JPS61110379A - Digital recording and reproducing device for magnetic tape - Google Patents

Abstract

PURPOSE:To improve a data error due to variation such as a wow and a flutter by obtaining a clock corresponding to variation in time base from the playback signal of a cue track on the basis of a phase comparison. CONSTITUTION:The playback signal from the cue track is equalized by an analog waveform equalizer 31 and and then inputted to a level detector 41, which outputs a binary plus pulse signal. This is inputted to an NOR circuit 43 directly and through a delay circuit 42 to detect the 0-1 inversion position of the plus pulse signal. A variable clock from a voltage-controlled oscillator 60, on the other hand, is frequency-divided by N through a frequency divider 46 and inputted to clock terminals of FFs 44 and 45. The output of a circuit 43 is applied to the set terminal of the FF 44 and phase-compared with the frequency-divided clock of the variable clock, and the Q1 output of the FF 33 and the Q2 output of the FF2 are converted into a DC voltage through a differential active filter 50 and fed back to the frequency control terminal of the oscillator 60. The controlled variable clock is outputted and the clock period is corrected according to variation in the time base of the data.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a magnetic tape digital magnetic recording and reproducing apparatus that records and reproduces PCM signals by distributing them to a plurality of tracks.

<Prior Art> As a reproduction system for a plurality of tracks, a digital reproduction system including time division processing as shown in FIG. 6 has been proposed for the purpose of reducing the circuit scale as much as possible.

Here, a thin film magnetic head is used as the head, but there is no difference if a wire-wound head using a core is used.

However, in the case of small and multi-truck vehicles.

Considering performance and productivity, the thin film magnetic head shown in one example is suitable.

In the figure, a magnetoresistive element 11 is connected to a constant current source 10.
A constant Vc current is applied to obtain a voltage signal due to changes in magnetic resistance. The capacitor 12 is a DC cut capacitor that prevents the direct current of the constant current source 10 from flowing into the amplifier circuit 14. ′! In combination with the resistor 13, a low-pass filter is constructed. Then, the amplification circuit 14 amplifies the signal to a required level to obtain an amplified reproduction signal.

The above circuits are provided as many as the number of tracks, and a PCM reproduction signal is reproduced and amplified from each track.

The signals are input to the analog multiplexer 15, which selects and outputs them sequentially in a time-division manner. That is, the circuits after the analog multiplexer 15 are shared between the tracks.

The reproduced signals sequentially selected by the analog multiplexer 15 are converted into digital signals by the A/D converter 16, and are digitally equalized in the digital waveform equivalent circuit 17 to reduce distortion and waveform interference of the reproduced signal. Do the following. The waveform-equalized digital signal is digital P
The signal is input to the LL circuit 18 and the decoding circuit 19, and a reproduced clock and reproduced data are extracted. In addition, digital PLL
Circuit 18. Decoding circuit 19Vi, for example, JP-A-59-92
It is described in detail in 410, etc., and the explanation will be omitted.

The reproduced data for each track thus obtained is serially input to the digital signal processing circuit 20, where it undergoes signal processing such as demodulation (parallel signalization) and error correction, and is then converted into an analog signal by the D/A converter 21. and outputs it as an analog audio signal.

The master clock generator 22 is a clock source for driving each circuit, and the frequencies of φ1 to φ3 are fixed with respect to a crystal oscillator or the like.

The above-mentioned so-called multiplexer method allows 15 analog multiplexers or less to be shared between each track, thereby reducing the size of one circuit.

Further, in the example shown in the figure, the circuits below the A/D converter 16 (all are digital circuits) have the advantage of being easily integrated into an LSI.

Incidentally, magnetic tape has wow and flutter of about 0 to 100 Hz, which causes recorded data on the tape to fluctuate over time. On the other hand, as described above, conventionally, the clock frequency of the master clock generator 22 is fixed, so that it cannot follow data fluctuations, resulting in data errors.

<Purpose of the Invention> The present invention focuses on the fact that the recording/reproduction signal on the cue track is easy to handle, and obtains a variable clock corresponding to time axis fluctuations from the reproduction signal of the cue track, thereby eliminating fluctuations such as wow and flutter. The purpose is to improve data errors.

<Example> An example of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a block diagram showing one embodiment of the present invention. Components fi having the same functions as those explained in FIG. 6 are designated by the same reference numerals.

Here, the distribution of variable clocks is as follows.

Analog multiplexer 15, A/D converter 16,
Digital waveform equivalent circuit 17rfi, phase detection circuit 30
The digital PLL circuit 18. The signal circuit 19 and other digital signal processing circuits (not shown in FIG. 1) use a variable clock φ.

The clocks φ2 . Drive using φ3.

Variable clock φ. Here, the amplified playback signal of the cue track is passed through an analog waveform equivalent circuit 31 to be integrated and equalized, and then inputted to the phase detection circuit 30 described above.

