Patent GB-1241933-A (GB)
Title: Deflection circuits for television display devices
IPC: H04N3/23
Filed: 1969-07-08
Abstract: 1,241,933. Cathode-ray tube circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 8 July, 1969 [11 July, 1968], No. 34297/69. Heading H4T. In an arrangement for varying the amplitude of the line frequency deflection sawtooth wave of a television display system in accordance with a function varying at the field frequency of the system the field frequency function is supplied via an electronic switch modulator during the forward strokes of the line sawtooth to a resonant circuit comprising a capacitor and an inductive portion which includes the line or field deflection coil, the period of the resonant circuit being twice the flyback period of the line sawtooth. The invention may be employed for pin cushion distortion correction in which case the field frequency function comprises a parabolic waveform and the line deflection coil only is included in the resonant circuit when EAST-WEST correction is required and may simultaneously be employed for colour correction as described in Specification 1,230,162 in which case a second electronic switch modulator is utilized and the field frequency function comprises a sawtooth wave. Referring to Fig. 1 and considering pin cushion distortion correction, the field frequency function is derived as a parabolic wave from the cathode of the field drive pentode 33 and developed across capacitor 49 as voltage waveform 50. The latter is then effective via winding 28 of transformer 27 and a winding 29 on the line transformer 3 to modify the amplitude of the line frequency sawtooth during the forward strokes of the latter as determined by a transistor 51 forming the electronic switch modulator and which is rendered conducting during the forward strokes by the voltage 53 derived from a winding 55. This results in a linearly varying current i p  flowing through winding 28, the amplitude of such current attaining a maximum value in the positive sense (at the end of the forward stroke period TH) determined by the instantaneousvalue of the voltage waveform 50. During the line fly-back period #TH transistor 51 is cutoff and the resonant circuit, consisting mainly of the mutual inductance of transformer 27, the parallel connected line deflection coil halves 18, 19 and capacitor 30 and which is arranged to have a period equal to twice the line fly-back period #TH, resonates, so that at the end of the period #TH the current i p  attain a maximum value in the negative sense and the next cycle of operation commences at the correct magnitude and polarity of the current i p . The modified current i p  is then transferred via the 1: 1 transformer 27 into the deflection coil circuit in which the normal deflection current i d derived from windings 6, 7 on the line transformer 3 flows so that the latter current is modified in accordance with the function required for EAST-WEST pin cushion distortion correction. For colour correction sawtooth waves 69, 70 derived from the field deflection transformer 31 are employed to modify the line deflection waveform by means of transformer 22 and an electronic switch modulator comprising diodes 65 rendered conductive during the forward line strokes by means of pulses derived from the winding 55 on the line transformer 3. In a modification the line deflection halves may be connected in series instead of in parallel (Fig. 2, not shown).