Communications: electrical – Digital comparator systems
Patent
1975-12-10
1978-03-28
Pitts, Harold I.
Communications: electrical
Digital comparator systems
307311, 340166EL, H04Q 300
Patent
active
040817938
ABSTRACT:
A device for reading out the charge condition of a phototransistor by means of sampling pulses, for example read out of a transistor to be selected from a matrix of phototransistors, a voltage which is a measure of said charge condition being taken from the emitter of the phototransistor. In order to avoid the storage effect owing to the time constant which depends on the differential resistance of the base-emitter-junction, the emitter circuit of the phototransistor includes a current source which at the instant of sampling is switched on, while furthermore the emitter voltage of the phototransistor is applied to a voltage comparator circuit which supplies a voltage for switching off the current source at the instant that said emitter voltage drops below a specified reference value. In the case of read-out after a dark period some charge is drained owing to the response time of electronic systems, which charge can be compensated for by simple injection means.
REFERENCES:
patent: 3735151 (1973-05-01), Frederiksen
patent: 3797894 (1974-03-01), Carp
patent: 3798559 (1974-03-01), Tomita
patent: 3872329 (1975-03-01), Dodson
patent: 3911268 (1975-10-01), Mori
patent: 4004158 (1977-01-01), Morgan
Pitts Harold I.
Trifari Frank R.
U.S. Philips Corporation
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