JPH0222574B2 - - 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 waveforms of the outputs 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 the clock pulse detection circuit 22. The waveform of the clock pulse is as shown by B in FIG. 5b, and is a pulse generated every time the input waveform is inverted. This clock pulse is sent to the sawtooth wave generation circuit 23. 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 has a pulse width as shown in A when the number is "1". is 1/2 compared to the case of the number "0", so the wave height is also approximately 1/2. This sawtooth wave is input to the voltage comparator 24. The output voltage of the reference voltage generating circuit 25 is input here, and compared with the sawtooth wave as shown in 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, the output voltage V _T of the reference voltage generation circuit 25 is lower than the output voltage V _T of the reference voltage generation circuit 25. Since only waveforms with high voltages become data as output pulses, an output waveform like D in FIG. 5b 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 pulse height value of the input pulse to the sawtooth wave generation circuit 23 is the same, but the pulse width is 1/2. It has become 2,
Since the charging circuit of the sawtooth wave generating circuit 23 is also the same, its charging curve is the same as in the case of Fig. 6A, and the width of the "0" waveform is equal to the width of the "1" waveform in the case of Fig. 6A. Therefore, the charging potential _VH of "0" is equal to the charging potential _VL of "1" in case A, and is therefore lower than the reference voltage V _T , and no output is produced like D in B. If we investigate the case where the tape speed is slow, we can see that when the tape speed is 1/2, the result is as shown in Figure 6 (c). That is, the pulse width of "1" in this case is A of C
The output of the sawtooth wave generating circuit 23 becomes as shown in C in the same figure, and even if it is "0", it becomes "1". ”, the output is also output and the output waveform is D in Figure 6 C.
This results 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 problems, and its purpose is to realize a demodulation circuit that accurately demodulates time information regardless of the tape speed, that is, regardless of the repetition frequency of the input pulse. It's about doing.

(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 pulse signal demodulation circuit that obtains demodulated data by comparing a sawtooth wave and a reference voltage is configured to generate the sawtooth wave using charging and discharging by a resistor and a capacitor, and the sawtooth wave generating circuit The present invention is characterized in that the charging time constant is configured to be variable in accordance with the peak value of .

(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. 5a, the input time information, biphase mark type digital information, is shaped by the waveform shaping circuit 21, the clock pulse detection circuit 22 outputs a clock pulse, and the sawtooth wave generation circuit 23' generates a sawtooth waveform. make a signal. The sawtooth wave generating circuit 23' is configured to generate a sawtooth wave using the charging/discharging time constant of the resistor R and the capacitor C, and the time constant can be varied by an external control signal. This waveform is similar to that in FIG. 5b and is shown as the C waveform in FIG. 2a.
This sawtooth wave enters the peak hold circuit 26, stores the potential due to the peak "0", and gives this value to the time constant control circuit 27. Time constant control circuit 27
generates a control signal for changing the time constant of the time constant circuit of the sawtooth wave generation circuit 23, for example. The time constant control circuit 27 provides a control signal corresponding to the output of the peak hold circuit 26 to the sawtooth wave generation circuit 23. As a result, the output voltage of the peak hold circuit 26,
That is, the time constant (for example, R) of the sawtooth wave generation circuit 23' is determined by the peak voltage of the sawtooth waveform of the sawtooth wave generation circuit depending on the width of "0" of the time signal, that is, the voltage proportional to the width of "0". The value changes. 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.

Next, we will consider the time constant circuit used in the sawtooth wave generation circuit. In the CR series circuit shown in FIG. 1b, the charging voltage e of the capacitor C is expressed as e=E{1-exp(-t/CR)} (1). “0” when pulse width is standard speed
If the pulse width of is t ₁ and the resistance value of the time constant circuit is R ₁ , the charging voltage e ₁ during the pulse width t ₁ is calculated as e ₁ =E{1−exp(−t ₁ /CR ₁ )} (2) When the tape speed increases and the pulse width of time information “0” reaches t ₂ as shown in the B waveform in Figure 2, the charging voltage e ₂ is (1 ) From the formula, e ₂ = E {1-exp(-t ₂ /CR ₂ )} (3) In order to output time information correctly, make it equal to the peak value of the sawtooth wave of the C waveform in Figure 2. R
When changing from R ₁ to R ₂ , e ₁ = e ₂ E{1−exp(−t ₁ /CR ₁ )} = E{1−exp(−t ₂ /CR ₂ )} ∴t ₁ /CR ₁ = t ₂ /CR ₂ ∴t ₁ /t ₂ = R ₁ /R ₂ (4) From equation (4), in order to equalize the charging voltage of C, that is, the peak value of the sawtooth wave, t ₂ must be 1/2 of t ₁ . When the value becomes , the time constant resistance may also be set to R ₂ =R ₁ /2. Similarly, when the tape speed decreases and the pulse width doubles, the resistance value R ₃ may be set to R ₃ =2R ₁ . Based on the above calculation results, FIG. 2 will be explained.
B is a case where the tape speed is doubled and the pulse width is halved. The clock pulse has a B waveform, the time width is shorter, and the voltage applied to the CR circuit is the same, so the peak value is lower, but since the output of the peak hold circuit 26 is also lower, the internal resistance of the time constant control circuit 27 is also lower. , 1/2, both the time t and the time constant resistance R become 1/2, and as is clear from equation (4), the peak value of the output voltage is the same as that at standard speed. The wave height value is the same as A in Figure 2. Since the output voltage V _T of the reference voltage generation circuit 25 is constant, as is clear from B in the figure,
Time information is output correctly. Figure C shows a case where the tape speed becomes slow. The pulse width t ₃ is twice the t ₁ at standard speed, but as explained above, the peak hold circuit 26 and the time constant control circuit 2
7 doubles the resistance of the time constant, and both the time t and the resistance R of the time constant double, so from equation (4), the peak value is the same as in the case of standard speed. This is as shown in Figure 2 C, where the pulse width of the input time information is 2.
This shows the case where it doubles. Although t ₃ is twice t ₁ , the time constant of the sawtooth wave generating circuit 23' is also doubled, so the charging voltage is the same as at standard speed, and the sawtooth waveform is as shown in C of the same figure. As a result, the output time information is also output correctly.

As explained above, even if the pulse width fluctuates due to changes in the tape speed of input time information, etc., the peak value of the sawtooth wave output from the sawtooth wave generation circuit is held, and the time constant control circuit generates a sawtooth waveform. By changing the time constant of the generating circuit and changing the charging time, a sawtooth wave with always the same peak value can be obtained, and by comparing it with a reference voltage, it is possible to obtain a signal that correctly demodulates the time information of the phased mark method.

As explained above, the present invention provides R in the CR time constant.
Although the circuit has been described as a circuit that changes C, a reactance circuit that changes C may be employed, and the time constant circuit is not limited to a CR circuit, but may also be an L/R circuit. 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 described in detail above, according to the present invention, correct demodulation can be obtained regardless of the slow speed of the tape or the frequency of the input time information, and the practical effects are great.

[Brief explanation of drawings]

Figure 1a is a configuration block diagram showing one embodiment of the present invention, Figure 1b is an explanatory diagram for calculation of the CR circuit, Figure 2
3 is a diagram showing an example of the external configuration of a tape locating device; FIG.
The figure shows the connection state between the tape locating device and the tape recorder. Figure 5 is a conventional example, where a is a conventional pulse signal demodulation circuit, b is an output waveform diagram of each stage when time information is input, FIG. 6 is a diagram showing output waveforms of each stage in a conventional demodulation circuit when tape speeds are different. 1...Information display section, 2...Numeric keypad, 3...Function key, 6...Recall key, 7...
Locate key, 10... Tape locate device, 2
1...Waveform shaping circuit, 22...Clock pulse detection circuit, 23, 23'...Sawtooth wave generation circuit, 24...
...Voltage comparator, 25...Reference voltage generation circuit, 26
...Peak hold circuit, 27...Time constant control circuit.

Claims (1)

[Claims] 1 Demodulating the pulse signal 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 obtaining demodulated data by comparing the generated sawtooth wave with a reference voltage. The circuit is characterized in that the sawtooth wave is generated using charging and discharging by a resistor and a capacitor, and the charging time constant is varied according to the peak value of the sawtooth wave generating circuit. A demodulation circuit for pulse signals.