| 摘要 |
1334534 Cathode-ray tube circuits RCA CORPORATION 19 April 1971 [11 March 1970] 11688/70 Heading H4T In a (television) cathode-ray tube display circuit arrangement for producing top and bottom pincushion distortion correction, the correction waveform, comprising parabolic shaped line frequency pulses amplitude and polarity modulated by the vertical deflection sawtooth (waveform D) is supplied from a low impedance output Z of the vertical deflection output amplifier 100 to the vertical scanning yoke 126, 126 and because of the high impedance of the yoke to the line frequency correction components the latter are introduced into the yoke by means of an "impedance matching" transformer the secondary 145 of which is connected in series with the yoke windings and the primary 142 of which together with a capacitor 146 resonates at line frequency and therefore presents a high impedance at the vertical deflection frequency across the yoke. Waveform E shows the actual yoke current during the upper and lower halves of the vertical scan, periods T1 and T2 respectively and to maintain the parabolic shape of the line frequency components a sample of the latter, developed across resistor 134, together with a sample of the vertical deflection current, developed across resistor 132 is employed in a negative feed-back path via resistor 129. A waveshaping network 155 supplies an S-shaping signal at terminal B to the B input of the vertical deflection generator 50 and centring is effected by means of adjustable resistor 136. For the production of the parabolic line frequency components the vertical sawtooth from terminal A of the vertical deflection generator 50 is supplied to the collector of transistor 62 and "chopped" into line frequency pulses by means of horizontal fly-back pulses supplied to the base electrode from the horizontal deflection generator 40. The "chopped" waveform is then amplified by transistor 64 and the parabolic shape is produced by a negative feed-back path which includes a first differentiating circuit comprising capacitor 75 and resistor 76, transistor 66 and a second differentiating circuit comprising capacitor 77 and a resistive portion formed by the input impedance of the base circuit of transistor 64. The phase of the correction is adjusted by resistor 73. Parameter values are given. |
