Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1996-01-25
1998-06-23
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
330293, H03F 134
Patent
active
057693846
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.
REFERENCES:
patent: 4173723 (1979-11-01), Temes et al.
patent: 4574249 (1986-03-01), Williams
patent: 5149980 (1992-09-01), Ertel et al.
patent: 5198660 (1993-03-01), Yokoyama
patent: 5256986 (1993-10-01), Flocke et al.
patent: 5296696 (1994-03-01), Uno
Baumgartner Richard A.
Blalock Travis N.
Doernberg Joey
Hornak Thomas
Hewlett--Packard Company
Lee John R.
Westin Edward P.
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