JPH0352107A - Recording and reproducing device for digital signal - Google Patents

Abstract

PURPOSE:To perform optimum waveform equalization by providing a coefficient multiplier with an optimum equalization constant of every head and a switching means for selecting the coefficient multiplier corresponding to the switching of the reproduced output of each head in each tap coefficient part of a transversal filter. CONSTITUTION:Based on the switching signal of an FF 40c, the coefficient selection switches 34c and 35c of the transversal filter 28 selectively connect the coefficient multipliers 34a and 35a to multipliers 31 and 32 when a magnetic head 19a scans a magnetic tape 17, and selectively connect the coefficient multipliers 34b and 35b to the multipliers 31 and 32 when a magnetic head 19b scans the tape 17. The tape coefficient of the coefficient multipliers 34a and 35a is set as the optimum equalization coefficient in accordance with the characteristic of the magnetic recording and reproducing system of the magnetic head 19a and a rotary transformer 25a, and the tape coefficient of the coefficient multipliers 34b and 35b is set as the optimum equalization constant in accordance with the characteristics of the magnetic recording and reproducing system of the magnetic head 19b and a rotary transformer 25b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital signal recording and reproducing apparatus that records and reproduces digital signals on a magnetic tape by helical scanning of a plurality of rotating magnetic heads.

[Conventional technology]

Conventionally, digital signal recording and reproducing devices such as digital video table recorders that record and reproduce high-definition signals on magnetic tape record and reproduce digital signals on magnetic tape at high density by helical scanning of a plurality of rotating magnetic heads.

At this time, important issues include the frequency characteristics of magnetic recording and reproducing systems such as magnetic heads and magnetic tapes, and nonlinear distortion of reproduced signals.

For example, when recording and reproducing an NRZ format digital signal on a magnetic tape with a bit interval T, the recording signal N
The highest repetition frequency fN of the RZ signal is the Nyquist frequency of 1 fN=H.

If the magnetic recording and reproducing characteristics are ideal frequency band characteristics up to the Nyquist frequency fN, as shown by the solid line A in FIG. The level becomes O at the (bit) position, and @L 7FL% 07F of each bit of the reproduced signal can be correctly determined without code errors.

Note that each arrow line in FIG. 4(a) indicates a code position at a bit interval T.

However, actual magnetic recording and reproducing characteristics deteriorate from the above-mentioned ideal frequency band characteristics based on the characteristics of the magnetic head, magnetic tape, and the like.

Therefore, as shown in FIG. 5, the waveform of each bit of the actual reproduced signal is a reproduced signal based on the code, and as shown in FIG. 5, inter-symbol interference occurs, resulting in a broken line waveform that is a combination of the solid line waveforms.

At this time, based on the threshold level indicated by the dashed-dotted line*1
1f,% 1 N, * 1'', a so-called code error occurs, and correct reproduction cannot be performed.

Therefore, this type of digital signal recording and reproducing apparatus includes an FIR type transversal filter as a waveform equalization circuit.

In the case of a symmetrical three-tap configuration, this transversal filter is formed as shown in FIG.
The playback signal of the head output supplied to the delay device [21,
(In step 31, the processing is delayed by a certain period of time, for example, the time of the bit interval T.

Further, an input terminal ill and both delay units t2+ . [3
Input terminal of the signal at 3 tap position of output terminal 1 {
l}, the signal at the 2-tap position of the output terminal of the delay device (3) is multiplied by the tap coefficient of the coefficient multiplier +61 t (7) as a tap coefficient section in the multipliers (4) and (5).

Then, the output signals x, y, and z of the multiplier (4), delay device (2), and multiplier (5) are added and combined by an adder (8).

At this time, if the reproduced signal at the input terminal tl1 is a signal with a pulse response waveform in which intersymbol interference has occurred as shown in Figure 4, the coefficient multiplier (as shown in Figure 7) In contrast to the small output signal y indicated by the solid line y in (a), the output signals x and z have the waveforms indicated by the broken lines x and z in Fig. 12(a).

Then, the coefficient unit +61 e ("If the tap coefficient of tl is the optimal value, the output signal y is the composite waveform of the output signals x and z.
The inter-symbol interference component of is canceled, and a signal whose waveform is equalized to 0 at the level of the adjacent code position is supplied from the adder (8) to the output terminal (9) as shown in FIG. 7(b). A reproduced signal without interference can be obtained.

As shown by the solid line B in Fig. 3, the frequency characteristics of the waveform equalized signal reach half-value level at frequency fN, and (1-b)fN-fN,fN~(L+b)fN(
b is the roll-off rate), when the hatched parts p and q become symmetrical,
Intersymbol interference is eliminated.

