| 摘要 |
<p>A double conversion television tuner has first and second mixers and uses both the sum and difference frequency signals from the second mixer. The picture component of the difference frequency is separated from the output of the second mixer using a first filter and then demodulated. A second filter passes the sum frequency signal and the second harmonic of the nominally fixed frequency local oscillator signal applied to the second mixer. A third mixer is coupled to the second filter and mixes the converted sum frequency signal with the second harmonic signal. The audio component of the resulting sound signal is demodulated. Because the sum and difference signals at the output of the second mixer are far apart in frequency, the first and second filters can be easily designed so as not to interact.</p> |
