JPH01155562A - Dc reproducing circuit of digital signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce the identification error of data by changing the characteristic of a feedback loop in a DC reproducing circuit in accordance with the output signals of plural channels. CONSTITUTION:The characteristics of low frequencies differ in a head 13A and a channel A being the transmission system, and a head 13B and a channel B being the transmission system. Consequently, the attenuation factors of attenuators 28 and 29 are varied with respect to the channel B, and the feedback quantity of low frequency components are varied, whereby the error rate of binary data is set to min. Namely, attenuation factors in which error rates become min. differ in accordance with respective channels A and B, and the compensation action of the low frequency components in the DC reproducing circuit can be set in optimum with respect to respective channels by adjusting the attenuators 28 and 29. Thus, the identification error of data can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a DC component reproducing circuit for transmitting, recording/reproducing digital signals.

(b) Conventional technology Digital signals such as NRZ (Non Return to Zpro) signals contain low frequency components up to the DC region as shown in Figure 3, so during transmission, the low frequency head range shown by the broken line is If the signal is interrupted, the baseline of the signal will fluctuate as shown in FIG. 4, and a 4+ error will likely occur on the receiving and reproducing sides.

On the other hand, in signal transmission via electric lines, there are cases in which a pair of signal lines is used to transmit digital signals and supply power at the same time. Low frequencies are cut off and transmitted. or,
When recording and reproducing digital signals, the low frequency head range of the digital signals is lost due to the differential response characteristics of the magnetic head.

Therefore, in the above example, baseline fluctuation occurs in the forest described above, increasing the possibility of code errors.

For this reason, conventionally, a DC regeneration circuit using a quantization feedback method has been used on the receiving side and the reproducing side to compensate for low-frequency wavefront components.

A conventional DC regeneration circuit is disclosed in Japanese Patent Application Laid-Open No. 129975/1984 (GIIB 20/14), and the configuration of this conventional DC regeneration circuit will be explained with reference to FIG. terminal 1
1), a digital signal having frequency components shown by solid lines in FIG. 6 is input. (2) is an adder, and the digital signal is passed through the low-pass filter (L P F
) '6+ is added to the feedback signal from the discriminator (5
) is applied to The discriminator (5) performs processing such as waveform shaping and data detection, and a 1.0 data signal is obtained from the output terminal (8).

By feeding back the low frequency components of this data signal and the 5 adder (2), the low frequency components shown by the broken line in FIG. 6 are restored. The pass characteristic of the low pass filter (6) is set to be very equal to the low frequency cutoff characteristic (shown by the broken line in FIG. 6) of the digital signal input to the input terminal nH.

By the way, in the above DC reproducing circuit, when the amplitude of the input signal fluctuates (especially when recording/reproducing digital signals such as a digital VTR, due to spacing loss, dropout, etc.) The balance between the compensation signals is lost, and stable compensation cannot be performed.

Therefore, the applicant proposed an improved circuit as shown in Fig.
), In FIG. 7, :9) is a variable gain amplifier, (l
O) is a level detector that detects the level of an input signal (rectifies and smoothes the input signal to obtain an output).

Components that are the same as those in FIG. 5 are given the same reference numerals.

In this improved circuit, the feedback region is controlled according to the level of the input signal M from the input terminal lI), and the compensation of low frequency components is stabilized.

Now, digital government-run recording/playback devices, such as Digital V
In TR, recording/reproduction is performed using a rotating head.

That is, a digital V that records/plays PCM video signals.
The reproduction system of the TR is shown in Figure 8.

In Fig. 8, (1) is the recording/reproducing head 13A.
) (13B) is a guide cylinder provided counterclockwise by 180 degrees, (12) is a magnetic tape which is two media, (14A
)(14A')(14B)(14B) are windings constituting a rotary transformer, and (15A)(15B) are preamplifiers to which each head corresponds.

09) is a waveform equalization layer, and 09 is a reproduction digital signal output terminal.

