JPH09204603A - Waveform equalizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an improved error rate with a small number of adjustments by making a transversal filter into two-stage constitution and at the same time facilitate circuit integration by forming it of a digital circuit. SOLUTION: A reproduced signal which is digitized in an A/D converter 12 is equalized by a transversal filter 14a. Equalized reproduced data is further compensated for waveform distortion in the transversal filter 14b of a following stage. After that, bit delay and addition processing are applied to the equalized data in a delay addition means 16. In a data detection circuit 18, the data (1, 0, -1) of ternary waveform is detected and converted into an original code, namely, data (1, 0).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform equalizer, and more particularly, for example, in a VTR having a digital circuit,
The present invention relates to a waveform equalizer that suppresses intersymbol interference caused by deterioration of characteristics of a low frequency portion and a high frequency portion during reproduction.

[0002]

2. Description of the Related Art A waveform equalizer 1 composed of a conventional analog circuit includes a delay circuit 2 and a (M tap) transversal filter 3, as shown in FIG. Are equalized. The equalized signal is
Since the detection is performed by the recording code (partial response code), the delay adding means 4 performs 1-bit delay and addition processing. Therefore, from the delay addition means 4,
A partial response (1, 0, -1) signal is output. This signal is supplied to the detection circuit 5, and the detection level calculation circuit 6 calculates the signal level of the signal. Then, the detection circuit 5 identifies the signal (1, 0, -1) of the ternary waveform from this signal level, and
The "1" and "-1" of the ternary waveform are changed to "1",
"0" is identified as "0". Therefore, the original code (1, 0) is output from the detection circuit 5.

[0003]

However, when the waveform equalizer is realized by an analog circuit as shown in FIG. 3, there is a drawback that the circuit becomes large-scale and expensive. In addition, since the transversal filter that constitutes the waveform equalizer requires many delay lines, it is difficult to form an IC. Hence,
A main object of the present invention is to provide a waveform equalizer composed of a digital circuit suitable for IC integration.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to an A / D converter for quantizing a reproduced signal, a first transversal filter for compensating for waveform distortion of the quantized reproduced signal, and a first transversal filter. And a second transversal filter for further equalizing the data equalized in (3).

[0005]

The reproduced data digitally converted by the A / D converter is input to the first transversal filter, where the waveform is equalized. The equalized reproduction data is further equalized in the second transversal filter in the subsequent stage in the same manner as in the previous stage. The equalized data is subjected to 1-bit delay and addition processing by the delay addition means. Therefore, the delay addition means outputs ternary waveform data (1, 0, -1) having the characteristic of the partial response code. Then, this data is applied to the data detection circuit and the level detection circuit, and the signal level of the reproduction data is detected in the level detection circuit. In the data detection circuit, data "1", "0" and "-1" are detected from the detected signal level and ternary waveform data, and the data "1" and "-1" are changed to "1". ,
"0" is identified as "0". Therefore, the signal of the original code, that is, the data (1, 0) is output from the data detection circuit.

[0006]

According to the present invention, since the circuit is constituted by a digital circuit, the circuit scale can be reduced. Further, by forming the transversal filter in two stages, a waveform equalizer with a small number of tap adjustments can be realized. The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a waveform equalizer 1 of this embodiment.
0 indicates two transversal filters 14a and 1
4b. The video signal reproduced by a reproducing head (not shown) is digitally converted by the A / D converter 12 and then applied to the transversal filter 14a in the preceding stage. There, the waveform distortion of the reproduced data is equalized. The equalized data is further given to the transversal filter 14b in the subsequent stage, and the waveform distortion not removed by the transversal filter 14a in the previous stage is equalized.

The reproduction data equalized by the two-stage transversal filter 14 is subjected to a process of 1-bit delay and addition in the delay addition means 16. Therefore, the delay addition means 16 outputs the partial response (1, 0, -1) data corresponding to the interleaved NRZI code. That is,
The waveform equalizer 10 of this embodiment is, for example, a digital VC to which partial response (PR) class IV is applied.
The frequency characteristic of PR (1, 0, -1) can be realized by performing 1-bit delay and addition processing in the delay addition means 16, which is used for R.

The reproduced data having the characteristic of PR (1, 0, -1) is supplied to the data detection circuit 18, and the level detection circuit 20 detects the signal level at the data detection point of the reproduced data. Based on this detection result, the data detection circuit 18 detects the data “1”, “0” and “−1”, sets the data “1” and “−1” to “1” and the data “0”. It is identified as "0". Therefore,
The data detection circuit 18 outputs the original code, that is, the data (1, 0).

Assuming that the number of taps is "M", the transversal filter 14a includes M-1 stages of delay circuits. That is, with reference to FIG. 2, the reproduction data digitally converted by the A / D converter 12 is delayed by the one-clock delay circuit 22 which is delayed by a clock cycle. The delayed data is provided to the gain adjuster 24, where data for correcting waveform distortion is generated. That is, in the gain adjuster 24, which gain adjuster 24 to select is determined by the delay time from the input reproduction data (main signal). Then, in the adder 26, the main signal and the output signal from the gain adjuster 24, that is, the signal having the opposite polarity to the main signal are added. In this way, the above operation is repeated until the waveform distortion is not detected by the adder 26.

Here, the transversal filter 1 in the preceding stage is used.
When the number of taps of 4a is “M” and the number of taps of the transversal filter 14b in the subsequent stage is “N”, the relationship between the number of taps and the error rate can be shown as in Table 1.

[0012]

[Table 1]

As the tap numbers "M" and "N" increase, the number of adjustment points increases, so it is desirable to set the value as small as possible. Further, in Table 1, the error rate represents a ratio when the error rate when the number of taps “M” = 5, “N” = 5 is set to “1.0”. As can be seen from Table 1, when the number of taps of the transversal filter 14a in the front stage is “M” = 9 and the number of taps of the transversal filter 14b in the rear stage is “N” = 0, that is, M taps shown in FIG. In the conventional waveform equalizer 1 having only the transversal filter 3, a good error rate (= 7.9) cannot be obtained even if many adjustment points are set.

Therefore, by setting the transversal filter 14a in the front stage to 5 taps of the symmetrical type and the transversal filter 14b in the rear stage to 4 taps, an error rate (= 1.
1) can be obtained. Also, the number of taps “M” = 4
By configuring the transversal filter 14 with “N” = 3, it is possible to reduce the number of adjustment points and obtain a good error rate.

The equalization characteristic of the transversal filter 14 can be arbitrarily changed by setting the tap coefficient 28 of the gain adjuster 24 to a desired value. In addition, regarding the number of symmetric taps in Table 1, two tap coefficients make one adjustment number. By forming the transversal filter 14 in the two-stage configuration as described above, it is possible to realize a waveform equalizer while suppressing deterioration of the error rate and having a small number of adjustment points. Further, since it is configured by a digital circuit, the circuit can be downsized while ensuring the performance equivalent to that of a conventional equalizer having a large circuit scale.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a transversal filter according to the first embodiment.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

 10 ... Waveform equalizer 12 ... A / D converter 14a, 14b ... Transversal filter 16 ... Delay addition means 18 ... Data detection circuit 20 ... Level detection circuit 22 ... Delay circuit 24 ... Gain adjuster 26 ... Adder

Claims (4)

[Claims] 1. An A / D converter for quantizing a reproduced signal, a first transversal filter for compensating for waveform distortion of the quantized reproduced signal, and data equalized in the first transversal filter. And a second transversal filter that further equalizes the waveform equalizer. 2. The waveform equalizer according to claim 1, wherein the first and second transversal filters have different numbers of taps. 3. The waveform equalizer according to claim 1, wherein the number of taps of the first transversal filter is a symmetrical 5 taps, and the number of taps of the second transversal filter is 4 taps. 4. The waveform equalizer according to claim 1, wherein the number of taps of the first transversal filter is four, and the number of taps of the second transversal filter is three.