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
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.
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