The RCA Selectron -- US Patent 2,645,724 Optical Readout

Jan A. Rajchman, Radio Corporation of America
Erik Stemme, The Royal Swedish Academy of Engineering Sciences
Applied: 24 June, 1950
Granted: 14 July, 1953

Block diagram of light from Selectron striking a photomultiplier

US Patent 2,645,724 images (OCR'd) 58 kB
US Patent 2,645,724 images (OCR'd) 58 kB

US Patent 2,645,724 text (OCR'd) 84 kB
US Patent 2,645,724 text (OCR'd) 84 kB

(Shift-click on each above link to allow side-by-side reading of both text and images.)

The '724 patent covers an advancement of the technique of optically sensing the status of a single bit (pixel) in the Selectron. (Basic optical detection was covered in
US patent 2,442,985.) Detecting the signal electrically from the Selectron tube itself was difficult. The signal current was many orders of magnitude less that the noise generated by the application of the fast-edged control signals applied to the tube. Detecting the light emitted from a stored bit (pixel) allows a unique way to "decouple" the signal from the noisy environment. '724 shows a way to detect the signal from the selected bit while the light from the entire array is still decaying. (The quiescent "storage" mode for the Selectron has all storage eyelets being flooded with electron streams. This causes all active bits' corresponding phosphor dots to illuminate. Selecting a bit extinguishes all BUT the desired bit to extinguish.
This patent teaches a way to detect the rapidly increasing light emanation from one pixel while many -- if not all -- others are slowly decreasing.

US patent 2,442,985