| 摘要 |
A differential amplifier (10) used as an IF filter and placed between an IF amplifier (2) and a first sound detector (9) in a television system. The IF amplifier produces IF signals for a sound carrier and a picture carrier at separate frequencies. The differential amplifier has frequency characteristics such that the gain at the sound carrier frequency is larger than that at the picture carrier frequency and that the gain in the band between the sound carrier and the picture carrier is smaller than that at the picture carrier frequency. The mixing of the higher harmonics of the video component into the frequency of the difference between the frequency of the sound carrier and the frequency of the picture carrier is thereby decreased. The sound detector transforms the signal from the differential amplifier to a second sound intermediate frequency corresponding to this frequency difference, and, when demodulated to the sound signal, buzz sound is decreased and S/N is improved.
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