JPH0222573B2 - - Google Patents

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, vocals, instrument performances, etc. are recorded independently on a multi-track (e.g. 8-channel) tape recorder, and then converted to a 2-channel stereo signal using a mixer to produce the final sound. Obtaining music information signals. Recently, a time code called SMPTE has been recorded on information recording tape at the same time as the recording. This time code records time and other information (for example, frame number, subframe number) for each unit area 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. The numeric keypad 2 is used to set the above-mentioned time information, memory number, etc. 3 is 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 button for storing time information etc. in the built-in memory; 7 is a RECALL button for recalling time information stored in the built-in memory; 8 is an information display section 1
This is a LOCATE button that outputs a control signal for locating to a tape recorder, etc., based on the time information displayed on the screen.

The tape locating device 10 having such a configuration has the following features:
As shown in FIG. 4, it is used by being connected to a tape recorder 12 via a cable 11. In this connected state, the tape recorder 12 can be remotely operated using the tape recorder operation key 5 of the tape locating device 10. When recording, set the tape to the initial position and set the time to ``0'', for example.
Set to H “0” M “0” S and start recording.

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 transmitted to the tape recorder 12 via the cable 11.
and recorded on tape. For example, a Biphase-Mark method is used as a recording method. 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. It's in control.

Next, a case will be described in which a biphase mark modulation signal employed as a time signal is demodulated. The signal of the biphase mark system is a binary digital signal as shown below.

At the boundary of a bit cell (one bit area), 0 and 1 are always inverted.

When the signal is "1", it is inverted from 0 to 1 or from 1 to 0 at the center of the bit cell, and when the signal is "0", it is not inverted. That is, the discrimination between "1" and "0" is not based on the pulse height but on the presence or absence of inversion in the bit cell.

An example of a demodulating circuit for this signal is shown in FIG. 5a, and the output waveforms of each circuit are shown in FIG. 5b. The outputs and waveforms of each stage correspond to A, B, C, and D. The output waveform of the waveform shaping circuit 21 is A in FIG. 5b.
This waveform corresponds to the binary number "101101". This waveform of A is used as a clock pulse by a clock pulse detection circuit 22. The clock pulse is shown as B in FIG. 5b, and is a pulse that is generated every time the input waveform is inverted. This clock pulse is passed to the sawtooth wave generation circuit 2.
Send to 3. The sawtooth wave generation circuit 23 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 when the number is "1".
Since the pulse width is 1/2 compared to the case of the number "0", the peak value is also approximately 1/2. This sawtooth wave is input to the voltage comparator 24. Here, the reference voltage generation circuit 25
The output voltage of is input and compared with a sawtooth wave like C in FIG. 5b. The high peak value V _H of the sawtooth waveform is higher than the output V _T of the reference voltage generation circuit 25, and the lower peak value
V _L is lower than the reference voltage V _T , and in this circuit, only waveforms with voltages higher than the output voltage V _T of the reference voltage generation circuit 25 serve as data as output pulses, so a waveform like D in Figure 5b is generated. The output is obtained. Here, V _H is the high peak value of the sawtooth wave, V _L is the low peak value, and V _T is the output voltage of the reference voltage generation circuit.

That is, the voltage comparator 24 only when the input is "0"
A pulse is output as a data input. This output is compared with the clock pulse shown in Figure B, 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, a 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 of A in Fig. 6 is shown in Fig. 5B.
An output of 101101 is obtained with the waveform explained in . 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 the same, the charging curve is the same as that in Figure 6A, and the width of the "0" waveform is equal to the width of the "1" waveform in Figure 6A. 0”
The charging potential V _H is the "1" charging potential V _L in case A.
is equal to, and therefore lower than the reference voltage V _T , D of B
There is no output like this. If you look into the case of slow tape speed, if the tape speed is 1/2,
It will look like Figure 6 C. That is, "1" in this case
The pulse width of is doubled like A in C,
Since it is equal to "0" shown in A in FIG. 6A, the output of the sawtooth wave generation circuit 23 becomes as shown in C in FIG.
Both in the case of ``1'' and in the case of ``1'', the output is output as shown in D 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,
Frequency response was poor.

The present invention has been made in view of the above-mentioned problems, and its purpose is to:
The object of the present invention is to realize a demodulation circuit that accurately demodulates time information.

(Means for Solving the Problems) The present invention, which solves the above problems, detects a clock pulse from a biphase mark modulated pulse signal, generates a sawtooth wave at the period of the detected clock pulse, and generates a sawtooth wave. A demodulating circuit for a pulse signal that obtains demodulated data by comparing the peak value of a sawtooth wave with a reference voltage, characterized in that the reference voltage is configured to be varied depending on the peak value of the sawtooth wave. It is.

(Function) The demodulation circuit of the present invention accurately reproduces 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 decreases. 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. As in the case of FIG.
Step 3 creates a sawtooth waveform signal. This waveform is the fifth
It is similar to Figure b, and is the C waveform of Figure 2A. This waveform enters the peak hold circuit 26, stores the sawtooth wave due to 0 captured as the peak, and applies this value to the variable reference voltage generation circuit 25', which responds to the peak value detected by the peak hold circuit 26. A reference voltage is generated, applied to the voltage comparator 24, and compared with the sawtooth waveform inputted from the sawtooth wave generating circuit 23 (C in FIG. 2A) to obtain the waveform D in the same figure.

Incidentally, 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. Since the tape speed is fast and the repetition frequency is high, the output of the waveform shaping circuit 21 is
This is the waveform of A in Figure 2 (b), and all pulse widths are 1/2 compared to 1. Therefore, the output of the sawtooth wave generating circuit 23 has the waveform shown in FIG. This output enters the peak hold circuit 26 as voltage information, and the peak is "0".
When the peak value is captured, the peak value is held and becomes the input to the variable reference voltage generation circuit 25'. 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 V _T shown in C in the figure will be obtained. , its highest value V _H is lower than its lowest value
_V
The waveform D is obtained, and the same output as the input time information is obtained.

Also, if the tape speed is 1/2 and the pulse width of the time information is wide and twice as long, the result will be as shown in Fig. 2 (c). The operation is the same up to the output of the sawtooth wave generation circuit 23, but since the pulse width is twice as large as shown in A in the figure, the peak value of the output of the sawtooth wave generation circuit 23 is approximately doubled. Also in this case, unlike the conventional fixed reference voltage generation circuit, the peak hold circuit 26 captures the high voltage (the peak value of the sawtooth wave in the case of "0"), and the variable reference voltage generation circuit 25' captures the high reference voltage, i.e. ,
A voltage V _T shown in C in FIG. 2 is generated, and the voltage comparator 24 obtains a waveform D in FIG. This is the same content as the input time information. As explained above,
According to the present invention, correct time information can be obtained regardless of the tape speed setting. Although the present invention takes as an example the case where the variable reference voltage generation circuit is controlled by the peak hold circuit, the present invention is not limited to this. An amplifier is installed after the sawtooth wave generation circuit,
The output of the peak hold circuit may control the gain of the amplifier. Furthermore, the present invention can be applied not only to tape locating devices, but also to all cases in which signals modulated by the biphasic mark method are demodulated.

(Effects of the Invention) As explained in detail above, according to the present invention,
By varying the output of the reference voltage generating circuit in accordance with the input level, correct demodulation can be obtained regardless of the slow speed of the tape or the frequency of the input information signal, which is highly effective in practice.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of the present invention, FIG. 2 is a comparison diagram of output waveforms of each stage when the tape speed changes by the demodulation circuit of the present invention, and FIG.
The figure shows an example of the external configuration of a tape locating device.
Fig. 4 is a diagram showing the connection state between the tape locating device and the tape recorder, Fig. 5 is a conventional example, a is a conventional pulse signal demodulation circuit, and b is an output waveform diagram of each stage when time information is input. , FIG. 6 is a diagram showing the output waveforms of each stage in the case of different tape speeds in a conventional demodulation circuit. 1...Information display section, 2...Numeric keypad, 3...Function key, 6...Recall key, 7...
Locate key, 10... Tape locate device, 2
DESCRIPTION OF SYMBOLS 1...Waveform shaping circuit, 22...Clock pulse detection circuit, 23...Sawtooth wave generation circuit, 24...Voltage comparator, 25...Reference voltage generation circuit, 25'...Variable reference voltage generation circuit, 26... peak hold circuit.

Claims (1)

[Claims] 1. A pulse that obtains demodulated data by detecting a clock pulse from a biphase 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 a peak value of a sawtooth wave.