A conventional matching unit is described hereinafter with reference to FIG. 12, which shows a block diagram of the conventional matching unit. High frequency signals ranging between from ca. 500 MHz to 900 MHz input to Antenna 1 for receiving signals of both the VHF and the UHF bands. An output from antenna 1 is fed into matching unit 12 having input terminal 2 and output terminal 3, and an output signal supplied from output terminal 3 is fed into electronic tuner 4. Tuner 4 selects the signal of a desirable channel and converts the signal into the given intermediate frequency (IF) signal, then outputs the signal from output terminal 5.
Between input terminal 2 and output terminal 3 of matching unit 12, a first series connecting unit formed of first switch 6 and low pass filter (LPF) 7 is interposed. A second series connecting unit formed of second switch 8 and band-pass filter (BPF) 9, and a third series connecting unit formed of third switch 10 and high pass filer (HPF) 11 are disposed in parallel with the first series connecting unit. A cutoff frequency of LPF 7 is approx. equal to the highest frequency among the channels of the VHF low-band (90–108 MHz in Japan, and 55 MHz–88 MHz in the USA). The frequencies of the VHF high-band.(170–222 MHz in Japan, and 170–216 MHz in the USA) pass through BPF 9. A cutoff frequency of HPF 11 is approx. equal to the lowest frequency among the UHF channels (470–770 MHz in Japan, and 470–806 MHz in the USA).
In the case of receiving a channel of the VHF low band, the matching unit turns on only first switch 6, so that the signal is supplied to LPF 7. As a result, the signals having frequencies over the VHF high band are attenuated. Further, in the case of receiving a channel of the UHF band, only third switch 10 is turned on, so that the signal is supplied to HPF 11, and the frequencies lower than the UHF band are attenuated. Those filter circuits provide each one of the frequencies input thereto with impedance matching between the antenna and the tuner.
However, the conventional matching unit is equipped with filters which carry out the impedance matching to respective frequency-bands, so that the circuit of the matching unit becomes complicated and bulky.
USPTO Backgrounds
USPTO Backgrounds