JPS643255Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is an input device for a CATV tuner, in particular, which prevents the occurrence of tuned waveform distortion, and also enables a reduction in the number of parts and power consumption.
This invention relates to an input device for a CATV tuner.

Generally, CATV tuners need to receive a wide range of frequency bands, so the tuning circuit is switched into multiple stages using switching diodes, and tuning diodes with a large capacitance change ratio are used. However, for devices that need to receive the upper frequency band of the super band, stable selection operation cannot be obtained due to the lead inductance, loss, etc. of the switching diode, so the method shown in Figure 1 is not recommended. As shown in Figure 1, the high frequency input signal from the VHF antenna (VHF ANT) - the VHF signal input terminal from the CATV cable is also the same (the same applies hereafter) - which has passed through filter 1 is divided into the VHF frequency band and the super band frequency band. A system is adopted in which the signal is divided into 2 and processed individually by a VHF processing section 2 and a super band processing section 3, respectively, and outputs an IF output. Of course,
A UHF input signal received by a UHF antenna (UHF ANT) is processed by a UHF processing unit 4. In order to separate the VHF input signal to the VHF processing section 2 and the super band input signal to the super band processing section 3, since the frequencies to be separated are close to each other, a normal UV splitter is required. Since it is not sufficient to use an LC filter circuit such as the one shown in FIG. 2, a switching method using a switching diode is used as shown in FIG.

A detailed circuit diagram of the input stages to the VHF processing section 2 and superband processing section 3 in the CATV tuner shown in FIG. 1 is shown in FIG. In the figure, 5 is a VHF antenna terminal, 6 is a filter corresponding to filter 1 shown in Figure 1, and 7 is a filter.
is a super band amplifier, 8 is a VHF amplifier, 9
10 is a changeover switch, 11 and 12 are power supplies, 13 is a variable resistor, 14 to 30 are resistors, 3
1 to 41 are coils, 42 to 53 are capacitors, 55 to 62 are switching diodes (hereinafter referred to as diodes), and 63 and 64 are tuning diodes.

In FIG. 2, the changeover switches 9 and 1 are
0 is interlocking, that is, the changeover switch 9 is connected to terminals a, b, c,
The changeover switch 10 is connected to terminals e, f, g, and h corresponding to the connection to terminal d. In the first tuning state obtained when the changeover switches 9 and 10 are connected to terminals a and e, respectively, the power supply 1
Diodes 58, 59, 6 by DC voltage of 1
0, 61, and 62, diode 56 is turned on, and diodes 55 and 57 are turned off. Therefore, the equivalent circuit in the first tuned state is the same as in the case of the present invention described later, and is as shown in FIG. 4A. Similarly,
The changeover switches 9 and 10 are connected to terminals b and f for a second tuning state, similarly connected to terminals c and g for a third tuning state, and further connected to terminals d and h. The equivalent circuits of the fourth tuning state obtained are shown in FIGS. 4B and 4B, respectively.
It will look like C and D. Note that the diode 55 shown in FIG. 2 is turned on during super band reception, that is, in the fourth tuning state shown in FIG. This is provided to eliminate traps, etc. that enter the super band due to resonance.

In this way, the first to third
A tuning state for the super band and a fourth tuning state for the super band are obtained, but in the case of the first to third tuning states, the diode 55
In addition, in the case of the fourth tuning state, the diode 5
6, 58 to 62 have no bias, so there is a drawback that distortion may occur. That is, if an alternating signal is supplied to the diode while the diode is in an unbiased state, the alternating signal is rectified, so to speak, and distortion occurs. Needless to say, if the diode is sufficiently reverse biased, the alternating signal will be completely blocked and the above rectification phenomenon will not occur.

The present invention aims to solve the above-mentioned drawbacks, and can prevent the occurrence of tuned waveform distortion, reduce the number of parts, and reduce power consumption.
The purpose is to provide an input device for CATV tuner. This will be explained below with reference to the drawings.

Figure 3 shows the circuit configuration of an embodiment of the present invention.
4A to 4D show equivalent circuits in the tuned state of the embodiment shown in FIG. 3, respectively. All the symbols in the figure correspond to those in FIG. As is clear from FIGS. 2 and 3, the configuration of the embodiment shown in FIG. 3 is different from the configuration of the conventional example shown in FIG.
27 and capacitors 52 and 53 are removed, and its operation can be considered to be basically the same as the conventional example shown in FIG. Therefore, the first to fourth tuning states obtained by switching the changeover switches 9 and 10 in four stages are as follows:
4A to 4D are equivalently the same as the conventional example shown in FIG. 2.

However, in the conventional example shown in FIG.
0, terminal e, f or g, and is turned on through resistor 27, whereas in the embodiment shown in FIG. 3, resistors 26, 27 and capacitor 52, 53
is removed, the power supply 11 is
It is turned on by applying a DC voltage of . Therefore, as is clear from FIG. 3, under the first to third tuning states, a bias is applied to the diode 55 (in the conventional example shown in FIG. 2, no bias is applied, Also under the first and second tuning conditions the diode 58,
There is no diode that is reverse biased, such as 59, and is unbiased under all tuning conditions.

Furthermore, in the present invention, the resistance values R ₁₄ ,
It is necessary that R ₁₇ , R ₁₈ and R ₂₂ be selected so as to satisfy the following conditional expression, and they are selected in this manner. That is, R ₂₂ /R ₁₇ +R ₂₂ <R ₁₄ /R ₁₈ +R ₁₄ Therefore, in the fourth tuning state, diodes 55 and 57 are turned on, and a reverse bias is applied to the other diodes.

As explained above, in the present invention, there is no diode that becomes unbiased in any of the first to fourth tuning states, so it is effective in preventing waveform distortion during tuning processing. This not only results in a reduction in the number of parts (the resistors 26 and 2 in the conventional example shown in Figure 2), but also results in a reduction in the number of parts.
7 and capacitors 52 and 53 are unnecessary),
This also leads to a reduction in power consumption.

Although the illustrated embodiment in FIG. 3 shows a tuning circuit configuration that divides the VHF frequency band into three bands and performs tuning, the present invention is not limited to this, and can also be applied to, for example, a two-band tuning configuration. Needless to say, it will happen.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of an input device for a CATV tuner, which is the premise of the present invention, and FIG. 2 is an explanatory diagram of a conventional input device for a CATV tuner.
FIG. 3 shows a circuit configuration in an embodiment of the present invention, and FIGS. 4A to 4D each show equivalent circuits in a tuned state in the embodiment shown in FIG. In the figure, 5 is the VHF antenna terminal, 6 is the filter,
7 is a super band amplifier, 8 is a VHF amplifier,
9 and 10 are changeover switches, 11 and 12 are power supplies, 13 is a variable resistor, 14 to 30 are resistors,
31 to 41 are coils, 42 to 53 are capacitors, 55 to 62 are switching diodes, and 63 and 64 are tuning diodes, respectively.

Claims (1)

[Scope of utility model registration request] VHF selection switching diode and
Via switching diode for VHF selection
a VHF tuning circuit that selectively tunes to a plurality of frequency bands of a VHF input signal; a VHF amplifier that amplifies the VHF input signal supplied through the VHF tuning circuit; a switching diode for super band selection; a super band tuning circuit that tunes to the frequency band of a super band input signal supplied via a super band selection switching diode; The VHF tuning circuit includes a plurality of switching diodes, and selectively supplies direct current voltage to the plurality of switching diodes via a changeover switch to switch the plurality of switching diodes. selectively on/off
In an input device for a CATV tuner configured such that a tuned circuit suitable for the VHF input signal is formed by turning it off, the above-mentioned
The switching diode for VHF selection is
When receiving a VHF input signal, a DC voltage is applied in the forward direction to selectively turn on the switching diode in the VHF tuning circuit, and when receiving the super band input signal, the switching diode is applied to the switching diode for selecting the super band. An input device for a CATV tuner, characterized in that it is configured so that a DC voltage is applied in a reverse direction via a switching diode.