Television line deflection arrangement.

摘要

With television displays and especially with such displays for colour projection television it is quite possible to obtain a display raster which exhibits distortions on its vertical sides, namely tilt and bow distortions. These may be corrected by the present line deflection arrangement which comprises a line output switching transistor (TR1), a load inductor (L1), an 'S' correction capacitor (C1) and the line deflection coil (Ly). The series arrangement of a current limiting inductor (L2) and diodes (D1 and D2) poled in opposite directions is connected in parallel with the deflection coil (Ly). A resistor (R1) and a transistor (TR2) are each connected in parallel with diode (D1) whilst a variable resistor (R2) is connected in parallel with diode (D2). A resistor (R3) shunts the base-emitter junction of transistor (TR2) whilst input terminals (10 and 11) are respectively connected to the base and collector of that transistor. In the absence of a signal at terminals (10 and 11) the circuitry shunting the deflection coils (Ly) acts as a centring circuit with a static offset current being produced through the deflection coils (Ly) which produces a static magnetic bias in the direction of line deflection. Transistor (TR2) operates in class A and is biased to its mid-conduction point so that it effectively provides a given impedance in parallel with resistor R1. To correct the geometric distortion the terminals receive a field frequency signal input which modulates the conduction of transistor (TR2) and hence its impedance at field frequency. To correct for tilt distortion this signal is a field frequency sawtooth whilst to correct for bow distortion this signal is a field frequency parabola, a combination of these signals being used to correct for a combination of these distortions. This modulation produces a modulated magnetic bias through the deflection coils (Ly).