JP3104762B2 - Digital signal playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal reproducing apparatus having a waveform equalizer.

[0002]

2. Description of the Related Art Generally, a DAT (Digital Audio Tape Recorder) has a magnetic head 1 as shown in FIG.
After the signal detected by the head amplifier 2 is amplified by the fixed gain amplifier 3, the signal is amplified by the waveform equalizer 4.
, And is detected by the digital detector 5 as a digital signal. In the case of DAT, since one type of tape is used, equalization can be performed only by passing through a fixed gain amplifier as shown in FIG.

However, in a VTR in which two or more reproduction speeds can be selected, the demodulation output of the luminance system fluctuates when the RF level fluctuates depending on the reproduction speed. To prevent this, as shown in FIG. 3, a variable gain amplifier 6 is inserted before the demodulation circuit 8 and the output of the variable gain amplifier 6 is detected by the AGC detector 7 and fed back to the variable gain amplifier 6 for AGC. I have. In this case, the detector 7 has a time constant suitable for the Y-system demodulation output.

[0004]

With this configuration, the optimum level can be supplied to the analog system circuit. However, when the waveform equalizer 4 and the digital detector 5 shown by the dotted lines are connected, the waveform and the like are reduced. The input level of the converter 4 is not always the optimum level. In this case, there is no problem if the bit rate is low as in 8-bit PCM and there is a margin for waveform equalization, but the transmission bit rate is high as in 16-bit PCM and the tape speed is 1% lower than in the case of normal speed. In some cases, when the tape used has various characteristics, waveform equalization is not sufficiently performed.

The present invention has been made in view of such a situation, and is intended to make the input level of the waveform equalizer the optimum level even if the input level changes.

In order to solve such a problem, a digital signal reproducing apparatus according to the present invention uses a signal reproduced from a medium as a medium.
Body mode, transmission bit rate, or modulation
Multiple waveforms, etc. that are equalized for at least one of them
Equalizer and one of the plurality of waveform equalizers,
Mode, transmission bit rate, or modulation method
Selection means for selecting based on the waveform, and a selection means provided before the waveform equalizer.
Variable gain amplifier and the output signals of a plurality of waveform equalizers.
That is, the output signal of the waveform equalizer selected by the selection means is
A detector for detecting and controlling the gain of the variable gain amplifier.
It is characterized by. In addition, solving such issues
In order to achieve this, another digital signal device of the present invention
The reproduced signal is transmitted according to the mode of the medium, the transmission bit rate,
Or at least one of the modulation methods
Multiple adaptive waveform equalizers to equalize and multiple adaptive waveforms
Set one of the equalizers to the mode of the medium,
Selection based on either the
Selection means and a variable gain increase provided before the adaptive waveform equalizer.
And a selection means out of a plurality of adaptive waveform equalizers.
Selected to optimize the input signal.
Detected output signal of adaptive waveform equalizer
And a detector for controlling the gain of the gain amplifier.
And

[0007]

The function of the medium among the output signals of a plurality of waveform equalizers is described.
Mode, transmission bit rate, or modulation method.
The output signal of the-option waveform equalizer been detected, it therefore is supplied to the variable gain amplifier is provided in front of the waveform equalizer, the input level of the waveform equalizer is adjusted to an optimum level You. In addition, the output signals of a plurality of adaptive waveform equalizers
Media mode, transmission bit rate, or modulation method
The output signal of the adaptive waveform equalizer selected according to the equation
Detected, which is provided before the adaptive waveform equalizer.
Adaptive gain equalization
The input level of the vessel is adjusted to an optimum level.

[0008]

FIG. 1 is a block diagram showing an embodiment of the present invention. A signal detected by a magnetic head 1 and amplified by a head amplifier 2 is converted into a digital signal via a variable gain amplifier 6 and a waveform equalizer 4. It is supplied to the detector 5. The output of the waveform equalizer 4 is detected by an AGC detector 7 and fed back to the variable gain amplifier 6.

The gain of the variable gain amplifier 6 is controlled by a signal supplied from the AGC detector 7, and the gain is adjusted so that the signal level supplied to the waveform equalizer 4 becomes an optimum value. Further, the variable gain amplifier 6 secures a sufficient band so as not to affect the waveform equalizer 4 at the subsequent stage.

In the thus constructed apparatus, the output level of the waveform equalizer 4 is fed back to the variable gain amplifier 6 even if the signal level obtained from the magnetic head 1 is different due to a difference in mode or a difference in tape characteristics. So
Since the variable gain amplifier 6 controls the signal level supplied to the waveform equalizer 4 to be constant, the waveform equalizer 4 performs amplitude equalization and phase equalization irrespective of the mode and tape. Does not fluctuate.

FIG. 2 shows an optimum waveform equalizer 4a, 4a for each medium.
FIG. 4 is a block diagram showing a configuration in the case of using b and switching between them by using a medium. As described above, even when a plurality of waveform equalizers are used, if the switching output is detected and fed back to the variable gain amplifier 6, each waveform equalizer can be used at an optimum input level.

