JPH1188200A - Filter bank circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate capacitance which additionally occurs by means of a stub line by serially connecting plural change-over means provided with a common terminal and two output terminals so as to permit the common terminal of a rear stage change-over means to be electrically connected to one output terminal of a front stage change-over means and also grounding the other output terminal of the change-over means which is connected to the last. SOLUTION: A filter band circuit is provided with a first relay group where connection is serially executed by the lines L2, L3, L4,... Ln constituting the first relay group with a relay common terminal 33 and a relay output terminal 32 of relays K1, K2,... Kn constituting the first relay group and also the common terminal 32 of the relay Ln connected to the last is grounded and the second relay group like the first one. Low-pass filters FL1, FL2,...FLn are connected between the respective unconnected output terminals of the first and the second relay groups. Signals are inputted/outputted from the lines L1 and L1' which are connected to the common terminal 33 of the relays K1 and K1' arrayed at the first.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a filter bank circuit, and more particularly to a means for reducing manufacturing costs.

[0002]

2. Description of the Related Art In general, communication using short-wave frequency (hereinafter referred to as short-wave communication) has a communication quality that fluctuates in a short cycle due to a fading phenomenon peculiar to short-wave. Today, when communication becomes available, it seems to be worthless. However, short-wave communication uses the ionospheric reflection of radio waves, so it is the only frequency band in which long-distance communication can be realized without using satellites.Moreover, equipment costs are lower than satellite communication. It is still used for shortwave broadcasting for Japanese people and weather broadcasting for ships.

[0003] FIG. 2 is a functional block diagram showing a basic configuration example of a transmission output stage in a shortwave broadcasting facility. The transmission output stage shown in this figure is composed of a power amplifier 22 having a low-pass filter 21 connected to the output side, and an antenna 23 connected to the low-pass filter 21.

[0004] In addition to the desired signal, the signal output from the power amplifier 22 often includes spurious signals (unwanted signals) containing harmonic components due to the non-linear characteristics of the amplifier and noise generated inside the amplifier. When radiated from the antenna 23, a high-level spurious signal is transmitted together with the desired signal, causing interference such as interference. Therefore,
As shown in FIG. 2, a low-pass filter 21 is provided on the output side of the power amplifier 22 to remove spurious signals. In actual short-wave communication, usually about ten filters having different frequency characteristics are required for each communication channel, and the filters are switched according to the frequency (communication channel) to be used. A circuit in which a large number of filter groups having different frequency characteristics are arranged and a necessary filter is selected and used is referred to as a filter bank circuit.

FIG. 3 is a functional block diagram showing a configuration example of a conventional filter bank circuit. The filter bank circuit shown in FIG. 3 includes a plurality of relays K1, K2, K3,... Kn having two output terminals 31, 32 and a common terminal 33, which are connected to the lines L31, L32 via the one output terminal 31. , L33,... A first relay group connected in parallel by L3n and grounding all the other output terminals 32, and a plurality of relays similarly having two output terminals 31, 32 and a common terminal 33 K1 ′, K2 ′, K3 ′,.. .Kn ′ are connected to the lines L31 ′, L32 ′, L33 ′ through the one output terminal 31.
... a second relay group connected in parallel by L3n 'and grounding all of the other output terminals 32, and the relays are arranged in the same order, for example, K1 and K1', K2 and K2 ', Between the common terminals 33 of the low-pass filters FL1, FL2, FL3, ...
FLn is connected.

[0006] When a short-wave frequency band signal output from the power amplifier 22 is input to the input terminal 40, the filter bank circuit selects a filter that most effectively suppresses spurious signals by controlling each relay described below. Then, the spurious signal is removed using this filter, and only the desired signal is output from the output terminal 50.

[0007] For example, the operation when selecting the filter FL3 will be described.
K3 'common terminal 33 and one output terminal 31 are connected,
Other relays connect the common terminal 33 and the other output terminal 32. Therefore, the signal input to the input terminal 40 is
Since it is led to the output terminal 50 via the lines L36 and L35, the relay K3, the filter FL3, the relay K3 ', and the lines L35' and L36 ',
The spurious signal is removed by the filter FL3.

[0008]

However, the above-mentioned conventional filter bank circuit has the following problems. That is, the above-described filter FL3
Explaining using an example where is selected, the lines L31, L32, L33, L34, L37, L38, connected to the unselected filter
... L3n and L31 ', L32', L33 ', L34', L37 ', L38', ... L3
n 'is a line L36, L35 and L35', L36 'through which a desired signal is transmitted.
In contrast, the stub line (capacitance line) has an open end, and as a result, there is a problem that the capacitance of the stub line is added to the filter FL3 and the attenuation characteristics of the filter FL3 deviate from the design values. For this reason, it becomes necessary to readjust the attenuation characteristics of each filter at the manufacturing stage, and the number of manufacturing steps is significantly increased, which causes a problem such as an increase in cost. The present invention
A filter bank which has been made in order to solve the above-mentioned problem relating to the conventional filter bank circuit, which eliminates the capacity additionally generated by the stub line due to the filter switching, thereby eliminating the need for readjustment of the filter attenuation characteristics at the time of manufacturing. It is intended to provide a circuit.

