|NotTaR of Television Sets : Deflection fundamentals
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Note: the following is just a brief introduction. For more detailed deflection
system theory of operation and sample circuits, see the document:
TV and Monitor Deflection Systems.
The electron beams in the CRT need to be scanned horizontally and vertically
in a very precise manner to produce a raster - and a picture.
For NTSC and PAL, the horizontal scan rates are 15,734 and 15,625 Hz
For NTSC and PAL, the vertical scan rates are 60 and 50 Hz (approximately)
The deflection yoke includes sets of coils for horizontal and vertical
scanning oriented at 90 degrees with respect to each other. Additional
coils are needed to correct for pincushion and other geometric defects.
The deflection circuits must be synchronized and phase locked to the
incoming video signal.
Therefore, we have the following functions:
- Sync separator to obtain horizontal and vertical synchronization pulses.
- Horizontal oscillator which locks to horizontal sync pulses.
- Horizontal drive followed by horizontal output which feeds deflection
yoke (and flyback for HV and other voltages), Yoke requires a sawtooth
current waveform for linear horizontal deflection. Horizontal output
in all but the smaller TVs is a large discrete power transistor, most
often an NPN bipolar type.
- Vertical oscillator which locks to vertical sync pulses. Yoke requires
sawtooth waveform for linear vertical deflection.
- Vertical drive/output which feeds vertical deflection yoke. Newer TVs
use ICs for vertical drive and output.
- Various additional deflection signals to correct for the imperfections
in the geometry of large angle deflection CRTs. These may be fed into
the normal deflection coils and/or there may be separate coils mounted
on the neck of the CRT.
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| About the vertical scan r..>>