Resizable Scanning Raster Generation in Television Optical Microscope

: pp. 49 - 56
Lviv Polytechnic National University
Lviv Polytechnic National University
Lviv Polytechnic National University
Lviv Polytechnic National University

High resolution cathode-ray tube (CRT) uses in television optical microscope (TOM) for lighting of investigated microobject (MO) [1–4]. Light, which goes through investigated MO, or reflected from it, projects on photosensitive target of photoelectron multiplier (PEM). On the output of PEM is generated electrical signal. Amplitude of this signal corresponds to the light, which coming from investigated MO. This signal is used to display researched MO image on television screen or personal computer screen. Resolution of CRT allows to generate scanning raster, which can has more then 4000×4000 elements of the image. Resolution of television screen is much lower (usually, doesn’t exceed 550×720 image formation elements). This feature of TOM allows to reduce size of scanning raster. In this way, is the possibility to get enlarged image of investigated MO or his part without loss of resolution. For getting enlarged image of selected part of researched MO is used offset of reduced scanning raster. For expansion of functionality, TOM generates scanning raster in television standard and in small-frame mode. Using of personal computer allows to form scanning raster by analog or digital-analog way. Independent offset of reduced raster requires special circuit solutions. One of these solutions is using of voltage-to-current converter VCC for precision current formation in load.

The block diagram is developed for sweep signal generation unit by one coordinate. Composition of block diagram includes control unit of operation modes, generator of sawtooth voltage signal, generator of offset signal, memory unit, digital-to-analog converter of signal, commutator, regulator of sweep signal amplitude, amplifier-limiter of scanning ray deviation signal. The block diagram of sweep signal generation unit for another coordinate is the same.

Main requirements of magnetic deflection system is defined. Shown, that main design parameters of magnetic deflection system, which influence on parameters of TOM is inductance of deflection coils, own resonance frequency, active resistance, maximum current, that is needed for deflection of light scanning ray to the outer point of raster.

Been analyzed requirements for voltage-to-current converter, which should provide strong precision of input signals to current in load converting, stability of current value, and high performance. They execute by scheme of direct current amplifier using direct current amplifier with deep negative feedback by current. Signal of negative feedback is formed on precision resistance, which is switched consistently with inductive load. All of the above requirements should be performed with minimal intake power. Shown charts of parameters of voltage-to-current converter from design parameters which using in deflection coils of magnetic deflection system.

Been defined minimum supply voltage of voltage-to-current converter, which is used for magnetic deflection system power with different design parameters. Also, shown, that using deflection coils with small inductivity needs less voltages of power supply, but leads to an increase of average power consumption. Defined main dynamic parameters of voltage-to- current converter using magnetic deflection system with different design parameters for scanning raster formation.

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