JPS6238022A - Demodulating circuit for pulse signal - Google Patents

Abstract

PURPOSE:To obtain correct demodulation regardless of slow/fast tape and the frequency of input information signal by changing the output of a reference voltage generating circuit in response to an input level. CONSTITUTION:Digital information of the biphase mark system being input time information is shaped by a waveform shaping circuit 21, a clock pulse detection circuit 22 forms a clock pulse and a sawtooth wave generating circuit 23 forms a sawtooth waveform signal. The waveform C enters a peak hold circuit 26. A sawtooth wave having a logical '0' caught as a peak is stored and the value is given to a variable reference voltage generating circuit 25'. Then the reference voltage in response to the peak value detected by the peak hold circuit 26 is formed and given to a voltage comparator circuit 24, compared with a sawtooth wave C inputted from the circuit 23 to obtain a waveform D.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a demodulation circuit for modulated pulse signals, and more specifically, to a demodulation circuit suitable for use in a tape locate device that can quickly locate the beginning of a tape recorder or the like. This invention relates to a pulse signal demodulation circuit.

(Prior art) In recording studios, etc., multi-track (for example, 8
Vocals, musical instrument performances, etc. are recorded independently on the tape recorder of each channel, and the final music information signal is obtained by converting it into a 2-channel stereo signal using a mixer. Recently, SMP is added to the information recording tape at the same time.
A time code called T'E is recorded in parallel with the recording. This time code contains time and other information (for example, frame riM4) for each unit area.
+subframe number) is recorded in an 80-bit data area. A tape locate device is a device used for recording and reading out such time codes.

FIG. 3 is a diagram showing an example of the external configuration of the tape locating device. In the figure, 1 is an information display section that displays time information. Numeric keypad 2 is the time information mentioned above.

Configure memory numbers, etc. Reference numeral 3 denotes a function key consisting of various control keys, and control information set with the function key 3 is displayed on a control status display section 4. A tape recorder operation key 5 remotely controls a tape recorder connected to the locate device 10. 6 is a store (STOP) button for storing time information etc. in the built-in memory; 7 is a recall (RECALL) button for calling up the time information stored in the built-in memory; and 8 is a button based on the time information displayed on the information display section 1. Locate (LOCAT) outputs control number 13 for locating to a tape recorder, etc.
E) It is a button.

The tape locating device e110 having such a configuration is connected to the tape recorder 12 via the cable 11 as shown in FIG.
It is used by connecting to. When connected like this,
The tape recorder 12 can be remotely operated using the tape recorder operation key 5 of the tape locating device 10. When recording, the tape is set to the initial position 8 and set to 1, the time is set to, for example, OJ) H"O" M "O" S, and recording is started.

In addition to music information, absolute time information displayed on the information display section 1 is recorded on the running tape in SMPTE code for each unit area. That is, in this case, the time information signal generated by the tape locating device 10 is sent to the tape recorder 12 via the cable 11 and recorded on the tape.

For example, is the recording method bi-phase? -ri (31phas
e-Mark) method is adopted. In this way, time information can be recorded along with music information on the same tape. In this case, the time information is music position information. When locating a tape, the time information modulated and recorded on the tape is read out and demodulated to obtain time information, so that the preset time information and the time information read from the tape recorder are equal. I'm paying $.

Next, the case of demodulating a bi-phase mark modulation signal employed as a time signal will be explained. The signal of the biphase mark system is a binary digital signal as shown below.

■At the boundary of a bit cell (1 bit area), O and 1 are always present.
Invert.

■When the signal is II I II, it is inverted from O to 1 or from 1 to O at the center of the bit cell, and when the signal is 0'', it is not inverted. That is, ``1'' and 0'.

This is determined not by the pulse height but by the presence or absence of inversion in the bit cell.

