JPS6361820B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data extraction device that extracts data having a plurality of signal levels, particularly data having binary signal levels, from an input signal.

As shown in Figure 1, when the binary input signal _S1 has a constant amplitude and there is no bias variation, by comparing the levels of the input signal _S1 at a constant level threshold voltage Eo as shown in the figure, input signal
The " ₁ " and "0" data of S1 can be easily extracted.

However, if the input signal S ₁ is a digital signal reproduced from a magnetic tape or a signal obtained from an optical frequency generator, and its frequency fluctuates, or as shown in Figure 2, amplitude fluctuations and bias If there is a fluctuation, comparing the levels of the input signal S ₁ at a constant level threshold voltage in this way will cause the input signal S ₁ to be ``1'' and ``0''.
data cannot be extracted.

Therefore, the inventor devised a data extraction device that can reliably and accurately extract data from an input signal even when the input signal has amplitude fluctuations and bias fluctuations.

FIG. 3 shows this data extraction device (reference example), in which the input signal S ₁ is passed through the buffer 10 to the positive peak clamp circuit 20 and the negative peak clamp circuit 3.
0.

The positive peak clamp circuit 20 and the negative peak clamp circuit 30 each include a capacitor C, a diode D, a resistor _R1 , and a resistor _R2 , and the directions of the diodes D are opposite to each other. Resistance R ₂
is made sufficiently large compared to the resistor R ₁ , so that the charging time constant becomes C·R ₁ , which is selected to be small enough not to malfunction due to noise. Further, the discharge time constant is C·R ₂ , which is selected to have a magnitude that does not follow the data waveform itself of the input signal S ₁ but follows amplitude fluctuations and bias fluctuations. Note that the clamp potentials of the positive peak clamp circuit 20 and the negative peak clamp circuit 30 are both set to the ground potential, for example.

Therefore, as shown in FIG. 2, the positive peak clamp circuit 20 outputs a positive peak clamp signal S P in which the positive peak of the input signal S ₁ is clamped to the ground potential, and therefore the negative peak is on the negative _side . is obtained, and the negative peak clamp circuit 30 obtains a negative peak clamp signal S _M in which the negative peak of the input signal S ₁ is clamped to the ground potential, and therefore the positive peak is on the positive side.

The positive peak clamp signal S _P and the negative peak clamp signal S _M are connected to the variable resistor 4 as an adder circuit.
0 and is supplied to one end and the other end of the variable resistor 40, and is a signal obtained by adding the positive peak clamp signal S _P and the negative peak clamp signal S _M from the movable element of the variable resistor 40 in an appropriate ratio, for example, 1:1, and therefore the ground potential. The signal S _A where the positive peak becomes the positive side and the negative peak becomes the negative side
is obtained. Note that the resistance of the portion of the variable resistor 40 from the mover to the circuit 20 side and the portion of the circuit 30 side is set to be sufficient compared to the resistance R ₂ so as not to affect the operation of the positive and negative peak clamp circuits 20 and 30. be made larger.

Then, the addition signal S _A obtained from the movable element of the variable resistor 40 is supplied to a level comparison circuit 50, where the levels are compared using the ground potential as a threshold voltage. As the level comparison circuit 50, one having hysteresis, such as a Schmitt trigger circuit, is used.

Therefore, according to this reference example, as is _clear from _{FIG .} Data of "1" and "0" can be extracted reliably and accurately.

However, according to this reference example, the input signal
When the data frequency of S ₁ changes, a problem arises if the discharge time constants of the positive peak clamp circuit 20 and the negative peak clamp circuit 30 are fixed as described above. That is, in this case, if the data frequency is too low, the discharge will follow the data waveform itself, making it impossible to obtain a clamp signal with positive peaks and negative peaks. Conversely, when the data frequency is too high, the discharge no longer follows the envelope of positive peaks and negative peaks.

