JPH0251307B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is directed to converting a received signal of a digital signal transmitted through a transmission system that cannot transmit DC components, such as a magnetic recording/reproducing system, into the original digital signal. The present invention relates to a signal identification device that can effectively reproduce signals.

[Technical background of the invention and its problems]

In recent years, with the development of digital signal processing technology, audio signals have been digitally encoded and recorded and played back.
Attempts have also been made to do this magnetically using a tape recorder. However, when restoring the original digital signal by demodulating the received/reproduced signal of a digital signal transmitted through a system in which direct current components cannot be transmitted, such as a magnetic recording/reproducing system, the loss of the original digital signal occurs. Errors in data identification caused by the DC component caused by Therefore, it is important to compensate for the DC component lost during transmission in order to widen the eye pattern at the time of data identification of the received signal and reduce the identification error rate.

By the way, heretofore, as a means of compensation for such DC components, that is, DC regeneration, for example, (i) IEEE TRANS.on MAG. Vol. MAG-16, No. 1, JANUARY 1980,
A method that uses the midpoint of the signal envelope as a reference voltage during data identification, as introduced in PP104-110, (ii) IEEE TRANS.on MAG Vol.MAG-14, No.4, JULY 1978, PP218-
222, which uses quantized feedback, is known. When demodulating received data using an integral detection method, the reproduced signal is generally amplified, waveform-equalized, and then integrated to identify it. In this case, if the above-mentioned waveform equalization is sufficiently performed, DC regeneration can be performed relatively easily using the method (i) above, but if the waveform equalization is insufficient, the above-mentioned (ii) It is necessary to use a relatively advanced quantization feedback method known as the method.

FIG. 1 is a schematic configuration diagram of a signal identification device employing this quantization feedback method, in which 1 is an adder circuit, 2 is a discrimination circuit such as a zero-crossing detector, 3 is a waveform shaping circuit consisting of a D-type flip-flop, etc. and 4 is PLL
This is a clock regeneration circuit that includes a circuit. The adder circuit 1 adds the received signal and a quantized feedback signal, which will be described later.The discriminator circuit 2 detects the zero-cross point of the output signal of the adder circuit 1, and operates in response to the clock from the clock regeneration circuit 4. A waveform shaping circuit 3 processes the output of the discrimination circuit 2 to reproduce a digital signal. Then, a part of this reproduced digital signal is filtered through a low frequency filter (LPF) 5 to generate the quantized feedback signal. In the figure, A is a signal input terminal, and B is a signal output terminal.

In this way, by adding the quantized feedback signal to the input signal (received signal) and then performing data identification, it is possible to effectively remove the influence of the DC level fluctuation of the input signal and perform data identification. It becomes possible to do so.

However, if data identification is performed after performing DC regeneration in this way, if there is a dropout in the input signal, the entire feedback loop that generates the quantized feedback signal will not converge, resulting in data identification errors. There is a problem that increases. That is, when magnetically recording and reproducing digital signals, signal dropouts are likely to occur due to dirt or scratches on the magnetic recording medium, or due to contact with the magnetic head. This dropout causes signal loss and a drop in level, as shown schematically in the envelope of the reproduced signal in FIG. 2, for example. Moreover, this dropout period T is generally several
It is relatively long, about 10μsec to 10msec. For this reason,
When such a dropout occurs in the input signal, the feedback loop of the DC regeneration system becomes unstable.
It will no longer converge. As a result, the feedback loop is not stabilized not only during the dropout period but also after the dropout period has elapsed, resulting in a problem that data cannot be identified reliably.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a highly practical signal identification device that can constantly and stably perform data identification of received signals while minimizing the adverse effects caused by dropout. Our goal is to provide the following.

[Summary of the invention]

The present invention is a signal identification device configured by adopting a quantization feedback method, which includes a dropout detection circuit to detect a dropout of an input signal (received signal), and when detecting this dropout, a feedback loop of the quantization feedback signal. It was designed to open up the .

That is, after adding a quantized feedback signal to a received signal of a digital signal transmitted through a transmission line that cannot transmit a DC component, when identifying this added output signal and reproducing the digital signal, the received When dropout occurs in the signal, the quantized feedback signal is prevented from being fed back to the adder circuit.

