| 摘要 |
In a multiband tuner, an input arrangement for selectively applying first and second local oscillator signals to a single input of a prescaler of a phase locked loop tuning system includes a first capacitor connected in series from the output of a first local oscillator to the prescaler input, a second capacitor and inductor connected in series from one output of a second local oscillator to the same prescaler input and a diode switching arrangement for selectively coupling a third capacitor between the junction of the second capacitor and the inductor and signal ground when the first local oscillator is enabled to operate. The first capacitor, inductor and third capacitor comprise a matching network for the output of the first local oscillator. The second capacitor and inductor form a series tuned circuit in the frequency band of the second local oscillator which rejects signals in the frequency band of the first local oscillator. The arrangement is particularly advantageous for allowing the UHF input of a prescaler intended for a VHF/UHF tuner to be used for dividing the frequency of a superband cable local oscillator signal as well as for dividing the frequency of a UHF local oscillator signal. |
