JPS6031369B2 - Amplitude equalization circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplitude equalization circuit suitable for equalizing amplitude distortion caused by fading in, for example, wireless communication.

The conventional amplitude equalization circuit has an input terminal 11 as shown in FIG.
A variable resistance element 13 is connected between the output terminal 12 and the output terminal 12 for adjusting the sharpness of the equalization characteristic.

A distributed constant line 14 of 1/the umbrella skin length of the center frequency of fading is connected between the output terminal 12 and a common terminal, that is, ground. A low output impedance signal source 15 is connected between the input terminal 11 and the common terminal. In this conventional circuit, the length of the line 14 must be changed as the fading center frequency changes. Therefore, an actual amplitude equalization circuit is composed of a coil 16 and a variable capacitor 7 as shown in FIG.

A series resonant circuit 18 is inserted in series between the line 14 and the common terminal. By changing the capacitance of the variable capacitor 17 and changing the resonant frequency of the resonant circuit 18, the length of the line 14 is equivalently changed. In the conventional circuit shown in FIG. 2, in order to increase the line length variable range, the resonant frequency of the series resonant circuit 18 must be changed greatly, that is, the inductance of the coil 16 and the capacitance of the capacitor 17 must be changed. The width must be increased.

However, it is difficult to obtain an element that can electrically change the inductance and can be used above the VHF band, and the range of change in the resonant frequency is determined by the range of change in the capacitance of the capacitor 17. For this reason, the actual situation is that it is not possible to equivalently change the line length significantly. In other words, when the center frequency of actual fading varies over a wide band, the amplitude distortion cannot be equalized. From this point, a variable capacitance element is connected between at least one of the input terminal and output terminal of the distributed constant line and the common terminal, and the capacitance value of the capacitance element is changed to change the center frequency of the amplitude equalization characteristic. It is proposed that

For example, as shown in FIG. 3 with the same reference numerals assigned to parts corresponding to those in FIG. ) 21 and 22 are connected, respectively. The common terminal side of the line 14 is connected to a voltage input terminal 24 for controlling a variable capacitance diode through a choke coil 23 for blocking an AC signal. In this example, variable resistance element 1
In this case, a Pm diode is used as the Pm diode, and DC blocking capacitors 25 and 26 are inserted in series at both ends of the Pm diode. Connection points between the capacitor and the PIN diode are connected to voltage input terminals 29 and 31 for controlling the PIN diode through AC signal blocking choke coils 27 and 28, respectively. Line 14 and variable capacitance diode 2
A DC blocking capacitor 32 is inserted in series between the connection point 1 and the output terminal 12. The input-output amplitude characteristic (■) of the circuit shown in FIG. 3 is expressed by the equation '1}. ), the resistance value of the PIN diode 13 is R, each capacitance of the variable capacitance diodes 21 and 22 is C, the characteristic impedance of the line 14 is Zo, its length is 1, the phase constant is 8, and there is no loss. Suppose there is. This characteristic day (mountain) is P
Resistance R of IN diode 13, variable capacitance diode 21
, 22 are changed as shown in FIGS. 4 and 5, respectively.

That is, by applying a control voltage between the terminals 29 and 31 and changing the resistance R of the PIN diode 13, the sharpness of the fading equalization characteristic can be changed as shown in FIG. By adding C and changing the capacitance C of the variable capacitance diodes 21 and 22, the center frequency of the fading equalization characteristic can be changed as is clear from FIG. On the other hand, the input-output amplitude characteristic H' of the subordinate circuit shown in FIG. 2 is expressed by equation '2}.

), the resistance value of the variable resistance element 13 is R, and the series resonant circuit 1 is
It is assumed that the inductance and capacitance of the coil 16 and capacitor 7 of 8 are L and C, respectively, the characteristic impedance of the line 14 is Zo, the length is 1, the phase constant is 8, and there is no loss. In this case, the center frequency of the writing characteristic can be found from [1} and equation (2) as follows.

In the case of the circuit shown in Fig. 3, B. C.

S81-(shin-sai)SinG1=o'4) By comparing these two equations, the inductance of the coil in the circuit of FIG. 2 can be expressed as C.Z in the circuit of FIG. That is, in the circuit shown in FIG. 3, by changing the capacitance C, the inductance of the coil 16 can be equivalently changed. As a result, compared to the circuit of FIG. 2, the circuit of FIG. 3 can vary the center frequency over a wider range. However, as shown in Figure 6, the amplitude characteristics of the circuit shown in Figure 3 have an anti-resonance point approximately midway between the center frequency fo and the zero frequency (DC), and the amplitude characteristics due to fading occur near this frequency. cannot be converted into

That is, in Fig. 6, △F2/2 is centered around the center frequency et al.
It is possible to equalize the band, but if △f is a frequency that is greater than the frequency difference between the anti-resonance frequency and the center frequency fo, equalization can be performed over a band of △F, /2 with fo as the center. There is a drawback that it cannot be done. The purpose of this invention is to provide an amplitude equalization circuit that can change the center frequency over a wide frequency band, eliminate the anti-resonance point that occurs between the center frequency and zero frequency (DC), and equalize over a wide frequency band. Our goal is to provide the following.

