Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2000-11-13
2004-08-17
Glick, Edward J. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S214100
Reexamination Certificate
active
06777659
ABSTRACT:
THE BACKGROUND OF THE INVENTION
The invention concerns an apparatus for detecting the phase and amplitude of electromagnetic waves, more specifically preferably in the optical and in the near infrared and ultraviolet range, comprising at least two modulation photogates which are sensitive to the electromagnetic waves (or photosensitive) and accumulation gates which are associated with the modulation photogates and which are not photosensitive or shaded, and electrical connections for the modulation photogates and the accumulation gates so that the latter can be connected to a reading-out device and the former can be connected to a modulating device, wherein the modulating device increases or reduces the potential of the modulation photogates relative to each other and also relative to the preferably constant potential of the accumulation gates corresponding to a desired modulation function.
Such an apparatus is known by the term ‘photomixing detector’ (abbreviated as PMD) from German patent applications Nos 196 35 932.5 and 197 04 496.4 and international patent application PCT/DE97/01956 based on the two applications referred to above.
The above-indicated applications are to the same inventor and were filed for the applicant of the present application, and reference is made to the entire disclosure of those previous applications insofar as described therein are the basic mode of operation, performance and possible uses of photomixing detectors. The present invention therefore does not discuss those fundamental functions of photomixing detectors but is concerned primarily with specific configurations and uses of photomixing detectors, by which the elements that are already known are optimised.
By virtue of the inherent mixing procedure which is implemented upon reception of the light which is modulated, reflected or emitted by an object, by the modulation photogates which are modulated with the same modulation function, the known PMDs are in a position directly to detect the transit time of the electromagnetic waves reflected by the object and therewith, besides lateral locational resolution which is ensured by means of a suitable optical system as in conventional cameras, simultaneously also to obtain items of spacing Information about the recorded pixels. Those PMDs therefore permit direct three-dimensional surveying and measurement of surfaces without the need for expensive evaluation procedures and recording procedures at various angles.
In order to achieve adequate sensitivity and depth resolution in the case of the known PMDs, the pixel surfaces must be sufficiently large so that, during the recording duration of an individual image, sufficient electromagnetic radiation is received from the various surface regions of the object and a suitable number of charge carriers is produced in the photosensitive material as ultimately the spacing information is obtained by way of the different number of charge carriers which occur at different moments in time at the modulation photogates and are accumulated by way of the immediately adjoining accumulation gates.
That entails a certain minimum size in regard to the area of the individual pixels. Problems can also occur with the conventional PMDs by virtue of the fact that very sharp light-dark boundaries of the object are produced in the image. If such a light-dark boundary falls by chance on the boundary region between adjacent modulation photogates, then the different number of charge carriers at the adjacent accumulation gates thus fakes a correlation result which leads to incorrect interpretation in the sense of depth information.
In addition the transit times in photosensitive pixel elements of that kind, which are of relatively large area, are comparatively long so that the band width or the limit value of the modulation frequency is usually only in the region of a few megahertz to a maximum of 100 MHz. Band widths of at least 1 GHz are desired in particular for the use of corresponding photosensitive detectors, for example in the opto-electronic art and in optical signal transmission.
In addition a higher level of functionality and flexible use of the PMD-pixels and PMD-arrays is desirable for different uses, for example for implementing different modes of operation with the same pixels, in particular for reasons of economy.
SUMMARY OF THE INVENTION
Having regard to the foregoing, the object of the present invention is to provide an apparatus for detecting the phase and amplitude of electromagnetic waves, having the features set forth in the opening part of this specification, which has a markedly improved band width, in which moreover misinterpretations of light-dark boundaries on imaged surfaces are less probable or even excluded, and with which a higher level of functionality and economy in practical uses is achieved.
That object is attained in that the modulation photogates like also the accumulation gates are provided in the form of long narrow parallel strips in mutually juxtaposed relationship, which group-wise form a PMD-pixel, and wherein the accumulation gates are in the form of reading-out diodes.
The fact that the modulation photogates and the accumulation gates are in the form of narrow long strips and the arrangement thereof in parallel directly mutually juxtaposed relationship results in very short channel lengths for the gates (the modulation gate strip width is referred to as the gate length, from MOS-transistor technology). The free charge carriers produced in or under the modulation photogates drift only transversely with respect to the strip direction by the short distance of the gate length to the adjoining accumulation gate, in which respect that drift is supported by a suitable electrical field on the part of the modulation voltage at the modulation photogates. As a result the drift times fall for example below 1 nanosecond so that accordingly it is possible to achieve a usable modulation band width of 1 GHz. Even if the individual strips of the modulation photogates and also the accumulation gates are relatively narrow, nonetheless by virtue of their corresponding length they can afford a sufficiently large photosensitive area while in addition it will be appreciated that a plurality of alternately arranged, strip-shaped modulation photogates and accumulation gates can be connected together to form a unit with almost a doubling of the optical filling factor. In that way virtually any pixel shapes and pixel sizes can be embodied by strip structures of that kind, without a limitation in terms of modulation band width.
The preferred embodiment of the invention provides that the individual modulation photogates are of a width which is greater than that of the respectively adjoining accumulation gates, while in addition the width of the modulation photogates should if possible be smaller than the diffraction limit of the imaging optical system for the modulated light detected by those elements, and should preferably be of the order of magnitude of the wavelength or a few wavelengths of that light or that electromagnetic wave. This means that, by virtue of diffraction effects, sharp light-dark boundaries can no longer accidentally fall on the region between two adjacent modulation photogates which are modulated in push-pull relationship. On the contrary the small dimensions of the modulation photogates in the transverse direction provide that a shadow or light-dark boundary must be spread over the full width of those gates so that both adjacent gates are equally still acted upon by light. In addition, with very long, correspondingly narrow modulation photogates, it is in any case highly improbable that a light-dark boundary extends precisely parallel to the direction of those strips. With the slightest inclination relative to the strips however at any event the two adjacent modulation photogates which are modulated in push-pull relationship are substantially equally acted upon with light from the light part and the dark part of the respective object whose image is produced.
The strip length of the modulation
Glick Edward J.
Kao Chih-Cheng Glen
Paul & Paul
Schwarte Rudolf
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