JPH01155560A - Dc reproduction circuit - Google Patents

Abstract

PURPOSE:To prevent the error of data discrimination by providing the adder of an input digital signal and the output of a variable gain amplifier through an attenuator in the previous stage of a level detector. CONSTITUTION:The level detector 10 basically outputs a signal proportional to the envelope of an inputted signal, and the gain of the variable gain amplifier 9 is controlled in correspondence with the output of the level detector 10. Consequently, a feedback quantity is correspondingly controlled when the amplitude of the input signal is fluctuated. The output of the second adder 12 where the output of the attenuator 11 and the digital signal from a terminal 1 are added is used for the input of the level detector 9. The fluctuation of a base line in the input signal of the level detector 9 is controlled in the same way as the output of a first adder 2. Thus, the malfunction of a compensation action can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION G) Industrial Application Field The present invention relates to a DC reproducing circuit for transmitting, recording/reproducing digital signals.

(b) Conventional technology NRZ (Non Beturn to zer)
o) Digital signals such as signals include low frequency components up to the DC region as shown in Figure 6, so if the low frequency region shown by the broken line is interrupted during transmission, the signal will be distorted as shown in Figure 4. This causes fluctuations in the baseline, making code errors more likely to occur on the receiving and reproducing sides.

On the other hand, in signal transmission via electric lines, there are cases in which a pair of signal lines is used to simultaneously transmit digital signals and supply power. is blocked and transmitted. or,
When recording and reproducing digital signals, the low frequency region of the digital signal is lost due to the differential response characteristics of the magnetic head.

Therefore, in the above example, the baseline fluctuates as described above, increasing the possibility of code errors.

To this end, DC regeneration circuits based on the quantization feedback method have been used to compensate for low frequency components on the receiving and reproducing sides.

A conventional DC regeneration circuit is disclosed in Japanese Unexamined Patent Publication No. 129975/1988 (G11B 20/14), and this conventional configuration will be explained with reference to FIG. Terminal (
1), a digital signal having frequency components shown by solid lines in FIG. 6 is input. (2) is an adder, and the digital signal is passed through the low-pass filter (LPF) +
It is added to the feedback signal from 61 and applied to the discriminator (5). The discriminator (5) performs processing such as waveform shaping and data detection, and a data signal is obtained from the output terminal (8).

By feeding back the low frequency component of this data signal to the adder (2), the low frequency component shown by the broken line in FIG. 6 is restored. The pass characteristic of the low pass filter (6) is set approximately equal to the low frequency cutoff characteristic (shown by the broken line in FIG. 6) of the digital signal input to the input terminal (1).

By the way, in the above-mentioned DC reproducing circuit, when the amplitude etc. of the input signal fluctuates (especially when recording/reproducing digital signals such as digital VTR), the amount of feedback is constant, so the balance between the compensated signal and the compensated signal is maintained. It will collapse and stable compensation will not be possible.

Therefore, the applicant proposed an improved circuit as shown in FIG.
). In FIG. 7, (9) is a variable gain amplifier, 00I
is a level detector that detects the level of the input signal. Components that are the same as those in FIG. 5 are given the same reference numerals.

In this improved circuit, the amount of feedback is controlled according to the level of the input signal from the input terminal (1), and the compensation of low frequency components is stabilized.

(c) Problems to be solved by the invention However, since the level detector σ■ in diagram M7 basically also detects the DC (low frequency) component of the input signal, fluctuations in the baseline are If extremely large, this baseline variation will appear in the output of the level detector.

In other words, the digital signal whose baseline (-dotted dashed line) as shown in FIG.
When input to , it is rectified (solid line in Figure 2 ('b))
By smoothing, an output as shown by the broken line in FIG. 2 (1) is obtained. Note that the level indicated by arrow GA) is the reference level of the level detector.

Therefore, even if the amplitude of the digital signal does not fluctuate much as shown in Figure 2 (sniff), the output of the level detector (101) fluctuates due to baseline fluctuations. ) will be changed even though the amplitude fluctuation is small. In other words,
The amount of feedback in the DC regeneration circuit changes almost independently of the input signal level, and the balance between the compensated signal and the compensation signal is lost. Additionally, compensation for low frequency components is no longer performed sufficiently, increasing the possibility of data identification errors.

