JP3109164B2 - Magnetic playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic reproducing apparatus,
In particular, the present invention relates to a magnetic reproducing apparatus for converting a video signal into a digital signal and reproducing a signal recorded on a magnetic recording medium using a so-called partial response method.

[0002]

2. Description of the Related Art Generally, in magnetic recording and reproduction, an equalizer (equalizer) is used to compensate for amplitude distortion, phase distortion, and the like due to recording and reproduction characteristics of a magnetic recording medium. In recent years, even in such magnetic recording / reproducing, an adaptive equalization method used in communication has been adopted.

[0003] Adaptive equalization has been conventionally developed as a technique for performing high-speed data transmission using a telephone line. In a telephone line, transmission line characteristics change depending on the connection state of the line. Therefore, if a fixed equalizer is used, the transmission path characteristics cannot be completely corrected, and the characteristics of the equalizer need to be adjusted adaptively.

In such a communication system, a method of transmitting a signal whose waveform or the like is known in advance and examining transmission path characteristics and then transmitting a necessary signal (automatic equalization) and a signal itself to be transmitted are used. There is a method (adaptive equalization) for examining transmission path characteristics. In any case, the purpose of the equalizer is to faithfully restore the transmitted signal waveform by automatically removing distortion from the received signal waveform that has been distorted when passing through the transmission path.

In order to consider the application of the above-described adaptive equalization to magnetic recording / reproducing, a magnetic recording / reproducing apparatus converts a video signal into a digital signal and uses a so-called partial response method to a magnetic tape (video tape). It is assumed that a digital VTR (video tape recorder) which records and reproduces data on a VTR. The partial response method is a method of shaping the spectrum of a code by positively utilizing intersymbol interference due to transmission characteristics of a transmission path (or a recording medium). For example, the partial response includes an NRZI code. , Interleaved NRZI codes and the like. A so-called precoder is provided on the recording side, and converts input data into an intermediate sequence in order to avoid propagation of code errors during reproduction (at the time of identification). FIG. 3 shows an example of a configuration on the reproduction side when the above-mentioned adaptive equalization method is employed in a digital VTR that performs magnetic recording and reproduction using such a partial response method.

In FIG. 3, a magnetic signal recorded on a magnetic tape (not shown) is converted into an electric signal by a magnetic head 101, amplified by a reproducing amplifier 102, and sent to a detection characteristic circuit 103. The detection characteristic circuit 103 is a detection characteristic (encode characteristic) of the partial response, and has a characteristic of (1 + D) in class IV. An output signal from the detection characteristic circuit 103 is an equalizer 1 composed of a so-called FIR (finite impulse response) filter or a transversal filter.
The signal is supplied to the decoding circuit 105 and subjected to adaptive equalizing processing. The signal is then supplied to the decoding circuit 105, where "1" or "0" is discriminated by level comparison (comparison) or the like, and the data sequence at the time of recording is decoded. Is performed.

The output d from the decoding circuit 105 is sent to an adder (error detector) 106, and the output y from the equalizer 104 is subtracted, whereby an error (residual error) e is extracted. Sent to adaptive control section 107. The output x from the detection characteristic circuit 103 is supplied to the adaptive control unit 107 as a so-called reference input. The adaptive control unit 107 adjusts the filter characteristic of the equalizer 104 so as to minimize the signal power of the error (residual). When a so-called transversal filter is used for the equalizer 104, the multiplication coefficient (tap coefficient) for each tap is adaptively modified and updated, and the characteristic of the transversal filter is changed to an electromagnetic wave during magnetic recording and reproduction. The adjustment is made so as to be close to the inverse characteristic of the conversion characteristic.

[0008] The output from the decoding circuit 105 is sent to a signal processing circuit 108, where reproduction of a synchronous block, error correction and the like are performed, and the output is sent to a video signal processing circuit 109 to restore the original image data. . In addition, although not shown,
Output data from the signal processing circuit 108 is sent to an audio signal processing circuit, a sub-code signal processing circuit, and the like, where each processing is performed.

[0009]

By the way, in an apparatus for recording and reproducing an image signal such as a VTR, it is conceivable to provide a so-called still image printing function using the obtained image signal. This is considered to be a high value-added and useful function because not only is it possible to display an image signal on a monitor, but also it is possible to enjoy a variety of uses by taking out one frame from the image signal and printing it as a still image.

In the case where such a still image printing function is provided, color correction for matching display colors on a color CRT (cathode ray tube) with colors printed on a color printer, and apparent resolution are improved. Image processing such as edge enhancement is required. Hardware increases due to such image processing, which contributes to an increase in cost.

The present invention has been made in view of such circumstances, and provides a magnetic reproducing apparatus for reproducing a magnetic recording medium on which an image signal is recorded, for example, having an image processing function for printing a still image. In this case, an object of the present invention is to provide a magnetic reproducing apparatus capable of preventing an increase in the amount of hardware.

