The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 15, 1989
Filed:
Jul. 06, 1988
Mark A Goodnough, Buellton, CA (US);
John A Stineman, Jr, Goleta, CA (US);
Alan W Hoffman, Goleta, CA (US);
Santa Barbara Research Center, Goleta, CA (US);
Abstract
A current mirror circuit 10 is coupled to a first and a second photodetector 18 and 20 and differentially couples together the two photodetectors to an amplifier 12 such that a resulting differential output current is independent of the intrinsic responsivity difference between the two photodetectors. The circuit includes a first transistor 14 having an input terminal coupled to an output terminal of the first photodetector and a second transistor 16 having an input terminal coupled to an output terminal of the second photodetector. A capacitance 22 is coupled between a control terminal of the first transistor and a control terminal of the second transistor, the control terminal of the first transistor further being coupled to the input terminal of the first transistor. A first switch 24 is coupled between the control terminal of the second transistor and the input terminal of the second transistor. A second switch 26 is coupled between the second transistor input terminal and an input of the transimpedance amplifier for coupling the output current signal to the transimpedance amplifier. Preferrably the transistors are MOSFETs operated in subthreshold. During calibration the first switch is closed and the photodetectors are illuminated by a reference flux. A voltage stored across the capacitance is shown to be expressive of the difference in threshold voltage between the two MOSFETs and also the logarithm of the ratio of detector responsivities.