JPS6132746B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital magnetic recording and reproducing device for recording and reproducing digital code signals, and in particular, to record the digital code signal in NRZ, and to adapt the reproduced signal waveform to the characteristics of the magnetic recording and reproducing device. The code signal is recorded and reproduced using a so-called partial response method in which the level of the code signal is identified as being in a different form from that at the time of recording, and then the signal waveform is converted and restored to the form of the original code signal.

Generally, the code signal is regenerated with a good signal-to-noise ratio by level-identifying the received signal waveform as a code signal in a form different from that at the time of transmission, taking into account the transmission characteristics of the signal transmission path, and then the regenerated code is A code signal transmission method that restores the code form of a signal to the code form of an original code signal is called a partial response method. In code signal transmission using this partial response method, distortion of the transmitted signal waveform based on the characteristics of the transmission path and deterioration of the frequency characteristics of the signal-to-noise ratio are taken into consideration. The low-frequency response is lower compared to the normal transmission line, exhibiting differential characteristics, and the low-frequency signal-to-noise ratio is significantly degraded. Received code signal waveform level identification is performed using a code format that is not affected much. As a result, it has the great advantage that, for example, it is possible to identify the level of the received signal waveform with a good signal-to-noise ratio, assuming that the signal waveform is a differentiated version of the transmitted signal waveform. . Therefore, code signal transmission using the partial response method has conventionally been widely used in high-speed digital transmission using coaxial cables, which do not have very good transmission characteristics.

On the other hand, in a magnetic recording/reproducing apparatus, the reproduced signal waveform of a recorded digital code signal suffers from exactly the same distortion of the signal waveform and a partial decrease in the signal-to-noise ratio based on the transmission characteristics of the transmission line. That is, the high frequency response decreases, or the low frequency response decreases compared to the middle frequency range, resulting in a differential characteristic and an increase in low frequency noise. Therefore, it is conceivable to apply the above-mentioned partial response method to magnetic recording and reproduction of digital code signals to achieve good recording and reproduction. That is, in a magnetic recording/reproducing apparatus, the high-frequency response decreases significantly during both recording and reproduction, and since the reproducing magnetic head has differential characteristics, low-frequency components close to DC components are significantly attenuated. Therefore, it is expected that a partial response method that performs signal processing that is compatible with such recording and reproducing characteristics will be extremely effective. However, regarding the recording/reproducing characteristics of a magnetic recording/reproducing device, the higher the density of recording, the more the amplitude fluctuations of the reproduced signal will occur. Therefore, if level identification is performed on the reproduced signal waveform as it is, the occurrence of code errors will significantly increase. In other words, even if the level of the reproduced signal is identified by assuming that a reproduced signal waveform obtained by differentiating the signal waveform at the time of recording is obtained by applying the partial response method, the signal level of the reproduced signal itself will not fluctuate. Therefore, the signal level for the differential waveform cannot be accurately identified. Therefore, merely applying the partial response method did not provide sufficient effects.

Further, in conventional digital magnetic recording and reproducing apparatuses, an amplitude detection method is exclusively used, but this amplitude detection method also poses a problem of large amplitude fluctuations in the reproduced signal during high-density recording. Therefore, conventionally, a threshold level for identifying the level of the reproduced signal waveform, that is, a so-called threshold voltage, is formed from a rectified output voltage obtained by peak rectifying the reproduced pulse signal waveform, and the threshold level always follows the amplitude fluctuation of the reproduced signal. By varying the amplitude, accurate level identification can be performed regardless of amplitude fluctuations of the reproduced signal. However, when the partial response method is applied to the magnetic recording and reproducing of digital code signals, for example, a differential signal obtained by differentiating a binary code signal and a delayed differential signal obtained by delaying the differential signal by 1 bit are used. When identifying the level of the reproduced signal waveform as a value code signal, even if the peak rectification of the reproduced signal waveform is performed to set the threshold level as described above, the highest peak level occurs in the ternary code signal waveform. Since the probability is significantly lower than that of a binary code signal waveform, it is extremely difficult to set a threshold level that constantly follows the amplitude fluctuations of the reproduced signal by simply peak rectifying the reproduced signal waveform as in the past. . In the end, in the past, even if the partial response method was applied to magnetic recording and reproduction of digital code signals, it was not sufficiently effective, and it was considered extremely difficult to perform digital recording and reproduction with good characteristics. .

