JPS6187413A - Channel selector - Google Patents

Abstract

PURPOSE:To attenuate a disturbance level appearing at a UHF antenna terminal by grounding a control voltage input terminal of a UHF input tuning filter at the reception of VHF. CONSTITUTION:A control voltage is fed to a variable capacitor of U, V input tuning filters 5, 9 from a voltage control terminal 10 via resistors R1, R2 to obtain an optional selectivity characteristic. Since a level of a VHF radio wave supply terminal 12 goes to an H level at the VHF reception, a transistor (TR)Q1 is turned on and a voltage applied to a UHF input tuning circuit 5 is grounded through a resistor R3. Since the resistor R3 is selected every small in comparison with the resistor R1, a voltage appearing at the UHF input tuning filter is lowered. Thus, the disturbing level appearing at the UHF antenna terminal is attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an up-down converter type tuning device.

Conventional configurations and their problems In recent years, up-down converter type tuners have been developed and commercialized mainly for 0ATVs.

A conventional up-down comparator type channel selection device will be explained with reference to FIGS. 3 to 5. Figure 1 is a circuit block diagram of a conventional channel selection device, where 1 is an up-converter section;
2 is a down converter section, and the input end of this down converter section 2 is connected to the output end of the up converter section 1.

3 is a LIHF antenna terminal, 4 is a UHF low-pass filter (hereinafter referred to as "UHELPF"), 5 is a UHF input tuning filter, 6 is an RF amplifier, 7 is an HF antenna terminal, 8 is a VHF low-pass filter (under uVHFLPFJ)
), 9 is a VHF input tuning filter, 10 is a voltage control terminal, 11 is a UHF power supply terminal, 12 is a VHF power supply terminal, 13 is a first mixer, 14 is a first local oscillator,
15 is a voltage control terminal, 16 is an 11th F amplifier, 17 is a second mixer, 18 is a second local oscillator, 19 is a second rF amplifier, 20 is an output terminal, and R1 and R2 are bias resistors.

The LIHF signal is input from the LJHF antenna terminal 3 to the RF amplifier 6 through the UHF LPF 4 and the UHF input tuning filter 5 having characteristics as shown in FIG. On the other hand, the VHF signal is transmitted through the VHF antenna cap 7.
From this, VHFLPF8 having the characteristics shown in FIG.
and is input to the RF amplifier 6 through the VHF input tuning filter 9. Each varicap of the input tuning filter 5.9 has a U/V common voltage ill T111 terminal 10.
Therefore, the same is true through bias resistors R1R2! l? ! ! Pressure is applied. The RF amplifier 6 is connected to a UHF power supply terminal 11 and a VHFIiii supply terminal 12, and when receiving UHF, the RF amplifier 6 operates as a UHF amplifier and amplifies the UHF signal. When receiving VHF, R
The F amplifier 6 operates as a VHF amplifier and amplifies the VHF signal. The RF multiplied signal is converted into an 11th F signal @(fat) by the first mixer 13. The first local oscillation frequency (fLl) is applied to the varicap of the first local oscillator 14 from the voltage control terminal 15 as fLl-rtt +f4 °°°"°°゛°゛°°゛°°゛°°°... ■ (However, 1. is the desired reception signal frequency a
), and its output is supplied to the first mixer 13. The first converted by the first mixer 13
The 1F signal (fel> is amplified by the 11th F amplifier 1G, and then the second IF signal (f12>
is converted to The second local oscillator 18 is fL2-fll-f12.
・・・・ ■or fL2”'fll+f12…°°°…°゛°°°°°°
゛ ■It is a fixed frequency oscillator that oscillates at frequency fL2. The 21st F signal (f
l 2 ) is amplified by the 21st F amplifier 19 and output from the output terminal 20.

However, in the conventional configuration as described above, the output level of the first local oscillator 14 added to the first mixer 13 is usually about O to +10 (dam), and the oscillation of the first local oscillator 14 when receiving VHF Frequency fLl is 900 to 1
When moving up to 40G (MHZ), there was a problem in that the radiation interference level of the first local oscillation frequency fLl appearing at the HF antenna terminal 3 reached a level that could not be reduced by the UHFLPF4.

OBJECTS OF THE INVENTION The present invention has been made to overcome the above-mentioned conventional drawbacks, and an object of the present invention is to provide an up-down converter type channel selection device with a low level of interference.

