Browse Prior Art Database

Differential Spot Scanning

IP.com Disclosure Number: IPCOM000095003D
Original Publication Date: 1965-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Atrubin, AJ: AUTHOR

Abstract

In a cathode ray tube scanner for scanning characters, it is desirable to produce two concentric light spots. The outer spot functions to provide signals to an automatic clipping level control circuit. The inner spot provides information for recognizing the character scanned. Heretofore, the outer spot is generated by defocusing and the time response of the apparatus for achieving the defocusing is limited. Here, the outer or large spot is generated by moving the small spot in an Archimedes spiral.

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Differential Spot Scanning

In a cathode ray tube scanner for scanning characters, it is desirable to produce two concentric light spots. The outer spot functions to provide signals to an automatic clipping level control circuit. The inner spot provides information for recognizing the character scanned. Heretofore, the outer spot is generated by defocusing and the time response of the apparatus for achieving the defocusing is limited. Here, the outer or large spot is generated by moving the small spot in an Archimedes spiral.

This is essentially achieved by applying sinusoidal signals pi/2 radians out-of- phase to the horizontal and vertical deflection circuits respectively of the CRT. The amplitudes of these signals are simultaneously varied linearly with time. The end or terminal point of one spiral is the beginning point of the next. The successive cycles are displaced by a constant distance. Since the time per cycle is constant, there is less illumination per unit area on the outer cycles than on the inner ones.

Sine wave generator 10 generates waveform A which is examined by peak detector 15, phase-shifted - pi/2 radians by phase-shifter 20 and entered into multiplier 25. The signals generated by 15 are entered into counter 30 which presents its output to integrator 35 and ramp generator 40. The ramp developed by 40 multiplies sine waves from 10 and 20 within devices 25 and 45, respectively. The output of 45 results in a waveform Y. This is applied to the ver...