To solve the above problem, the smoothing time constant of the level detector α is increased. ■ Countermeasures can be considered such as obtaining the input to the level detector (1 (11) from the output (4) of the adder (2). However, with the method (■), there is a delay in the control signal due to an increase in the time constant. This poses a problem.Also, in method (2), unless the feedback rate is kept low, the system will oscillate, but if the feedback rate is low, compensation for low frequency components will not be sufficient.

B) Means for Solving the Problems In the present invention, an adder for the input digital signal and the output of the variable gain amplifier via an attenuator is provided before the level detector.

(e) Effect: In other words, the input digital signal and the reduced variable gain amplifier output are added in the adder, thereby suppressing the baseline fluctuation of the input signal of the level detector'\. Therefore, fluctuations in the output of the level detector due to factors other than fluctuations in the amplitude of the input signal are suppressed, and the drawbacks of the conventional example are eliminated.

(F) Embodiment Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment. In the figure, the same parts as in FIG. 7 are given the same reference numerals.

(1) is a terminal into which a digital signal such as a reproduced NRZ signal is input, (2) is a first adder, (5) is a data discriminator (identifies the value of 1 and O), (61 is a low-pass filter that extracts the feedback signal, (8) is the output terminal of the digital signal compensated for the low frequency component, (9) is the variable gain amplifier, σ■ is the level detector, and σ] is the variable gain amplifier (
9) Attenuator for attenuating the output, 0 is the second adder.

The level detector σω includes, for example, a rectifier circuit and a smoothing circuit, and basically outputs a signal proportional to the envelope of the input signal. The gain of the variable gain amplifier C1l is controlled according to the output of this level detector (9). Then, when the amplitude of the input signal to the terminal (1) becomes large, the gain is controlled to become large. Therefore, when the amplitude of the input signal fluctuates (in digital signal recording/reproducing devices, changes in the contact state between the head and the recording medium,
This is caused by dust, scratches, etc. on the surface of the recording medium), and the amount of feedback is controlled accordingly.

The input of the level detector (9) is an attenuator αD.
The sum of the output and the digital signal from terminal (1) is used (the second adder (17J output)).

Therefore, fluctuations in the baseline of the input signal of the level detector (9) are suppressed, similar to the output of the first adder (2). Therefore, malfunctions in the compensation operation that occur in the prior art can be prevented.

The attenuator all is inserted so that the feedback loop formed by providing the second adder (1z) does not oscillate. It is set to an appropriate value taking into consideration.

In the embodiment shown in FIG. 1, the output of the variable gain amplifier (9) is used as one input of the second adder C121 (common elements are used), but the low-pass filter It is also possible to use a configuration in which the outputs of (6) are added with a predetermined gain, or the output of the data discriminator (5) is supplied to another low-pass filter or the like and added.

(G) Effects of the Invention As described above, according to the present invention, fluctuations in the baseline in the input signal to the level detector are suppressed, so that the output of the level detector correctly corresponds to the input signal level. becomes. Therefore, since the gain of the variable gain amplifier is correctly controlled, the operation of the DC regeneration circuit will not be erroneous, and data identification errors can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram for explaining the problems of the prior art, Fig. 6 is a diagram showing the frequency characteristics of a digital signal, and Fig. 4 is a baseline diagram. FIG. 5 is a block diagram showing a conventional example, FIG. 6 is a frequency characteristic diagram according to FIG. 5, and FIG. 7 is a block diagram showing a second conventional example. . (2)...first adder, (5)...data identifier,
(6)...Low bass filter, (9)...Variable gain amplifier, ti■...Level detector, (121...Second adder.

Claims (1)

[Claims] (1) In a DC regeneration circuit for a digital signal transmitted or regenerated in a system having a low frequency cutoff factor, a first adder receives the digital signal as an input, and a data discriminator receives the output of the first adder as an input. a filter means for extracting a low frequency component of the output of the data discriminator; a variable gain amplifier inputting the output of the filter means; a level detector controlling the gain of the variable gain amplifier; A second adder that adds signals related to data discriminator outputs and supplies the sum to the level detector, and supplies the variable gain amplifier output to the first adder.