JPS623610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic equalizer that equalizes amplitude distortion occurring in a transmission line where low frequency signals are attenuated relatively greatly, such as in a long distance cable section.

As an automatic equalizer that equalizes amplitude distortion occurring in a cable section, there is a slope AGC used in the PCM communication system. As shown in FIG. 1, the tilted AGC has a frequency characteristic that emphasizes high frequencies, and the degree of emphasis on the high frequency components varies depending on the internal parameters of the tilted AGC. The internal parameters are determined such that the peak power of the equalized output signal is constant. However, the length of the cable used for low-speed data transmission is extremely long, and the transmission loss in the low frequency band is extremely large, resulting in the slope of the frequency characteristics shown in Figure 1.
AGC cannot achieve equalization.

An object of the present invention is to provide an automatic equalizer that operates normally even over long distance cable sections.

Figure 2 shows the transfer function of a paper cable with a diameter of 0.5 mm. As can be seen from FIG. 2, the cable loss increases as the frequency increases, and the loss also increases in the low frequency band. Therefore, it is sufficient that the frequency characteristic T of the equalizer is given by the following equation.

T()=b( _a0 + _a1j (f/ _f0 )+ _a2j (f/ _f0 ) ² +... _aNj (f/ _f0 ) ^N )(1) (0≦f≦ _f0 ) However, f ₀ is the upper limit frequency of the band, and b corresponds to the amount of DC attenuation. Also, frequency characteristics
A filter that realizes (f/f ₀ ) ⁿ can be constructed from the following transversal filter.

That is, a delay line with taps whose time interval is given by T and weighting coefficients for each tap output are... ^na -2, ^na -1, ^na 0, ^na 1, na ² ...
A frequency characteristic j(f/f ₀ ) ⁿ is realized by a transversal filter given by a multiplier that multiplies .... Therefore, T=1/f ₀・l ₁ /l ₀ , and lJ,
l ₁ is an integer. To realize a transversal filter that gives j(f/f ₀ ) ⁿ , a transversal filter with infinite taps is required, but from an engineering perspective, it is more meaningful to approximate it with a transversal filter of finite length. be. There are several known methods for approximating the objective function j(f/f ₀ ) ⁿ using a finite-length transversal filter, and one method will be described for reference.

It is defined as

It is sufficient if ERROR(f) becomes 0 within the band, but this requires an infinite number of taps (k=∞).
Therefore, the tap coefficient that minimizes the root mean square of ERROR(f) is defined as optimal. That is, ∫ ^f0 ₀ |ERROR(f)| ² df→MIN (a) Equation (a) is a quadratic equation with respect to n ^a k, and the quadratic coefficient is positive. Therefore, there is always one minimum value,
It can be found by partially differentiating equation (a) with each tap coefficient and finding that the value becomes zero.

∴∂／∂ _o a _k ∫ ^f0 ₀ ｜ERROR(f)｜ ² df＝0 ∂／∂ _o a _k ∫ ^f ₀ ｜ERROR(f)｜ ² df =∂／∂ _o a _k ∫ ^f0 ₀ ERROR(f )・ERROR ^* (f)df =∫ ^f0 ₀ j (f/f ₀ ) ⁿ 2jsin2πftk −2 _o a _k df=0 ∴ _o a _k = −1/f ₀ ∫ ^f0 ₀ (f/f0) ⁿ sin2πftk
df(b) By executing formula (b), the tap coefficient can be obtained.

Considering jf/f ₀ as an example, jf/f ₀ can be approximated by the following equation.

jf/f ₀ ≒sinπ/2 f/f ₀ −0.2sinπf/f
₀ = −0.1e ^j 〓 ^T

Claims (1)

[Claims] 1. N+1 filters that emphasize high frequency components in proportion to the n-th power of frequency (n=0, 1,...N) or its approximation, and N+1 first multipliers that multiply the coefficient a _o , N+1 second multipliers that multiply the multiplication results of each of these multipliers by the coefficient b, and the N+
A first adder 1 that adds the multiplication results of one first multiplier, a second adder that adds the multiplication results of the N+1 second multipliers, and the addition output of the second adder and the ideal A difference circuit that obtains an error signal with respect to the waveform, the output of the first adder, each output of the N+1 second multipliers, and the error signal are input, and the coefficient a
An automatic equalizer comprising an arithmetic circuit that controls _o and b. 2. A filter that emphasizes high frequency components in proportion to frequency, a first multiplier that multiplies the output of the filter by a coefficient _a1 , and a first adder that adds the output and input of the first multiplier; A second multiplier that multiplies the output of the second adder by a coefficient b, a detection circuit that detects the peak voltage of the equalized output signal from the second multiplier, and a detection circuit that receives two sine waves with different frequencies. An automatic equalizer comprising: a control circuit that controls each of the coefficients a ₁ and b so that the peak voltage of each equalized output signal is constant.