Blanking circuit, Electrical Engineering

Blanking circuit: The saw tooth sweep voltage applied to the X places moves beam across the CRT tube in a straight horizontal line from left to right during the sweep or trace time. A comparatively slow movement of the spot will appears as solid line, provided the rate of movement exceeds the ehreshold of persistence of vision. Below this threshold limit, a moving spot is perceived. On The other hand, the the comparatively rapid movement of sot will appear as thin and dim line, or may be invisible. Thus if the retrace or fly back time is very small, the spot remains invisible. In an ideal case the fly back time, T is zero and hence the spot while moving from right to left remains invisible. However in actual practice the fly back time is not zero and therefore the retrace (moving of beam from right to left its starting point) may cause confusion. Thus the retrace should be eliminated or blanked out. The retrace is blanked out by applying a high negative voltage to the grid during the fly back period T. The blanking voltage is usually developed (or triggered) by sweep generator.

Z-axis Modulation: it is also called as intensity modulation. Z axis modulation is done by inserting a signal between he ground and the cathode (or control grid). Z-axis modulation is applied during normally visible portion of the trace.

The Z-axis modulation can be used for brightening the display. Periodic positive pulses are applied in the grid (alternative negative pulses are applied to cathode) brighten the beam during its seep period. These periodically brighten spot may be used as markers for time calibration of the main waveform.



Posted Date: 7/12/2012 6:13:37 AM | Location : United States

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