[0012]

According to the present invention, there is provided a magnetic reproducing apparatus for reproducing magnetic data recorded on a magnetic recording medium, comprising: a filter serving as an equalizer for compensating characteristics of a reproduced signal from a magnetic head; A decoding circuit that decodes an output signal from the filter; an adaptive control function unit that adaptively adjusts the characteristics of the filter based on an input signal to the filter and an input / output signal to the decoding circuit; An image processing function unit that performs image processing on magnetic data obtained from the decoding circuit and outputs the processed data, and performs the same hardware processing for the adaptive processing in the adaptive control function unit and the image processing in the image processing function unit. The above-mentioned problem is solved by realizing using.

Here, an image signal is recorded on the magnetic recording medium, and the image processing may be, for example, color correction or edge enhancement for printing a still image. Also,
The same hardware is a CPU, a DSP (Digital Signal Processor) or the like, and the same hardware is used to set the execution of the algorithm for adaptive control and the execution of the algorithm for image processing in a mode. The two functions may be realized by switching according to time or by performing the processing in a time-division manner.

[0014]

Since the adaptive control function and the image processing function are realized using the same hardware, it is possible to add an image processing function for still image printing or the like without increasing hardware. Become.

[0015]

FIG. 1 is a block circuit diagram showing a schematic configuration of a reproduction system of a digital VTR as described above as an embodiment of a magnetic reproducing apparatus according to the present invention. In FIG. 1, a magnetic signal recorded on a magnetic tape (not shown) is converted into an electric signal by a magnetic head 11 in a mechanical block (not shown) of the VTR, and is then amplified by a reproducing amplifier 12. The signal is sent to the detection characteristic circuit 13. The detection characteristic circuit 13 has a characteristic of (1 + D) which is a detection characteristic (encode characteristic) of the partial response described above. An output signal from the detection characteristic circuit 13 is supplied to a filter 14 which is a main part of the equalizer. As the filter 14, a so-called FIR (finite impulse response) filter or a transversal filter is generally used, and its filter characteristics are adaptively adjusted by an adaptive control function unit 17 described later.
An output signal from the filter 14 is supplied to a decoding circuit 15, and is output as "1" by level comparison (comparison),
A determination of "0" is made, and the data sequence at the time of recording is decoded.

The adder (error detector) 16 is a decoding circuit 1
An error (residual error) e is extracted by subtracting the output y of the filter 14 of the equalizer from the output d of 5 and the error e is sent to the adaptive control function unit 17. Adaptive control function unit 17
The output x from the detection characteristic circuit 13 is supplied as a so-called reference input. This adaptive control function unit 17
Modifies and updates the coefficient (tap coefficient) of the filter 14 so that the signal power of the error (residual) is minimized, so that the equalizer characteristic is close to the inverse characteristic of the electromagnetic conversion characteristic at the time of magnetic recording and reproduction. It is adjusted so that That is,
The filter 14 and the adaptive control function unit 17 constitute a so-called adaptive filter, and the adaptive equalizer can be regarded as one using an adaptive filter for an equalizer.

The output signal from the decoding circuit 15 is sent to a signal processing circuit 18 where reproduction of a synchronous block, error correction and the like are performed, and then sent to a video signal processing circuit 19 to output the original image data. Restore is performed. A part of the output from the video signal processing circuit 19 is, for example, an image processing function unit 2 that performs color correction, edge enhancement, and the like for printing a still image.
Sent to 1. The adaptive control function unit 17 and the image processing function unit 21 are realized by software using the same hardware 20 having a memory or the like in a CPU or DSP. An output signal from the image processing function unit 21 is sent to an interface circuit 22 and sent to, for example, a video printer via an output terminal 23 or to a communication line via an output terminal 24, for example.

Here, the following two methods can be considered to execute the adaptive algorithm of the adaptive control function unit 17 and the image processing algorithm of the image processing function unit 21 using the same hardware 20. First, about one method,
An image reproducing apparatus using a video signal processing circuit 19 without a frame memory for a still image is considered.
In such an apparatus, the reproduction state cannot be set until the operation ends after the start of the still image printout.
In such a case, it is not necessary to operate the adaptive equalization algorithm during the printout operation, so that hardware for adaptive equalization can be allocated for image processing.

Next, as another method, in the case of an image reproducing apparatus provided with a dedicated frame memory for printing a still image, the image reproducing operation is continued even during the printing operation. The image processing algorithm is executed in a time-division manner.

Next, an example of a specific configuration of a so-called adaptive filter including the filter 14 and the adaptive control function unit 17 will be described with reference to FIG. This figure 2
, The reference input x from the input terminal 14 _IN is a delay element corresponding to the number of taps, for example, four delay elements 21a,
1b, 21c, and 21d. Input x ₀ and the delay elements 21a from the input terminal 14 _IN, 21
b, 21c, 21d, x _-1 , x _-2 , x _-3 , x
_-4 are coefficient multipliers 22a, 22b, 22c, 2
The signals are sent to 2d and 22e, multiplied by filter coefficients (filter tap coefficients) w ₀ , w ₁ , w ₂ , w ₃ and w ₄ , respectively, and then added. That is, the coefficient multipliers 22a,
2b are added in an adder 23a, the output from the coefficient multiplier 22c and the output from the adder 23a are added in an adder 23b, and likewise in the adders 23c and 23d, the respective coefficient multipliers 22d, The outputs from 22e are also sequentially added and output as y and sent to the decoding circuit 15. Each filter coefficient w ₀ , w ₁ , w ₂ , w ₃ , w ₄ is
Modification is performed by a coefficient modification (update) control signal from the adaptive control function unit 17.

