JPS60258761A - Pulse reproduction circuit in digital magnetic recording - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a circuit that reproduces correct pulses by suppressing waveform distortion due to low frequency band cutoff that occurs in digital magnetic recording.

[Background of the Invention] In the digital signal reproduced by magnetic recording, low-frequency cutoff occurs during the recording and reproduction process, and the low-frequency component is lost, resulting in a sag in the waveform and erroneous reproduction of pulses. Sometimes. DC regeneration is necessary to suppress this.

FIG. 1 shows a DC regeneration circuit using quantization feedback used in digital signal transmission. 1 is signal Kugata terminal, 2 is AGC
3 is an adder circuit, 4 is a comparator for quantizing a signal, 5 is a timing latch circuit, 6 is a low-pass filter, 7 is a timing pulse input terminal, and 8 is a pulse output terminal. The operation of this circuit will be explained using FIG. When a waveform signal with a sag as shown in (a) is input from the signal terminal, this signal is determined by a comparator and becomes a rectangular wave. The comparator used here detects the level difference between two inputs and quantizes it to detect high level or low level.One side is grounded, the other is the signal terminal, and the The average value of the potential is made equal to the ground. The rectangular wave output from the comparator is latched by the timing pulse extracted from the input signal. The low frequency components of the latched signal are extracted by a low pass filter, resulting in a waveform as shown in (b). The waveform obtained by adding this signal to the input signal in an adder circuit is the correct pulse with sag compensated for as shown in (c).
This signal becomes the input signal of the comparator.

If the input signal (,) has amplitude fluctuations, the following problem occurs. This is because the amplitude of the comparator's output signal is constant, even though the input signal fluctuates in amplitude.

The input signal of the comparator produces waveform distortion such as sag due to insufficient compensation in the low frequency range as shown in (d) or (e), and reverse sag due to overcompensation. In order to suppress this amplitude fluctuation, A
A GC circuit is usually used. However, the reproduction signal of magnetic recording has a larger fluctuation range in the amplitude direction than the signal of a communication channel, and it is difficult to make the amplitude of this signal constant without causing waveform distortion using an AGC circuit.

Roughly speaking, this is a drawback of circuits using AGC circuits.

Often occurs in magnetic recording. Problems when a signal has a long dropout period, such as a dropout in a recording medium, will be explained. When a signal with a missing period as shown in Fig. 3(a) is determined by a comparator, for example, if the missing period is determined to be a high level, the output signal of the low-pass filter will have a DC component as shown in Fig. 3(b). It becomes a waveform with . The signal obtained by adding this to the input signal has a waveform having a DC component as shown in FIG. 2(c). At this time, the DC level of the signal after the missing period shifts and deviates from the normal comparator level. This also applies when the comparator determines that the missing period is at a low level.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a quantization feedback circuit which eliminates the above-mentioned drawbacks of the prior art and has good characteristics capable of dealing with signals having long dropout periods.

[Summary of the invention]

In the present invention, instead of providing an AGC circuit in front of the feedback circuit, quantization is achieved by detecting the amplitude fluctuation component of the input signal and controlling the amplitude of the feedback signal in proportion to the amplitude of the input signal. A feedback circuit is configured to prevent unnecessary feedback of direct current components even when there is a drop period in an input signal. In addition, since the output waveform of the comparator is a rectangular wave, if a slice circuit is used as a circuit to control the amplitude of the feedback signal, an amplitude control circuit with less waveform distortion can be realized by simply controlling the slice potential. can.

[Embodiments of the invention]

FIG. 4 shows a quantization feedback DC regeneration circuit according to the present invention.

9 is a signal input terminal, 10 is an addition circuit, 11 is a comparator, 12 is a timing latch circuit, 13 is a slice circuit, 14 is a low-pass filter, 15 is an amplitude fluctuation detection circuit,
16 is a timing pulse input terminal, and 17 is a signal output terminal. The operation of this circuit will be explained using FIG. When No. 48 whose amplitude fluctuates as shown in FIG. 5(a) is input from the signal input terminal, the signal is divided into two paths.

