JPH0577214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a filter circuit for a tuner consisting of a plurality of filters that divides a signal band such as a television signal into a plurality of signal bands. Concerning a small number of filter circuit configurations.

[Background of the invention]

Regarding filter circuits consisting of a plurality of filters that divide signal bands, a circuit is known in which switching diodes are provided at the input and output of each filter to select the receiving band, as shown in Japanese Patent Laid-Open No. 60-74731. ing.

This circuit is effective when the reception frequency is low, but in frequency bands above the UHF band, sufficient separation between the filters cannot be obtained, and the influence of other bands appears within the passband, resulting in large losses. , the characteristics deteriorate.

[Purpose of the invention]

The purpose of the invention is to eliminate the drawbacks of the prior art,
It is an object of the present invention to provide a filter circuit which is less influenced by other filters even in high frequency bands such as the UHF band, and therefore has good characteristics.

[Summary of the invention]

In order to increase the isolation between the filters, the inputs and outputs of the filters having successive reception bands, which have a particularly large influence, are connected through a series connection of two or more non-conducting diodes.

[Embodiments of the invention]

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

FIG. 1 shows a filter circuit used at the input of a tuner that receives CATV signals of 50 to 80 MHz. In FIG. 1, 1 is a signal input terminal, and 2 is an output terminal. 3 to 7 are current terminals, and filters 8 to 1
2, the switching diodes 13 to 26 are switched into conduction and non-conduction states. 27 and 28 are bypass capacitors for cutting off direct current, 29 to 33 are bypass capacitors for grounding, and 34 to 50 are bias resistors. Filters 8 to 11 are band pass filters, and filter 12 is a high pass filter, and their respective circuit configurations are shown in FIGS. 2 and 3. In the bandpass filter shown in FIG. 2, 51 is an input terminal, 52 is an output terminal, and 53 is a ground terminal. In addition, 54 to 57 are capacitors, 58 to 61
is a coil. In the high-pass filter shown in FIG. 3, 62 is an input terminal, 63 is an output terminal, and 64 is an input terminal.
is the ground terminal. Further, 59 to 69 are capacitors, and 70 and 71 are coils. The reception passband is 54~96MHz for filter 8 and 96~96MHz for filter 9.
168MHz, filter 10 270~450MHz, filter 11 168~270MHz, filter 12 450MHz
~800MHz. The operation of the filter circuit is, for example, when operating the filter 10, a voltage is applied to the terminal 5, and the switching diode 17,
18, 23, and 25 become conductive, and the other switching diodes become non-conductive. the result
The 270-450MHz signal passes through the filter circuit.
The operation is similar when receiving signals in other bands.

With such a configuration, for example, in the case of filter 10 and filter 11 in which the pass bands are continuous, switching diodes 19, 24 and 2 are connected to filter 11 when filter 10 is in operation.
0,26 becomes a non-dynamic state, and filter 1
During zero operation, switching diodes 17, 23 and 18, 25 are non-conductive with respect to filter 10. In this way, filter 10 and filter 1
Since two reverse biased switching diodes are connected in series between the input terminal and the output terminal of the filter, the degree of separation between the two filters is increased. Similarly, two reverse biased switching diodes are connected in series between filters 10 and 12 or between filters 9 and 11, resulting in a configuration that increases separation between filters with continuous passbands. ing.

FIG. 4 shows the attenuation characteristics of the circuit of FIG. 1.
When there is one reverse biased switching diode between the input or output of a conventional filter, the influence of the adjacent filter at high frequencies in the UHF band causes a 1 to 2 dB difference within the passband.
However, in the filter circuit configuration of the present invention, the influence of other filters is small, no traps occur in the passband, and good characteristics are obtained.

Although the example of FIG. 1 shows the case of five filters, two reverse biased switching diodes can be connected between the inputs and outputs of filters with continuous passbands regardless of the number of filters. Bye. Furthermore, it goes without saying that if the number of switching diodes reversed in direction is three or more, the separation between both filters can be further ensured.

〔Effect of the invention〕

According to the present invention, sufficient separation from adjacent filters that have a large influence on the characteristics within the receiving band can be obtained even in a high frequency band, so that a filter with good characteristics can be provided.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a filter circuit of the present invention that divides a signal band by a plurality of filters, Figs. 2 and 3 are circuit diagrams of a filter used in the embodiment of Fig. 1, and Fig. 4 is an embodiment. FIG. 3 is a characteristic diagram showing the attenuation characteristics when the filter circuit of FIG. 8-12...Filter, 13-26...Switching diode.

Claims (1)

[Claims] 1 at least first and second filters whose pass bands are different from each other and whose normal bands are adjacent and continuous; and two filters connected between the input terminal of the first filter and the signal input terminal and connected in series in the forward direction to each other. a first switching diode consisting of diodes, and a first switching diode connected between the output terminal of the first filter and the signal output terminal and connected in series in the forward direction and in the same direction as the first switching diode. a second switching diode consisting of two diodes; and a second switching diode connected between the input terminal of the second filter and the signal input terminal, connected to each other in the forward direction, and having the same orientation as the first switching diode. a third switching diode consisting of two directionally connected diodes;
two switching diodes connected between the output terminal of the filter and the signal output terminal, connected in series in the forward direction, and connected in the same direction as the third switching diode.
A filter circuit comprising a fourth switching diode consisting of four diodes.