(The figure shows a (PG) head for cylinder rotation detection, with a guide cylinder (Ill K, fk cut magnet (21)
A) Detect the magnetic flux of (21B). Magnet (2] A) (2
1B) have opposite polarities to each other, and as in FIG. 9 (Cl), signals of positive and negative polarity are obtained.

□□□ is an amplifier, (24A) and (24B) are comparators for separating bipolar signals, and both comparators (
The outputs of 24A) (24B) are sent to delay circuits (25A) (25
B) is delayed by a predetermined amount, and the example R-S flip-flops are alternately set and reset. The output of this R-S flip-flop (26) (FIG. 9(d)) 7>f is used as an RF switching pulse to control the changeover switch Q8). For example, the R-S flip 70 knob and the operating force are H.
When the level is low, the terminal (16A) is selected, and when the level is L, the terminal (16B) is selected.

By the operation of this changeover switch (181), the output of each preamplifier (15A) (15B) (Fig. 9 fa) (b))
are made continuous (synthesized) and become as shown in FIG. 9(e).

By the way, in a digital signal recording/reproducing apparatus, the recorded signal is, as shown in FIG. Contains signals. This preamble and postamble are
The length is set to such an extent that the effective signal section will not be affected by uneven rotation of the cylinder or timing deviation of the RF switching signal. The preamble and postamble are provided for the purpose of speeding up clock recovery for identifying data in a valid signal section (speeding up the pull-in of the PLL circuit).

09 Problems to be Solved by the Invention Now, in the configuration shown in FIG. 8, rotary transformers (14A>(14A<)(14B
) (14B'), the output signal (9th
There are differences in frequency characteristics, amplitude levels, etc. (hereinafter referred to as inter-channel characteristic differences) between FIG. 9(a) and FIG. 9(b).

Therefore, in a fixed DC regeneration cycle as shown in Figure 5 or Figure 7, if the constant is matched to the characteristics of one channel (the thread corresponding to one magnetic head), the compensation for the other channel will be compensated. Errors occur, increasing the possibility of data identification errors.

(2) Means for Solving the Problems Accordingly, the present invention provides a switching means for changing the characteristics of the feedback loop of the DC regeneration circuit in accordance with the output signal of the reversion channel.

(e)) Effect Therefore, the characteristics of the feedback loop of the DC regeneration circuit are! Since the switching is performed according to the output of the & channels, the compensation characteristics of the DC regeneration circuit can be optimized, and data identification errors can be reduced.

(f) Example Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment, and FIGS. 10 and 11 are characteristic diagrams related to the embodiment.

In the drawings, those common to the conventional example are marked with the same reference number 3, and their explanation will be omitted. 12a is an attenuator 1.2 for level adjustment corresponding to the playback output from the Q @ Ki 1 head (13A) (13B), and a level detector;
9) Adjust the output level. The second selector switch selects one of the outputs of the attenuators 1.2 and 4.

Also, the second changeover switch is controlled by the same RF switching pulse (Fig. 9(d)) as the changeover switch (18).In other words, the attenuation is controlled according to each head (13A) (13B) and its transmission system. 1.2 (c) 29) is selected. η is a head switching signal generator that creates RF switching pulses, and is a delay circuit (25A) (25B).
, R-S7 lip-flop □□□.

As described above, there are differences in characteristics between each head (13A) (13B) and its transmission system. For example, as shown in FIG. 11, the head (13A) and its transmission system (channel A
) and head (13B) and its transmission system (y-yannel B
) have different low frequency characteristics. Therefore, if the characteristics of the feedback loop captive QO bus filter (6) in the DC regeneration circuit are matched to channel A;'), a compensation error will occur for channel B.

Therefore, for channel B, the attenuation rate of attenuator 2 (attenuator 2) is varied, and the amount of feedback of low frequency components is varied so that the error rate of binary data is minimized.

