JPS59221814A - Digital signal reproducing device for cassette tape - Google Patents

Abstract

PURPOSE:To reproduce a digital signal from a cassette tape by clamping an audio signal from a cassette recorder, making its output pass through a BPF constituted of an operational amplifier, and waveform-shaping it by a zero crossing comparator. CONSTITUTION:A reproducing signal from an earphone terminal of a cassette recorder becomes an input signal. Said signal is clamped to about + or - 0.7V by diodes D1, D2, and an unnecessary high frequency signal is eliminated by an LPF constituted of R1 and C1. A band pass filter is constituted of an operational amplifier, its band frequency is set to fL and fH, and when R3/R2 is set to a suitable value being larger than ''1'', an AC waveform which is swung up and down is obtained centerning around voltage VS divided by a resistance R4 and R5 between voltage VC and an earth. A zero crossing comparator CMP waveform-shapes an AC wavform which has passed through a BPF, to a pulsative square wave. In this way, a reproducing performance can be improve remarkably by shaping a waveform to a square wave.

Description

[Detailed Description of the Invention] Recent advances in semiconductor technology have made it possible for personal computers to become one of the lowest? The advent of home computers [Yoji, computers are becoming more popular among the masses.

One such inexpensive external peripheral device for a burner computer is an audio cassette tape recorder.

This is a device that uses a commercially available audio cassette tape recorder as it is to record pulsed digital signals on an audio cassette tape that was originally used to record analog audio signals and sounds, and can be used as an inexpensive and readily available external storage device. , it can be said to be convenient.

However, since audio cassette tape recorders are originally designed to record analog audio signals and are not manufactured for recording and playing back digital signals, they are not reliable enough to be used as external storage devices for personal computers. Good and difficult.

In particular, the performance varies widely depending on the type, manufacturer, and model number of the cassette tape recorder in terms of recording and reproducing digital signals (and as a general-purpose external storage device, it is still insufficient. There are many faces.

The present invention overcomes the deficiencies described in the conventional art! By improving the reliability of the reproduction of digital signals from audio cassette tapes by 70%, it is possible to make more effective use of the cost and popularity of audio cassettes. It is something to do.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings. As a digital signal recording method using an audio cassette, there is an FSK method shown in FIG.

This rL is “l” and “0” indicating the logic of the digital signal.
``1 jj'' is expressed with twice the frequency of ``0''vc, and the duty cycle is the same, so it can be regarded as a type of alternating current signal, and is suitable as a signal to be handled by an audio cassette. It has become.

In this embodiment, using this FSK recording method, a reproduction signal for reproducing a digital signal from a cassette tape is
This is the input signal shown in the figure. The first clamp section clamps the signal to approximately ±0.7V with the voltage across the diodes D, D2, and D2, which allows normalization of the input signal. The resistor R□ functions as a protective resistor and, when combined with CL, as a low-pass filter, and functions to remove unnecessary high-frequency signals 7 at the time of input and smooth the waveform t.

A bandpass filter is composed of an operational amplifier &. Its characteristics are shown in FIG.

Assuming that the band frequencies of the band pass filter are xfL and fH and the gain is 7a, the solenoids are calculated from the following equation.

3 ......[3] Formula % Formula % It is necessary to determine so that it straddles both one law of two frequencies. Further, it is necessary to set the value to an appropriate value larger than aba1 (OdB).

The output of this bandpass filter is between voltage Vc and GND
The voltage is divided by resistors R4 and R6 between n and constant voltage Vsf, and an alternating current waveform that swings above and below the center is obtained.However, harmful high-frequency waveform components are removed and only the effective components are n1. The zero-zero cross comparator OMF, which remains, is for shaping the AC waveform passed through the band-pass filter 7 into a pulse-like rectangular wave. In this circuit,
The key point is to match the reference voltage of the comparator [the voltage of the child terminal of the operational amplifier OP of the bandpass filter] to ensure that the zero cross of the waveform is taken.

Further, it is necessary to adjust the logic level of the output of this zero-cross comparator to the logic input of the personal computer.

As described above, the circuit shown in one embodiment of the present invention can be constructed with a relatively simple circuit, and furthermore, the reproduction performance can be significantly improved.

As a result of the remarkable improvement in playback performance, it becomes easier to use the popular and easily available audio cassette tape recorder as an external storage device for personal computers, and as a result, it contributes to the spread of personal computers themselves in society. It is predicted that the impact will be large.

[Brief explanation of the drawing]

(Figure 1 in the figure is audio)? A block diagram showing the FSK method, which is a digital signal recording method using r,
FIG. 2 is an embodiment of the present invention, and is a block diagram showing a circuit for reproducing digital signals from a cassette tape using the F8 recording method. FIG. 8 is a characteristic diagram of a bandpass filter composed of operational amplifiers. Patent applicant Takayoshi Hayashi Mychik representative patent attorney Figure 3

Claims (1)

[Claims] In the process of reproducing digital signals from a cassette tape, the input signal is clamped, passed through a band-pass filter consisting of an output operational amplifier, and further waveform-shaped by a zero-cross comparator to obtain a digital signal output. t A digital signal reproducing device for cassette tapes.