JPS6227443B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION So-called magnetic recording cards, which are paper cards or plastic cards coated with magnetic recording material, are often used as input/output media for data processing devices. The magnetic material coated on this magnetic card uses a wide range of ferromagnetic materials depending on the purpose, and unlike magnetic tape, the material is not limited. In addition, the thickness of the magnetic material is several μm to 20 μm.
It is often about a certain degree.

This card reading is performed by bringing a ring-shaped magnetic head into contact with the card and driving the card at a constant speed, similar to a magnetic tape device.

When the magnetic layer of a card is thin, a simple coating method similar to that used for ordinary character printing is often used as a coating method, and the variation in thickness is greater than that of magnetic tape or the like.

Since magnetic cards are portable by general users, their magnetic recording surfaces are susceptible to physical and magnetic damage. Morphological deformation of the card or poor surface roughness in the case of paper cards becomes an unstable factor in contact between the magnetic head and the card surface and in constant speed running of the card.

All of these phenomena appear as changes in the read signal level during magnetic recording and reproduction, indicating that magnetic cards have many factors that make data reading errors more likely than magnetic tapes.

In order to improve the reliability of magnetic card reading characteristics with many drawbacks, the present invention provides a plurality of read signal detection levels, automatically selects the detection level according to the magnitude of the read signal level, and stabilizes the magnetic card reading characteristics. The present invention relates to a magnetic recording/reproducing circuit that is capable of obtaining a reproduced signal.

In general, in a magnetic recording/reproducing circuit, the detection level of the read signal is set to a specific value that provides the overall highest read reliability, taking into account the relationship that it is lower to allow for a drop in the read signal and higher to eliminate noise. It will be done. Therefore, in order to lower the detection level and widen the variation range of the read signal level, it is necessary to distinguish between noise and the original signal using a discrimination element other than the level. Furthermore, in signal reproduction using a so-called self-clocking magnetic recording system in which a data signal and a clock signal are extracted by verifying the bit intervals of the resulting signal bit string, bit shifts caused by lowering the detection level must be reduced.

In order to solve these requirements, the present invention focuses on the general characteristics of a magnetic card read signal, that is, when limited to only the magnetic recording medium and the signal reproduction process, the S/N ratio and waveform of the magnetic read signal depend on the medium. The focus is on the fact that the efficiency is almost constant regardless of differences in thickness or poor contact during the regeneration process.
FIG. 1 shows a reproducing circuit showing an embodiment of the present invention. A reproduced signal from a reading head 1 is amplified by an amplifier 2 to a level that can be operated at a subsequent stage, and this signal is applied to a plurality of level detectors 3, 4, and 5 having stepwise different determination levels.

Each time the signal exceeds one of the decision levels, each subsequent monostable multivibrator 6, 7,
8 and outputs a pulse having a fixed time width, for example, 1/2 of the minimum bit repetition time (T). A circuit 10 which ORs these pulses in an OR circuit 9 and extracts the trailing edge of the pulses as a read signal output pulse train constitutes a circuit having a variable determination level depending on the read signal level.

FIG. 2 shows the waveforms of read signals with two different levels as solid lines 11 and dotted lines 12, and the detection levels corresponding to the three level detectors 3, 4, and 5 in FIG. (shown only)
and each logic element output until obtaining the final read signal pulse is made to correspond to a solid line signal 11 and a dotted line signal 12,
The solid and dotted lines are shown with the same numbers as each logical element.

As shown in the operation example in Figure 2, by using this regeneration circuit, even if a low detection level is set, the applied read signal level remains relatively stable (the maximum possible detection level in Figure 2). In the example, the level of noise 1 shown in FIG. 2 is 5 for the solid line signal 11;
The signal can be detected without deteriorating the bit shift characteristics by excluding the three parts.

[Brief explanation of the drawing]

FIG. 1 is an electrical system diagram of a magnetic recording/reproducing circuit according to an embodiment of the present invention, and FIG. 2 is an operational diagram thereof. 3, 4, 5... Level detector, 6, 7, 8...
Monostable multivibrator, 9...OR circuit,
10...Pulse generation circuit.

Claims (1)

[Claims] 1. The output of the reading head is applied to a plurality of level detectors having categorically different judgment levels, the outputs of the detectors are OR'ed, and the read signal is obtained at the trailing edge of the OR output. A magnetic recording/reproducing circuit.