〔Effect of the invention〕

Thus, according to the present invention, data identification is performed while effectively compensating for DC level fluctuations of the received signal using the quantized feedback signal fed back;
Further, when a dropout occurs in the received signal, the feedback of the quantized feedback signal is prevented and data identification is performed on the received signal itself, so that identification errors due to instability of the feedback loop do not occur. In addition, the adverse effects of dropout at times other than the dropout period can be minimized, and as a result, the error rate at the time of data identification can be reduced. Moreover, by detecting dropout and opening the feedback loop, it is possible to easily and effectively prevent the feedback loop from becoming unstable, which has great practical advantages.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a schematic diagram of an apparatus according to an embodiment of the present invention, in which the same parts as those of the conventional apparatus shown in FIG. 1 are denoted by the same reference numerals. This device is characterized by a dropout detection circuit 6 which receives a received signal input from the input terminal A and detects its dropout, and a dropout detection circuit which is provided between the LPF 5 and the addition circuit 1. 6
A switch circuit 7 is provided which receives the output of the quantized feedback signal and opens the feedback loop of the quantized feedback signal. Then, when dropout is not detected, the switch circuit 7 forms the feedback loop and switches the quantization feedback method by the adder circuit 1, the discriminator circuit 2, etc. to the first one.
The system is configured as shown in the figure to perform data identification with DC reproduction compensation of the input signal. Further, when the dropout detection circuit 6 detects a dropout, the switch circuit 7 opens the feedback loop constituted by the LPF 5. Therefore, at this time, the input signal is directly supplied to the discriminator circuit 2 via the adder circuit 1,
Data identification processing is performed on this signal as it is.

The LPF 5 is realized, for example, as a first-order CR waveform filter using an operational amplifier 11 as a buffer, as shown in FIG. The frequency characteristics of the LPF 5 must be determined in consideration of the frequency characteristics of, for example, a magnetic recording/reproducing system (transmission system), a waveform equalizer, an integrator, and the like. Then, the switch circuit 7
may be constructed using an analog switch 13 equipped with a driver circuit 12 as shown in FIG.

Furthermore, as for the dropout detection circuit 6 that detects the dropout of the input signal, for example, as shown in FIG.
5. The delay circuit 16 may be used. As illustrated in FIG. 7, the peak detector 14 is composed of an absolute value detection circuit 14a and an integration circuit 14b, and thereby detects the envelope level of the input signal. The level comparator 15 compares this envelope level with a predetermined threshold value to detect the occurrence of dropout. The threshold value is determined depending on the level range of the input signal in which the feedback loop operates stably. The dropout detection result detected by this peak detection and level comparison is obtained by compensating for the time delay in signal processing from the adder circuit 1 to the LPF 5 through the delay circuit 16 and the processing time delay in peak detection and level comparison. is output.

Thus, according to the present device configured in this way, when a transmission signal in which the DC component has been lost is identified and a digital signal is regenerated and restored, even if a dropout occurs in the transmission signal, there is no adverse effect of the dropout other than the dropout period. It never invites. Therefore, data identification can be performed stably and reliably while regenerating the lost DC component, and data identification errors can be significantly reduced.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the spirit thereof. It is also applicable to DC reproduction and data identification in transmission systems other than magnetic recording and reproduction systems.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a conventional data identification device.
FIG. 2 is a diagram showing dropout of a transmission signal, FIG. 3 is a schematic configuration diagram of an apparatus according to an embodiment of the present invention, and FIG.
Figure 5 is a configuration diagram of the LPF in the same embodiment, Figure 5 is a configuration diagram of the switch circuit in the same embodiment, Figure 6 is a configuration diagram of the dropout detection circuit in the same embodiment, and Figure 7 is a configuration diagram of the peak detector. It is. DESCRIPTION OF SYMBOLS 1...Addition circuit, 2...Discrimination circuit, 3...Waveform shaping circuit, 4...Clock regeneration circuit, 5...Low frequency generator, 6...Dropout detection circuit, 7...
switch circuit.

Claims (1)

[Claims] 1. An adder circuit for adding a received digital signal and a quantized feedback signal transmitted through a transmission system that cannot transmit DC components, and means for identifying the output signal of the adder circuit and reproducing the digital signal. , a means for generating the quantized feedback signal by applying a low frequency signal to the reproduced digital signal, a dropout detection circuit for detecting dropout of the received signal, and the addition circuit for adding the quantized feedback signal when detecting the dropout. What is claimed is: 1. A signal identification device comprising: a switch circuit for preventing a signal from returning to the signal;