obtain BLIP operation will be... 

Series/Parallel Scan with time delay and integration remains the principal approach to advanced thermal imaging systems. However, for applications where only a small number of resolution elements are needed, two-dimensional staring detector arrays with CCD or CID readout are being considered [8.106]. This does away with the scanner and a focal optics used with conventional systems. However, to compensate for nonuniformities, both dc offset and gain correction must be made on a pixel by pixel basis. Detector responsivity and readout nonlinearities will increase the number of computations needed for sufficient correction and only experience with the stability of different types of arrays will determine how often the correction algorithms must be calibrated [8.107,108]. 

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