Electronic imaging camera with microchannel plate

Imaging apparatus for an electronic imaging camera responds to a scene image by converting photons into electrons representative of the scene image. A microchannel electron multiplier, including a microchannel plate, having an output surface at its output side is coupled to receive the electrons representative of the scene image and operates to intensify the electron representation of the scene image. A charge transfer device in the form of a charge coupled device (CCD), directly coupled to the output surface responds to the electron output to produce an electric signal representation of the scene image received by the camera. The electric signal representation is read out of the CCD by clock voltages and may have the form of a serial picture sample output. A signal processor may be provided to develop a video output from the sample output.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an imaging apparatus for use in an electronic 
imaging camera and includes a charge transfer device such as charge 
coupled device (CCD) or the like. The invention is concerned more 
particularly with imaging apparatus which produce an electric signal 
representation of an image received by the camera. The electrical signal 
representation can be processed to provide a video output. 
2. Prior Art 
Of interest as pertinent general prior art are a number of U.S. Letters 
Patent identified as follows: 
______________________________________ 
U.S. Pat. No. 
Inventor(s) Issue Date 
______________________________________ 
3,585,439 Robert J. Schneeberg 
June 15, 1971 
3,922,576 Charles M. Redman 
November 25, 1975 
3,958,079 Arthur L. Case et al. 
May 18, 1976 
4,015,115 Donald G. Corcoran 
March 29, 1977, and 
4,178,528 Andrew J. Kennedy 
December 11, 1979. 
______________________________________ 
It is known from U.S. Pat. No. 4,253,120 to Peter A. Levine issued Feb. 24, 
1981 and entitled "Defect Detection Means for Charge Transfer Imagers" to 
position a charge coupled device (CCD) in the optical path of a low 
resolving power imaging optics which project an image on a light 
responsive surface of the CCD. The CCD is operatively associated with a 
source of clock voltages and responds to clock pulses therefrom to effect 
delivery of a serial picture sample output corresponding to the image 
projected on the surface of the CCD. The serial picture sample output is 
processed electronically by a signal processor to derive a video output. 
The imager as disclosed is of the frame or field type; CCD imagers of this 
type are known, for example, from U.S. Pat. No. 4,032,976 to Peter A. 
Levine, issued June 28, 1977 and entitled "Smear Reduction in CCD Imagers" 
which discloses in detail a CCD Imager including storage registers which 
can be associated with a clock voltages source suitable for reading out 
signals stored in the imager. 
It is known from U.S. Pat. No. 4,338,627 to John J. Stapleton, issued July 
6, 1982 and entitled "LED/CCD Multiplexer and Infrared Image Converter" to 
utilize a CCD sensor to develop a stored charge image of signals coupled 
to the CCD sensor from a light-emitting diode (LED) array, the signals 
from the array being coupled to the CCD via a bundle of optical fibers. At 
predetermined intervals, for example every six microseconds, the stored 
charges are shifted out of the CCD sensor and subsequently amplified and 
used for image reconstruction. 
In recent years, microchannel electron multipliers have become known, the 
multipliers include microchannel plates to effect electron multiplying, 
these microchannel multipliers being particularly useful in image 
amplifiers. The microchannel plates are characterized by high electron 
gain, low noise, high spatial resolution, high speed, small weight and 
relatively low power consumption. As used in image intensifiers, the 
microchannel plate is usually associated with a photocathode upon which an 
optical image or the like to be intensified is projected. Electrons 
produced by the photocathode are used as input electrons to individual 
ones of the channels in the microchannel plate, these electrons in each 
individual multiplier channel are in effect amplified by generation of 
secondary electrons, the electron output from the plate being projected on 
a phosphor screen or the like to enable a user to view an intensity 
enhanced version of the image which was initially projected on the 
photocathode. An exemplary camera tube, utilizing a microchannel plate, is 
disclosed in the U.S. Pat. No. 4,120,002 to Albert J. Lieber issued Oct. 
10, 1978 and entitled "Streak Camera Tube", the microchannel plate being 
associated with a photocathode and a phosphor screen. The screen is 
coupled to a fiber optic plate. 