An object of the present invention is to solve the above-mentioned conventional problems, and to record a digital code signal in a code format suitable for recording and reproduction characteristics by applying a partial response method, and to record a digital code signal in a code format that is suitable for recording and reproduction characteristics, and to be independent of amplitude fluctuations of the reproduction signal. It is an object of the present invention to provide a digital magnetic recording and reproducing device which can accurately record and reproduce digital code signals by accurately identifying the level of a reproduced signal waveform.

That is, the digital magnetic recording and reproducing apparatus of the present invention is a digital recording and reproducing apparatus that records, reproduces and restores a desired binary code signal.
When recording a value code signal, record a recording binary code signal formed by modi-euro 2 conversion of the binary code signal and a binary code signal obtained by delaying the converted output binary code signal by 2 bits. and the desired 2
When reproducing and restoring the value code signal, in the ternary code signal formed by analog addition of the reproduced signal waveform of the binary code signal for recording and the delayed signal waveform obtained by delaying the reproduced signal waveform by 1 bit, The desired binary code signal is reproduced by forming a binary code signal having a signal level of 1 corresponding to each of the signal levels representing +1 and -1, and further comprising: In order to make the threshold level for signal level identification of the reproduced signal follow the amplitude fluctuation of the reproduced signal, the threshold for level identification is set based on the peak value of the voltage sampled at each bit position of the reproduced signal waveform. be.

The invention will be explained in detail below by way of example embodiments with reference to the drawings.

Examples of the configuration of the recording system and the reproducing system of the digital magnetic recording/reproducing apparatus of the present invention are shown in FIGS. 1a and 1b, respectively, and the signal waveforms of each part are shown in FIG. 2.

First, the operating principle of the recording/reproducing apparatus of the present invention will be outlined. That is, for example, 2 shown in signal waveform B in FIG.
The reproduced signal waveform obtained by recording the value code signal becomes a signal waveform C obtained by differentiating the signal waveform B. Therefore, at the time of reproduction, the differential waveform of the reproduced signal and the differential waveform of the reproduced signal delayed by 1 bit are added in analog form and converted into the form of a ternary code signal shown in signal waveform D. Therefore, it takes 3
By forming a binary code signal in which the "0" level in the value code signal waveform is "0" and the "+1" level and the "-1" level are both "1" levels, a desired binary code signal can be obtained. Play and restore.

On the other hand, during recording, the signal is recorded with the expectation that the reproduced signal waveform will be in a form obtained by differentiating the recorded signal waveform, so that the desired ternary code signal can be restored by converting the code signal waveform during reproduction as described above. Do the following. For example, a recording signal waveform is formed by performing modulus-2 conversion between a desired binary code signal shown in signal waveform A and a binary code signal obtained by delaying the converted output binary code signal by 2 bits. That is,
When the signal levels of both input code signals are "0" and "1" or "1" and "0", respectively, the signal level of the output code signal is set to "1",
The signal levels of both input code signals are both “0”
Alternatively, when both are "1", a logical operation is performed to set the signal level of the output code signal to "0", thereby converting the signal waveform A of the desired binary code signal into the signal waveform B in advance, and then transmitting it to the magnetic recording medium. to be recorded. Therefore, even if the reproduced waveform of the binary code signal to be recorded becomes a differential waveform of the original signal waveform during the recording and reproduction process, the signal level of the reproduced signal can be identified without code errors and with a good signal-to-noise ratio. You will be able to do it accurately.

That is, in the recording system of the apparatus of the present invention shown in FIG. The value code signal is delayed by 2 bits by two cascaded 1-bit delay elements 5 and 6, and then fed back to the converter 1 for modulus 2 conversion. That is, between the 2-bit delayed conversion output signal and the input binary code signal A, as described above, both "0, 1" and "1, 0" are set to "1", and "0, 0" and " 1,
The conversion output binary code signal B is formed by performing a logical operation of modulus 2 in which both 1 and 2 are set to 0.The conversion output binary code signal B is amplified to an appropriate level by the recording amplifier 2, and then Then, the data is recorded on the magnetic tape 4 by the recording magnetic head 3.

Incidentally, the reproduction system signal consists of differentiation of a signal waveform according to the above-mentioned recording and reproduction characteristics, ternary encoding by analog addition of the differentiated waveform signal with a 1-bit delayed signal, and conversion of the ternary code signal into a binary code. If the processing process is a forward conversion process in the so-called partial response method, the modi-euro 2 conversion in the recording system is a reverse conversion process for pre-coding in which the code format of the desired binary code signal is converted in advance in preparation for the forward conversion. It can be seen as a process of transformation. It goes without saying that the cascade connection of the 1-bit delay elements 5 and 6 described above can be replaced with a 2-bit delay element if an appropriate commercially available product is available.

