JP2003229791A - Equalizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To widen the bandwidth of an equalizer. <P>SOLUTION: An equalizer comprises resistors 8 and 10 of a T-tipe resistor attenuator 2, which are connected in series between an input terminal 4 supplied RF signals in a wide frequency band and an output terminal 6, and a resistor 12, which is connected between an interconnection point of the resistors 8 and 10 and a reference potential point. A serial resonant circuit 14 is connected in shunt with the resistors 8 and 10, the resonance frequency is set to an upper side frequency in the wide frequency band. The resistor 12 and a parallel resonant circuit 20 are connected in series, and the resonant frequency is set to a lower side frequency in the wide frequency band. Capacitors 26 and 28 are connected in shunt with the resistors 8 and 10. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equalizer (equalizer) for improving the frequency characteristic of a high-frequency signal whose frequency characteristic has been displaced due to transmission through a coaxial cable in, for example, a joint hearing system. .

[0002]

2. Description of the Prior Art The equalizers described above are often used, for example, in relay amplifiers that are interposed in the lines of a joint hearing system. By the way, the digitization of the joint hearing system is imminent. In digitization, it is necessary to widen the band of the relay amplifier. For example, conventionally, it was sufficient to be able to amplify a high frequency signal of 70 MHz to 450 MHz.
To 770 MHz, the relay amplifier needs to be able to amplify. Moreover, the specifications of the relay amplifier are the same as before, and there is a demand for wider bandwidth. Along with this, the conventional equalizer circuit cannot satisfy the new standard, and it is necessary to widen the band.

FIG. 2 shows an equalizer circuit which has been conventionally used. The conventional equalizer circuit includes a T-type resistance attenuator 2. This T-type resistance attenuator 2 is
First connected in series between the input terminal 4 and the output terminal 6
And a second resistor, for example resistors 8 and 10. A third resistor such as a resistor 12 is connected between the interconnection point of these resistors 8 and 10 and a reference potential point such as a ground potential point. These resistors 8, 10, 1
2 has the same resistance value, for example.

A series resonance circuit 14 is provided in parallel with the resistors 8 and 10.
Are connected. The series resonance circuit 14 is composed of, for example, a series circuit of a reactor 16 and a capacitor 18. The resonance frequency of the series resonance circuit 14 is set to a frequency near 450 MHz, for example. A parallel resonance circuit 20 is connected in series with the resistor 12. The parallel resonance circuit 20 is composed of, for example, a parallel circuit of a reactor 22 and a capacitor 24. The resonance frequency of the parallel resonance circuit 14 is set to, for example, about 70 MHz.

In this equalizer, for example, 450 MHz
In the vicinity, since the series resonance circuit 14 resonates in series, 45
A high frequency signal near 0 MHz is transmitted from the input terminal 4 to the output terminal 6 with almost no attenuation. on the other hand,
In the vicinity of 70 MHz, the parallel resonant circuit 20 resonates in parallel, so that the high-frequency signal from the input terminal 4 is transmitted through the resistors 8, 10
Almost passes through and is greatly attenuated. A high frequency signal from around 450 MHz to around 70 MH has a frequency characteristic of being attenuated between a state where it almost passes and a state where it is almost attenuated according to its frequency. The outline of this frequency characteristic is shown by the solid line in FIG. The curve characteristic of this frequency characteristic is the reactor 16, 22, the condenser 18, 24.
Is determined by the value of. The dotted line in FIG. 4 shows the ideal frequency characteristic of the equalizer circuit.

[0006]

In such an equalizer, when the values of the reactors 16 and 22 and the capacitors 18 and 24 are changed in order to cope with the above-mentioned wide band, the curve characteristics deviate from the ideal values. The characteristic shown by the dotted line in FIG. 2 is present, and there is a problem that the curve characteristic is less bulged at low frequencies and the curve characteristic is bulged too much at high frequencies.

It is an object of the present invention to provide an equalizer which can obtain a desired characteristic even if the band is widened.

[0008]

The equalizer according to the present invention has an input terminal, an output terminal, and a reference potential point. A high frequency signal in a wide frequency band is supplied to the input terminal. Further, the equalizer has a T-type resistance attenuator. The T-type resistance attenuator includes first and second resistors connected in series between the input terminal and the output terminal, and further includes an interconnection point of the first and second resistors. It also includes a third resistor connected to the reference potential point. A series resonance circuit is connected in parallel with the first and second resistors. This series resonance circuit has a series resonance frequency at an upper frequency in the broadband frequency band. A parallel resonant circuit is connected in series with the third resistor. The parallel resonant circuit has a parallel resonant frequency at a lower frequency in the broadband frequency band. First
And reactance means are connected in parallel to the second resistor and the second resistor, respectively.

In the equalizer thus constructed, by providing the reactance means, each resonance frequency of the series resonance circuit and the parallel resonance circuit can be deviated from each resonance frequency of the base. Further, the Q of both resonance circuits can be set to a value different from the original Q. Therefore, an equalizer having a desired frequency characteristic over a wide band can be realized by appropriately selecting the reactance means.

As the first and second reactance means,
Capacitive means can be used. As capacity means,
Fixed or variable capacitors can be used. By using the capacitive means, the capacitive means is connected in parallel to the series resonant circuit,
The resonance frequency is higher than the original frequency, and Q is large. Therefore, the curve of the frequency characteristic at a high frequency becomes sharper than the curve of the original frequency characteristic and becomes closer to the desired curve. Further, the capacitance means is connected in series to the parallel resonance circuit, the resonance frequency is higher than the original frequency, and Q becomes large. Therefore, the curve of the frequency characteristic at a low frequency becomes sharper than the curve of the original frequency characteristic, and becomes closer to the desired curve.

