| 摘要 |
A tuner stage of a satellite receiver system, receiving a signal from a low noise block for selecting a required channel carrier frequency, that comprises: an oscillator (20) for providing output signals at a selected frequency that have a 90 DEG phase difference; first and second mixers (18a,18b) for mixing the signal from the low noise block with the signals from the oscillator (20); a means (22) for introducing a further 90 DEG phase shift between the output signals of the mixer (18a,18b) at a required frequency that is equal to the difference between the selected frequency and the required channel carrier frequency; a first switchable summer (24) for summing the signals from said means; and a filter (26), whose centre frequency equals the required frequency, for filtering the summed signals. <IMAGE> |
