JPS6226601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable
It concerns an amplitude equalizer.

Generally, the characteristics, distortion, etc. of a transmission path are not fixed and often involve some kind of variation. For example, amplitude distortion occurs and fluctuates due to selective fading in a wireless transmission path. For example, an automatic amplitude equalizer is required to automatically remove such distortion and maintain the transmitted signal quality. This type of equalizer is often used in digital signal transmission systems, and generally consists of several delay lines connected in series that are equal to the reciprocal of the signal transmission speed in the baseband band, and each connection point (tap), the equalizer (Principles of Data
``Communications'' 1968, published by Mc Graw-Hill (Chapter 6)) is well known. However, since this equalizer performs control by varying the gain of each tap, as the number of taps increases, the circuit size becomes enormous, and the amount of delay is the reciprocal of the data transmission speed. The same selection must be made. Therefore, it cannot be applied as is to a system in which the transmission speed is close to the reciprocal of this delay amount, and it lacks versatility.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate these drawbacks and provide a delay-free distortion amplitude equalizer that has a small circuit scale and is independent of transmission speed.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of an amplitude equalization circuit according to the present invention. In FIG. 1, 1 and 3 are signal branching circuits, 4 and 7 are signal combining circuits, 2 and 5 are delay circuits having the same amount of delay, and 6 is a variable attenuation circuit. Here, the input signal supplied to the input terminal 101 is e ^j 〓 ^t , and the delay circuit 2,
The delay time at 5 is τ. α is the attenuation amount in circuit 6, and the signals at connection points 104 and 105 are respectively
If A ₁ and B ₁ , then A ₁ = α{e ^j 〓 ^t + e ^j 〓 ^(t-2 〓 ⁾ } …(1) B ₁ = e ^j 〓 ^(t- 〓 ⁾ …(2) , the signal at the connection point 106 is C ₁ =A ₁ +B ₁ =e ^j 〓 ^(t- 〓 ⁾ × {1+α(e ^j 〓 ^t +e ^-j 〓 ^t )} = e ^j 〓 ^t ×e ^-j 〓 ^t { 1+2αcosωt} …(3).

Therefore, the transmission characteristic (transfer function) T ₁ (ω) from the input to the output is T ₁ (ω)=(1+2αcosωτ)e ^−j 〓〓 (4). Here, the characteristic functions of amplitude, phase and delay time are S ₁ (ω), θ ₁ (ω) and D ₁
(ω), then T ₁ (ω)=S ₁ (ω)・e ^j 〓 ¹⁽ 〓 ⁾ …(5) S ₁ (ω)=1+2αcosωτ …(6) θ ₁ (ω)=−ωτ …( 7) D ₁ (ω) = −αθ ₁ (ω) / αω = τ (constant) ...(8) Therefore, if α changes, S ₁ (ω) will change, but θ ₁ (ω) will change to α , does not depend on ω, so D ₁
(ω) is always constant and does not cause delay distortion.
In other words, only the amplitude versus frequency characteristics can be equalized without causing any delay distortion. As a design example, when designing an amplitude equalizer that can be used in the frequency domain (band) of frequencies ₁ to ₂ ( ₂ > ₁ ), an equalizer that generates a positive first-order slope should have τ ₁ = 1 /2 ₁ , as an equalizer that generates a negative first-order slope, τ ₂ = 1/2 ₂ , positive 2
As an equalizer that generates the next curvature component, τ ₃ =
It is sufficient to design three types of equalizers that are 1/( ₁ + ₂ ).

Figure 2 shows S ₁ when changing the attenuation rate α.
It is a figure showing the movement of (ω). 0~π and π~
negative and positive first-order slopes in the 2π region, respectively;
The ranges of -π/2 to π/2 and π/2 to 3π/2 are ranges that can be used as positive and negative second-order or high-order curvature equalizers, respectively. As is clear from the figure, the present invention can be easily extended to an automatic amplitude equalization circuit by simply varying α.

FIG. 3 shows an example of this. 21, 22, and 23 each have the same configuration as in FIG. 1, and by selecting τ, they can be set as amplitude equalizers for a positive first-order slope, a negative first-order slope, and a positive second-order curvature. It is something that 8 is an AGC amplifier; 9 is a circuit that detects transmission distortion by detecting the shape of the spectrum of the received signal and controls the equalizers 21 to 23; 201 is an input terminal; and 202 is an output terminal.

