JPH0738384A - Tuner - Google Patents

Abstract

PURPOSE:To simplify the configuration of an input circuit comprised by using variable capacitance diodes with different change ratios and to reduce a circuit scale by using by sharing the amplifier element part of the input circuit, arranging plural variable tuning filters in accordance with respective bands, and switching the variable tuning filter corresponding to a reception band. CONSTITUTION:A circuit for a television signal inputted to a tuner is selected corresponding to the reception area of respective bands decided in advance, and it is outputted to a terminal 28 via respective circuits and an intermediate frequency filter 25, an intermediate frequency amplifier circuit 26. In other words, the input circuit for which plural numbers are required for each band independently in a conventional system can be used by sharing the amplifier element part of the circuit, arranging the variable tuning filters 7-9 in accordance with respective bands, and switching the variable tuning filter 7-9 corresponding to the reception band. For example, the variable tuning filter 8 is selected by band change-over switches 3, 30 for the band 11, and the variable tuning filter 9 for the band III.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input circuit of a television tuner which receives a television signal including a cable broadcast.

[0002]

2. Description of the Related Art With the development of cable broadcasting (hereinafter abbreviated as CATV), the frequency band in which a television signal can be received is VHF.
It is expanded so that it can be continuously received from the Low band to the UHF band.

Further, in recent years, an integrated circuit having active elements of a mixing circuit and an oscillation circuit capable of receiving this wide frequency band has been developed. Some of these integrated circuits have a mixing circuit and an oscillation circuit independently for each band.

In the prior art using an integrated circuit having a mixing circuit and an oscillation circuit independently for each band, is there a tunable filter independently for each band?
Alternatively, a method has been proposed in which the variable tuning filter and the amplification element are shared and the bandpass filter is divided and independent. (For example, Japanese Unexamined Patent Publication No. 2-58415) Prior art in which a variable tuning filter is independently present in each band, for example, in FIG. 2, when the band division is not substantially equal, the frequency band of each band The type of variable capacitance diode used can be changed according to the width, but in this case, an amplifier element is required for each band, and the circuit scale becomes large.

Further, when the variable tuning filter and the amplifying element shown in the above disclosed example are shared, the variable capacitance diode formed in each band is also shared, so that the band is divided into substantially equal parts. If this is not the case, a variable capacitance diode having a capacitance change ratio necessary for a wide variable range band must be adopted even in a narrow variable range band. In this case, in general, the variable resistance diode has a larger series resistance as the change ratio increases, so that it is characteristically to share the variable capacitance diode with a large change ratio in a band with a narrow variable range. It is a disadvantage.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to simplify the configuration of a plurality of input circuits respectively configured by using variable capacitance diodes having different change ratios and reduce the circuit scale.

[0007]

In order to achieve the above object, the present invention shares the amplifying element portion of a plurality of input circuits,
Arranging a plurality of variable tuning filters composed of variable capacitance diodes and inductors for determining the tuning frequency,
The variable tuning filter is switched by a switch according to each band.

[0008]

In the present invention, the circuit scale can be reduced by sharing the amplifying element section of a plurality of input circuits. Also, by switching a plurality of variable tuning filters according to each band, it is possible to select a variable capacitance diode according to the frequency band of each band, and the method of dividing each band can be selected relatively easily and freely. it can.

[0009]

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

FIG. 1 shows a block diagram of an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an input terminal of the tuner,
2, 3, 30 and 31 are switches for switching between bands I, II and III, 4 and 29 are input circuits, 7 and 8 and 9 are variable tuning filters of the input circuits, and 10 and 32 are high frequency amplification circuits of the input circuits. , 13, 14, 15 are inter-stage variable tuning filters, 16, 17, 18 are mixing circuits, 19, 20, 21 are oscillating circuits, 22, 23, 24 are tank circuits of respective oscillating circuits, and 25 is an intermediate frequency filter. , 26 are intermediate frequency amplifier circuits, and 28 is an output terminal. Here, each of the mixing circuit, the oscillation circuit, and the amplification circuit is a part of the integrated circuit 27.

