The ways of increasing an operation speed of the formation of an illuminating raster in a scanning television optical microscope are analyzed. The raster is formed by a digital-to-analog method using a precise voltage-to-current converter. Vast functioning possibilities of the microscope provided by forming the raster of changeable size and changeable resolution as well as by moving the scanning raster of a reduced size to an arbitrary point on the cathode ray tube screen require that the time of deflection of the illuminating scanning beam to a point with specified coordinates and required accuracy be controlled. We propose a hardware solution for increasing the operation speed, which will significantly reduce the time of forming the scanning raster in discrete mode.
To ensure the high accuracy of conversion of the input voltage into the current of an electronic beam deflector coil, a voltage-to-current converter is realized in the form of dc amplifier with strong negative current feedback. A negative feedback signal is formed on a precision resistor connected in series with an inductive load, that is, the coil of an electronic beam deflector. The accuracy of the iput-voltage-to-load-current transformation is determined by the amplification factor without the negative feedback operation. As a rule, the amplification factor exceeds 1000, and the transformation factor of the voltage-to-current converter is close to unity.
Depending on the amplitude of the input signal, the amplifier stages of the voltage-to-current converter can operate either in a linear mode or in a saturation mode. The latter appears due to the break in the feedback loop caused by the large difference between the input signal amplitude and negative feedback signal amplitude. There are given analytical expressions for determining the settling time of the inductive load current with prescribed accuracy. An interactive mode of the scanning television optical microscope operation is proposed. The essence of the STOM interactive operation mode is that the instant when the code of the next coordinates of the illuminating raster element is delivered to the system is determined by the current settling time (obtained with the prescribed accuracy) and the duration of an illumination pulse.
Two block diagrams have been proposed which, in the interactive operation mode, generate normalized pulses, whose duration is equal to the duratin of transient for the inductive load current settling. A block diagram of the scanning television optical microscope that takes into account the duration of the transient that corresponds to the settling time of the illuminating scanning beam in different STOM operation modes has been developed.
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