On the other hand, in the reproduction system of the apparatus of the present invention shown in FIG. A reproduced signal waveform C is obtained which is differentiated and whose high frequency components are attenuated. That is, when the recording current is reversed from negative to positive by the binary code signal waveform B, a positive pulse waveform is obtained, and when the recording current is reversed from positive to negative, a reproduced signal waveform C is obtained that has a negative pulse waveform. It will be done. A reproduced signal C having such a waveform is supplied to an equalizer 9 via a reproduction amplifier 8. Equalizer 9
In the process of magnetic recording and reproduction, the high frequency components are attenuated and the reproduced signal waveform is differentiated. First, the high frequency response is compensated for, and the high frequency component is attenuated and differentiated into a form similar to a ternary signal waveform. The signal level identification of the corrected signal is not forcibly handled as a binary code signal in the code format at the time of recording, but rather is handled smoothly and accurately as a ternary code signal. That is, in order to clearly form a ternary code signal according to the partial response method, the reproduced signal waveform C that has undergone high frequency compensation and the reproduced signal waveform C are
The bit-delayed signal waveform is added in an analog manner and converted into a ternary code signal waveform D. This 3
The value sign signal waveform D is approximately + at the bit position.
Since it has a signal level corresponding to 1, 0, or -1, by setting the signal level of +1 and -1 at each bit position to 1 and the signal level of 0 to 0, a binary code is created. Convert to signal. As a result, the original desired binary code signal A before being precoded during recording is reproduced. Restoration conversion from the ternary code signal D to the binary code signal A is performed by the differential amplifier 10, level comparators 12 and 13, and OR circuit 15 shown in FIG. A reference signal having a threshold level for identification is supplied from an automatic threshold control (ATC) voltage generation circuit 14.

That is, by guiding the ternary code signal D from the equalizer 9 to the differential amplifier 10 and finding the difference signal between the signal level and 0 level at each bit position of the ternary code signal D, +1 and -1 A + output signal and a - output signal respectively corresponding to are taken out.
Note that the - output signal has its polarity converted and is taken out in the form of a positive voltage. In order to clearly identify and encode the signal levels of both the + and - output signals, the + and - output signals are supplied to level comparators 12 and 13, respectively, and the signal levels of these output signals are A level comparison is performed with a threshold level signal having a signal level approximately 1/2 that of the signal level. As a result, both output signals are clearly +1
When it is confirmed that the comparison output signal has a signal level corresponding to -1, a comparison output signal of +1 is taken out. Then, these level comparison output signals are led to the OR circuit 15 so that when the ternary code signal D has a signal level of +1 or -1 at that bit position, an OR gate output signal of +1 is obtained. do. This OR gate output signal shows the same signal waveform as the original binary code signal A. This OR gate output signal is supplied to the D flip-flop 16, subjected to waveform shaping, and then taken out from the output terminal as a reproduced binary code signal.

The signal processing in each process in the above-described reproduction system is performed under the control of a clock signal generated by controlling the reproduction circuit 11 using timing information extracted from the reproduction signal C by the equalizer 9. The reproduced clock signal is taken out from the output terminal and used for restoring the reproduced output binary code signal.

The reference signal for setting the threshold value for the level comparison performed by the level comparators 12 and 13 in order to check the signal levels of +1 and -1 in the above-mentioned converted output ternary code signal is indicated by the dotted line in FIG. 1b. Automatic threshold control (ATC) voltage generation circuit 14 shown in a box
Supplied from. In this ATC voltage generation circuit 14, the + output signal and the - output signal, both of which are taken out as positive polarity voltages, from the differential amplifier 10 are
Through the switches S ₁ , S ₂ and _the diodes D ₁ , D ₂ respectively, _the capacitor C _p
to charge the battery. If the clock pulse that closes switches S ₁ and S ₂ is a short time centered on the bit position, then the peak value of the converted output ternary code signal at each bit position is taken as a positive voltage. Can be rectified. Therefore, since the probability that +1 or -1 will occur in the ternary code signal waveform is approximately 1/2, a in the equalizer output signal waveform D shown in FIG.
For example, even if there is an amplitude fluctuation in the reproduced signal waveform as described above, with a probability that is sufficiently greater than the probability that a peak level higher than the signal level of +1 will occur, as shown in the point, the signal will always follow the amplitude fluctuation and maintain the appropriate level. +
A voltage value corresponding to a signal level of 1 or -1 can be stably extracted. Also, a potentiometer R connected in parallel with the charging capacitor C _p
The discharge time constant CR, which is determined by , can be set to a small value corresponding to the period of the regenerated clock pulse. Therefore, by adjusting the potentiometer R, the threshold level to be extracted can be changed to an appropriate value in a sufficiently stable manner in response to amplitude fluctuations of the reproduced signal waveform. Note that the discharge time constant CR mentioned above is preferably set to about 10 to 100 times the bit interval, that is, the period of the clock pulse.

