Patent GB-990872-A (GB)
Title: Improvements in or relating to area scanning systems and to visual display systems
IPC: H04N3/12
Filed: 1961-08-03
Abstract: 990,872. Circuits employing bi-stable magnetic elements; television receivers. IIT RESEARCH INSTITUTE. Aug. 3, 1961 [Aug. 5, 1960], No. 28262/61. Headings H3B and H4F. Magnetic cores are switched in sequence to generate pulses for scanning an area 65 such as a television screen. Electroluminescent material is arranged at the cross points of horizontal and vertical wires 51, 52 &c. and 21, 22 &c. The usual return sweep is eliminated at the end of each line scan. The return sweep at the end of a vertical scan or line frame may also be eliminated. Horizontal scanning.-Cores 11, 12, 13 &c. have a graded bias winding 67 connected to terminals 69, 70. The number of turns on a core and the corresponding bias decreases from left to right. A sweep winding 77 connected to terminals 78, 79 links each core with the same number of turns. An alternating bias current 68, Fig. 2, and a sweep current 80, Fig. 3, are fed to the bias and sweep windings and the cores are switched from positive to negative saturation in sequence from right to left. They are then switched from negative to positive saturation in the same sequence and so on. There is no return sweep. The pulses generated are of the form 91, 94, 129, Fig. 6, but with condensers 141, 142 cross output windings 102, 101 &c. on the cores, the output becomes a succession of damped wave trains 91<SP>1</SP>, 94<SP>1</SP>, 129<SP>1</SP>, Fig. 7, each long enough to activate the luminescent material for the periods between successive pulses in accordance with a video input on terminals 201, 202. Vertical scanning.-A vertical line of cores 41, 42 &c. has a graded bias winding 151 which, with the aid of a battery 175 applies a positive bias decreasing from core to core from 41 downwards in one group. In a further group of cores, the bias increases negatively. At point 176 of the saw tooth wave of sweep. current all the cores are negatively saturated and the cores of the two groups switch in sequence during the rising portion 176 to 177 of the sweep wave. The cores are restored during the sweep back in the steep portion of the wave 177 to 178 which falls in the blank period of the video cycle. For interlaced scanning, odd numbered cores 41, 43 &c. would form one group and even numbered cores 42 &c. the second group. Sinusoidal drive for scanning.-Cores 1, 2, 3, Fig. 8 &c. are wound with two sets of graded drive windings, one set 801, 802, 803 all being biased in the same direction and the other set comprising two groups of cores (odd numbers and even numbers) biased in opposite directions for interlaced scanning. The windings are graded according to sinusoidal functions. Output windings 401, 402, 403 &c. are arranged as before with condenser 1001, 1002, 1003 &c. to provide damped wave trains. An alternating current supply on terminals 901, 902 switches the cores in sequence, a condenser 903 and an inductor 904 being effective to split the phases of the currents i 1 , i 2 , Fig. 10, in the two series of windings 701 &c. and 801 &c. by 90 degrees. The magnetomotive forces of the bias windings 701 &c. on eight cores A to H are plotted against time in curves A 1 , B 1  ... H 1 , Fig. 12. The magnetomotive forces of the winding 801 &c., which are all of the same polarity are shown in curves A 2 , B 2  ... H 2 . The cores are switched at the times indicated by A, B... H producing series of pulses A 3 , B 3  ... H 3 , A 4'  B 4  ... H 4  &c., Fig. 11.