FIG. 3 shows an example in which various digital audio modes such as PCM audio of an 8 mm VTR and analog signals and video signals are handled. This device has two systems, an analog signal system and a digital signal system. The digital signal system has adaptive waveform equalizers 41a to 41e at the subsequent stage of the variable gain amplifier 6a, and the output of the changeover switch 9a. The feedback from the side to the variable gain amplifier 6a via the AGC detector 7a.

The waveform equalizers used here are, for example, adaptive ones, each having a different mode of the medium (metal-deposited tape / metal-coated tape), a different transmission bit rate (L mode / N mode), and a modulation method. (E.g., biphase / 8-10 modulation), the waveform equalizers are switched to dedicated ones. The adaptive waveform equalizer detects an input signal and internally sets characteristics so that characteristics are optimal for the signal. Since the output signal after the waveform equalization is detected even if the characteristic fluctuates, the input level of the waveform equalizer can be set to the optimum level of the waveform equalizer.

In the analog system, a demodulation circuit 8 is provided at a stage subsequent to the variable gain amplifier 6b, and an input signal of the demodulation circuit 8 is converted to an AGC signal.
The signal is detected by the detector 7b and fed back to the variable gain amplifier 6b.

With such a configuration, the AGC detector 7
The time constants of a and 7b can be adjusted to optimal values for each system.

FIG. 4 shows the output signal of the variable gain amplifier 6 as A /
The signal is supplied to a digital equalizer 10 comprising a digital filter via a D converter 11 and the output thereof is supplied to a level slicer 12
Is output via the. And digital equalizer 1
The output signal of 0 is detected by the AGC detector 7, the detected signal is converted into an analog signal by the D / A converter 13, and is fed back to the variable gain amplifier 6.

This apparatus performs A / D conversion of a reproduced RF waveform and performs waveform equalization by a digital equalizer comprising a digital filter. By changing the characteristics of the digital equalizer, automatic equalization and the like are performed. It is possible to switch the chemical characteristics. Also in this case, the AGC detector is provided after the waveform equalization, and the result is fed back to the variable gain amplifier, whereby A
The input range of the / D converter 11 can be used effectively.

[0018]

As described above, according to the digital signal reproducing apparatus of the present invention, the output of the variable gain amplifier is controlled by a plurality of waveform equalizers ,
Other supplies to the plurality of adaptive waveform equalizer, the plurality of wave <br/> equalizer, or equalizer the plurality of adaptive waveform
That is, the mode of the medium, transmission bit rate, or modulation method
Waveform equalizer or adaptive waveform selected according to
Detects the output signal of the equalizer and controls the gain of the variable gain amplifier.
Media mode, transmission bit rate
If the signal level input to the waveform equalizer or the adaptive waveform equalizer changes due to the use of a different signal or modulation method , the waveform equalizer or the adaptive
It is possible to provide an input signal of the optimum signal level to the waveform equalizer, it has the effect of enabling an optimal waveform equalization regardless of changes in environmental conditions.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a digital signal reproducing apparatus to which the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a second embodiment.

FIG. 3 is a block diagram showing a configuration of a third embodiment.

FIG. 4 is a block diagram showing a configuration of a fourth embodiment.

FIG. 5 is a block diagram showing a configuration of an example of a conventional device.

FIG. 6 is a block diagram showing the configuration of another example of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic head 2 Head amplifier 3 Fixed gain amplifier 4 Waveform equalizer 5 Digital detector 6 Variable gain amplifier 7 AGC detector 8 Demodulation circuit 9 Changeover switch 10 Digital equalizer 11 A / D converter 12 Level slicer 13 D / A converter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 5 / 09,20 / 10

Claims (2)

(57) [Claims] 1. A signal reproduced from a medium, wherein a signal of the medium is reproduced.
Code, transmission bit rate, or modulation method
Multiple waveform equalizers that perform waveform equalization corresponding to either
When, Any one of the plurality of waveform equalizers is used to
Mode, transmission bit rate, or modulation method
Selecting means for selecting based on the A variable gain amplifier provided before the waveform equalizer, Selecting means of the output signals of the plurality of waveform equalizers
Detecting the output signal of the waveform equalizer selected by
And a detector for controlling the gain of the variable gain amplifier.
A digital signal reproducing device characterized by the above-mentioned. 2. A signal reproduced from a medium is transmitted to said medium.
Mode, transmission bit rate, or modulation method
Multiple adaptive waveforms for waveform equalization corresponding to either
An equalizer and one of the plurality of adaptive waveform equalizers,
Body mode, transmission bit rate, or modulation method
Selection means for selecting based on the above, and a variable gain amplifier provided before the adaptive waveform equalizer
Among the plurality of adaptive waveform equalizers,
Selected to optimize the input signal.
Performed the output signal of the adaptive waveform equalizer and
A digital signal reproducing device comprising: a detector for controlling a gain of the variable gain amplifier .