The second figure shows an example of a track pattern on a magnetic tape. Multiple data tracks 2, 2 . ... and a cue track 3. Cue track 3V'i, as shown, data tracks 2, 2 . This is a wide track provided separately from the 1-time division processing, and the modulation method on the knee track 3 is also FM (Frequency Modulation).
duration) method, and the recording density is low. However, Data Track 2.2. . . . Due to tape fluff fluctuations, data tracks 2, 2 .・
. . . It is possible to perform phase detection using the data of the cue track 3 instead.

FIG. 3 shows an example of FM modulation. In order from top to bottom.

These are a data string, a recording signal by FM modulation, a read signal, and an integrally processed reproduction signal. FM modulation Ld, N
RZ I (Non-Return to Zer.

Similarly to I), a bit "1" corresponds to inversion, and a bit "0" corresponds to no inversion, but the boundaries between bits are also inverted. In this way, FM modulation is
It is characterized in that there is at least one change in VC per bit. In this respect as well, the use of the cue track 3 is advantageous for phase detection.

As mentioned above, cue track 3 is data track 2,
2. ...and can be handled independently of the multiplexer system, and the phase can be detected directly and continuously from the cue track 3, and the detection circuit can be easily used with a normal gate circuit that does not require calculations. FIG. 4 shows an example of the block configuration of the phase detection circuit 30, and the phase detection circuit 30 has the voltage VcE! J4 clear, phase comparator 40. It consists of a so-called PLL circuit configuration of a low-pass filter 50° and a voltage controlled oscillator 60, and a variable clock φ is generated by the voltage controlled oscillator 60.

I am getting .

FIG. 5 shows a more specific example of the circuit. The amplified reproduction signal obtained from the cue track 3 is integrated and equalized by the analog waveform equalizer 31 and then input to the level detector 41 of the phase detection circuit 30.

A level detector 41 compares it with a predetermined level.

Obtain positive pulse signals of 0'' and 1'. This is directly connected to the exclusive NOR circuit 43 through the delay circuit 42.
Vc is input, and the inversion position of '0'' and '1'' of the positive pulse signal is detected.

On the other hand, the voltage controlled oscillator 60 is set in advance to a standard frequency by a resistor Ro, a capacitor C0, and a variable resistor Rv, that is, a frequency that is approximately the same value as the master clock (see Fig. 6) when wow and flutter is at a minimum. It is assumed that The variable clock φ is the output of this voltage controlled oscillator 60. is divided by 1/NVc by the 1 frequency divider 46,
It is input to the clock terminal of flip-flops 44 and 45. Then, the output of the exclusive NOR circuit 43 is applied to the set terminal Ki of the flip-flop 44,
The phase of the variable clock φ0 is compared with the branch clock. Phase comparison result (Q1 output of flip-flop 44,
The Q2 output of the flip-flop 45 is converted into a DC voltage through the differential active filter 50 and fed back to the frequency control terminal of the voltage controlled oscillator 60.

As a result of the above, the oscillation frequency of the voltage controlled oscillator 60 is controlled in conjunction with the phase comparison. Also, this controlled variable clock φ. are derived, and as explained in FIG. 1, for example, the analog multiplexer 15, the A/D converter 16 . The signal is distributed to the digital waveform equivalent circuit 17.

As a result, wow and flutter causes 1 reload track and 3
By detecting the above time axis fluctuation, the system timing clock is changed, and in turn, the data track 2
,2. Since the clock period is corrected in response to the time axis fluctuation of the data, data errors caused by wow and flutter can be dramatically improved.

<Effect of the invention> As described in detail above, according to the present invention.

With a simple configuration, it is possible to provide a useful magnetic tape digital recording and reproducing apparatus that improves data errors caused by fluctuations such as wow and flutter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram explaining an embodiment of the present invention and a diagram explaining reproduced waveforms, FIG. 4 is a block diagram of the main part of FIG. 1, and FIG. 5 is a specific circuit diagram of FIG. 4. . FIG. 6 is a block diagram illustrating a conventional example. 2...Data track, 3...Cue track, 1
0... Constant current source, 11... Attenuation resistance effect element. 14... Amplification circuit, 15... Analog multiplexer. 16... A/D converter, 17... Digital waveform equivalent circuit, 18... Digital PLL circuit, 19...
Decoding circuit, 22... Master clock generator, 30.
... Phase detection circuit, 31 ... Analog waveform equivalent circuit,
40... Phase comparator, 50... Low pass filter,
60...voltage controlled oscillator, φ. ...Variable clock.

Claims (1)

[Claims] 1. In an apparatus for recording and reproducing digital signals on a magnetic tape having a plurality of tracks, a means for performing phase comparison using signals on the cue track of the magnetic tape, and a variable frequency operating clock for reproduction processing based on the phase comparison. 1. A magnetic tape digital recording and reproducing device comprising means for: