JPH0230107B2 - JIKIKIROKUYOMITORIHOSHIKI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reading information recorded on a magnetic recording medium using the F2F frequency modulation method.

In this type of reading system, it is necessary to reproduce the read clock signal from the read signal, and conventionally, this reproduction has been carried out in the following manner. That is, the clock signal generation time for the bit currently being read is estimated by performing a predetermined calculation based on the cycle time of the previous adjacent bit that has already been read, and a clock signal is generated at that time. However, the circuits used for this purpose, such as arithmetic circuits and counters, are complex and have the disadvantage of being expensive when fabricated on a single-chip LSI.

On the other hand, when reading, when the magnetic recording medium is a magnetic card, for example, changes in the moving speed of the magnetic recording medium inevitably cause jitter in the cycle time of the read bits, causing reading errors. In order to eliminate reading errors caused by this jitter, it is sufficient to provide a margin for determining "1" data or "0" data for each bit, but conventionally, this margin is ``The drawback was that there was a big difference between the data and the data.

In view of the above-mentioned drawbacks, the object of the present invention is "1"
It is an object of the present invention to provide a magnetic recording/reading method which can achieve a balance between data determination margins of "0" and "0" and can realize reproduction of a read clock signal with an inexpensive configuration.

The present invention includes a counter that counts the cycle time of read bits, a circuit that performs a predetermined operation based on count data of the cycle time of the adjacent bit that has been read, and a register that temporarily stores the operation result. It is characterized by executing a 5/8 calculation, and is particularly suitable for a reading method when the moving speed of a magnetic recording medium changes.

Examples of the present invention will be described below while comparing them with conventional examples.

FIG. 1 shows a block diagram of a demodulation method to which this method is applied.

The F2F frequency modulation signal reproduced by the magnetic head is input to terminal 101. This signal is the control circuit 1
bit cycle time counting circuit 10 through 02
Time counting is performed at 3. The control circuit 102 detects the falling and rising edges of the input signal and controls the counting circuit 103 and the comparison circuit 106. Based on this count data, the arithmetic circuit 104 performs a predetermined arithmetic process, and the result of the arithmetic operation is held in the register 105. Subsequently, the cycle time of the next bit is counted by the counting circuit 103, and the comparator circuit 106 compares this counted data with the operation data of the previous bit held in the register 105, and when they match, the data is output to the terminal 107. output data from terminal 108 and a read clock pulse from terminal 108.

The principle of conventional demodulation will be explained in more detail with reference to FIG.

In FIG. 2, for convenience, "1" data 201,
The explanation will be made using the same time axis for the "0" data 202. When such a signal is input, assuming that the currently read bit is the n-th bit, judging from the cycle time T of the n-1th bit of the previous adjacent bit, the “1” data is The direction of the read error is the direction in which the speed of the magnetic recording medium is reduced and the cycle time becomes longer, so that the bit cycle time of the "1" data 201 becomes T1. Conversely, in the direction of the read error of "0" data, the speed of the magnetic recording medium is accelerated and the cycle time is shortened, so that the bit cycle time of "0" data 202 becomes T0. At this time, the time t _d in Figure 2 is the data judgment time, and in the case of "1" data, it is a 2F signal (the period is twice that of the 0 signal), so the signal level must be inverted at this time. Must be. Furthermore, since it is an F signal in the case of "0" data, it must be a signal with no inversion at this time. In this way, the degree of deceleration and acceleration of the magnetic recording medium is "1".
Accurate reading can be performed as long as the range Δt ₁ ' does not exceed t _d even if the cycle time of data is extended, and the range Δt ₀ does not exceed t _d even if the cycle time of "0" data is shortened. But this time
_td does not take into account changes in the moving speed of the magnetic recording medium, is set at 3/4T from the start point of the bit cycle time, and is estimated to be the center of the margin at the middle of the cycle time.

However, judging from the bit cycle time margin, the bit cycle time margin for "1" data continues to slow down to Δt ₁ in Figure 2, and compared with the bit cycle time margin Δt ₀ for "0" data, it becomes "0". ``The data bit cycle time margin has become smaller,
The balance will be severely disrupted.

In addition to these drawbacks, magnetic recording media that are operated manually, such as with magnetic cards, are generally accelerated in many directions, and for this reason, a narrow margin for the bit cycle time of "0" data can lead to read errors. The disadvantage is that it is easy to cause

The principle of demodulation of the present invention which eliminates such drawbacks will be explained with reference to FIG.

As already explained with reference to FIG. 2, it is determined that the maximum margin is when the bit cycle time margin Δt ₁ of the "1" data 301 and the bit cycle time margin Δt ₀ of the "0" data 302 are equal. As a result, taking into account the lengthening of the bit cycle time for "1" data and the shortening of the bit cycle time for "0" data due to the decrease and increase in the moving speed of the magnetic recording medium,
When the data judgment time _td is calculated, the cycle time T of the previous bit that has already been read is found.
The value is close to 5/8 of .

Using this principle, the arithmetic circuit 1 in FIG.
04 is configured to obtain 5/8 of the cycle time count value from the counting circuit 103, and a comparison circuit 106 compares it with a series of count data of the next bit sent from the counting circuit 103. When the count value of the previous bit reaches 5/8, the data is determined and the output data is sent from the terminal 107, and the read clock pulse is set to be output from the terminal 108. 8 like this
In the case of 5/5 arithmetic, the number of logic elements can be reduced by about 10% because the number of calculation steps is reduced compared to the conventional configuration for 3/4 arithmetic, and it is possible to reduce the number of logic elements by approximately 10%. As a result, we were able to reduce costs by 1/3.

As explained above, according to the present invention, F2F
When reading magnetically recorded information using the frequency modulation recording method, it has a well-balanced wide operating margin for "1" data and "0" data, and uses a low-cost circuit configuration with a reduced number of logic elements. method can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a demodulation circuit to which the present invention is applied, FIG. 2 is a timing chart of the conventional method, and FIG. 3 is a timing chart of the present invention. In the figure, 102: control circuit, 103: bit cycle time counting circuit, 104: arithmetic circuit, 10
5: Register, 106: Comparison circuit, 201, 30
1: “1” signal, 202, 302: “0” signal.

Claims (1)

[Claims] 1 In a demodulation method that reproduces information recorded on a magnetic recording medium using the F2F frequency modulation method, when reproducing a read clock from a read signal, the cycle of adjacent bits that have already been read from the time when reading started for the bit being read A magnetic recording reading system characterized in that the reading clock is generated at a time when five-eighths of the time has elapsed.