JPH0749604Y2 - PCM signal playback device - Google Patents

Description

[Detailed Description of the Invention] [Outline of the Invention] This invention is a PCM signal recording / reproducing apparatus suitable for use in a digital VTR, in which the PCM signal is cut off at a low frequency to obtain a first output signal. Forming a low-frequency component from the high-frequency component to obtain a second output signal, and adding the first output signal and the second output signal to obtain a reproduction signal. A low frequency component blocked by a rotary transformer or a rotary transformer can be compensated, and a digital signal containing a large amount of low frequency component can be recorded on a magnetic tape.

[Conventional technology]

A digital VTR which digitizes a video signal and records it on a magnetic tape by a rotary head is known. When a video signal is digitized in a digital VTR and recorded on a magnetic tape, if the digital video signal is recorded on the magnetic tape without the run-length limitation as in NRZ, it becomes difficult to reproduce the digital video signal. In the NRZ, 1 is a high level and 0 is a low level, which is inverted at a bit boundary.

That is, when run length limitation is not performed like NRZ, many DC components are contained in the digital signal recorded on the magnetic tape. On the other hand, the tape head system has a differential characteristic, and the signal recorded on the magnetic tape is taken out via the rotary head. Therefore, when the signal recorded on the magnetic tape is reproduced by the rotary head, the low frequency component in the reproduced signal is cut off. Therefore, if the digital signal recorded on the magnetic tape contains many DC components, it becomes difficult to reproduce the digital signal.

[Problems to be solved by the invention]

Therefore, as a digital signal to be recorded on the magnetic tape,
It is conceivable to adopt a PCM signal with a strong run length limitation, for example, a CMI code or a Biphase code (the frequency spectrum is shown in FIG. 6) PCM signal, but since the recording wavelength of such a PCM signal becomes shorter, Not suitable for digital VTR.

On the other hand, as a digital signal to be recorded on a magnetic tape, a weak run-length limited PCM signal such as Miller code, Miller ² (M ² ) code (the frequency spectrum is shown in FIG. 5), EFM (Eight Fourteen Modulation) Sign of
Although it is possible to adopt a PCM signal, the recording wavelength of such a PCM signal is not short, but on the other hand, there is a drawback that suppression of low frequency components cannot be expected to the left.

Therefore, an object of the present invention is to provide a PCM signal recording / reproducing apparatus which can reproduce a digital signal containing a large amount of direct current components on a magnetic tape without strong run length limitation.

In magnetic recording, the lower the frequency of a signal, the greater the crosstalk between adjacent tracks. Therefore, when a digital signal with many low frequency components is recorded on a magnetic tape, the deterioration of the S / N ratio due to crosstalk becomes a problem.

The other purpose of this device is not affected by crosstalk
It is to provide a recording / reproducing apparatus for PCM signals.

[Means for solving problems]

This invention records a PCM signal on a magnetic tape, supplies the reproduced PCM signal reproduced from this magnetic tape to a low-frequency cutoff circuit, cuts off the low frequency band, and obtains a first output signal. The reproduction PCM signal reproduced from is supplied to an equalizer that reproduces a high frequency band to reproduce the high frequency band component, and a low frequency band component is formed from the high frequency band component to obtain a second output signal. Is a recording / reproducing apparatus for a PCM signal, in which the reproduced signal is obtained by adding the output signal of 1) and the second output signal.

[Operation] Since the tape head system has a differential characteristic, and the reproduction signal from the rotary head 1 is taken out through the rotary transformer, the reproduction waveform of the digital video signal output from the reproduction amplifier 3 is higher than that of the recording waveform. The low frequency components are cut off.

Therefore, although the low-frequency component is emphasized by the equalizer 4, the low-frequency component is blocked in the reproduction signal supplied to the adder 6 via the high-pass filter 5.

On the other hand, the output of the equalizer 7 is supplied to the comparators 8 and 9, and the outputs of the comparators 8 and 9 are supplied to the decoder 10. The output of the decoder 10 is supplied to the adder 6 via the low pass filter 11. These equalizer 7, comparators 8 and 9, decoder 10, low-pass filter 11
Is for forming a low frequency component corresponding to the low frequency component blocked by passing through the tape head system or the rotary transformer. This low frequency component is supplied from the low pass filter 11 to the adder 6.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, the rotary head 1 reproduces the digital video signal recorded on the magnetic tape 2. The reproduction signal of the rotary head 1 is supplied to the reproduction amplifier 3 via a rotary transformer (not shown).

Since the tape head system has a differential characteristic and the reproduction signal from the rotary head 1 is taken out through the rotary transformer, the reproduction waveform of the digital video signal output from the reproduction amplifier 3 is a low frequency component compared to the recording waveform. Is cut off.
That is, when the recording signal as shown in FIG. 2A is recorded, the reproduction signal has the low-frequency component cut off and becomes as shown in FIG. 2B.

The output of the reproduction amplifier 3 is supplied to the adder 6 via the equalizer 4 and the high-pass filter 5 and also to the equalizer 7. As shown in FIG. 3, the equalizer 4 has a characteristic (for example, full cosine roll-off) that emphasizes low frequencies. The equalizer 4 enhances the S / N ratio by emphasizing the low frequency component suppressed by passing through the tape head system and the rotary transformer. The high-pass filter 5 has a cut-off frequency substantially equal to a cut-off frequency of a low-pass filter 11 described later, and the high-pass filter 5 blocks low-frequency components of the output signal of the equalizer 4.

As described above, the reproduction signal supplied to the adder 6 via the equalizer 4 and the high-pass filter 5 is as described above.
The low frequency component is blocked by the tape head system and the rotary transformer.

On the other hand, the output of the equalizer 7 is supplied to the comparators 8 and 9, and the outputs of the comparators 8 and 9 are supplied to the decoder 10. The output of the decoder 10 is supplied to the adder 6 via the low pass filter 11. These equalizer 7, comparators 8 and 9, decoder 10, low-pass filter 11
Is for forming a low frequency component corresponding to the low frequency component blocked by passing through the tape head system or the rotary transformer. This low frequency component is supplied from the low pass filter 11 to the adder 6.

The adder 6 adds a low frequency component to the reproduction signal that has passed through the equalizer 4 and the high pass filter 5. After the output of the adder 6 is supplied to the comparator 12 and the waveform is shaped,
It is taken out from the output terminal 13. In this way, the low-frequency component blocked by the tape head system and the rotary transformer is compensated by the output from the low-pass filter 11.

That is, the equalizer 7 has a high frequency reproduction type characteristic as shown in FIG. Specifically, the partial response is equalized. The output of the reproduction amplifier 3 is supplied to the equalizer 7, and the signal of the frequency component as shown in FIG. 2E is extracted from the equalizer 7.

The output of the equalizer 7 is supplied to the comparator 8 and the comparator 9. As shown in FIG. 2E, the output of the equalizer 7 becomes larger than a predetermined level at the rising edge of the recording waveform and becomes smaller than the predetermined level at the falling edge of the recording waveform. When the output of the equalizer 7 becomes higher than a predetermined level, the output of the comparator 8 becomes high level as shown in FIG. 2F. When the output of the equalizer 7 becomes lower than a predetermined level, as shown in FIG. 2G,
The output of the comparator 9 becomes low level.

The outputs of the comparators 8 and 9 are the decoder 10
And is decoded as shown in FIG. 2H. That is, the decoder 10 forms a pulse signal that rises when the output of the comparator 8 goes high and falls when the output of the comparator 9 goes low.

The output of the decoder 10 is supplied to the low pass filter 11.
The second output from the decoder 10 is output by the low-pass filter 11.
As shown in FIG. I, a low frequency component corresponding to the cutoff amount is taken out by passing through a tape head system or a rotary transformer. This low frequency component is supplied to the adder 6.

In this way, the output of the low-pass filter 11 compensates the low-frequency component of the reproduction signal taken out through the equalizer 4 and the high-pass filter 5, which is blocked by the tape head system and the rotary transformer. Therefore, when recording a digital video signal on the magnetic tape 2, this digital video signal can be directly recorded by NRZ.

[Effect of device]

According to this invention, the low-frequency component of the recording signal blocked by the tape head system and the rotary transformer is added by the equalizer 7, the comparators 8 and 9, the decoder 10, and the low-pass filter 11. Therefore, when a digital signal is recorded on the magnetic tape 2, it is not necessary to use a code that strongly restricts the run length, and the digital signal can be directly recorded as in NRZ. If a digital signal can be recorded by NRZ, the recording wavelength is not shortened, the recording information density can be increased, and the encoder and the decoder are not required, so that the circuit scale can be reduced.

Further, according to this invention, the low-frequency component is not reproduced from the magnetic tape 2 but is formed once after being identified, so that the influence of crosstalk from the adjacent tracks can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a waveform diagram used for explaining one embodiment of the present invention, and FIGS. 3 and 4 are frequency characteristics of an equalizer in one embodiment of the present invention. FIG. 5 is a spectrum diagram of the M ² PCM signal, and FIG. 6 is a spectrum diagram of the Biphase PCM signal. Description of main symbols in drawings 2: Magnetic tape, 4, 7: Equalizer, 5: High-pass filter,
6: Adder, 11: Low pass filter.

Claims (1)

[Scope of utility model registration request] 1. A reproducing means for reproducing a PCM signal recorded on a magnetic tape, and a first equalizing means having an equalizing characteristic for emphasizing a low frequency component of the reproduced PCM signal reproduced by the reproducing means. A low-frequency cutoff means for cutting off a low-frequency component of the output of the first equalization means to obtain a first output signal, and a high-frequency reproduction type equalizer for the reproduced PCM signal reproduced by the reproduction means. Second equalization means for performing equalization, pulse reproduction means for performing pulse reproduction according to the output of the second equalization means, and second output by extracting the low frequency component of the output of the pulse reproduction means A reproduction device for a PCM signal, comprising: a low-frequency extraction means for obtaining a signal, and an addition means for obtaining a reproduction signal by adding the first output signal and the second output signal.