Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-04-21
2001-09-11
Evans, F. L. (Department: 2877)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140AG, C250S208100, C348S241000, C348S300000
Reexamination Certificate
active
06288387
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to infrared detection methods, and relates more particularly to improvements in such detection methods whereby the method and circuitry to perform the corrective signal processing to compensate for known or intrinsic optical signal intensity errors to the image plane of systems using electronics electro-optics sensors is provided to detect a thermal signature which would otherwise be less detectable.
In modern electro-optical sensor systems, solid-state electronic devices are used to perform the function of sensing incident radiation at the image plane of the system, integrating this signal, and multiplexing it for processing by systems electronics. Examples of the solid-state electronic devices are the charge coupled device (CCD) used in video cameras and infrared focal plane arrays that are used in many civilian and military systems. For these arrays two principal component materials are used to realize their fabrication. These are the incident radiation sensing detector material and the readout integrated circuit. The detector materials is chosen and optimized for sensing specific incident radiation wavelengths, and the readout is selected for its properties in realizing the desired signal processing to multiplexing functions.
Novel signal processing circuitry is described that allows correction of optical system non-uniformities to be performed on focal plane array. In effort to reduce the size and weight of modern infrared focal plane array systems, slower f-number optical systems with shorter cold shields are often used. In these systems, the signal and background intensity levels at the image focal plane decrease with increasing distance from the optical center axis. This results in a situation where some of the signal dynamic range is lost due to the off-axis optical effects. The incorporation of on-focal plane array signal processing electronics that correct for these off axis optical effects allows the full dynamic range of the sensor to be achieved, thus allowing a lower-cost and higher performance system to be realized.
In previous scanning and staring focal plane arrays the response to incident radiation (signal chain transimpedance) have been designed such that it is the same for each detector channel. In these systems and in an ideal sense, an incident signal that is non-uniform will produce an output signal from the sensor that has the same non-uniform characteristic. It is possible, however, to calculate based on the design of the optical system, the optical signal intensity errors that will be present. In the case of many infrared systems the signal intensity that reaches the focal plane array decreases on the focal plane with distance from the optical center axis. This effect typically results in a decrease in signal level of 20 percent or more from a signal at the optical center axis. This signal loss therefore accounts for more than 20 percent of the available dynamic range for the sensor output. The off-axis signal intensity error increases with slow optics, shorter cold shields, and larger focal plane arrays. The signal loss places additional systems requirements on the analog to digital converter and subsequent signal processing electronics.
Since the intrinsic behavior of these optical systems is known, it is possible to design into the focal plane array a corrective gain that is spatially correlated to the errors introduced from the optical system. This invention describes the methods and circuitry for performing this corrective gain processing for scanning and staring infrared focal plan arrays. Two specific circuit areas are described for this corrective processing. These are the areas of the transimpedance amplifier and the background signal charge skimmer.
There is prior art developed in the areas of the optical systems, electro-optics sensors, in the circuitry associated with these devices, but the specific circuitry developed and employed as presented in this application is deemed unobvious and novel. However, it should be noted that similar circuitry and methods within the scope of this invention could be used to realize the corrective signal processing for a wide range of electro-optical sensors and systems.
One object of the invention is to provide on-focal plane signal processing electronics for the correction of optically introduced non-uniformities applicable to infrared, visible and other electro-optical sensors in a wide range of applications and markets.
Another object of the invention is to allow the use of lower-cost, smaller and lower weight optical systems which are more likely to generate optical signal errors to focal plane.
A further object of the invention is to provide such optical systems which are benefit from the incorporation of such on-focal plane signal processing electronics.
SUMMARY OF THE INVENTION
The invention resides in a device for enhancing signal detection comprising a sensory array of sensing elements extending in columns and in rows in first and second orthogonally disposed directions, respectively and a datum selected on the array for reference relative to the columns and rows (x, y). A plurality of circuit chains is provided and each is associated with a given column of the sensing elements for processing a signal into recognizable form. Each of the circuit chains taken relative to the datum has a means for producing a gain different from that of a circuit chain associated with a column of the sensing means located coincidentally with the datum.
Ideally, the array is defined by a planar image surface made up of the plurality of the sensing elements and the datum is a point on the array coincident with an optical central axis. Each of the circuits associated with a column of the sensing elements has a circuit portion defined by a capacitive transimpedance amplifier and skimmer circuit portion. The capacitive transimpedance amplifier portion of each of the circuit chains associated with a given column of the sensing elements has a capacitance which differs from the circuit chain associated with the column of sensing elements located coincidentally with the datum. The skimmer circuit portion of the circuit chain associated with the ones of the columns of sensing elements other than that located coincidentally with the datum has a capacitance which differs from the capacitance of the skimmer circuit portion of a circuit chain associated with the circuit chain associated with the sensing elements coincident with the datum.
Preferably, each column of the sensing elements extends in the first given direction (columns) and each of the circuit chains associated with the column of sensing elements is connected to one another to effect communication therebetween in the second orthogonally disposed direction (rows). Each of the circuit chains is multiplexed to effect function in the second given orthogonally disposed direction. Also, the array of the sensing elements is row addressed and column addressed by a plurality of multiplexers.
The invention further resides in a method of enhancing a signal comprising the steps of providing a sensory array comprised of a plurality of sensory elements arranged in rows and columns; selecting a datum on the array and referencing the rows and columns of the sensing elements relative to the datum; determining a prescribed gain for signals generated from a given column of the sensing element taken relative to the strength of a signal from sensory elements at the datum; and processing signals generated by a given column of the sensing elements in a dedicated circuit chain having an preassigned gain value capable of compensating for signal strength which is less than that of a signal detected at the datum.
The method ideally is further characterized by interconnecting circuit chains in each column of sensing elements with one another and by configuring each circuit chain associated with a given column of sensing element to an established prescribed gain by altering the capacitance of that circuit chain relative to the capacitance
Black Stephen H.
Woolaway, II James T.
Evans F. L.
Lenzen, Jr. Glenn H.
Raytheon Company
Schubert William C.
Smith Zandra V.
LandOfFree
Apparatus and method for performing optical signal intensity... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for performing optical signal intensity..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for performing optical signal intensity... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2515334