An example of a demodulating circuit for this signal is shown in FIG. 5(a), and the waveform of the output of each circuit is shown in FIG. 5(b). The outputs and waveforms of each stage correspond to A, B, C, and D. The output waveform of the waveform shaping circuit 21 is the waveform A in FIG. 5(b),
It corresponds to the binary number "101101". This waveform of A is used as a clock pulse by the clock pulse detection circuit 22. The clock pulse is as shown by B in FIG. 5(b), and is a pulse generated every time the input waveform is inverted. This clock pulse is sent to the sawtooth wave generation circuit 23. Sawtooth wave generation circuit 2
3 is a circuit that charges a capacitor and outputs it every time a clock pulse is input, and the time constant is constant, so the output waveform is as shown in A for the number 1''.
Since the pulse width is 1/2 compared to the case of the number tt O+e, the peak value is also approximately 1/2. This sawtooth wave is input to the voltage comparator 24. The output voltage of the reference voltage generation circuit 25 is input here and compared with the sawtooth wave as shown in C in FIG. 5(b).

The high peak value VH of the sawtooth waveform is higher than the output vT of the reference voltage generation circuit 25, and the lower peak value Vt is lower than the reference voltage VT.
Since only a waveform with a higher voltage becomes data as an output pulse, an output waveform like D in FIG. 5(1)) is obtained. Here, VH is the high peak value of the sawtooth wave, VL is the low peak value, and V is the output voltage of the reference voltage generation circuit.

That is, a pulse is output as the data input of the voltage comparator 24 only when the input is "0". This output is compared with the clock pulse shown in FIG. 8, and the number is read by determining whether it is ``0'' or 1'' depending on the presence of the clock pulse and the presence or absence of data output.

Next, the case where the repetition frequency of the time information pulse increases by increasing the speed of the tape will be explained with reference to FIG. The waveform in FIG. 6(a) is the waveform explained in FIG. 5(b), and the output of 101101 is multiplied by 1q. Considering the case where the tape speed doubles and the pulse repetition frequency doubles, the input pulses to the sawtooth wave generation circuit 23 have the same peak value, and the sawtooth wave generation circuit 23 Since the charging circuit is also the same, its charging curve is the 6th one.
Same as in the case of figure (a), the width of the waveform of M O11 is the 6th
Since the width of the waveform is equal to 1" in the case of figure (A), the charging potential VH of 110 IT is 1" in the case of (A).
Full 1! It is equal to the potential VL, and therefore lower than the reference voltage VT, and no output is produced as in (b) D. When examining the case where the tape speed is slow, when the tape speed is 172, the result is as shown in FIG. 6 (c). That is, in this case, the pulse width of °1" is doubled as shown in A in (c), and is equal to 0", which is not shown in 8 in FIG. The output will be as shown in C in the same figure (c), and II O
Both in the case of +1 and in the case of 111 II, outputs are output as shown in the same figure, resulting in completely different time information.

(Problems to be Solved by the Invention) As described above, time information is not accurately demodulated when the tape speed is fast or slow. That is, the frequency response was poor.

The present invention has been made in view of the above problems, and its object is to provide a demodulation circuit that accurately modulates time information to 11 regardless of the tape speed, that is, regardless of the repetition frequency of the input pulse. The aim is to realize this.

(Means for solving the problem) The present invention to solve the above problem detects a clock pulse from a modulated pulse signal of a bi-phase mark method, generates a sawtooth wave at the period of the detected clock pulse, The pulse signal demodulation circuit obtains demodulated data by comparing the peak value of the generated sawtooth wave with a reference voltage, characterized in that the reference voltage is variable depending on the peak value of the sawtooth wave. It is something.

(Function) The demodulation circuit of the present invention can accurately reproduce modulated data even when the tape speed increases and the input pulse repetition frequency becomes high, and even when the tape speed decreases and the input pulse repetition frequency becomes low. It will demodulate to .

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, and the same parts as in FIG. 5 are designated by the same numbers. Figure 5 (
As in the case above, the input time information, bi-phase mark type digital information, is shaped by the waveform shaping circuit 21, the clock pulse detection circuit 22 generates a clock pulse, and the harmonic generation circuit 23 generates a sawtooth waveform signal. make. This waveform is similar to that shown in Fig. 5 (b), and C in Fig. 2 (a).
It is a waveform. This waveform enters the peak hold circuit 26, stores the sawtooth wave due to O that is captured as a peak, and gives this value to the variable reference voltage generation circuit 25'. A voltage is generated and applied to the voltage comparator 24, and the sawtooth wave generation circuit ff12
By comparing it with the harmonic waveform inputted from step 3 (C in (a) of FIG. 2), a waveform similar to that shown in FIG. 2 is obtained.