According to this invention, a variable resistance element is connected between an input terminal and an output terminal, a distributed constant line is provided between one of the input terminal and output terminal and a resonant terminal, and the input terminal and the output of the distributed constant line are A variable capacitance element is connected between at least one of the terminals and the common terminal, and an inductance element is connected in parallel with the variable capacitance element. . The impedance of this inductance element is selected to be sufficiently larger than the impedance of the surrounding circuit, that is, the impedance of the variable capacitance element connected in parallel. Since the impedance of the inductance element becomes small at frequencies lower than the center frequency, insertion loss between input and output becomes large, and the anti-resonance frequency does not occur. For example, as shown in FIG. 7 with the same reference numerals assigned to parts corresponding to those in FIG. 3, in the present invention, a coil 33 is connected as an inductance element in parallel with the variable capacitance diode 22 via a DC blocking capacitor 34.

The inductance value of the coil 33 is near the frequency L
The impedance of the coil 33 is selected so as to be sufficiently large compared to the impedance of the surrounding circuit. In this way, the amplitude characteristic between the input and output of the circuit shown in FIG. 7 becomes equal to the amplitude characteristic between the input and output when the coil 33 is not provided. On the other hand, since the impedance of the coil 33 is zero at zero frequency (DC), the insertion loss between the input and output of the equalization circuit shown in FIG. 7 becomes large near the fog frequency.

This situation is shown in FIG. In this case, the solid line is the amplitude characteristic between each input and output when the coil 33 is provided, and the broken line is the amplitude characteristic when the coil 33 is removed. In this way, the coil 33 acts to eliminate the anti-resonance point located between the center frequency fo and the droplet frequency without changing the characteristics near the center frequency fo. As a result, the equalization circuit of the present invention including the coil 33 can equalize fading over a wide frequency range around the center frequency fo. Moreover, the variable capacitance elements 21, 2
By changing the capacitance value of 2, the center frequency fo can be changed over a wide frequency range as described above. The circuit of FIG. 9, which is relative to the circuit of FIG. 7,
That is, it is clear that the same effect as described above can be obtained even if the distributed constant line 14 is connected to the input terminal 11 side. In the example shown in FIGS. 7 and 9, the above effect is not impaired even if the variable capacitance diodes 21 and 22 are not made equal in capacitance and change in capacitance and are used with different characteristics. Furthermore, an inductance element 33 may be connected in parallel with the variable capacitance diode 21. Also, variable capacitance diode 2
Separate inductance elements may be connected to both 1 and 22, respectively. Further, the variable capacitor on either the input side or the output side of the distributed constant line 14 may be omitted.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of a conventional amplitude equalization circuit, Fig. 2 is a circuit diagram showing a conventional amplitude equalization circuit, Fig. 3 is a circuit diagram showing an example of a proposed amplitude equalization circuit, and Fig. 4 is a circuit diagram showing an example of a proposed amplitude equalization circuit. The figure is a curve diagram showing how the input/output amplitude characteristics change when the resistance value R of the variable resistance element 13 is changed in the circuit of Figure 3.
Curve diagram 6 showing how the input/output amplitude characteristics change when the capacitance value of the variable capacitance diode is changed in the circuit shown in the figure.
The figure is an input/output characteristic curve diagram of the circuit in Figure 3, Figure 7 is a circuit diagram showing an example of an amplitude equalization circuit according to the present invention, and Figure 8 is a curve diagram showing input/output amplitude characteristics of the circuit in Figure 7. , FIG. 9 is a circuit diagram showing an example of a circuit that is in a relative relationship with the circuit shown in FIG. 11... Input terminal, 12... Output terminal, 13... Variable resistance element, 14... Distributed constant line, 15... Signal line, 21, 22...
...Variable capacitance element, 23, 27, 28...Choke coil for signal blocking, 24...Variable capacitance diode control voltage input terminal, 29,31...P
IN diode control voltage input terminal, 25, 26, 32
~34...DC blocking capacitor. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1. In an amplitude equalization circuit having an input terminal, an output terminal, and a common terminal, and having a certain amplitude equalization characteristic, the variable resistance element connected between the output terminal and the output terminal; a distributed constant line provided between the terminal or between the output terminal and the common terminal;
a variable capacitance element connected between at least one of the input terminal and output terminal of the distributed constant line and the common terminal; An amplitude equalization circuit comprising an inductance element having an impedance larger than the impedance of the capacitance element.