JPS6219005Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an antenna circuit that improves images when receiving a UHF band in a television receiver. The antenna circuit of a conventional television receiver has a UHF tuner 1 and a VHF tuner 2, as shown in Figure 1.
external antenna terminals 3, 3 and 4, 4 respectively for
is connected via an antenna changeover switch 5 , and a built-in rod antenna 9 is connected to the antenna changeover switch 5 through a U/V filter 8 consisting of a coil 6 and a capacitor 7. First, when using an external antenna, the antenna selector switch 8 is set to terminals 10, 11 and 1 in the state shown in the figure.
2 and 13 are short-circuited, and when receiving UHF band, the UHF tuner 1 is connected from the external antenna terminals 3 and 3.
When receiving the VHF band, signals are supplied to the balloon 14 from terminals 4 and 4 in the state shown in the figure as described above.
The signal is applied to the VHF tuner 2 via the changeover switch 5 and the desired station of each band can be received. On the other hand, when using the rod antenna 9, move the sliding pieces 15 and 16 of the antenna changeover switch 5 in the direction of the arrow A.
, and short-circuit the terminals 11, 17 or 13, 18 in the direction of the arrow B, and short-circuit the terminals 17 or 1 corresponding to the UHF band and VHF band, respectively.
A received signal is supplied from 8. However, in the above configuration, in the case of UHF band,
When the selector switch 5 uses either an external antenna or a rod antenna, the terminal is interposed between the antenna selector switch 5 and the rod antenna.
Isolation with UHF tuner 1
Since the signal supplied to the UHF tuner 1 is not perfect, the noise figure (abbreviated as NF and referred to as noise figure) for the signal supplied to the UHF tuner 1 is poor. Therefore, the present invention provides a novel antenna circuit that eliminates the above-mentioned drawbacks, and will be described below with reference to the drawings. FIG. 2 shows an antenna circuit according to the present invention, and FIG. 3 shows another embodiment of the same circuit, and the same elements as in FIG. 1 are given the same figure numbers. In FIGS. 2 and 3, 19 and 20 are switching diodes,
21, 22 and 23, 24 are coupling capacitors, 2
5, 26, 27, and 28 are bias resistors that apply a predetermined bias to the switching diode;
9 and 30 are coils for correcting the junction capacitance of the switching diode, 31 is a U/V splitter having a built-in filter corresponding to the UHF band and VHF band, and 32 is a DC power supply terminal. Next, the case of using the external antenna and the case of using the rod antenna shown in FIG. 2 will be explained. () When using an external antenna The antenna selector switch 5 is set to the state shown in the figure, terminals 10, 11 and 12, 13 are short-circuited, and when receiving the UHF band, +B voltage is applied from the terminal 32 of the UHF tuner 1. appears, and therefore, a positive voltage from the DC power supply terminal 32 is applied to the cathode side of the switching diode 19 via the bias resistor 25, resulting in a reverse bias, and the diode 19 is cut off, so that the UHF tuner 1 has no terminal. 3 and 3 are added to it, and it is electrically isolated from the antenna changeover switch 5 . When receiving VHF band, the received signal from terminals 4 and 4 is transferred to terminals 12 and 13 of antenna selection switch 5 .
via the VHF tuner 2, and can receive desired stations in the VHF band. () When using a rod antenna When the sliders 15 and 16 of the antenna changeover switch 5 are moved from the state shown in the figure in the direction of arrow B and the UHF band is received, the +B voltage is applied to the terminals 11 and 17 of the antenna changeover switch 5 and the junction capacitance. The signal is applied to the anode side of the switching diode 19 via the correction coil 29, the switching diode 19 is turned on, and the received signal from the rod antenna 9 is connected to the diode 19 and the coupling capacitor 2.
Joined UHF tuner 1 via 2, 21,
You can receive desired stations in the UHF band. When receiving VHF band, switch the antenna selector switch 5 .
Since the terminals 13 and 18 of the VHF band are short-circuited, the received signal from the rod antenna 9 is applied to the VHF tuner 2, and a desired station in the VHF band can be received. Next, Figure 3 shows the built-in rod antenna with U/V
Example using a splitter, when using an external antenna
When receiving the UHF band, +B voltage is applied to the cathode sides of switching diodes 19 and 20 via terminals 10 and 11 and bias resistors 25 and 28 in the illustrated state, and switching diodes 19 and 20 are cut off. same as above
The UHF tuner 1 and the antenna changeover switch 5 are electrically isolated, and the received signals from the terminals 3, 3 are applied to the UHF tuner 1. In the state shown in Figure 3, when receiving VHF, terminal 4,
The received signal from 4 is applied to VHF tuner 2 via terminals 12 and 13 of antenna changeover switch 5 , so that a desired station in the VHF band can be received. On the other hand, when the rod antenna 9 is used in FIG. 3, the sliders 15 and 16 of the antenna changeover switch 5 are moved in the direction of the arrow B in the same manner as described above, and the switching diodes 19 and 2 are switched in accordance with each band.
Turn 0 on and off. That is, when receiving the UHF band, +B voltage is applied to the anodes of the diodes 19 and 20 in the coils 29 and 3.
0 and both the diodes 19, 20
is turned on, and the received signal received by the rod antenna 9 is transmitted to the U/V splitter 31, the coupling transformer 33, the coupling capacitors 21, 22, 23, 24,
via switching diodes 19, 20
In addition to the UHF tuner 1, the antenna changeover switch 5 is isolated from the receiving signal path of the UHF tuner 1, and at this time, the UHF tuner 1 can receive a desired station. On the other hand, when receiving the VHF band, the rod antenna 9
The received signal received by the U/V splitter 3
1. It is connected to the VHF tuner 2 via the terminals 13 and 18 of the antenna changeover switch 5 , and can receive a desired station in the VHF band. In the above description, the junction capacitance correction coils 29 and 30 are connected to the switching diode P-
It compensates for the influence of N-junction capacitance and also serves as a bias to the switching diode. As described above, according to the antenna circuit of the present invention,
When switching between an external antenna and a rod antenna using an antenna switching switch, it is possible to avoid intervening the antenna switching switch in the receiving signal path when receiving the UHF band, and in particular, it is possible to improve the noise figure.

[Brief explanation of the drawing]

FIG. 1 shows a conventional antenna circuit, and FIGS. 2 and 3 show the same circuit according to the present invention. Explanation of main drawing numbers. 1...UHF Chuyuna, 2...
...VHF tuner, 5 ... antenna changeover switch, 9 ... rod antenna, 19, 20 ... switching diode.

Claims (1)

[Scope of utility model registration request] a pair of UHF antenna terminals connected to a UHF external antenna; a pair of VHF antenna terminals connected to a VHF external antenna; a UHF tuner connected to the pair of UHF antenna terminals;
a tuner, a rod antenna for UHF and VHF, a switching diode AC-connected between one of the UHF antenna terminals and the rod antenna, and a common terminal of the first terminal group connected to the
A common terminal of a second group of terminals is connected to the power terminal of the UHF tuner, and a common terminal of the first group of terminals is connected to the power terminal of the UHF tuner, and the first and second terminals of the first group of terminals are connected to the anode and of the switching diode, respectively. A changeover switch is connected to the cathode in a DC manner, and third and fourth terminals of the second terminal group corresponding to the first and second terminals are respectively connected to the rod antenna and the VHF antenna terminal. , the changeover switch controls on/off of the switching diode to
An antenna circuit characterized by being isolated from a tuner and switching between the VHF external antenna and the rod antenna.