FIG. 4 is a block diagram of a specific circuit of the control circuit 9. 10, 11, and 12 have center frequencies of ( ₀ + ₁ ), ( ₀ - ₁ ), and _0, respectively.
(where ₀ is the center frequency of the signal band and ₁ is an appropriate frequency), 13, 14 and 15 are level detectors, 16 and 17 are differential amplifiers, and 18 to 20 are resistors. be.

FIG. 5 shows the amplitude versus frequency characteristics of wave generators 13, 14, and 15. However, B is the signal bandwidth.
The differential amplifier 16 compares the outputs of the level detectors 13 and 14, that is, the signal components (signal power) on the low frequency side and the high frequency side of frequency ₀ , extracts the difference, and outputs 1
An output X is output according to the next slope and its polarity. On the other hand, the differential amplifier 17 is connected to the level detector 1
By comparing the average value of the outputs of 3 and 14 with the output of the level detector 15, that is, the signal component near frequency ₀ , and extracting the difference, depending on the second-order and higher-order curvature components and their polarities, Outputs output Y.
In addition, when equalizing only the first-order slope, use wave generator 1.
2. Detector 15 and differential amplifier 17 are not required;
Also, when equalizing only the second-order and higher-order curvatures,
Differential amplifier 16 is not required. Differential amplifier 1
The output signals X and Y of 6 and 17 are selectively, respectively,
A variable attenuator (FIG. 1) to be controlled is supplied.

As explained above, according to the present invention, by appropriately selecting the delay time (τ) and varying the attenuation rate (α), the required frequency range and maximum equalized amplitude can be arbitrarily set. An amplitude equalization circuit is obtained. Furthermore, it is also possible to obtain an automatic amplitude equalization device that can automatically select an equalization region and equalization characteristics as necessary. Moreover, since the delay is flattened over the entire band, it is also suitable for equalizing second-order and higher-order curvatures.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the variable equalizer section according to the present invention, FIG. 2 is an amplitude characteristic diagram when the delay amount is constant and the attenuation rate is varied, and FIG. 3 is an automatic equalizer according to the present invention. 4 is a block diagram of an embodiment of the equalizer, FIG. 4 is a block diagram of an embodiment of the control circuit in FIG. 3, and FIG. 5 is a block diagram of an embodiment of the control circuit in FIG.
It is a characteristic diagram of ~12. In addition, in the figure, 1 and 3 are signal branch circuits,
4 and 7 are signal synthesis circuits, 2 and 5 are delay circuits, 6 is a variable attenuator, 8 is an automatic gain control amplifier, 9 is a control circuit, 10 to 12 are wave generators, 13 to 15 are level detection circuits, 16, 17 is a differential amplifier, 18-20
is a resistor, and 21 to 23 are equalizers.

Claims (1)

[Scope of Claims] 1. A variable amplitude equalizer that equalizes a signal having amplitude distortion characteristics within a certain frequency band, comprising a first means for branching the signal into two, and one of the first means. a second means connected to the output of the second means and having a delay time determined by the frequency band; a third means for branching the output signal of the second means into two;
a fourth means connected to one output of the means and having the same delay time as the delay time; and a fifth means for synthesizing the other output of the first means and the output of the fourth means. , a sixth means for variably attenuating the output of the fifth means, and a seventh means for synthesizing the other output of the third means and the output of the sixth means to generate an equalized signal. An amplitude equalizer comprising: 2. An amplitude equalizer having an input signal terminal that receives a signal having an amplitude distortion characteristic within a certain frequency band, an output terminal, and an amplitude versus frequency characteristic that equalizes the amplitude distortion characteristic; A second amplitude equalization means is provided in series between the input signal terminal and the output signal terminal, and each of the amplitude equalization means is connected to a first means for branching the signal into two;
a second means connected to one output of the means and having a delay time determined by the frequency band;
a third means for branching the output of the means into two; a fourth means connected to one output of the third means and having a delay time equal to the delay time; and the other output of the first means. and the output of the fourth means, a sixth means for variably attenuating the output of the fifth means, and the other output of the third means and the sixth means. and a seventh means for synthesizing the outputs of the amplitude equalizing means and outputting the output of the amplitude equalizing means, and the seventh means is connected to the output of the amplitude equalizing means at the final stage, and is connected to the output of the amplitude equalizing means at the final stage, and is configured to determine the polarity of the amplitude distortion characteristic according to the shape of the power spectrum of the signal. and eighth means for detecting the amplitude and controlling the sixth means.