Structure of the Invention In order to achieve the above object, the present invention provides channel selection i! The first resistor of the i resistor is inserted between the voltage control terminal, the UHF input tuning filter, the HF input tuning filter, and the control voltage input terminal of the voltage 11 control terminal and the HF input tuning filter. a 20th resistor inserted between the voltage control terminal and the control voltage input terminal of the VHF input tuning filter, a third low resistance resistor, and a switch circuit; and a switching circuit that grounds the control voltage input terminal of the UHF input tuning filter via the third resistor.

According to this configuration, when receiving VHF, by lowering the control voltage of the UHF input tuning filter, the tuning frequency of the UHF input tuning filter is lowered, and by utilizing the fact that the higher frequency is reduced, the UHF antenna terminal is connected to the UHF antenna terminal. It is possible to attenuate the radiation interference level of the first local oscillation frequency that appears.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

No. 18 is a circuit block diagram of a U-■ input tuning filter section of an up-down converter type tuning device according to an embodiment of the present invention, in which the same components as those shown in FIG. , and the explanation thereof will be omitted. In FIG. 1, Ql is a switching transistor, R3
is the collector resistance of transistor Q1, and R4 is the base resistance.

The collector of the transistor Q1 is connected to the connection point between the UHF input tuning filter 5 and the resistor R1 via the resistor R3, the emitter is grounded, and the base is connected to the resistor R4.
It is connected to the VHF power supply terminal 12 via. Note that resistors R+ and R2 are more than 10 times larger than resistor R3.
A high resistance value is selected.

Next, the operation will be explained. From the voltage control terminal 10 to the resistor R1,
Control voltages are applied through R2 to the varicaps of the U and ■ input tuned filters 5.9, respectively, to obtain arbitrary selectivity characteristics. When receiving VHF, the HF WH wave supply terminal 12 becomes high level, so the switching transistor Q1 turns on, and the UHFXD tuning filter 5. The voltage applied to is grounded through resistor R3. By the way, since the resistor R3 is chosen to be much smaller than the resistor R1, the voltage applied to the LJ HF tuned filter 5 can be lowered.

On the other hand, when receiving UHF, VHF power supply pane 1? Since no power is applied to the transistor Q1, the transistor Q1 does not conduct. Therefore, the voltage at the voltage control terminal 10 is directly applied to the UHF input tuning filter 5.

FIG. 2 shows the selectivity characteristics when the control 11i pressure of the LJHF input tuning filter is changed. In a conventional circuit, the tuning frequency changes in the range from fl to t2 depending on the desired input signal, so when receiving VHF, for example, 90G (M
The selectivity characteristic of the signal H7) changes by a maximum of X (dB). On the other hand, the selectivity characteristic a at the tuning frequency f1 is the selectivity characteristic of the UHF input tuning filter 5 during VHF reception according to this embodiment, and this characteristic is determined by the change in the desired input signal during VHF reception. is almost unchanged.

According to this embodiment, by providing the U/VlJJ conversion circuit in the UHF input tuning filter 5, it is possible to reduce the radiation interference level of the first local oscillation frequency (fLl) appearing at the UHF antenna terminal 3 during VHF reception. It can be attenuated.

As described in detail, according to the present invention, the selectivity characteristics of the input tuning circuit can be maximized by simply adding a U/V switching circuit without adding a voltage control terminal. It is possible to attenuate the level of interference appearing at the uHF antenna terminal.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of the U-■ input tuning filter section of a tuning device in an embodiment of the present invention, and FIG. 2 is a circuit block diagram of the tJ H
An explanatory diagram of the selectivity characteristics of the F panono tuning filter, Fig. 3 is a circuit block diagram of a conventional channel selection device, and Fig. 4 is an explanatory diagram of the characteristics of U I-I F L P F of the same channel selection device. Fifth
The figure is an explanatory diagram of the characteristics of V HF l-PF of the same station selection 'JAt. 5...UHF input tuning filter, 9...VHF input tuning filter, 10...Voltage control terminal, R1-R3.
...Resistance, (transistor agent Yoshihiro Morimoto Figure 1 H Tsunakawa 3 Number of skins

Claims (1)

[Claims] 1. Voltage control terminal, UHF input tuning filter, and VH
a high-resistance first resistor inserted between the voltage control terminal and a control voltage input terminal of the UHF input tuning filter; and a control voltage input of the VHF input tuning filter. a second resistor of high resistance inserted between the terminal and the third resistor of low resistance, and a switch circuit, and the UHF input tuning filter is connected through the third resistor during VHF reception. A channel selection device equipped with a switching circuit that grounds the control voltage input terminal.