| 摘要 |
<p>1,094,307. Colour television; transistor amplifying circuits. SIEMENS A.G. Feb. 25, 1965 [Feb. 26, 1964], No. 8104/65. Headings H4F and H3T. Phase distortion imparted to a colour subcarrier signal as a function of the amplitude of the luminance signal with which it is combined is removed by passing the composite signal through a first, linear channel 24, which delays the signal so as to introduce a predetermined phase shift of the sub-carrier, and then combining it at point 44 with the original subcarrier signal which is passed through a second channel including a non-linear stage 30 which modifies the sub-carrier amplitude as a function of the amplitude of the luminance signal. By appropriate adjustment of the delay of channel 24 and the characteristic of stage 30, the combined sub-carrier at point 44 may be rendered free from phase distortion. In the second channel the composite signal is applied to stage 30 but only the sub-carrier is selected from the output by band-pass filter 39. The channel includes band-stop filters 29 and 40 to remove signal components at one-half and twice the sub-carrier frequency, which are introduced by non-linearity, and a phase-correcting circuit 42, 43. In stage 30, transistor 31 is connected as a common emitter amplifier with a degenerative feedback emitter load formed of a second transistor 34 acting as a constant-current source and an array of diodes 35-38 connected to individually adjustable bias circuits. The diodes become conductive at different levels of the luminance component of the composite signal. The diode biases are adjusted to produce a desired variation in the amplitude of the sub-carrier component with the amplitude arranged to fall to zero at the luminance level where no phase distortion occurs. The circuit illustrated is included in an arrangement, Fig. 2 (not shown), which also includes means for compensating for differential amplitude distortion.</p> |