However, when the transversal filter shown in FIG. 6 is provided, the tap coefficients are fixed and do not change, so good waveform equalization cannot actually be performed.

In other words, in the case of a device that plays magnetic tape using a two-head helical scan, a pair of rotating magnetic heads are installed on a cylinder 180 degrees apart, and both magnetic heads are alternately switched every half rotation of the cylinder to generate magnetic Scan the tape.

Then, the reproduction outputs of both magnetic heads are combined to form a reproduction signal, and this reproduction signal is supplied to the input terminal (1) in FIG.

In this case, the characteristics of the magnetic recording and reproducing system change each time the reproduction output of the head is switched, based on the characteristic difference between the magnetic head, the rotary transformer, etc. (hereinafter referred to as the characteristic difference between the heads).

Therefore, unless the tap coefficient as an equalization constant is changed every time the playback output of the gold head is changed to the optimum equivalent constant, it will not be possible to compensate for the difference in characteristics between the heads, and good waveform equalization will not be possible. I can't give it.

Therefore, Japanese Patent Application Laid-Open No. 61-16071 (GLIB 2
No. 0/10) describes that the waveform equalization circuit includes an adaptive transversal filter shown in FIG.

The transparsal filter in Fig. 8 corresponds to the variable gain inverting amplifier (10), the multiplier (5), and the coefficient unit (7), which correspond to the multiplier (4) and coefficient unit {6} in Fig. 6. The output signal of the delay device (2) and the output signals of the inverting amplifier (to+, (river) are added by an adder (8) to perform waveform equalization on the reproduced signal.

In addition, the output signal of the adder (8) is filtered through a bandpass filter (
12ls 03) and both filters fl2)
, 031 extracts high frequency and low frequency components, and the output signals of both filters +121 s t+3+ are supplied to a peak detector H* (+51) to peak detect the high and low frequency components.

And the coefficient controller is 0! Both detectors (14 + I
(The detection level of I5i is compared, and the gain of inverting amplifier t+o+e (Ill is variably controlled so that both levels are equal, and the tap coefficient is varied so as to compensate for the characteristic difference between the heads.

[Problem to be solved by the invention]

When equipped with the adaptive transversal filter shown in Fig. 8, the frequency characteristics of the reproduced signal are analyzed by comparing the levels of the high and low frequencies, and based on the results of this analysis, the Since the tap coefficients are determined and changed, there is a problem in that the accuracy of the tap coefficients is low and optimum waveform equalization cannot be performed.

In order to improve the accuracy of the tap coefficients, multiple band-pass filters and peak detectors are installed to subdivide the reproduced signal into multiple frequency components, detect the level of each frequency component, and accurately analyze the frequency characteristics. It is possible that
In this case, there are problems in that the circuit scale becomes significantly large and processing such as control of tap coefficients based on analysis results becomes extremely complicated.

SUMMARY OF THE INVENTION The present invention provides an overall recording and reproducing apparatus for technical signals which has a relatively simple configuration and which performs waveform equalization of an optimal equalization constant on a reproduced signal by switching tap coefficients each time the reproduction output of a head is switched. purpose.

[Means to solve the problem]

In order to achieve the above object, the digital signal recording and reproducing apparatus of the present invention includes a coefficient unit for an optimum equalization constant for each head in each tap coefficient section of a transversal filter serving as a waveform equalization circuit, and a coefficient unit for an optimum equalization constant for each head. switch means for selecting each of the coefficient multipliers in response to switching of the reproduction output, and switching means for selecting the respective coefficient multipliers in accordance with the switching of the reproduction output, and switching the waveform equalization characteristic of the reproduction signal in accordance with the switching of the reproduction output.

[Effect]

In the device of the present invention configured as described above, the tap coefficient of the transversal filter is set to the optimum equalization constant tap corresponding to the reproduction signal by selecting the switch means according to the switching of the reproduction output of each rotating magnetic head. Switch to coefficient,
Waveform equalization characteristics change.

And traditional adaptive transparsulfui? Since each coefficient multiplier is simply selected by a switch means without analyzing the frequency characteristics of the reproduced signal such as a multiplier and determining the tap coefficients based on the results, it is possible to switch the tap coefficients with a simple configuration and achieve the best results. waveform equalization is performed.

〔Example〕

An embodiment will be described below with reference to FIGS. 1 and 2.

Figure 1 shows the case where the magnetic tape is applied to a two-head helical scan type digital video tape recorder.
This drum (a pair of rotating magnetic heads (19a) mounted 180 degrees apart,
19b), the magnetic tape is alternately helically scanned.

