JPS61239727A - Input circuit of tuner - Google Patents

Abstract

PURPOSE:To reduce noise, to increase a gain, and to decrease small gain deviation by providing two input signal terminals for the UHF band and VHF band without using a mixer which mixes a signal of the UHF band and a signal of the VHF band including the CATV broadcasting band with each other. CONSTITUTION:An input filter 5 consists of a filter group of filters corresponding to the 1st - the 4th divided bands of a band of 50-900MHz; and one of power terminals corresponding to the 1st - the 4th bands is selected to select one of the 1st - the 4th bands according to an applied voltage and part of an RF signal inputted from an input terminal 2 which corresponds to the necessary band is outputted from an output terminal 11. When a voltage is applied to a power terminal 6, a switching circuit 4 turns on and a signal of the UHF band inputted from an input terminal 1 is outputted from an output terminal 11 through a balun 3 and the switching circuit 4 and the signal from the input terminal 2 is cut off by the input filter 5 at this time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an input circuit for a tuner that receives a series of RF flaw signals ranging from the l'HF band to the UHF band. The present invention relates to an input circuit suitable for receiving input using input means.

[Background of the invention]

A switching device that divides one continuous frequency band into multiple frequency bands and consists of bandpass filters corresponding to each band, and electrically selectively passes one frequency band among the multiple frequency bands. At least one diode is placed in series on the input side and output side of the signal passing line of each bandpass filter, and each bandpass filter is connected in parallel to form an input filter. The provided filter is described in Japanese Patent Laid-Open No. 57-72410. This is suitable for receiving CATV broadcasts or receiving television broadcasts that are input from the VHF band to UHF% through a single transmission line, but
This is inconvenient when receiving signals sent through two F-band transmission lines), and in this case, the
As described in No. 26990, the UHF band transmission line signal and V
A mixer must be provided before the input filter to combine either the IIF band transmission line signal or the CATV broadcast band transmission line signal. For this, in addition to the input filter losses, this mixer j 0
There were problems such as a loss of "14"""', a poor noise figure of 1"5, a decrease in gain, and an increase in deviation within the reception band.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an input circuit for a tuner that does not use a mixer and has a low-loss UHFHF band reliability terminal and a VHFHF band reliability terminal, each independently.

[Summary of the invention]

A switching circuit that inputs the UHF band signal to the parallel connection point of the divided input filters and switches the band division filters that make up the input filter, without using a mixer to combine the UHF band signal and the VHF band signal. We considered an input circuit equipped with two input terminals: a signal input terminal for the 'UHF band with enhanced high-frequency separation and a signal input terminal for the VHF band, which includes the CATV broadcasting band.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 9.

FIG. 1 is a block configuration showing the first embodiment, and 1 is a UH
F signal input terminal, 2 is l'HF signal input terminal, 3 is a balun circuit that performs balanced-unbalanced transmission mode conversion, 4 is a switching circuit, 5 is an input filter, 6 is a UHF band power supply terminal, 7 is a 1 is a power supply terminal for the first band, 8 is a power supply terminal for the second band, 9 is a power supply terminal for the fifth band, 10 is a power supply terminal for the fourth band, and 11 is an RF signal output terminal.

In the figure, the input filter 5 has a frequency of 50 to 900 MHz.
A power supply corresponding to the first to fourth bands is composed of a filter group as described in Japanese Patent Application Laid-open No. 57-7.2410, which is composed of filters that divide the band into four bands, ie, the first to fourth bands. One of the first to fourth bands is selected by selecting one of the terminals and applying a voltage, and from the RF flaw signal output terminal 11 corresponding to the band among the RF flaw signals inputted from the input terminal 2. Output. When a voltage is applied to the power supply terminal 6, the UHF band signal inputted from the input terminal 1 is outputted from the output terminal 11 via the switching circuit 3 and the switching circuit 4, which turns on the switching circuit 4, and at this time, The signal from input terminal 2 is input to input filter 5.
will be blocked.

Fig. 2 shows the block configuration of the second embodiment, and the difference from the first embodiment is that a switching circuit is incorporated in the balloon 3 in Fig. 1, and the baln shown in 12 is used. That's true.

The operation is similar to that shown in FIG.

FIG. 5 is a first concrete example of the block circuit of the first embodiment shown in FIG. In the figure,
13 and 14 are UHF band balanced input terminals, 15 is CA
VHF signal input including TV broadcast band! 16 is the balun transformer, 17 is the UHF band power supply terminal, 18 is the 4th band power supply terminal, 19 is the 5th byte power supply terminal, 20 is the second
A power terminal for the band, 21 is a power terminal for the first band, 22
are RF signal output terminals, 23 to 30 are bypass capacitors, 31 to 47 are resistors, 48 to 58 are high frequency switching diodes, and 59 is a band pass filter for the first band.
□, 60 is a band pass filter for the second band, 6
1 is a band pass filter for the third band, and 62 is a fourth band pass filter.
: Band bypass filter, 63 is a bypass filter.

