| 摘要 |
PURPOSE: To eliminate image disturbance when an analog broadcast program is received in a CATV receiver capable of receiving both analog and digital broadcast programs. CONSTITUTION: An up-converter 12 is used to select a station from a received high frequency signal and distributes the signal into signals 12a, 12b and they are respectively given to each one input terminal of mixers 13, 14. A signal 15a from a local oscillator 15 whose phase is shifted by 90 deg. at a 90 deg. phase shifter 16 is fed to the other input of the mixer 13 and a signal 15b from the local oscillator 15 is fed to the other input of the mixer 14. A 90 deg. phase shifter 17 is connected to the output of the mixer 14 and its output signal is added to the output signal from the mixer 13 at an adder 18, from which an analog IF signal is outputted to an output terminal 19. The output signals from the mixers 13, 14 are outputted respectively to output terminals 20a, 20b as digital I/Q detection outputs. Image disturbance of an analog IF signal is simply eliminated by having only to insert the 90 deg. phase shifter 17 into the path for the IF signal in this way. |