During recording, the video signal at the input terminal (a)) is supplied to the recording processing circuit (1), which converts the video signal into a digital signal, then interleaves, error correction code, and synchronizes the video signal. It is modulated by adding signals, address signals, etc.

Furthermore, the output signal of the recording processing circuit (2I) is transmitted to the recording amplifier (23
a) and (23b) alternately.

Both recording amplifiers (23a). The output signal of (23b) is transmitted to the recording/reproduction switching circuit (24) and the rotary transformer (25a).
). (25b) through the magnetic head (19a), (19
b), and the video signal is digitally recorded on the magnetic tape (18).

Next, during reproduction, the magnetic head (19a). The playback output of (19b) is sent to the playback amplifier (26a) via the rotary transformer (25a), (25b) and the recording/playback switching circuit (24).
, (26b).

At this time, the magnetic heads (19a) and (19b) alternately scan the magnetic tape on the rotating drum (every half rotation (= every ISO°) τa, τb, and sequentially reproduce each track on the magnetic tape. Therefore, the playback amplifier (26a), (26
b) The output signals are shown in Figure 2 (a) and (b).
l} It becomes an intermittent signal every rack.

This intermittent signal is based on the signal format of recording and playback, with a redundant preamble section at the beginning and end, and a post? Ampoule part (
Data section (D) that has actual information between Pr) and (Po)
It becomes a signal arranged at t.

In addition, the bridle portions (Pr) and (Po) usually have
A continuous signal at the Nyquist frequency is recorded.

Then, the output signals of both reproduction amplifiers (26a) and (26b) are combined by a reproduction signal switch that is switched in conjunction with the recording signal switch, and from this switch 271 a three-tap configuration as a waveform equalization circuit is output. The reproduced signal is supplied to an FIR type transversal filter (c).

This transversal filter (c) consists of the delay units [2+, +31, multipliers +41, +61,
It has the same delay device (8) as the adder (8), multiplier (at) S (301), adder (t), and the tap coefficient section of the multiplier (ta++), (3η).
, (to), coefficient multipliers (34a), (34b), (34b) for each head consisting of ROM or RAM or variable resistance
5a), (35b) and coefficient selection switches (34c), (
35c) and is formed with gold.

On the other hand, a PG head is provided near the rotating drum, and a pair of magnets (37a) and (37b) are attached to the rotating drum so as to precede the rotating magnetic heads (19a) and (19b). ing.

? As a result, the polarities of the magnets (37a) and (37b) facing the PG head (36) are set to be opposite, and the magnets (37a) and (37b) based on the rotation of the rotating drum (18)
When the magnetic flux change f P G hetsu l' ・, :3u: is detected, the detection output of this head (36) is I゛6
The pulses are amplified by the amplifier section, and pulses of positive and negative polarity shown in FIG. 2(C) are supplied from the amplifier to comparators (39a) and (39b) for waveform shaping.

Furthermore, based on the comparison between the positive and negative reference levels +Vr, -Vr and the level of the input pulse, the comparators [, 39a), (3
9b), pulses of positive polarity and pulses of negative polarity are separately extracted and shaped.

And a comparator (39a). The output signal of (39b) is the delay device (40) for timing adjustment of the switching control circuit 00l.
a), (40b) Set terminal (S), reset terminal <r of flip 7 flip (40C) for signal generation via i
＞Supplied to

At this time, the flip-flop (40c) is connected to the magnetic head (19a) based on the delay of the delay devices (40a) and (40b).
, (19b) are set and reset in synchronization with the tape scan of flip-flop (40c).
No. to Φ? A switching signal shown in Figure (d) is generated.

This switching signal causes each switch to
)t (35C) is the magnetic head (18a). The reproduction signal that is switched in synchronization with the switching of the reproduction output in (18b) and supplied to the transversal filter 4 is as shown in FIG. 2(e).
As shown in Figure (a). A continuous signal is obtained by combining the intermittent signals in (b).

Then, the reproduced signal is delayed by the bit interval T in the delay device ea t (301, and the input signal of the delay device 4,
A multiplier (31), K2 is applied to the output signal of the delay device (30).
The tap coefficient is multiplied by the delay device ■} and the multiplier l31.
). The output signals of ■■■ are combined by an adder.

Based on the switching signal of the flip-flop (40c), the coefficient selection switches (34c) and (35c) operate the coefficient multipliers (34a) and (35a) when the magnetic head (19a) scans the magnetic tape (17). ) Select k and connect to multiplier 0++, @2, magnetic head (19b)
When scanning the magnetic tape A7RT, the coefficient multiplier (3
4b), select (35b) and get the multiplication profit t3+1,
Connect to GZ.