Further, the capacitance value of the capacitance means connected in parallel with the first resistor can be set smaller than the capacitance value of the capacitance means connected in parallel with the second resistor.
In this case, at high frequencies, the capacitance means with a small value connected to the first resistor mainly functions to affect the frequency characteristics at high frequencies. At low frequencies, the high-value capacitive means connected to the second resistor mainly function to influence the frequency characteristics at low frequencies.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Similarly to the conventional equalizer shown in FIG. 3, the equalizer according to the first embodiment shown in FIG.
Resistance attenuator 2, series resonant circuit 14 and parallel resonant circuit 2
It has 0. However, the series resonance circuit 14 has a wide band,
For example, in the band 70 MHz to 770 MHz used in the digitized CATV, the upper frequency,
For example, the parallel resonant circuit 20 has a resonant frequency near 770 MHz, and the parallel resonant circuit 20 has a lower frequency in the band, for example, 70 MHz.
It has a resonance frequency near MHz.

Further, the resistors 8, 10 of the T-type resistance attenuator 2 are
Further, a reactance means, for example, a capacitance means, specifically, fixed capacitors 26 and 28 are connected in parallel. The value of the fixed capacitor 26 connected in parallel with the resistor 8 is set smaller than the value of the fixed capacitor 28 connected in parallel with the resistor 10. For example, the value of the capacitor 26 is set to 2.5 pF, and the capacitor 28
The value of is set to 20 pF, which is set to a value of 8 times. The value of the capacitor 26 is substantially equal to the value of the capacitor 18 of the series resonance circuit 14, and the value of the capacitor 28 is larger than the value of the capacitor 18 and is 10 times. Further, the value of the capacitor 28 is equal to that of the capacitor 2 of the parallel resonance circuit 20.
It is larger than 4 and about 13 times.

By the way, for example, the value of the resistor 8 is 47Ω,
The value of the resistor 10 is set to 51Ω and the value of the resistor 12 is set to 56Ω. The value of the capacitor 18 of the series resonance circuit 14 is set to 2 pF and the value of the same reactor is set to about 20 pH. The value of the capacitor 24 of the parallel resonance circuit 20 is 1.5p.
The reactor 22 is set to F and the value of the reactor 22 is set to about 3 nH.

In the equalizer thus constructed, since the capacitors 26 and 28 are provided, the resonance frequency of the series resonance circuit 14 changes. Since the capacitors 26 and 28 are connected in parallel to the series resonance circuit 14, the frequency of the series resonance circuit 14 is greatly influenced by the capacitor 26 having a small value, and the series resonance frequency is set to a high frequency side. , And increase the Q value.
As a result, the portion indicated by the symbol a in the frequency characteristic of the conventional equalizer as shown by the dotted line in FIG. 2 is the same as the portion indicated by the symbol b in the frequency characteristic of this equalizer as shown by the solid line in FIG. In addition, there is little bulge and it becomes sharp.

Further, since the capacitors 26 and 28 are provided, the resonance frequency of the parallel resonance circuit 20 also changes. Since the capacitors 26 and 28 are connected in series to the parallel resonant circuit 20, the capacitor 28 having a large value has a great influence on the frequency of the parallel resonant circuit 20, and the parallel resonant frequency is moved to the lower side. . In addition, the value of Q is increased. As a result, the portion of the frequency characteristic of the conventional equalizer shown by the dotted line in FIG. 2 is indicated by the symbol c, and the portion of the frequency characteristic of this equalizer indicated by the solid line in the same diagram is indicated by the symbol d. Moreover, the bulge is small and it becomes sharp.

In the above-mentioned embodiment, as the capacitance means,
The fixed capacitors 26 and 28 are used, but variable capacitors can also be used. In this case, the bulge of the portions indicated by the reference signs b and d can be changed by changing the value of the variable capacitor.

[0018]

As described above, according to the present invention, a desired frequency characteristic can be obtained even with an equalizer for a wideband high frequency signal.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an equalizer according to an embodiment of the present invention.

FIG. 2 is a frequency characteristic diagram when the equalizer of FIG. 1 and a conventional equalizer have a wide band.

FIG. 3 is a circuit diagram of a conventional equalizer.

4 is a frequency characteristic diagram of the equalizer of FIG.

[Explanation of symbols] 2 T type resistance attenuator 8 10 12 resistors 14 Series resonance circuit 18 Parallel resonance circuit 26 28 Capacitor (capacity means)

Claims (3)

[Claims] 1. A first terminal and a second terminal connected in series between an input terminal to which a high-frequency signal in a wide frequency band is supplied, an output terminal, a reference potential point, and the input terminal and the output terminal. First resistor, and a third resistor connected between the interconnection point of the first and second resistors and the reference potential point, and Connected in parallel to the resistor and having a series resonance frequency at an upper frequency in the broadband frequency band, and a series resistor connected in series with a third resistor to a lower frequency in the broadband frequency band. An equalizer comprising: a parallel resonance circuit having a parallel resonance frequency; and reactance means connected in parallel to each of the first and second resistors. 2. The equalizer according to claim 1, wherein the first and second reactance means are capacitive means. 3. The equalizer according to claim 2, wherein the capacitance value of the capacitance means connected in parallel with the first resistor is smaller than the capacitance value of the capacitance means connected in parallel with the second resistor. The equalizer that has been set.