JPS6227444B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic recording and reproducing devices such as magnetic disk devices, magnetic tape devices, and magnetic drum devices, and more particularly to a signal detection circuit that detects a signal by comparing a reproduced signal with a reference voltage.

One of the modulation methods for magnetic recording and reproducing devices is a modulation method that uses phase discrimination, such as frequency modulation.
There are modified frequency modulations, etc., but even in this case, an amplitude detection method may be used to detect the start mark of data or the start mark of phase discrimination.

Conventionally, when performing this type of amplitude detection, an input signal is amplified, compared with a threshold value, and converted into a binary level. However, if an area without magnetization reversal is used as the start mark, noise pulses may be generated due to defects in the recording medium, worsening the signal-to-noise ratio, or the time constant of the readout circuit may be affected when switching from writing to reading. It took a considerable amount of time for the amplitude to stabilize. In order to improve these problems, a method is used in which the signal waveform is differentiated and then the amplitude is detected. This is because noise pulses caused by media defects have smaller frequency components than the signal, improving the signal-to-noise ratio, and using a smaller time constant due to differentiation, the time required for the signal amplitude to stabilize can be shortened. .

Figure 1 shows an example of the detection process when using post-differentiation amplitude detection in the modified frequency modulation method.
As shown in the waveform 1' after differentiation with respect to input signal 1, a step-like amplitude change occurs when the data changes from continuous "1" to continuous "1" and then "0". 2 is a threshold or slice level that follows a certain percentage of the peak level of the waveform, but if the tracking time constant is increased, if the amplitude decreases in steps due to the recorded data pattern, the slice signal as shown in slice signal 3 will increase. An undetectable signal is generated. If this undetectable signal continues for a long time, it may be mistaken for a start mark. These problems similarly occur in an amplitude detection method using an automatic gain control circuit and a fixed slice level.

An object of the present invention is to provide a signal detection circuit with a small error rate in an amplitude discrimination method.

Another object of the present invention is to provide a novel signal detection circuit that is not affected by changes in data patterns.

Generally, a signal waveform reproduced from a recording medium used in a magnetic recording/reproducing apparatus is attenuated as the recording frequency increases. When differentiated for peak detection, the frequency characteristics are reversed and the amplitude increases as the recording frequency of the signal waveform increases, resulting in step-like amplitude changes depending on the data pattern. Therefore, by inserting a low-pass filter, it is possible to attenuate signal waveforms with high recording frequencies and improve amplitude fluctuations due to data patterns.

Describing the configuration of the present invention, the present invention includes a transducer, an amplifier, a first low-pass filter,
A differentiator, a zero-crossing detector, and a signal processing circuit are connected in series in this order, and further, between the differentiator and the signal processing circuit, the output of the slice level generator to which the output of the differentiator is input is connected to the other input. In a signal detection circuit for a reproduced signal of a magnetic recording/reproducing device or the like to which a level detector is connected, a second low-pass filter is provided between the differentiator and the slice level generator and level detector. This is the inserted signal detection circuit.

The present invention will be explained below by way of examples with reference to the drawings.

FIG. 2 shows an embodiment of the present invention regarding a magnetic recording/reproducing device, and FIG. 3 is a diagram showing waveforms at each part thereof.

In FIG. 2, a transducer 4 converts information on the recording medium into an electrical signal. The converted electrical signal is amplified by an amplifier 5, passes through a first low-pass filter 6, and then is input to a differentiator 7. 1st
An example of the output signal of the low-pass filter 6 is shown in 1 in Fig. 3.
4, and the waveform 15 is obtained by differentiating the signal waveform 14 with the differentiator 7. When the amplitude of this differential waveform 15 is switched from a continuous "1" pattern to a continuous "1" and "0" pattern, a step-like amplitude change occurs due to the pattern effect. 8 is a zero crossing detector,
In combination with the differentiator 7, a peak detector is configured that outputs pulses corresponding to positive and negative peak points of the input waveform. Next, in the present invention, the differentiator 7 and the level detector 1
The differential waveform 15 is input to a second low-pass filter 9 newly provided between the filter 1 and the filter 1, and a waveform 16 is output. The high frequency components of the waveform 16 are attenuated by the second low-pass filter 9, so by setting the second low-pass filter 9 to appropriate characteristics, continuous "1" pattern amplitude, continuous "1", "0" ``The amplitude of the pattern can be made equal. Naturally, due to variations in the frequency characteristics of the transducer, the amplitude ratio of the continuous "1" pattern and the continuous "1" and "0" patterns changes, but it is greatly improved compared to the output waveform 15 of the differentiator 7. As a result, the output of the slice level generator 10 to which the output of the second low-pass filter 9 is input, that is, the slice level 17, is not affected much by the data pattern, and the peak amplitude of the signal waveform 16 input to the level detector 11 is also Since the influence of the data pattern is reduced, missing bits due to level detection will no longer occur, as shown in the output signal 18 from the level detector 11 in FIG.

For the above reasons, the time constant of the slice level generator can be increased, and the peak hold characteristic that follows the peak level of the waveform can be further improved. Another advantage is continuous “1”,
The dip in the center seen in the differential waveform of the "0" waveform is also improved because the third harmonic is attenuated.
Therefore, a stable level detection output unaffected by pattern effects as shown in the waveform 18 can be obtained, and a stable signal pulse can be outputted by the signal processing circuit 12 together with the output of the peak detection circuit 8.

The effects described above are achieved not only by making the slice level follow the peak level of the signal and detecting the level, but also by controlling the signal amplitude to a constant value using an automatic gain control circuit and comparing it with the slice level at a constant value. It is equally effective in the method of

Further, the circuit according to the present invention is effective not only for detecting a starting mark without magnetization change, but also for a general amplitude discrimination method in which input signals are discriminated based on their amplitude.

As explained above, according to the present invention, in a method of amplitude detection after differentiating an input waveform, a stable amplitude detection output can be obtained by inserting a low-pass filter between the differentiator and the level detector. As a result, it is possible to provide a magnetic recording/reproducing device with a low error rate.

[Brief explanation of the drawing]

FIG. 1 shows a time chart when a conventional circuit is used, FIG. 2 shows a block circuit diagram of an embodiment of the present invention, and FIG. 3 shows a time chart for explaining the operation of FIG. The symbols used in the drawings indicate the following. 4...transducer, 5...amplifier, 6...
...first low-pass filter, 7...differentiator, 8...zero-crossing detector, 9...second low-pass filter, 10...
... Slice level generator, 11 ... Level detector, 12 ... Signal processing circuit, 13 ... Output terminal,
14... Input signal of differentiator 7, 15, 15'...
Output signal of differentiator 7, 16, 16'...15, 1
The signal after passing through the second low-pass filter 9 at 5', 17
...10 output signals, 18...11 output signals.

Claims (1)

[Claims] 1 A transducer, an amplifier, a first low-pass filter, a differentiator, a zero-crossing detector, and a signal processing circuit are connected in series in this order, and the differentiator is further connected between the differentiator and the signal processing circuit. In a signal detection circuit for a reproduced signal of a magnetic recording/reproducing device, etc., to which a level detector whose other input is the output of a slice level generator whose output is input is connected, the differentiator, the slice level generator, and the level detector are connected. A signal detection circuit characterized in that a second low-pass filter is inserted between the detector and the detector.