A circuit is selected for the television signal input to the tuner in accordance with a predetermined reception band of each band, and an intermediate frequency filter 25 and an intermediate frequency amplification circuit 26 are used to pass through the respective circuits to obtain a terminal 28. Is output to. Here, for example, in the case of band I, the switch 2, the input circuit 4, the interstage variable tuning filter 13, the mixing circuit 16, the oscillation circuit 19, and the tank circuit 22 are selected, and in the case of band II, the switch 3, the input circuit 29, and the stage. Variable tuning filter 14, mixing circuit 17, oscillating circuit 20, tank circuit 23 are selected, and in case of band III, switch 3, input circuit 2
9, inter-stage variable tuning filter 15, mixing circuit 18, oscillation circuit 21, and tank circuit 24 are selected.

The feature of the present invention resides in the switch 30. The switch 30 commonly uses a plurality of input circuits individually required for each band, shares the amplification element section thereof, and arranges a plurality of variable tuning filters corresponding to the respective bands. The feature is that the tuning filter is switched. For example, in the case of band II, the variable tuning filter 8 is selected by the band changeover switches 3 and 30, and in the case of band III, the variable tuning filter 9 is selected by the above switch.

With this configuration, the input circuit, which conventionally requires a plurality of individual bands, can be greatly simplified, and when the bands are not divided into equal parts, the frequency bands of the respective bands are reduced. The variable tuning filter can be constructed by changing the type of variable capacitance diode used.

[0015]

According to the present invention, in a tuner for receiving a television signal including a CATV, a plurality of input circuits, which are conventionally required individually for each band, share the amplifying element section, By arranging a plurality of variable tuning filters according to the band and switching the variable tuning filters according to the reception band, the input circuit can be greatly simplified. Also, according to the frequency band of each divided band, it is possible to configure the variable capacitance diode of the variable tuning filter by changing the type of each band, and band division with good interference performance without impairing tracking performance. Can be done easily.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a tuner for receiving a television signal including a CATV according to the present invention.

FIG. 2 is a circuit block diagram of a tuner for receiving a television signal including a CATV according to the related art.

[Explanation of symbols]

1 ... tuner input terminal, 2, 3, 30, 31 ... band changeover switch 4,5, 6, 29 ... input circuit, 7,
Variable tuning filters 10, 11, 12, 32, ...
High frequency amplifier circuit, 13, 14, 15 ... Inter-stage variable tuning filter, 16, 17, 18 ... Mixing circuit, 19, 20, 21
... oscillation circuit, 22, 23, 24 ... tank circuit of each oscillation circuit, 25 ... intermediate frequency filter, 26 ... intermediate frequency amplification circuit, 27 ... integrated circuit including mixing circuit, oscillation circuit and intermediate frequency amplification circuit, 28 … Output terminal.

Front Page Continuation (72) Inventor Mitsuharu Yamashiro 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock Company, Hitachi Ltd. AV Equipment Division

Claims (2)

[Claims] 1. A television tuner for receiving a television signal including a cable broadcast by dividing it into at least two or more bands, and a common amplifying element section of an input circuit, and at least two or more variable input circuits. A tuning filter and a switch for switching the variable tuning filter of the input circuit are provided,
A tuner characterized in that the variable tuning filter is switched according to a band to be received. 2. A television tuner for receiving a television signal including a cable broadcast by dividing it into at least two or more bands, and an amplifying element section having a shared input circuit and at least two or more variable input circuits. A tuning filter and a switch for switching the variable tuning filter of the input circuit are provided,
A tuner comprising a variable capacitance diode having a variable capacitance change ratio according to a reception bandwidth of a band for receiving a variable capacitance diode forming each of the variable tuning filters.