GB929263A - Improvements relating to charge storage pick-up tubes - Google Patents

Abstract

929,263. Cathode-ray tube circuits. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 7, 1959 [June 5, 1958], No. 17946/58. Class 40 (7). A non-linear feed-back path is provided between the signal electrode and a beam intensity control electrode of a cathode potential stabilized pick-up tube to reduce the variation in the " restoration potential " (i.e. the lowest potential which the target reaches in equilibrium) which occurs when the light intensity of the object varies. Fig. 2 shows the (non-linear) relationship between the restoration potential V<SP>1</SP>(s) and the potential swing S at the target of the tube and to correct for this an amplifier 9 (Fig. 1) having a suitable non-linear characteristic is connected in a feed-back path, including a fixed gain pre-amplifier 8 and a levelling clamp circuit 10 ... 12, between the signal electrode 2 and the cathode 5 of the pick-up tube 1. The amplifier 9 provides positive feed-back and the gain, which varies from a relatively high-level to a relatively low-level for signals produced by an increasing light intensity, is so offset by the variation in gain of the pick-up tube (which varies directly with light intensity) that the product of the two gains is less than unity for all light levels. Oscillation does not, therefore, occur. The invention, which is applicable to image type tubes and tubes of the photo-conductive type, is stated to produce a substantial reduction in discharge lag without causing either loop or discharge initiability. The non-linear amplifier 9 may employ a cathode-ray tube in which the inputsignal causes the beam to traverse a suitably shaped aperture to produce an output signal having the desired non-linear relationship to the input signal.