JPS6254873A - Fixed-head type digital magnetic reproducing device - Google Patents

Abstract

PURPOSE:To suppress folding distortion due to sampling and to constitute the titled reproducer with multifunction without increasing the circuit scale by switching the amplification band of an amplifier for a signal from a magnetic head in proportion to the tape speed. CONSTITUTION:The signals read out from the N-pieces of tracks of a magnetic tape 1 by N-pieces of magnetic heads 2-1-2-N are voltage-amplified by an amplifier consisting of operational amplifiers 18-1-18-N. The amplified signals go through a multiplexer 8, an A/D converter 9, a digital equalizer circuit 10, a data detector circuit 11, and a data synthesizer circuit 12, and an original digital signal is reproduced, and outputted from an output terminal 13. In the meantime, when the tape speed is switched, each circuit 8-12 is controlled to change their clock frequencies by a tape speed switching circuit 19 which change overs the tape speed, and at the same time, the gain-bandwidth product of the amplifiers 18-1-18-N is controlled. For example, when reproducing with a tape speed two times of that of recording, the clock frequency and the gain- bandwidth product is controlled to become double.

Description

[Detailed Description of the Invention] B] Industrial Application Field The present invention relates to a fixed head type digital magnetic reproducing device;
Particularly, No. 1g processing method C when reproducing all digital signals recorded on two multi-tracks in the width direction of a magnetic tape;
related.

(B) Conventional technology A fixed head type digital magnetic recording/playback device usually records up to multiple tracks in the width direction of a magnetic tape using a plurality of magnetic heads, so its playback circuit is as shown in Figure 4C. The structure is as follows.

That is, N tracks of the magnetic tape (1) (recorded by Tomoshin 9t - a plurality of magnetic heads (2-1) to (2-N)
After reproducing the output signal from each head, each head output signal is sent to an amplifier (3
-1) to (3-N) voltage amplification circuit (4-1)
The waveform is equalized by ~(4-N). The equalization circuit outputs are respectively output from data detection circuits (5-i) to (5-N)('
: A binary signal 'pjt' is converted and then the original digital signal C of one series is restored from the data synthesis circuit 16)C.

The digital signal is, for example, an A/D converter of an analog audio signal.
In the case of a converted signal, the original back door signal is restored by D/A conversion.

On the other hand, in the case of such a fixed head type digital magnetic reproducing device, there is a problem that the circuit scale becomes large because a processing circuit is required for each track. Accordingly, a t-circuit system has been proposed by introducing a digital time-division processing method. (For example, JP-A-59-924101!), JP-A-Sho 5
9-92411).

In this method, as shown in FIG. 5, a plurality of magnetic heads (2-1) to (2
-N) and sends the ratio signal to amplifiers 1-1) to (3
-N) respectively, and after t, the multiplexer (8) C converts the analog time-division multiplexed signal into a digital time-division multiplexed signal. The waveform is equalized by the digital equalization circuit (10C, and then the binary signal g is converted by the data detection circuit αυ. (12 is the output of the above-mentioned @4 figure) The same original digital signal C as the output from the terminal (7): This is the t-th data synthesis circuit to be restored, and the restored signal is output from the output terminal αJ.

(c) Problems to be Solved by the Invention In such digital time-division processing, a sampling frequency that is twice or more of the signal band 1 is required in order to sample the signal read from the magnetic head. For example, data of 5 M゛BPS t-20) Rack C is divided into two, tape speed is 4.76cm/le
When reproducing the signal recorded at step e, the signal in the Nyquist frequency band of 75KH2 shown by the curve (&) in FIG. 6C is reproduced. The Nyquist frequency is the highest repetition frequency of the NRZ signal, and the NRZ signal at the time of recording is shown in Figure 6C:
0) exists, but it is 15QKH2 due to the loss that occurs in the electromagnetic conversion system such as the tape and head.
The upper and lower bands are attenuated.

Therefore, if the sampling frequency is set to 500KH281 degrees, there will be little signal deterioration due to sampling distortion such as aliasing distortion.

Note that this value of 3 Q Q KHz corresponds to twice the data bit frequency of 150 KHz per F rack.

In addition, for the amplifiers 1-1) to (3-N) in Fig. 5, the sampling frequency including the reproduced signal and noise is 300 KH2 [:], and the sampling frequency is set to 150 KH2 to prevent aliasing distortion.
It is desirable to limit the band so that the signal level is sufficiently lowered in 2.

@I: If you increase the tape speed and play back data on the recorded tape in a short time, consider that there are two Cs. For example, the tape speed will be twice the tape speed of 4761Δ1C, that is, 9.
5a+/see, as shown in Figure 7C; the band of the ζ2 reproduced signal is twice that of curve (a) shown in Figure 6C;
Go up.

It should be noted that the sampling frequency ζ and the tape speed shall be increased proportionally to 600KH2+2. The sampling frequency is generally more mature than the frequency divided by the oscillator, etc. Therefore, it is easier to change the division ratio. As shown in Figure 7 (I: At steady speed (4,76 m/see), the frequency characteristics are curved! (e
), and if the tape speed is twice C, the playback signal will look like song #(a); twice the frequency ≦ double, so it cannot be amplified with this characteristic, so the amplifier It is necessary to set the band to +11(d).

On the other hand, the amplifier characteristic 1-a line (d) characteristic C2
Of course, it is possible to amplify the signal at a steady speed, that is, the Nyquist frequency of 75 KHz, but as mentioned above (:15
When signals and noise of QKHz or higher are output from the amplifier, aliasing distortion becomes a problem.

