| 摘要 |
<p>1,204,036. Colour television. MULLARD Ltd. (Philips Gloeilampenfabrieken N.V.). 5 Jan., 1968, No. 850/68. Addition to 1,106,944. Heading H4F. In a circuit arrangement for demodulating a PAL system colour sub-carrier signal F, a signal T having the same frequency as the subcarrier and a phase not 90 degrees different from the phases in which the red and blue colourdifference signals R-Y and B-Y are modulated on the sub-carrier and with a constant amplitude at least equal to the amplitude of the modulated sub-carrier, is added to the sub-carrier in adding stage 1, and a similar signal-T of opposite polarity, i.e. 180 degrees differing in phase, is also added to the sub-carrier in adding stage 1a. The output of adder 1 is fed via delay line DL having a delay period equal to the reversal period of the R-Y component in the subcarrier, i.e. one television line period, to an envelope detector 2, and the output of adder 1a is fed directly to an envelope detector 3 of opposite polarity. The outputs of detectors 2 and 3 are combined to give the blue colour difference signal (B-Y). To obtain the red colour-difference signal (R-Y) the output of delay line DL is fed to an envelope detector 5 and the output of adder 1 is fed via a damping member 4 simulating the decrease in amplitude on the delay line, to an envelope detector 6. The rectifiers in the two detectors 5 and 6 are alternately made operative by means of a switching signal so that the polarity of the resulting R-Y signal at the combined output of detectors 5 and 6 is constant and does not change polarity from line to line, i.e. as described in the parent Specification 1,106,944. The improvement of this Specification over the parent Specification is that the (B-Y) component is derived without an associated D.C. component. Variation in the phase position of the carrier signal T causes the two colour signals R-Y and B-Y to be influenced differently and this effect may be utilized for adjusting the hue of the colour television receiver.</p> |