It is known from the U.S. Pat. No. 4,237,488 to Yasuo Takemura, granted 
Dec. 2, 1980 and entitled "Blemish Compensating System for a Solid State 
Image Pick-Up Device" to provide a solid state image pick-up device in the 
form of pick-up elements arranged to store electrical charges 
corresponding to an optical image formed on the light sensitive portions 
thereof, the pick-up elements being formed as part of a CCD pick-up 
device. Electronic circuitry is provided to energize a drive circuit which 
causes the CCD device to produce electrical signals corresponding to an 
optical image received via a color strip filter. 
It has long been known from U.S. Pat. No. 3,688,143 to Albert Lieb et al., 
granted Aug. 29, 1972 and entitled "Multi-Diode Camera Tube with 
Fiber-Optics Faceplate and Channel Multiplier" to provide a camera tube 
which includes a microchannel plate used as an image intensifier in front 
of a photodiode array. Image light incident to the photocathode surface is 
converted into electrons, which are subsequently amplified by the 
microchannels of the plate. The output side of the microchannel plate is, 
as is conventional, a phosphor screen which converts the electrons 
produced in the microchannels back to visible light which is thereafter 
detected by a multidiode disk. 
The camera tube of Lieb et al., supra, requires that electrons produced by 
the microchannels be converted to visible light which must be thereafter 
detected by the multidiode disk to produce an electrical signal output, a 
distinct disadvantage. 
SUMMARY OF THE INVENTION 
In one aspect, the present invention can be viewed as imaging apparatus for 
use in an electronic imaging camera which includes means responsive to an 
image received by the camera of the scene to be reproduced for converting 
photons into electrons representative of the scene image. At least one 
electron multiplier, which may be constituted by a microchannel electron 
multiplier having plate means is provided. The multiplier includes an 
output surface at its output side and is coupled to the converting means 
representative of the image. The multiplier provides an intensified 
electron representation of the image. A charge transfer device, which may 
be a charge coupled device (CCD), is coupled to the output surface and is 
directly responsive to its electron output for producing an electric 
signal representation of the image received by the camera. 
In another aspect, the present invention can be seen as imaging apparatus 
for use in an electronic imaging camera which includes means responsive to 
an image of a scene received by the camera for converting photons into 
electrons representative of the scene image. Means including an output 
surface at its output side is coupled to the converting means and is 
responsive to electrons therefrom for intensifying the electron 
representation of the scene image. A charge transfer device, which may 
comprise a charge coupled device (CCD), is coupled to the output surface 
and is directly responsive to its electron output for producing an 
electrical signal representation of the scene image received by the 
camera. 
The present invention can be viewed as being in an electronic imaging 
camera which includes instrumentalities responsive to an optically 
produced image of the scene to be reproduced for producing an electrical 
signal representation thereof. The improvement comprises means responsive 
to the scene image for producing electrons representative of the scene 
image. A microchannel electron multiplier, which may include plate means, 
responds to the electrons representative of the scene image and includes 
an output surface. A charge transfer device, which may comprise a charge 
coupled device (CCD) is coupled to the output surface and is directly 
responsive to electrons therefrom for developing the electric signal 
representative of the scene image received by the camera. 
An object achieved by the present invention accordingly is to provide 
imaging apparatus for use with an electronic imaging camera which does not 
require an intensified electron representation to be converted into an 
optical image before transfer to a charge transfer device. 
Another object achieved by the present invention is to provide imaging 
apparatus for use with an electronic imaging camera which does not require 
intermediate conversion of electrons representing an intensified electron 
representation of a scene image to photons before the energy is 
transferred to a charge transfer device. 
An additional object achieved by the present invention is to provide an 
improved electronic imaging camera which obviates a need to provide a 
photodiode layer in a charge transfer device and effects direct charge 
transfer to individual capacitance pickup portions thereof. 
An additional object achieved by the present invention is to provide an 
imaging camera which is simple, compact and reliable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1-3, an electronic imaging camera constructed in 
accordance with the present invention, is illustrated comprising an output 
signal processor 10 and a clock voltages source 11 which effect the 
transfer of signals which may constitute a serial picture sample output to 
the signal processor 10. 
The imaging camera illustrated in FIG. 1, includes conventional imaging 
optics 12 positioned in front of a microchannel electron multiplier 13, so 
as to focus light from a scene to be imaged onto a phosphor screen 14, or 
another photocathode electron emitting member of the microchannel electron 
multiplier 13. The microchannel electron multiplier 13 includes a 
microchannel plate 15 constituted by a bundle of individual multiplier 
channels which determine or otherwise transfer electrons to an anode 16, 
which acts as an anode with respect to the electron source constituted by 
the phosphor screen 14. The anode 16, which may be of the same composition 
and construction as a conventional photocathode of a microchannel electron 
multiplier, is in direct contact with an electron receiving surface of a 
charge transfer device, illustrated as a charge coupled device (CCD) 17 so 
as to inject or transfer secondary electrons produced by the individual 
microchannels of the microchannel plate 15 into the individual capacitance 
sites in the charge coupled device 17, the transfer being effected via an 
electrode member constituted by the anode 16 which is operated at a 
voltage level considerably above the phosphor screen 14, consequently 
acting as an anode with respect to the phosphor screen 14, and as an 
electron transferring member with respect to the charge coupled device 17, 
the input surface of which is operated at a voltage above the bias voltage 
applied to the anode 16. As shown in FIG. 2, the microchannel plate 15 is 
a disk having a plurality of individual microchannels. 
The electrode member 16, in one possible version of the electronic image 
camera of the present invention, can be constituted simply of the same 
structure which ordinarily would be used as a photocathode in a 
microchannel electron multiplier of conventional construction, as 
indicated above. In this case, it is clear that the orientation of the 
microchannel electron multiplier, with respect to the scene to be imaged, 
is reversed so that the member which would otherwise be a conventional 
output phosphor screen, acts as the photocathode, while that member which 
would otherwise be the photocathode operates as the output member of the 
microchannel electron multiplier and allows injection of electrons from 
the microchannel multiplier 13 directly into capacitance sites in the 
charge coupled device (CCD). 
Microchannel plates are electron multiplying, vacuum electronic devices 
frequently used in image intensifier tubes for intensification of an 
optical image. In the present invention, a microchannel electron 
multiplier 13, which includes a microchannel plate 15 is used in the 
special orientation, as noted above, reversing the roles of the 
photocathode and phosphor screen. 
Microchannel plates are characterized by high electron gain, low noise, 
high spatial resolution, high speed, small weight, relatively low power 
consumption, and long operational life. 
Physically, a microchannel plate, such as the plate 15, is made of lead 
silicate glass and is a two dimensional array of hollow glass fibers 18 
(FIGS. 2 and 3) fused together into a thin disk. The inside surface of the 
hollow glass fibers 18 is covered by a resistive secondary emission film 
diagrammatically shown at 18A in FIG. 3 which is electrically connected to 
an input plate 19 and the output plate 20, which may be respective thin 
electron-permeable nichrome electrodes of the microchannel plate 15. In 
some cases, the thin plates 19, 20 may be apertured, the apertures being 
aligned with the individual hollow glass fibers thereby allowing electrons 
from the phosphor screen 14 readily to pass into the hollow fibers 18 and 
the secondary electrons produced therein to exit the plate 15. The purpose 
of the plates 19, 20 apertured or not is to effect application of a 
positive, for example +650 volts, between the exit and entrance of the 
microchannels. It is to be understood that the respective phosphor screen 
14 and the anode 16 can be designed to perform additionally the respective 
functions of the plates 19, 20, allowing these plates to be eliminated as 
separate components. The hollow glass fibers 18, forming the 
microchannels, have an inside diameter in the 8- to 45-um range, but may 
be even smaller depending on the resolution sought to be achieved. The 
channel length-to-diameter ratio (L/D) is typically on the order of 40 to 
48 for conventional plates. Such plates are suitable for practicing the 
present invention. Of course, the smaller the diameter, the greater the 
resolution. 
As shown in FIG. 3, the microchannels defined by hollow fibers 18 
preferably are not perpendicular to the input and output surfaces but 
typically are positioned at a 5.degree. to 10.degree. bias angle, as 
illustrated in FIG. 3 by the fibers 18. The purpose of the bias angle is 
to assure a first electron impact near to the channel entrance, reduce ion 
feedback and improve the uniformity of image transmission. The input plate 
19 and the output plate 20, as shown in FIG. 3, are insulated from one 
another and held in spaced relationship by a spacer ring 22 made, for 
example, of high strength glass. A potential of about +650 volts is 
applied between the plates 19 and 20. 
OPERATION 
The operation of the electronic imaging camera of FIG. 1 is described 
below, reference being made to FIG. 4 which illustrates a conventional 
charge transfer device (CCD), adapted for use in the camera of the present 
invention. Firstly, an image, which may change, is projected or focused 
onto the phosphor screen 14, the microchannel plate 15 receives electrons 
representing the optical image from the phosphor screen 14 and produces an 
intensified version thereof by virtue of the secondary electrons produced 
therein. These secondary electrons are coupled into the charge coupled 
device 17 causing individual capacitance sites therein constituting a 
first register to become charged. 