Therefore, in order to solve these problems, we will consider a method C in which the amplification band of the amplifier is switched according to the tape speed C and the amplification band T. As a method for changing this amplification band, for example, the method shown in FIG. 8 is known.

That is, when an inverting amplifier is configured using an operational amplifier (141f), the amplification band can be changed by connecting the feedback resistor αG and the parallel capacitor ση using the switch (151). All appropriate (-) Select g2 with switch a9 open and 7th
In the curve (d) in the figure, the amplifier characteristic of the curve m(e) in the figure can be obtained with the switch α stage closed.

However, it is a fixed head type magnetic reproducing device with multi-track configuration [Dual use 71? :jj! In this case, a switch and a capacitor are required for each track, resulting in an increase in circuit scale.

In view of the above-mentioned problems, the present invention provides a plurality of amplifiers for amplifying the output signals of a plurality of magnetic heads, and a multi-signal system for converting the output of each amplifier into a time-division multiplexed signal. t and the multiplexer output signal 'j)? J@Kyu Analog to Digital Converter A
/D converter, a digital equalization circuit that receives the conversion output m9 and performs waveform equalization by time-sharing processing, a data detection circuit that converts the output signal of the equalization circuit into binary data C, and the data detection circuit. Fixed head magnetic reproducing device I equipped with a data synthesis circuit that restores the original digital signal using the output data of: A tape speed switching circuit that switches the running speed of the magnetic tape is provided, and the output signal from the tape speed switching circuit is used to restore the original digital signal. The clock frequency of each circuit is changed in proportion to the overall speed, and the amplification band of the amplifier is changed in proportion to the speed.

(E) Function According to this gmfit, which consists of the above-mentioned configuration, the amplification band 1 of each amplifier is adjusted according to the output signal from the tape speed switching circuit.
:Can be switched.

(f) Implementation example Embodiments of the present invention will be described below with reference to FIG.

The signals read out from the N tracks of the magnetic tape (1) by the N magnetic heads (2-1) to (2-N) are as follows:
The voltage is amplified by the ratio amplification circuit C, which is composed of operational terms (18-1) to (18-N)C. It should be noted that an operational amplifier having a variable gain band product (a value expressed at a frequency at which the gain is doubled) is used.

Next C: The amplified signal is sent to the multiplexer (8), A/D converter (9), digital equalization circuit (1G, data detection circuit αυ, and data synthesis circuit) in exactly the same way as in FIG. As expected, the original digital signal is restored and output to the output terminal C131.

On the other hand, when changing the tape speed, is C2 at that speed? Switching tape speed switching circuit From Sumihiki 2, each circuit (8) ~
It is controlled to change the clock frequency of the mackerel, and
Gain band products of the operational amplifiers (18-1) to (18-N) are controlled.

For example, when reproducing the tape at twice the recording speed, the clock frequency and the gain band product of the operational amplifier are controlled to be twice the normal speed. As shown in Figure 2, the amplification band C is controlled so that the frequency-gain characteristics shown by the thin solid line become the characteristics shown by the thin broken line, and the closed loop gain of the amplifier is set as shown by the thin dashed line C. When the speed is high, C2 can obtain a frequency characteristic shown by a thick solid line, and when the speed is double, C2 can obtain a frequency characteristic shown by a thick broken line.

To change the gain band product of the operand @, for example, the sixth
All you have to do is change the current value of the emitter side current source 4 of the differential amplification stage that makes up the entire S2 operational amplifier shown in the figure. I don't.

(Effects of the Invention As mentioned above, if the present invention C is binary, the amplification band of the magnetic head signal amplifier can be changed in proportion to the tape speed 12 ≦ Nielly, the aliasing distortion due to sampling C2 can be suppressed. In addition, since the amplification band can be changed without adding any circuit components, it is possible to provide a multifunctional fixed head type digital magnetic reproducing apparatus without increasing the circuit scale.

[Brief explanation of drawings]

Figure 1 shows a fixed head type digital magnetic reproducing device according to the present invention [2]. Figure 2 is a diagram explaining the amplification band switching principle of the present invention, Figure 3 is an example of the amplification band switching method of the present invention, and Figure 4 is a diagram explaining the conventional a position. ,
Figure 5 shows a conventional example of a digital time-division multi-current processing system;
The figure shows the frequency spectrum of the magnetic head number output in a steady chip speed wave, Figure 7 shows the frequency spectrum at twice the tape speed, and Figure 8 shows a conventional example of a circuit system for switching the amplifier mounting. . (2-1) to (2-N)...magnetic head, (8)-...
・Multiplexer, (9)...A/D converter, (IG
...Digital equalization circuit, υ...Data detection circuit, tta-...Data synthesis circuit, uI...Tape speed switching circuit.

Claims (1)

[Claims] (1) A device that reproduces digital signals distributed and recorded on multiple tracks on a magnetic tape, which includes multiple magnetic heads that read the signals of each track on the magnetic tape and amplifies the output signal of each magnetic head. a multiplexer that converts each amplifier output into a time-division multiplexed signal; an A/D converter that sequentially converts the multiplexer output signal from analog to digital; and a waveform equalizer that receives the converted output signal and performs time-division processing. a data detection circuit that converts the output signal of the equalization circuit into binary data; a data synthesis circuit that restores the original digital signal using the output data of the data detection circuit; and a tape speed switching circuit for switching the speed, and the output of the tape speed switching circuit controls the clock frequency of each of the multiplexer, A/D converter, digital equalization circuit, data detection circuit, and data synthesis circuit. A fixed head digital magnetic reproducing device characterized in that it is configured to control the amplification band of an amplifier.