Abstract: A method for providing user adjustable variable gain for a night vision device which utilizes an image intensifier tube, wherein the image intensifier tube has a given life expectancy, the image intensifier tube is subjected to factory calibration for providing an optimum output during operation, wherein the calibration undesirably differs from tube to tube and is adjustable by variable control means coupled to the tube, whereby when one tube is substituted for another the difference in calibration causes non-optimum performance, the method including the steps of: determining minimum and maximum gain limits associated with the optimum output of the night vision device; factory calibrating gain limiting means according to the determined minimum and maximum gain limits, wherein the gain limiting means are associated with the image intensifier tube and for limiting the variable control means; and, tethering the gain limiting means to the image intensifier tube.

Abstract: The delinearization circuit includes a first analog switch which is switchable in accordance with the duty cycle of the pulses in an input pulse train, between a given voltage and ground, to form a pulse train of constant amplitude. An intermediate signal is formed by time averaging the output of the first switch. A second analog switch, switchable in accordance with the duty cycle of the input pulse train between the intermediate signal and ground, forms a second pulse train which is time averaged to provide an output signal proportional to the square of the amplitude of the input signal pulse train. In a second embodiment of the invention, a maximum value circuit is utilized to select the greater of the intermediate signal and a reference voltage and the second switch is switched between the selected signal and ground.