Note that the above-mentioned threshold level setting method for level identification of a multi-level code signal waveform is also applicable to the level identification of a ternary code signal of a partial response reproduction conversion output in a magnetic recording/reproducing device for a digital code signal. be able to. In other words, it can be widely applied to level identification of multilevel code signal waveforms when signal waveforms are generally distorted due to signal transmission such as recording and reproduction, and amplitude fluctuations occur in received and reproduced signals. A similar effect can be obtained in that accurate level identification can be performed regardless of amplitude fluctuations.

That is, in the same way as described above for the reproduction signal conversion output ternary code signal of a partial response type digital magnetic recording and reproducing device, the signal level at each bit position of the multi-value code signal waveform whose signal level is to be identified corresponds to the signal level at each bit position. The extracted voltages are peak-rectified with a time constant corresponding to the cycle of state changes such as amplitude fluctuations occurring in the multilevel code signal, and the levels are compared based on the peak rectified output. By setting the threshold level of , it is possible to set the threshold value that always follows the amplitude fluctuation of the code signal whose level is to be discriminated. Furthermore, if the highest signal level in the multilevel code signal waveform for which level identification is to be performed can be identified and extracted at appropriate time intervals, instead of extracting the signal level for each bit position, Extract only the level, perform peak rectification with a time constant commensurate with the above-mentioned time interval, divide and multiply the peak rectified output voltage, and set thresholds for level comparison for each signal level of the multilevel code signal. You can also do it like this.

As is clear from the above description, according to the present invention, in a digital magnetic recording/reproduction device, the high frequency response is greatly reduced, and the low frequency response is also significantly lower due to the differential characteristics based on the characteristics of the winding of the magnetic reproduction head. However, by applying the partial response method, the binary code signal is converted into a ternary code signal and the signal level of the reproduced signal is identified. Code signals can be faithfully reproduced with a good noise ratio. Moreover, it is not adversely affected by amplitude fluctuations in the reproduced signal that occur when such digital magnetic recording and reproduction are performed at high density. Therefore, by accurately identifying the reproduced signal level in a state with a good signal-to-noise ratio, it is possible to magnetically record and reproduce digital code signals with an extremely low bit error rate without causing code errors due to adverse effects of the recording and reproduction characteristics. can be done.

[Brief explanation of the drawing]

FIGS. 1A and 1B are block diagrams showing configuration examples of a recording system and a reproducing system, respectively, in the magnetic recording and reproducing apparatus of the present invention, and FIG. 2 is a waveform diagram showing signal waveforms of each part thereof. 1...Moji Euro 2 converter, 2, 8...Amplifier, 3, 7...Magnetic head, 4...Magnetic tape,
5, 6... 1-bit delay element, 9... Equalizer, 1
0...Differential amplifier, 11...Clock regeneration circuit,
12, 13...Level comparator, 14...Automatic threshold control (ATC) voltage generation circuit, 15...OR circuit,
16...D flip-flop, _S1 , _S2 ...open/close switch, _D1 , _D2 ...diode, _Cp ...capacitor, R...potentiometer.

Claims (1)

[Claims] 1. In a digital recording/reproducing device for recording, reproducing and restoring a desired binary code signal, the desired binary code signal is
When recording a value code signal, record a recording binary code signal formed by modi-euro 2 conversion of the binary code signal and a binary code signal obtained by delaying the converted output binary code signal by 2 bits. , in reproducing and restoring the desired binary code signal, the recording 2
Signal level at each bit position of a signal waveform representing +1 and -1 in a ternary code signal formed by analog addition of a reproduced signal waveform of a value code signal and a delayed signal waveform obtained by delaying the reproduced signal waveform by 1 bit. By comparing the absolute value of , and the voltage level obtained by peak-rectifying and dividing the signal levels into positive polarity, the binary code having a signal level of 1 corresponding to each of the signal levels is obtained. A digital magnetic recording/reproducing device characterized by forming a signal.