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:
Jun. 23, 1998
Filed:
Jan. 25, 1996
Richard A Baumgartner, Palo Alto, CA (US);
Travis N Blalock, Santa Clara, CA (US);
Thomas Hornak, Portola Valley, CA (US);
Joey Doernberg, San Carlos, CA (US);
Hewlett-Packard Company, Palo Alto, CA (US);
Abstract
Circuitry and circuitry layout are provided to achieve a high percentage of photoreceiver area to total area and to stabilize the voltage at the base node of a phototransistor. Voltage stabilization is achieved by a servo circuit in which a negative feedback loop from the base node to an emitter node maintains a bias point, so that photocurrent is efficiently delivered to charge transfer circuitry. In the preferred embodiment, the base node is connected to a gate of a first transistor having a drain that is connected to a source of constant current and to a gate of a second transistor that functions as a source follower. The source of the second transistor is connected to the emitter node of a phototransistor. As photocurrent is generated by the reception of light, an integration capacitor is charged. The relatively high percentage of photoreceiver area to total area is achieved by contributions from a number of factors, including the design of the servo circuit, use of a single transfer amplifier to service an entire row of phototransistors, and pairing the phototransistor circuits in order to permit efficient sharing of common circuit paths and circuit components.