[0009]

According to a first aspect of the present invention, there is provided a filter bank circuit according to the present invention, wherein a plurality of switching means having a common terminal and two output terminals are provided in a subsequent stage. A first switching unit group in which the common terminal of the switching unit and one output terminal of the switching unit in the preceding stage are connected in series so as to conduct, and the other output terminal of the switching unit connected to the rear end is grounded; A second switching means group having the same configuration as the first switching means group, comprising a switching means of the first switching means group and a switching means of the second switching means group via a filter means, The other output terminals are connected to each other, and a common terminal of the switching means arranged at the head of the first switching means group and the second switching means group is used as an input / output terminal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a functional block diagram showing an embodiment of a filter bank circuit according to the present invention. The filter bank circuit shown in this example has a plurality of relays K having two output terminals 31 and 32 and a common terminal 33.
1, K2, K3, ... Kn are the common terminal 33 and one output terminal 32.
A first relay group in which one terminal 32 of a relay Kn connected in series and connected to the rear end via lines L2, L3, L4,. , 32 and a plurality of relays K1 ′, K2 ′, K3 ′,.
Kn 'is connected in series with the lines L2', L3 ', L4', ... Ln 'via the common terminal 33 and one output terminal 32, and is connected to the last terminal of the relay Kn'. A second relay group with 32 grounded, for example, K1 and K1 ', K2 and K2',
Low-pass filter FL between the other output terminals 31
1, FL2, FL3, ..., FLn are connected. The input and output of signals are performed from the lines L1 and L1 'connected to the common terminal 33 of the relays K1 and K1' arranged first.

The filter bank circuit shown in FIG. 1 transmits the short-wave frequency band signal output from the power amplifier 22
When input to the input terminal 10 provided at the end of L1, a filter that most effectively suppresses spurious signals is selected by the control of each relay described later, and the spurious signals are removed using this filter, and the filter is connected to the end of the line L1 '. Only a desired signal is output from the output terminal 11 provided.

[0012] For example, the operation when the filter FL3 is selected will be described.
K3 'common terminal 33 and one output terminal 31 are connected,
The other relay connects the common terminal 33 and one output terminal 32. Therefore, the signal input to the input terminal 10 is
Track L1, Relay K1, Track L2, Relay K2, Track L3, Relay
Since the signal is led to the output terminal 11 via the K3, the filter FL3, the relay K3 ', the line L3', the relay K2, the line L2 ', the relay K1', and the line L1 ', the spurious signal is removed by the filter FL3.

At this time, in the filter bank circuit according to the present invention, the lines connected to the unselected filters are:
While being separated from the line related to the filter FL3 transmitting the desired signal by the relays K3 and K3 ′, one output terminal 32 of the relays Kn and Kn ′ connected to the end of the series connection is grounded. Therefore, even if the isolation characteristics between the common terminal 33 and the output terminal 32 in the relays K3 and K3 'are poor and the signal leaks to the lines below L4 and L4', the stub line does not have an open end. Therefore, no additional capacitance due to the stub line is generated, so that the problem that the attenuation characteristic of the filter FL3 deviates from the design value due to the stub line capacitance can be prevented.

[0014] By arranging the filters in ascending order of the cutoff frequency, the filters FL1 and FL2 will
Since the cut-off frequency is lower than 3, the isolation characteristics between the common terminal 33 and the output terminal 31 of the relay are poor, and even if a signal leaks to the output terminal 11 via FL1 and FL2, FL
3 does not disturb the damping characteristics.

The case where the filter FL3 is selected has been described above. However, even if any other filter is selected, no capacitance due to the stub line is generated for the above-described reason.

In the above-described embodiment of the present invention, a configuration using a relay as the switching means has been described. However, a semiconductor element such as a PIN diode may be used as the switching means.

[0017]

According to the present invention, as described above, a filter bank circuit is constituted by using the first switching means group and the second switching means group including switching means such as relays connected in series and the filtering means. Therefore, it is possible to prevent the line connected to the unselected filter means from becoming a stub line and generating unnecessary capacitance, and thus readjustment of each filter characteristic at the time of manufacturing which was necessary for the stub line capacitance. Is unnecessary, which is very effective in realizing a filter bank circuit with reduced manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing an embodiment of a filter bank circuit according to the present invention.

FIG. 2 is a functional block diagram illustrating a basic configuration example of a transmission unit in a shortwave broadcasting facility.

FIG. 3 is a functional block diagram illustrating a configuration example of a conventional filter bank circuit.

[Explanation of symbols]

FL1, FL2, FL3,... FLnLow-pass filter K1, K2, K3,.. .Kn Relays constituting the first relay group K1 ', K2', K3 ',. Kn '··· Relays constituting the second relay group L1, L2, L3,... · Ln ··· Lines L1', L2 ', L3', ···· Ln 'constituting the first relay group ..Lines constituting the second relay group 10 ... Input terminals 11 ... Output terminals 31, 32 ... Relay output terminals 33 ... Relay common terminals

Claims (1)

[Claims] A plurality of switching means having a common terminal and two output terminals are connected in series so that a common terminal of a switching means in a subsequent stage and one output terminal of a switching means in a preceding stage are connected to each other, and are connected at the end. A first switching means group in which the other output terminal of the connected switching means is grounded, and a second switching means group having the same configuration as the first switching means group, wherein the first switching means The switching means of the group and the switching means of the second switching means group are connected via filter means to the other output terminals, respectively, at the beginning of the first switching means group and the second switching means group. A filter bank circuit, wherein a common terminal of the arranged switching means is an input / output terminal.