Each filter 59 to 62 of the first to fourth bands is 50 to 90oM from the VHF band including the CATV broadcast band to the UHF band.
The band spanning Hz is divided, and the first band is 50~
90#ffz, the second band is 90~170Aff (the third band is a filter that selectively passes each band of 170~27QMIIz, and the fourth band is 270~900MH
The bypass filter has a circuit configuration as shown in Fig. 4, with 64 an RF signal input terminal, 65 an RF signal output terminal,
66 is a high frequency ground terminal, 67 to 71 are capacitors, 72
, 75 is a bypass filter that uses a coil to attenuate the outside band with two traps. Moreover, the bandpass filter for the first to third bands has a circuit configuration shown in FIG.
is an RF decoding input terminal, 75 is an RF signal output terminal, 76 is a high frequency ground terminal, 77-80 are capacitors, 81-84
is 1 in the upper and lower frequency bands of the passband in the coil.
This is a filter that forms one trap and attenuates frequencies outside the band.

For example, when receiving the third band, a voltage is applied to the terminal 19 for the RF multiplied signal from the VHF signal input terminal 15, and the diodes 51, 55, 54, and 52 are connected to the resistor 4.
4 and 45 are rendered conductive, all remaining diodes are reverse biased to be rendered non-conductive, and only the signal in the third band is output from the output terminal 22. 1st. Second. A similar selection is possible for the fourth band.

Furthermore, the selection of the UHF band signal is made by terminal 1 of the balloon 16.
A voltage applied to terminal 17 causes diode 4B to be connected to resistor 4.
The diode 50 is made conductive by the current flowing through the diode 50.
, 52, 54, 56, and 5B are reverse biased to make them non-conductive, and outputted from the output terminal 22. Note that the diode 50 must be selected to have a sufficiently small reverse current, and the diode 49 must prevent deterioration of high frequency isolation.

〔Effect of the invention〕

According to the present invention, without using a mixer that combines UHF band signals and VHF band signals including CATV broadcasting band,
2 signal input terminals for UHF band and signal input terminal for VHF band
Since it is possible to realize an input circuit with two input terminals, it is possible to realize low noise, high gain, and small gain deviation in tuners, etc., and it is also possible to realize a double converge type channel that receives a series of RF signal bands from 50 to 900 MHz. - Dual system of RF signal input (UHF band input and VHF band input)
can be easily realized.

Note that in this embodiment, a bypass filter is used for the fourth band, but it goes without saying that the same effect can be obtained with a bandpass filter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
The figure is a block diagram showing the second embodiment, Figure 3 is a circuit diagram starting a specific example of the first embodiment, Figure 4 is a circuit diagram of a bypass filter, and Figure 5 is a circuit diagram of a bandpass filter. , 6th
The figure is a circuit diagram showing a specific example of the balloon used in the second embodiment. 1... UHF signal input terminal 2... VHF signal input terminal 3... Balloon 4... Switching circuit 5
...Input filter 6...UHF band power supply terminal 7
...First band power terminal 8...Second band power terminal 9...Third band power terminal 10...Fourth band power terminal 11...RF signal output terminal 12...・Noilsin 15.14...UHF balanced signal input terminal 15...U
HF signal input terminal 18...4th band power terminal 19...3rd band power terminal 20...2nd band power terminal 21...1st band power terminal 22...RF signal Output terminal 59... first band band pass filter 60...
2nd band bandpass filter 61...Most of the 3rd band bandpass filter 1 Figure 9s2 Figure

Claims (1)

[Scope of Claims] 1) An input circuit for a tuner that receives RF signals ranging from a VHF band to a UHF band, comprising an input means connected to a UHF signal input terminal and inputted with a UHF signal, and an input circuit from the input means. A switching means for passing or blocking the output depending on the presence or absence of a command, and a VHF input terminal connected to the VHF signal input terminal.
an input filter circuit that passes only a designated specific band of VHF signals among F-band signals and blocks VHF signals of other bands, the output side of the switching means and the input filter circuit An input circuit for a tuner, characterized in that an output side is connected to a common RF signal output terminal. 2) The input circuit according to claim 1, wherein the input means comprises a circuit for converting a balanced transmission mode into an unbalanced transmission mode. 3) The input circuit according to claim 1, wherein the switching means is incorporated in the input means.