In other words, as shown in Figure 10, the attenuation rate (K^) (KB) at which the error L/-F is the minimum is set for each channel (
A, B) are different, m table 128) f29
By adjusting +, the compensation operation for the low frequency component 1 of the V DC regeneration circuit can be optimally set for each channel.

Attenuator J, 2f2 by second changeover switch (30)
81t2'! According to the switching, the output of the adder (2) will fluctuate, and there is a possibility that the clock recovery using the preamble will not be performed promptly. On the other hand, −C is the second
The embodiment shown in the figure is valid.

In the embodiment shown in Fig. 2, a third changeover switch 3υ is provided to select the changeover switch (switching time of one barrel (rising and falling timing of RF switching pulse (Fig. 2 (a))).
For a predetermined period including 1, the control terminal of the l1lTf amplifier (9) is connected, and the DC regeneration circuit (1) and (4) loops are cut off. In other words, since unnecessary changes in the output of the adder 12) during this period are not fed back, the above-mentioned problem does not occur. Incidentally, since the switching of the selector switch II is performed during the postamble/preamble period, there is no need for DC regeneration. or.

According to *i in FIG. 2, the influence of waveform distortion caused by switching at the first changeover switch t181 can also be removed. In the embodiment of FIG. 2, one of the attenuators is selected as in the embodiment of FIG. 1, except during the period when the variable gain amplifier 9) is cut off (see FIGS. 1 and 2).

For the period during which the variable gain amplifier: 9) is cut off, R
Like the F switching pulse, it is created in response to the rotation of cylinder j11). In other words, the comparator (24A) (
24B) It can be created by delaying the output (less than the delay amount of the cardboard circuit (25A) (25B)) and triggering the monomulti.

In the above harmonic example, by changing the gain in the feedback loop, it is possible to compensate for the difference in characteristics of the head and its transmission system.
71:i to b can also be achieved by switching the characteristics of the low-pass filter 61.

(G) Effects of the Invention As described above, according to the present invention, in a DC regeneration circuit to which a digital signal in which the output of the reversion channel is input in a time-division manner, the output of the reversion channel is Since the characteristics of the feedback loop are switched according to the frequency, compensation for low frequency components can be optimally performed in each channel. Therefore, it is possible to reduce errors in data identification, which is effective.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of one embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment, Fig. 3 is a diagram showing the frequency characteristics of Digital No. 1, and Fig. 4 is a diagram showing baseline fluctuations. FIG. 5 is a block diagram of a conventional example, FIG. 6 is a wave number characteristic diagram for explaining the principle of the conventional example, and FIG. 7 is a block diagram showing a second conventional example. 8th
The figure is a block diagram of a reproduction system of a digital VTR, and FIG. 9 is a waveform diagram related to FIG. 8. Fig. 1.0 is a characteristic diagram showing the relationship between uXI attenuation rate and error rate, and Fig. 11 is a characteristic diagram showing the frequency characteristics of each channel. (2)...adder, (5)...data identifier,...
6)...Low pass filter, (9)...Variable gain amplifier, i+o+...Level detector, (13A) (13
B)...Magnetic head, 12-(29)...Attenuator,
(30)81)...Selector switch. Junto Sanyo Electric Co., Ltd. agent Patent attorney Takuji Nishino (1 other person) Yumi fDU ■
-Taste Figure 3 Figure 4 Dry) Gidalli [Mo Figure 5 Figure 6 Four vs. Dark Mantissa Figure 7 Figure Illusion Figure 11 ^8 to 8 ■ , OU v Φ -no -no -no Nノ
−ノward ζ power is full

Claims (1)

[Claims] (1) In a DC reproducing circuit using the quantum feedback method in which reproduced signals from a plurality of magnetic heads are combined into one signal system and inputted, the feedback loop of the DC reproducing circuit corresponds to the reproduced signals from the plurality of magnetic heads. A DC reproducing circuit for a digital signal recording/reproducing device, characterized in that the characteristics of the DC reproducing circuit are changed.