SU672640A1 - Device for reproducing digital information from magnetic tape - Google Patents

Description

I

The invention relates to instrumentation, namely, devices for reproducing digital information from a magnetic tape.

A device for reproducing information from a magnetic tape, containing a reproduction head, a preamplifier, a two-pole high-level threshold detector, a positive and negative peak detectors, a two-pole peak detector, AND, OR circuits, two pulse generators, two inverters, a trigger, a shaping circuit, is known. output pulses and an error indicator connected in a specific way 1.

This device is intended to reproduce - information from a magnetic tape recorded in a non-returning to zero (BVN) manner.

The disadvantages of this device are considerable complexity, low noise immunity, especially for impulse noise, and device malfunction in the presence of parasitic amplitude modulation (PAM) of the useful signal simultaneously with a low signal-to-noise ratio, which always takes place at low speeds of reproduction and reproduction.

The closest in technical essence is a device for reproducing digital information from a magnetic tape, containing a magnetic reproduction head associated with a magnetic tape, a series-connected preamplifier, an absolute level detector, a differentiator, and a bistable multivibrator and a pulse noise suppression circuit. connected to the logical element And 2.

However, the reliability of recovering digital information recorded on a magnetic tape at low speeds is low.

The aim of the invention is to increase the reliability of reproduction of digital information recorded at low tape speeds, and to simplify the design of the device.

The goal is achieved by the fact that the device is equipped with a threshold element, an input connected to an absolute level detector and an output to an I logical element, and the output of a differentiator is simultaneously connected to a bistable multivibrator and to a pulse suppression circuit. FIG. 1 is a block diagram of a device for reproducing digital magnetic recording information; in fig. 2 - timing diagrams for the operation of the device. The device contains a magnetic reproduction head 1, conjugated with magnetic tape 2, connected in series preamplifier 3, absolute level detector 4, the output of which is simultaneously connected to differentiator 5 and threshold element 6. The device also contains a bistable multivibrator 7 and pulse suppression circuit 8 inputs simultaneously connected to the differentiator 5, and the outputs - to the logical element And 9. In addition, the output of the threshold element 6 is connected to one of the inputs of the logical element And 9, the output of which is connected to the shaper 10 output pulses. The impulse noise suppression circuit 8 comprises a series-connected comparator 11 integrating circuit 12 and Schmidt trigger 13. The principle of operation of the device is as follows. A two-pole digital information signal, previously recorded on a magnetic tape, for example by a BHHM method, reproduced by head 1 from a magnetic tape 2, is amplified by a preamplifier 3 and fed to the input of an absolute level detector 4, which forms a unipolar digital information signal. Further operation of the device is explained. With FIG. 2. The signal contains a typical information signal 14, as well as a noise signal 15 having a small amplitude, and a duration commensurate with the duration of the information pulse. Such an interference signal may occur at the input of the device under the influence of the magnetic head, for example, various background noise from power sources, noise from the tape. After detector 4, signals simultaneously arrive at differentiator 5 and threshold element 6. After differentiation, a signal 16 is formed, which has two polarities and takes a zero value at the transition from one polarity to another at a time instant coinciding with the peak of the original signal 14. At the same time, the transition through the zero of the signal 16 does not depend on the change in the amplitude of the original signal 14. In a similar way, a differentiated signal 17 is generated from the noise from the original signal 15. The differentiated signal simultaneously arrives at the bistable Multivibrator 7 and the comparator 11 of the impulse noise suppression circuit 8. The output of the bistable multivibrator 7 produces positive pulses 18, the falling edges of which correspond to the moment of change of the sign of the differentiated signal from negative to positive, i.e. the peaks of the original signals 14 and 15. Next, the pulses 18 go to one of the inputs of the logic element I. At the output The comparator 11 produces positive pulses 19, which coincide with the negative half-periods of the differentiated signal. After the comparator, the pulses arrive at the integrating circuit 12. To more effectively suppress the impulse noise, the trigger level of the comparator 11 is set relatively low, and the time constant of the integrating circuit 12 can be chosen from the following condition:. where tjy, is the time constant of the integrating circuit 12; fc is the duration of the information signal. The signal 20 after the integrating circuit 12 enters the Schmidt trigger 13, with a threshold of 21 and a release threshold of 22. The Schmidt trigger 13 produces positive pulses 23 arriving at one of the inputs of the logic element I. When the input signal 14 arrives at the threshold element 6, the latter passes from the first state to the second and at its output a pulse 24 is formed under the condition that the input signal level exceeds the specified value of the reference voltage 25. The value of the reference voltage 25 is selected based on the specified ratio Ping-shum at the input of the device relative to the minimum level of the useful signal. Since the input level of the 15 noise is below the level of the reference voltage 25 of the comparator 6, the latter does not go from the first state to the other. Therefore, at the output of the threshold element 6, the output pulse will be absent. Logic element AND 9 responds to the coincidence of pulses 18, 23 and 24 and at the output generates a pulse 26, the falling edge of which coincides with the peak of the input signal 14. This also eliminates erroneous pulses at the output of the logic element AND 9, thereby also at the output of the device, effects of noise signals 15, the duration of which is commensurate with the duration of the useful signal 14. From the output of logic element 9 and 9 pulse 26 is fed to the driver of the output pulses 10, which forms the output pulse 27 of the required duration and amplitude, while m the front edge of the output pulse 27 coincides with the peak of the useful signal 14.

Claims (2)

1. US Patent No. 3581.297, cl. 340-174.1, publ. 1971. 2. US patent number 3617904, cl. 328-117, publ. 1971. 2f: tS t I, ta / / 2k I hjr Figg