| 摘要 |
PURPOSE:To obtain a TV tuner capable of a consecutive tuning with which a band switching operation is unnecessary from VHF through UHF, by mixing the oscillation output of a frequency higher than the TV signal to be received with the oscillation output of a fixed frequency and thus obtaining a local oscillation output of a differential frequency between the above-mentioned two oscillation outputs through a mixing circuit. CONSTITUTION:The wide-band signal covering from the VHF through UHF bands and supplied to the terminal 17 is amplified by the RF amplifier 18 having an automatic gain control function and then supplied to the mixing circuit 20 through the filter 19 of a low band or a band pass type. On the other hand, the variable oscillating circuit 22 oscillates the frequency of abour 2-3GHz, and this frequency is variably controlled by the control voltage applied from the terminal 21. Then the output of the oscillating circuit is mixed with the output given from the fixed oscillator 24 through the mixing circuit 23 to be supplied to the mixing circuit 20 in the form of the local oscillation signal. The signals of 91.25MHz+58.75MHz- 765.25MHz+58.75MHz are used for the local oscillation signal. As a result, a consecutive channel selection is possible over the VHF through UHF bands. |
