|
An intensified reticon scanner has been developed at Kitt Peak National Observatory for medium resolution astronomical spectroscopy. In this system, a dual reticon (2 x 936 pixels) is used to measure the light emitted at the output phosphor of an image intensifier. While the gain of the image tube system was sufficient to render the random readout noise of the reticon detector insignificant, the overall sensitivity of the instrument was initially limited by variations in the fixed-pattern noise associated with the reticon readout. The elimination of these variations required modifications in the reticon clock drivers and in the data handling techniques used. The stabilization of the fixed-pattern noise was accomplished by thermally controlling the environment surrounding the FET switches used to produce the clock signals that read out the array, and by filtering the switched output signals. The clock voltages were adjusted not to minimize the amplitude of the fixed-pattern noise, but rather to minimize the variation in the fixed-pattern noise observed, as small variations in the clock voltages were introduced. The resulting large fixed noise pattern is removed from the data by the subtraction of a bias scan - a readout of the array taken with no input signal. The bias scans and all data scans are 1024 elements in length. Each portion of the dual reticon is clocked as though it were this long. The overscan pixels are then used to measure exactly any small variations in the fixed-pattern noise which can then be subtracted from the data.
|
