| 摘要 |
A universal highly integrated television tuner is provided for receiving television signals of many different types and standards from terrestrial or cable sources. The input signals are supplied to an RF attenuator forming part of an automatic gain control loop. A tracking low noise amplifier supplies the signals to a tracking filter. The filtered signals are supplied to a first frequency changer 105, 108, 110, which performs up-conversion to a high first intermediate frequency. The resulting signal is filtered before being supplied to a second frequency changer performing down-conversion to a conventional second intermediate frequency. The resulting signals are supplied to an automatic gain control detector and to second intermediate frequency filters. The detector detects the signal level upstream of the single channel filtering. Both frequency changers comprise image reject mixers which receive local oscillator signals from tunable local oscillators controlled by hybrid mash fractional N phase locked loop synthesisers.
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