As an adaptive algorithm used in the adaptive control function unit 17, many methods have been proposed. As one specific example, an LMS (least mean square, least mean square) algorithm will be described. In the following description, the number of the delay elements is generalized to L, and the delay elements 21 ₁ , 21 _{2 ,.}
And At this time, the first input x ₀ and each of these delay elements 21 _1, 21 _2, ..., each output x from 21 _{L
-1, x -2, ···, x} -L each coefficient multiplier 22 _0,
22 _1, 22 _2, ..., is transmitted to the 22 _L, the filter coefficients are w _0, w _1, w _2, ..., is multiplied by w _L, as being added is sent to the adder I have.

The input data and the delay elements 21 in the k-th sample period time of the data sequence of the input x (time _{k) 1, 21 2, ···} , each delay output data from the 21 _L, respectively x _k , _Xk-1 , _xk-2 , ..., x
_{When kL} is set, the input vector X _k to be subjected to the FIR filter processing is set as X _k = [x _k x _k-1 x _k-2 ... x _kL ] ^T (1). T in the equation (1) indicates a transposed symbol. With respect to this input vector X _k , if the above filter coefficients (weighting coefficients) are w _k0 , w _k1 , w _k2 ,..., W _kL and the FIR filter output is y _k , (2)
It looks like an expression.

Y _k = w _k0 x _k + w _k1 x _k-1 + ... + w _kL x _kL (2) Further, a filter coefficient vector (weight vector) W
_{If k} is _defined as W _k = [w _k0 w _k1 w _k2 ... w _kL ] ^T ... (3), the input / output relationship is y _k = X _k ^T W _k = W _k ^T X _k (4) If the desired response and d _k, the error epsilon _k and the output is expressed as _{ε k = d k -y k =} d k -X k T W k ··· (5). The following equation is used to update W _k so that ε _k approaches 0.

W _{k + 1} = W _k −μ ▽ _k (6) In this equation, μ is a gain factor that determines the speed and stability of adaptation, and ▽ _k represents a gradient. The LMS algorithm, ▽ _k is not estimated from the short-term average of epsilon _k ^2, used by partially differentiating epsilon _k ² directly. ▽ _k = δε _k ² / δW = −2ε _k X _k (7) Substituting this equation (7) into the above equation (6), the coefficient update equation becomes W _{k + 1} = W _k +2 με _k X _k (8)

The present invention is not limited to the above embodiment. For example, the specific configuration of the filter 14 and the algorithm used for the adaptive control function unit 17 are not limited to the FIR filter and the LMS algorithm of the above embodiment. It is not limited to. The applicable device is not limited to a digital VTR, and the present invention can be applied to an analog VTR, a device for reproducing a magnetic disk on which image signals are recorded, and the like.

[0026]

As is apparent from the above description, according to the magnetic reproducing apparatus of the present invention, in a magnetic reproducing apparatus for reproducing magnetic data recorded on a magnetic recording medium, a reproduction signal of a magnetic head is reproduced. An adaptive filter is used as an equalizer for compensating the characteristics. After decoding the output signal from this filter, and performing image processing and output, the adaptive processing algorithm in the adaptive filter and the image processing algorithm are the same hardware. Since it is executed using hardware, it is possible to add an image processing function for still image printing or the like without increasing hardware, and it is possible to add high added value without increasing the cost of the apparatus. .

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a schematic configuration of a reproduction system of a digital VTR as an embodiment of a magnetic reproducing apparatus according to the present invention.

FIG. 2 is a block circuit diagram showing a specific example of an internal configuration of an adaptive equalizer (adaptive filter) used in the embodiment.

FIG. 3 is a block circuit diagram showing a schematic configuration of a reproduction system of a digital VTR used for explaining a conventional technique.

[Explanation of symbols]

 11: magnetic head 13: detection characteristic circuit 14: filter (equalizer) 15: decoding circuit (comparator) 16: adder (error detector) 17 ... Adaptive control function unit 18 ... Signal processing circuit 19 ... Video signal processing circuit 20 ... Same hardware 21 ... Image processing function unit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-46908 (JP, A) JP-A-5-40907 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/91-5/956 G11B 5/09 321

Claims (1)

(57) [Claims] 1. A magnetic reproducing apparatus for reproducing magnetic data recorded on a magnetic recording medium, a filter serving as an equalizer for compensating characteristics of a reproduced signal from a magnetic head, and a decoding circuit for decoding an output signal from the filter. An adaptive control function unit that adaptively adjusts the characteristics of the filter based on an input signal to the filter and an input / output signal to the decoding circuit; and image processing of magnetic data obtained from the decoding circuit. An image processing function unit for outputting, wherein the adaptive processing by the adaptive control function unit and the image processing by the image processing function unit are realized using the same hardware.