Therefore, when the magnetic head (19a) scans the tape, the coefficient m (34a). Waveform equalization is applied to the reproduced signal using the characteristic based on the tap coefficient (35a), and the magnetic head (
When scanning the tape 19b), the coefficient multiplier (34b), (
Waveform equalization is applied to the reproduced signal using the characteristics based on the tap coefficients of 35b).

The tap coefficients of the coefficient multipliers (34a) and (35a) are determined by the magnetic head (19a) j rotating transformer (25a
) is set to the optimum equalization constant according to the characteristics of the magnetic recording and reproducing system, and the tap coefficients of the coefficient multipliers (34b) and (35b) are as follows.
The optimum equalization constant is set according to the characteristics of the magnetic recording/reproducing system of the magnetic head (19b) and the rotating transformer (25b).

Therefore, the coefficient selection switch (34C), (
．． 35c), optimum waveform equalization can be applied to the reproduced signal regardless of differences in characteristics between heads.

Immediately after the tap coefficients are switched, optimal waveform equalization cannot be performed transiently, but at this time, the reproduced signal becomes the redundant preamplifier (Pr) or postamplifier (PO) signal. Therefore, no inconvenience will occur.

Then, the reproduced signal after waveform equalization outputted from the adder is supplied to the reproduction processing circuit (4l).
In step 1), the reproduced signal is demodulated, and then subjected to time axis interpolation, error correction processing, dinning, etc. based on the detection of the synchronization signal and address signal, and then returned to an analog signal.

This analog signal is output to the output terminal Oz as a reproduced video signal.
supplied to

In the embodiment described above, the present invention is applied to a case where a transversal filter e2Ft- having a three-tap configuration is used, but the present invention can also be applied to a case where a transversal filter gold having a different number of taps from that of the embodiment is used.

Furthermore, the number of rotating magnetic heads, the content of digital signals, etc. are not limited to the embodiments.

For example, every four and a half rotations of the rotating drum, simultaneous scanning of three consecutive tracks by three rotating magnetic heads and simultaneous scanning of three consecutive tracks by the remaining three rotating magnetic heads are alternately performed. When six rotating magnetic heads are installed on a rotating drum and three channels of playback signals are generated simultaneously, as in the case of Transversal filter f: for parallel processing
, a coefficient unit for the optimum equalization constant of each head and a switch means for each channel are provided in the tap coefficient section for each same tap position of this filter, and three coefficient units corresponding to the playback output of each channel are provided for each half rotation. All you have to do is select.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

In order to select the coefficient unit of the optimum equalization constant for each head by the switch means in accordance with the switching of the reproduction output of each rotating magnetic head, and to switch the waveform equalization constant of the transversal filter,
Characteristics between heads can be easily adjusted without performing complex processing such as analyzing the frequency characteristics of the reproduced signal and determining tap coefficients based on the results, which is required when using conventional adaptive transversal filters. Optimal waveform equalization 4 that compensates for the difference can be performed.

[Brief explanation of drawings]

1 and 2 show an embodiment of the digital signal recording and reproducing apparatus of the present invention, FIG. 1 is a block diagram, and FIG.
) to (e) are waveform diagrams for explaining operation, Figure 3 is an explanatory diagram of ideal magnetic recording and reproduction characteristics and reproduction signal characteristics without inter-symbol interference, and Figures 4 (a) and (b) are inter-symbol interference diagrams. Figure 5 is an illustration of reproduction errors due to inter-symbol interference. Figure 6 and Figure 558 are used for waveform equalization (one magnetic tape, (
19a), (19b)...Rotating magnetic head, (c)
・Transversal filter, (34+, (to)・
... Tough coefficient section, (34a). (34b), (35a
), (35b) . ．． ．． Coefficient unit, C34c), t35c
)...Coefficient selection switch.

Claims (1)

[Claims] (1) In a digital signal recording and reproducing device that records and reproduces digital signals on a magnetic tape by helical scanning of a plurality of rotating magnetic heads, and performs waveform equalization on the reproduced signal using a transversal filter, each tap of the transversal filter is provided. The coefficient unit is provided with a coefficient unit for an optimum equalization constant for each head, and a switch means for selecting each coefficient unit in response to switching of the reproduction output of each head, and the waveform equalization characteristic of the reproduction signal is set as described above. A digital signal recording and reproducing device characterized in that switching is performed in accordance with switching of reproduction output.