One passes through the comparator 11 and the latch circuit 12, and is input to the slice circuit 13. The other is that the amplitude fluctuation detection circuit 15 extracts a fluctuation component and inputs it to the slice circuit g&13, which controls the slice potential.

The slicing circuit 13 slices the former rectangular wave in proportion to the amplitude of the input signal as shown in FIG. 5(b). The output of this circuit is a rectangular wave having an amplitude proportional to the amplitude fluctuation as shown in FIG. 5(c), and a low frequency component as shown in FIG. 5(cl) is extracted by a low-pass filter. The signal obtained by adding this signal to the input signal in the adder circuit 10 is the fifth signal.
The resulting waveform has the sag compensated for as shown in FIG. In the method described above, even if the input signal has amplitude fluctuations, appropriate low-frequency components are always fed back.

Furthermore, a signal with a missing period will be explained.

When a signal with a missing period as shown in FIG. 6(a) is determined by a comparator, for example, even if the missing period is determined to be a high level, the amplitude fluctuation detection circuit detects that the signal is zero. Therefore, the output of the slice circuit is suppressed to zero. Therefore, the high level is not fed back, and the signal has the normal comparator level even during the missing period (Fig. 6 (b)), and the output signal of the low-pass filter also has the normal comparator level as shown in Fig. 6 (Q). The waveform will be as follows.

The signal obtained by adding this signal and the input signal will no longer have unnecessary DC components as shown in FIG. 6(d), and the signal after the missing period will no longer deviate from the comparator level. Naturally, even if the missing period is determined to be a low level, the comparator level will not deviate during the missing period.

As described above, by providing a circuit in the feedback loop that controls the amount of feedback according to the amplitude of the input signal, it is possible to eliminate quantization feedback even in systems such as magnetic recording and reproducing processes where amplitude fluctuations are large and dropouts occur. This makes it possible to perform direct current reproduction, and realize a pulse reproduction circuit for digital magnetic recording.

〔Effect of the invention〕

Quantization feedback was devised as a relay point for digital signal transmission, and the conventional method was inappropriate as a pulse regenerator for digital VTRs and the like.

This is because VTRs have problems such as amplitude fluctuations due to spacing loss between the head and tape, dropouts due to lack of tape magnetic powder, and head blanking periods. However, by using the present invention, the above problems were solved and the present invention could be applied to digital VTRs as well. In addition, the present invention can be applied to digital audio tape recorders and the like.

Although the feedback path filter has been described above as a low-pass filter, other filters may be considered depending on the characteristics of the input signal, and the present invention is naturally applicable to that case as well.

[Brief explanation of drawings]

A block diagram of a conventional quantization feedback DC regeneration circuit shown in FIG.
Figure 2 is a waveform diagram for explaining the operation of the circuit in Figure 1, Figure 3 is a waveform diagram when there is a signal drop period in the circuit in Figure 1, and Figure 4 is quantized feedback DC regeneration according to the present invention. A block diagram of the circuit, FIG. 5 is a waveform diagram for explaining the operation of the circuit of FIG. 4, and FIG. 6 is a waveform diagram when a signal drop period exists in the circuit of FIG. 4. 9...Signal input terminal, 10...Addition circuit, 11...
・Comparator, 12...timing latch circuit, 1
3... Slice circuit, 14... Low pass filter,
15... Amplitude fluctuation detection circuit, 16... Timing pulse input Fig. 1 7 2nd port 'll''i31] Fig. 4

Claims (1)

[Claims] Quantization feedback consists of a comparator that quantizes a signal and outputs a rectangular wave, a filter that extracts a predetermined frequency component from the output signal of the comparator, and a circuit that inputs the signal obtained by adding the output of the filter to the input signal to the comparator. A pulse regeneration circuit consisting of a circuit includes a detection circuit for detecting amplitude fluctuations of an input signal, and a circuit for converting the output of a comparator into a rectangular wave having an amplitude proportional to the amplitude of the input signal based on the signal detected by the circuit. A pulse regeneration circuit characterized by: