Lucent Technologies Inc.

Bell Telephone Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Aristides Antony Yiannoulos

Kenneth R Laker

Paul E Fleischer

James P Ballantyne

A novel analogue to digital (A/D) converter semiconductor integrated circuit intended for digitizing signals generated by a physical stimulus sensing electronic apparatus, and more particularly, for digitizing signals generated by an array of photo-integrator circuits of an active pixel sensor (APS) imaging device. The A/D converter is a modified single slope integration type, wherein the reference ramp signal exhibits predetermined nonlinearity and offset. The nonlinearity and offset of the reference ramp signal track the nonlinearity and offset components in the signal being digitized, the latter being nonlinearity and offset components contributed by sources appearing in advance of the A/D conversion point in the signal acquisition and processing path of a digital camera system. In particular, the ramp generator for an A/D converter intended for an APS imaging array is partly a replica of the active photo-integrator circuit used in the APS pixel array fabricated on the same semiconductor substrate as the APS array. The ramp generator differs from a photo-integrator in that it produces output by responding to input provided by a current source rather than a photo-sensing device. As the ramp generator and the signal path nonlinearities and offsets track regardless of manufacturing variations and variations in operating conditions, the A/D conversion process successfully linearizes and removes offsets from the signal path, self calibrating against manufacturing variations and self adjusting against variations in operating conditions. The A/D converter further provides white balancing and gamma correction functionality for APS imager cameras. White balancing is performed by using different valued current sources in the ramp generators providing A/D conversion reference ramp for each different color in the color space sampled by the APS array. Gamma correction is performed by clocking the counter of the A/D converter with a clock frequency varying with time. The A/D converter replaces costly and technically less effective digital signal processing (DSP) means which were previously required.

Linearizing offset cancelling white balancing and gamma correcting

A field-effect photo-transistor, being a three-terminal photosensing electrical device, based on integrated metal oxide semiconductor (MOS) technology. The device features a high output impedance which makes it particularly suitable as a photosensor for active pixel imaging arrays. Unlike the bipolar photo-transistor, which is a device well known in the art, the field-effect phototransistor is more compatible with MOS VLSI (Very Large Scale Integration) technology by inherently being a unipolar type device. Active pixel imaging arrays based on the disclosed invention can be integrated on the same semiconductor substrate with conventional digital or mixed signal processing functions to produce single-chip image processors for video or still picture cameras.

Field-effect photo-transistor

An arrangement for protecting inductive load switching transistors during overvoltage conditions is disclosed. The arrangement comprises a Zener diode coupled between the collector and base of the switching transistor, where the Zener diode will break down during inductive load-created overvoltage conditions and turn on the transistor. A major portion of the surge current will then flow through the activated transistor. In a particular integrated circuit realization of the arrangement, the Zener diode is formed in the same semiconductor area as the transistor by extending a portion of the base diffusion region downward to contact the buried collector region.

Protection of inductive load switching transistors from inductive surge

A capacitor-resistor-capacitor (CRC) element for active filter realization, which is fully integrable and compatible with MOS technology, is described. The incorporation of the CRC element in a semiconductor integrated circuit active filter also is described. The structure of the CRC filter element is closely analogous to a depletion mode MOS field effect device, except that the channel zone 26 is doped to a level which substantially precludes conductivity modulation at the usual operating voltages. However, the doping level is such as to enable the use of the channel zone as a semiconductor resistance element. Thus, the N-channel CRC element realized in the NMOS technology comprises a first capacitance composed of the gate 27, gate dielectric 38, and resistive channel 26, paralleled by the resistive channel 26 itself constituting a resistor, and then the underlying PN junction capacitance between the N-type resistive channel 26 and the underlying P-type semiconductor body portion 21. An active low-pass filter consists of two CRC elements and an operational amplifier and utilizes the positive feedback principle.

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Wyomissing Hills, PA, United States of America

Aristides Antony Yiannoulos