Note that the output clock of the clock pulse detection circuit 22 is outputted to the outside as a clock signal, and is used as a clock for necessary signal processing. Let us consider the case where time information is input to this demodulation circuit when the tape speed is high. Waveform shaping circuit 2 because the cheating speed is fast and the repetition frequency is high.
The output of No. 1 has the waveform of A in FIG. 2 (b), and the pulse widths are all 1/2 of those of (1). Therefore, the output of the harmonic generation circuit 23 has the waveform shown in FIG. 2C, and its peak value is approximately 1/2. This output enters the peak hold circuit 26 as voltage information, and when the peak "0" is captured, the peak value is held, and the variable reference voltage generation circuit 26
′ is input. The output reference voltage of the variable reference voltage generation circuit 25' changes according to the input voltage, and if it is adjusted to output a voltage approximately 0°8 times the held voltage, the value of VT as shown in C in the same figure can be obtained. Therefore, the value is lower than the highest value VH and higher than the lowest value VL.As a result of comparing the output of the harmonic generation circuit 23 with the voltage comparator, the waveform of D in the same figure ((b) in Figure 2) is obtained. The same output as the input time information is obtained.

Further, when the tape speed is 1/2 and the pulse width of the time information is wide and twice as long, the result is as shown in FIG. 2 (c). Although the operation is the same up to the output of the harmonic generation circuit 23,
Since the pulse width is twice as large as , the peak value of the output of the harmonic generation circuit 23 is approximately twice as large. Also in this case, unlike the conventional fixed reference voltage generation circuit, the peak hold circuit 26 captures a high voltage (the peak value of the harmonic in the case of "O"), and the variable reference voltage generation circuit 25' captures a high voltage quasi-V, That is, the VT shown in C in FIG. 2(C) is generated, and the voltage comparator 24 obtains the waveform D in FIG. 2(C).

This is the same content as the input time information. As described above, according to the present invention, correct time information is obtained regardless of the tape speed setting.

The present invention uses a peak bold circuit as an example to control a quasi-voltage generating circuit for changing cars, but the present invention is not limited to this.An amplifier is provided in connection with the harmonic generating circuit, and a peak hold The gain of the amplifier may be controlled by the output of the circuit.Also, the present invention can be applied not only to a tape locating device, but also to any case where a signal modulated by the biphase mark method is demodulated. I can do it.

(Effects of the Invention) As described above in detail, according to the present invention, by changing the output of the reference voltage generation circuit according to the input level, regardless of the slow speed of the tape or the frequency of the input information signal, , correct demodulation can be obtained, and the practical effect of F is great.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of the present invention, and FIG.
The figure is a comparison diagram of the output waveforms of each stage when the tape speed changes by the demodulation circuit of the present invention, Figure 3 is a diagram showing an example of the external configuration of the tape locating device, and Figure 4 is a diagram showing the configuration of the tape locating device and the tape recorder. Diagrams showing the connection state, Fig. 5 is a conventional example, (a) is a conventional pulse signal demodulation circuit, <b> is an output waveform diagram of each stage when time information is input, and Fig. 6 is a conventional example. FIG. 7 is a diagram showing output waveforms of each stage when the tape speed is different in the demodulation circuit. 1... Information display section 2... Numeric keypad 3...
Function key 6...Recall key 7...Locate key 10
... Tape locate device 21 ... Waveform shaping circuit 22 ... Clock pulse detection circuit 23 ... Harmonic generation circuit 24 ... Voltage comparator 25
...Reference voltage generation circuit 25'...Variable reference voltage generation circuit (
'26... Peak Bold Circuit Patent Applicant Fostex Co., Ltd. Agent Patent Attorney Osamu Ijima Fuji (
] Figure 2 Bit cell D-1--

Claims (1)

[Claims] Demodulated data is obtained by detecting a clock pulse from a bi-phase mark modulated pulse signal, generating a sawtooth wave at the period of the detected clock pulse, and comparing the peak value of the generated sawtooth wave with a reference voltage. 1. A pulse signal demodulation circuit, characterized in that the reference voltage is varied according to the peak value of a sawtooth wave.