Radiant energy – Photocells; circuits and apparatus – Signal isolator
Patent
1983-07-29
1986-12-16
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Signal isolator
455602, G02B 2700
Patent
active
046299017
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a photo coupler and, more particularly, to improvement in its photo detector.
TECHNICAL BACKGROUND
A p-i-n diode, an avalanche photo diode and a photo transistor, such as a bipolar transistor, which are employed as photo detectors in conventional photo couplers posses many defects.
The p-i-n diode and the avalanche photo diode are two-terminal elements, and hence have the drawback that they have no function of isolation from the next-stage element. The p-i-n diode and the avalanche photo diode are supplied with a relatively high voltage for operation by irradiating their depletion layers with light. The avalanche photo diode has the serious shortcoming of producing much noise which is due to light that results in an avalanche multiplication.
The photo transistor using a bipolar transistor has a gain as small as 100 or so and has a large base resistance, and hence it possessses the defect of very low-speed operation.
FIGS. 1A and 1B show examples of the arrangements of conventional photo couplers.
FIG. 1A illustrates a photo coupler which employs a GaAs light emitting diode 1 as a light emitting element and a p-i-n diode 2 as a photo detector.
Reference numeral 3 indicates a packaging case in which the light emitting diode 1 and the p-i-n photo diode are housed. There are times when the photo detector 2 is an avalanche photo diode. In operation, an input signal I.sub.1 flows in the light emitting diode 1 to generate light h.nu. and a current I.sub.2 flows in the p-i-n photo diode 2, developing an output signal across a load resistor R.sub.L. This arrangement is defective in that a relatively large bias source is needed and in that a special consideration must be paid to its coupling with a circuit of the next stage.
FIG. 1B shows a conventional photo coupler using a bipolar transistor 4 as the photo detector. The light h.nu. from the light emitting diode 1 is amplified by the bipolar photo transistor with its base floating. The bipolar transistor has a large base resistance and has the defect that the operating speed is low.
As described above, the conventional photo couplers posess serious drawbacks in practical use.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a photo coupler which employs a static induction transistor, static induction thyristor or field effect transistor as the photo detector to permit operation with such high sensitivity, high speed, low voltage and low current as have been unobtainable in the past.
The photo coupler of the present invention has a portion having connected thereto a static induction transistor, or static induction thyristor coupled with one light emitting element through a light transparent insulator and has the advantages that it operates with very high sensitivity, high speed, low voltage and low current and permits simplification of circuit structures following the photo detector; therefore, the photo coupler of the present invention has a great industrial value.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a diagram showing the arrangement of a conventional photo coupler using a two-terminal diode as the photo detector;
FIG. 1B is a diagram showing the arrangement of another conventional photo coupler employing a bipolar transistor as a photo transistor serving as the photo detector;
FIGS. 2A through 2C are diagrams illustrating the arrangement of an embodiment of the photo coupler of the present invention which employs a static induction transistor as the photo detector;
FIG. 3 is a diagram illustrating another emobdiment of the photo coupler of the present invention which uses, as the photo detector, a static induction transistor having an MIS gate;
FIGS. 4A and 4B are diagrams illustrating the arrangement of another embodiment of the photo coupler of the present invention which employs a static induction thyristor as the photo detector; and
FIG. 5 is a diagram illustrating the arrangement of another embodiment of the present invention which uses an optical fiber as a light tra
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G. Krause, "Opto-Couplers Used to Provide DC Power for Control of Thyristors", Sep. 1976, Elektronik, vol. 25, No. 9, p. 72.
"Semiconductor Research Foundation"
Messinger Michael
Nelms David C.
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