In view of this, the present invention seeks to propose a data extraction device that can reliably and accurately extract data from an input signal even if the input signal has not only amplitude fluctuations and bias fluctuations but also frequency fluctuations. It is something to do.

FIG. 4 shows an embodiment of the invention, showing a positive peak clamp circuit 20 and a negative peak clamp circuit 30.
An analog switch _SW is connected in series to the discharge resistor _R2 . On the other hand, the output signal D _O of the level comparison circuit 50
0, a trigger pulse P _T is obtained at the rising and falling edges of the output signal D _O ,
This is supplied to a monostable multivibrator 70. The output signal M _O of the monostable multivibrator 70 is supplied as an on/off control signal to the analog switch _SW of the positive peak clamp circuit 20 and the negative peak clamp circuit 30 through the level shift circuits 80 and 90. The other configurations are the same as in FIG. 3.

Therefore, comparing when the data frequency is a certain frequency ₁ and when the data frequency is 1/2 frequency ₂ , ₁
, the output signal D _O , trigger pulse P _T and control signal M _O become as shown in FIG. 5A, and the analog switches of the positive and negative peak clamp circuits 20 and 30
The duty factor during the period in which _SW is turned on increases, and the discharge time constant equivalently decreases as shown by line 1 in FIG. Conversely, when ₂ , the output signal D _O , trigger pulse P _T and control signal
M _O becomes as shown in Figure B, and the duty factor during the period when the analog switches _SW of the positive and negative peak clamp circuits 20 and 30 are turned on becomes smaller, as shown by line 2 in Figure B. Equivalently, the discharge time constant increases.

Therefore, according to this embodiment, the input signal S ₁
Even if the data frequency of the input signal S P changes, the discharge always follows the envelope of the positive peak and negative peak without following the data waveform of the input signal _S1 , and the positive peak clamp signal S _P and the negative peak The peak clamp signal S _M can be reliably obtained.

According to the data extraction device of the present invention described above, the input signals are supplied to the positive peak clamp circuit and the negative peak clamp circuit, and the respective clamp signals, which are clamped to a predetermined potential, are added together at an appropriate ratio. Then, by supplying the added output to a level comparison circuit and comparing the level with a predetermined value, data is extracted from the input signal, so even if the input signal has amplitude fluctuations and bias fluctuations, the input signal Data can be extracted reliably and accurately from

Furthermore, according to the present invention, in addition to the above-described configuration, a switch means is provided for switching the time constants of the positive peak clamp circuit and the negative peak clamp circuit, so that the time constants of the positive peak clamp circuit and the negative peak clamp circuit can be changed in accordance with the frequency of the data output from the level comparison circuit. Since the switching means is controlled, data can be reliably and accurately extracted from the input signal even if the input signal has frequency fluctuations.

[Brief explanation of drawings]

Figure 1 is a waveform diagram for explaining a conventional example, Figure 2 is a waveform diagram for explaining a conventional example and a reference example, and Figure 3 is a waveform diagram for explaining a conventional example and a reference example.
The figure is a circuit diagram showing a reference example, FIG. 4 is a circuit diagram showing an embodiment of the present invention, and FIG. 5 is a waveform diagram for explaining the operation of the embodiment. 20 is a positive peak clamp circuit, 30 is a negative peak clamp circuit, 40 is a variable resistor (summing circuit),
50 is a level comparison circuit, and _SW is an analog switch.

Claims (1)

[Claims] 1. A positive peak clamp circuit and a negative peak clamp circuit to which an input signal is supplied, and respective clamp signals clamped to predetermined potentials by the positive peak clamp circuit and the negative peak clamp circuit are supplied. and a level comparison circuit that extracts data from the input signal by comparing the level of the signal output from the addition circuit with a predetermined value. In the data extraction device, a switch means is provided for switching the time constants of the positive peak clamp circuit and the negative peak clamp circuit, and the switch means is controlled in accordance with the frequency of the data output from the level comparison circuit. A data extraction device characterized in that it is configured to: