Silicon phototransistor vidicon

The use of silicon phototransistor arrays as high gain targets in vidicon camera tubes is shown to provide a sensitivity advantage. An analysis of device operating parameters indicates that signal enhancement can be obtained during both the write and read portions of an array element's duty cycle. Maximum effective signal amplification is secured by choosing a design which recharges the collector-base storage capacitance mostly during the read interval. Expressions for the effective signal gain in terms of transistor common base current gains and elemental capacitances have been derived, and the effects of phototransistor operation on vidicon sensitivity, image persistence, and dynamic range have been considered. Experimental transistor arrays have been fabricated and have been used for the first successful demonstration of phototransistor signal gain under the usual conditions of vidicon operation. Signal gains exceeding 70 have been recorded.     

An economical color-television camera utilizing a silicon vidicon for electronic color separation

A new image device designed to electronically separate two kinds of color components from an optical image utilizing photoelectric properties of the surface of a silicon-vidicon target, and an economical color-TV camera using this device are proposed. This system requires neither special construction of a camera tube target to obtain index signals for color separation nor bias lighting. Crosstalk components present in the color signals from the color camera tube are corrected by circuitry. This color camera is about three times as high in sensitivity as that using an antimony trisulfide vidicon. It has many other features, including the capability of imaging a fixed object, without burn-in for a long time, as well as high reliability and long life.     

Electron images of vidicon cathodes

Excessive patchiness of the emission from the oxide-coated cathodes used in cathode-ray tubes, camera tubes and traveling-wave tubes can have adverse effects on their performance or useful life. There is a simple technique for forming an electron image of a CRT cathode directly on the view screen. This technique, which has been known for more than 30 years, may be used to show patchiness when it exists, but it has not been possible in the past to image the cathode of a camera tube because of the lack of a built-in display mechanism (phosphor-coated view screen) and because of the peculiar geometry of the electron guns. A technique has now been devised for displaying the electron images of vidicon cathodes. This technique comprises) 1) priming the optical image-sensing surface with uniform light, 2) projecting a "pinhole snapshot" electron image of the cathode on the image-sensing surface with an unscanned beam and storing it there, and 3) reading out the stored image with the normal scanning beam and displaying it on a CRT monitor. Photographs of electron images of vidicon cathodes obtained in this manner are shown in this paper.     

Transient response of vidicon photoconductors

An expression for the rise and decay times of vidicon photocurrents as a function of incident illumination is derived for a certain class of vidicon photoconductors. The approach taken is semiempirical in that certain parameters in the derived expression are obtained directly from vidicon manufacturer's data sheets. Regults compare well with the manufacturer's published results.     

Hard-vacuum pyroelectric vidicon: suitable materials

A new mode of operation of the pyroelectric Vidicon is reported. This mode does not require a soft vacuum and the tube is operated hard. Requirements for suitable pyroelectric materials are discussed and the results of experiments operating in this mode are presented.     

Mathematical model to describe vidicon operation

A theoretical development is presented that describes the operation of a vidicon. Output current is determined for an arbitrary distribution of intensity and wavelength of illumination falling on the face of the vidicon. The nonlinear behavior of the photoconductor is taken into account. The effect of progressive erasure of the stored charge on the rear of the photoconductor with the motion of the electron beam is included. The readout beam is assumed to be Gaussian with either a circular or elliptical cross section. The effect of the electron beam on lines other than that being scanned is included. Variation in electron beam spot size across the face of the vidicon is also considered. Correlation with published output data is presented. The apparent phase shift of objects, especially at high beam currents, can be significant. Numerical results for the cases of line and sinusoidal targets are discussed in detail.     

The Epicon™camera tube: An epitaxial diode array vidicon

The structure and processing of epitaxial silicon diode array targets for vidicon camera tubes are described with emphasis on the way they differ from conventional silicon diode array targets. These targets, called Epicon^™vidicon targets, are generally similar to other silicon vidicon targets, but have the p-type boron diffused islands replaced by pyramidal or mesa-like structures that extend through the oxide apertures and up and over the oxide. The target is a self-registered conducting cap-type structure and does not require a resistive sea for its operation. It has some additional advantages in its structure and its processing over the other silicon diode array target. A comparison of the results of some selective epitaxy processes is briefly made. Some of the operating characteristics of the tube are described.     

High light-level blooming in the silicon vidicon

Blooming occurs in silicon-vidicon targets because more hole-electron pairs are created at a given point by the incident light signal than can be removed by the action of the scanning electron beam. The excess carriers move laterally in the target through diffusion and, as a result, the blooming has the following properties- 1) the Slope of the blooming curve on semilog paper does not depend on the size of the incident light spot, i.e., at a given overload intensity, all circular spot sizes add the same excess amount to their radii; 2) the radius of a bloomed spot increases linearly with the log of the incident intensity; 3) the Slope of the blooming curve does not depend on beam current; however, the intensity at which the blooming begins does depend directly on the beam current. At very high incident-light intensities, a dramatic increase in the blooming is observed. This can be attributed to diffusion under conditions where the minority carrier level has become equal to the majority carrier level.     

Ramp mode operation of a pyroelectric vidicon

A new mode of operating a pyroelectric vidicon is demonstrated. It uses a linearly rising voltage ramp applied to the target connection to generate the positive bias across the target necessary for efficient tube operation. The theoretical relationship between lag (time response of the tube to a step impulse signal) and readout efficiency is examined. Lag measurements of a tube operating in ramp mode are used to find the readout efficiency under different operating conditions, and the importance of the beam energy spread of the electron gun in determining the operating efficiency is emphasized.     

A positive-reading silicon vidicon for X-ray imaging

A silicon vidicon that uses an n on p silicon diode array for a target was designed. The electron beam landing energy is 600 eV, and all the diodes are charged to a reversed bias by secondary electron emission. With the high electron beam energy, it is possible to sharply focus the beam into a sheet beam, which can be used to simultaneously bombard several separate linear diode arrays in a detector scheme for a bent-crystal X-ray spectrometer. By such a method, the bandwidth requirement of the data-transmission system is reduced by a factor equal to the number of separate linear arrays that are simultaneously bombarded. Data are presented on the diode-charging mechanism, with emphasis on the method used to determine the potential of the diode n-surface. Examples are shown of the tube being used to detect 25-keV X-rays.     

A developmental tricolor vidicon having a multiple-electrode target

Color television cameras which are now widely used require three separate camera tubes to supply the simultaneous primary color information transmitted by the compatible system. This paper describes a developmental tricolor camera tube of the vidicon type for use in a single-tube color camera. The ability to generate the three simultaneous signals is achieved in the tricolor vidicon by means of a multiple-electrode target structure having three interlocking groups of color-sensitive strips connected to separate output terminals for each primary color. A single low-velocity electron beam scans the photoconductive target. No special requirements are made on the beam with respect to focus or scanning accuracy. Registry of the three signals is inherent in the design of the target. The performance of the developmental cameras which have been constructed to date does not equal the three-tube image orthicon camera from the standpoint of sensitivity, color fidelity, and uniformity. In its present state, the tube is potentially useful for industrial and scientific purposes where sufficient light is available and structural defects do not obscure the information desired. To extend its range of application, the development of more sensitive photoconductors and improved methods of fabrication are required.     

Analysis and perfomance characteristics of an intensified silicon vidicon tube

Typical performance characteristics for intensified silicon vidicon tubes are given. The tube can be operated at 5 × 10^-7_ fc faceplate illumination. A 40 percent modulation depth at 400 TV lines per raster height has been achieved at a 300-nA signal level. When operating at 200-nA signal, typical decay lag performance shows less than 20-nA signal 50 ms after the illumination is removed. Theoretical and experimental performance at low light levels are compared. The design of the electron optical system of the intensifier section is considered with respect to distortion and center and edge resolution. Two important target parameters, collection efficiency and resolution, are also considered theoretically and experimentally. A simple model for the collection efficiency is given; theory and experiment compare well. The effect on resolution of discrete diode spacing and target thickness is given and this is coupled with other modulation transfer parameters to predict the overall modulation transfer of the device. Critical performance characteristics are given for sample tubes.     

Limitations of the lead oxide vidicon for dual-energy digital subtraction angiography

Dual-energy digital subtraction angiography (DSA) can be performed, with some modifications, using existing systems designed for conventional DSA work. However, the video camera generally found in such installations, the lead oxide vidicon, places significant limitations on the image quality of dual-energy DSA. If the video camera is operated in a 60 Hz, 266 line progressive scanning mode to maintain a nominal 30 subtraction images/s frame rate, the maximum available X-ray pulse width is limited to 5 ms. The resulting required increase in low-energy kVp reduces the dual-energy signal-to-noise ratio by approximately 40% for cardiac dual-energy DSA imaging. In addition, the performance of the video camera with respect to read-out lag is much more important for dual-energy DSA than conventional single-energy imaging. Measurements show that lag reduces the iodine contrast in dual-energy DSA by up to 20% when a 30 Hz vertical scan mode is used, and by up to 27% when a 60 Hz vertical scan mode is employed. Replacement of the lead oxide vidicon with a CCD camera removes these limitations.     

A new silicon vidicon with a CdTe—Si target

A new type of a silicon vidicon target which utilizes blocking contacts between bulk semiconductor and a high resistive layer has been developed. The high resistive layer forms a blocking contact to the bulk and works also as a "resistive sea" layer, reducing complex fabrication processes. Structure of the target, tube characteristics, and video patterns are presented.     

A silicon vidicon target with electronically variable light sensitivity and spectral response

A silicon vidicon target structure is shown in which light sensitivity and spectral response are controlled by varying the band bending and depletion region depth at the light incident surface. Light sensitivity control ratios of over four orders of magnitude are demonstrated, making the new target suitable for use over a wide range of light conditions without the aid of a mechanical aperture. The use of the light control structure as a high-speed electronic shutter with image sampling times as low as several microseconds is also discussed.     

Bivicon®—A new double vidicon

The Bivicon is a 1½-in vidicon with two guns and targets. It can generate excellent color signals utilizing a two-frame system in which the luminance signal is projected onto one target and the chrominance information onto the other.     

Alternative pedestal generation scheme gives flickerfree pictures from a pyroelectric vidicon chopper camera

An alternative way of generating the pedestal current in a pyroelectric vidicon (p.e.v.) is described. The better uniformity of the pedestal current gives less flicker when the p.e.v. is used in the 25 Hz chopper mode. A more uniform tube response is expected, being useful when temperature measurements, based on the local video level, are made.     

Infrared television: performance of pyroelectric vidicon at 8 to 14 ?m

The performance of a television camera using the 2.54cm pyroelectric vidicon has been measured and compared with an analysis that attempts to identify the factors limiting the performance of the system.