Referring to FIG. 4, it is assumed that the imager, which is formed in part 
by the charge coupled device (CCD) 17, is an imager of the field transfer 
type (sometimes termed an imager of the "frame" transfer type). Such CCD 
imagers are known in the art, and by way of example, are described in some 
detail in the above-mentioned U.S. Pat. No. 4,032,976 to Peter A. Levine. 
As shown in FIG. 4, such a two-phase CCD imager includes an array 200, 
designated as register A (constituting the above-mentioned first 
register), a temporary storage array 202, designated as register B, and an 
output register 204, designated as register C. The B and C registers are 
masked; that is, means are provided for preventing electrons injected into 
the A register from reaching either the B or the C register during 
injection. 
The A and B registers are divided into separate channels, respectively 
numbers 1 . . . Q, each extending in the column direction. Extending in 
the column direction, between each pair of adjacent channels, is a channel 
stop provided for isolating charges in adjacent channels from each other. 
Each pair of adjacent electrodes K and L of each respective channel 
defines a discrete picture sampling element (shown as a dashed rectangle 
206). The electrodes K and L, per discrete picture sampling element, 
constitute two-phase structures for ensuring unidirectional signal 
propagation in response to applied clock voltages from the source of clock 
voltages 11 (FIG. 1). 
In particular, during the occurrence of each successive television field 
period, each picture sampling element 206 of array 200 accumulates a 
charge proportional to the electrons injected thereinto from the 
respective microchannels during that field period. At the end of each 
field period (during the vertical blanking interval, for example, of 
commercial television), the charge signals which have accumulated are 
transferred, in parallel, in the column direction from the A register to 
the B register by the application of the multiple phase clock voltages 
.phi..sub.A1, .phi..sub.A2, .phi..sub.B1, .phi..sub.B2. During the 
occurrence of the next field (in particular, during each successive 
horizontal line blanking interval of commercial television) clock phase 
voltages .phi..sub.B1 and .phi..sub.B2 are operated to transfer a line of 
picture samples at a time from the B register to the C register. (Dashed 
rectangular boxes 208 and 210 indicate stages of the C register, each of 
which stores a picture sample). During each successive television 
horizontal line time, the respective picture samples then stored in the C 
register are transferred sequentially out of the C register to form the 
serial picture sample output from the CCD 17 (FIG. 1). The transfer out of 
the C register usually occurs at the highest clock rate, namely, the clock 
rate of clock phase voltages .phi..sub.C1 and .phi..sub.C2, applied to the 
C register from the source of clock voltages 11 (FIG. 1). Therefore, 
normally the serial output of picture samples also occurs at this clock 
rate. 
As the charges in the A register are transferred out, new electron charges 
are injected, these charges having amplitudes and patterns representing a 
new or changed image. As a result, the serial picture sample output from 
the charge coupled device 17 can represent a constantly changing image or 
several static images. The output can be recorded on tape, disks, 
cassettes or the like, can be fed to a computer or the like to be used or 
stored therein. The signal can be used for television viewing or 
broadcast. Indeed, the signal can be used to obtain a hard copy or other 
print of an image received by the imaging camera either directly or from 
storage. 
It is to be appreciated that with appropriate filters and imaging optics, 
the electronic imaging camera herein described can be adapted to color 
picture production, for example, either for television video or hard copy 
formats. Three channels, one for each primary color, could be provided, 
the channels could use the same objective optics. Separate plural or one 
charge coupled device could be arranged to be coupled to one or another of 
three microchannel electron multipliers. 
Alternatively, two channels could be utilized and the third color signal 
could be derived electronically from the two received colors as is well 
known in the art. Alternatively, a beam splitter could be stationed behind 
the imaging optics to divert a part of the image beam to a CCD array 
having a plurality of red, green and blue color stripes arranged in a 
well-known manner across the face thereof. 
It is to be understood that the foregoing description and accompanying 
drawings relate to an exemplary embodiment of the present invention which 
has been sent out by way of example, not by way of limitation. It is to be 
appreciated that numerous other embodiments and variants are possible 
within the spirit and scope of the present invention, its scope being 
defined by the appended claims.