Browse Prior Art Database

LOG OUTPUT BLACK OPTICAL SENSOR

IP.com Disclosure Number: IPCOM000026935D
Original Publication Date: 1994-Jun-30
Included in the Prior Art Database: 2004-Apr-07
Document File: 2 page(s) / 78K

Publishing Venue

Xerox Disclosure Journal

Abstract

Proposed is the use of a logarithmic type amplifier at the output of an optical reflectance sensor in an Infrared (IR) densitometer. The logarithmic amplifier replaces a linear circuit having digitally selectable modes for high gain operation that provide low quantization errors. A logarithmic output sensor simplifies the sensor circuitry and does away with digital control lines when the reflectance sensor light emitting diode (LED) is continuously on. The high dynamic range of the logarithmic amplifier improves signal to noise ratio quantization errors at low level outputs.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 69% of the total text.

Page 1 of 2

XEROX DISCLOSURE JOURNAL

LOG OUTPUT BLACK OPTICAL SENSOR U.S. C1.358/44 John D. Sotack

Proposed Classification

Int. C1. H04n 09/07

Proposed is the use of a logarithmic type amplifier at the output of an optical reflectance sensor in an Infrared (IR) densitometer. The logarithmic amplifier replaces a linear circuit having digitally selectable modes for high gain operation that provide low quantization errors. A logarithmic output sensor simplifies the sensor circuitry and does away with digital control lines when the reflectance sensor light emitting diode (LED) is continuously on. The high dynamic range of the logarithmic amplifier improves signal to noise ratio quantization errors at low level outputs.

In operation, the reflectance sensor LED is sourced by a fixed current to establish a logarithmic response. Using a sensor range of 10-90 percent reflectance, the gain of the logarithmic amplifier is adjusted to obtain a dynamic range of 1OOO:l in 3.4 percent steps per bit. The level is assumed to be digitized with an 8 bit digital to analog converter. An offset voltage representing the largest amount of light received by the collector diode, is adjusted so the output does not exceed the 90 percent reflectance level. This is the maximum amount of light that may be generated by such means: a new

LED, clean optics, or a diode having higher than normal sensitivity. The sensor output is then equal to the offset voltage plus a constant times the log of the light curren...