JPH0918301A - Waveform shaping circuit - Google Patents

Abstract

PURPOSE: To provide a waveform shaping circuit capable of improving the reproducibility of the duty factor of reproducing control signals. CONSTITUTION: This circuit is constituted of the waveform shaping circuits 7 and 8 of different sensitivity for waveform-shaping input signals, a switch 12 for selecting one of the waveform shaping circuits 7 and 8, a level detector 9 for detecting the level of the frequency of the input signals and a flip-flop 10 for controlling a switching means corresponding to the detected result of the level detector 9. Then, corresponding to the detected result of the level detector 9 of the input signals, the waveform shaping circuits 7 or 8 capable of shaping waveforms is selected. Thus, the reproducibility of the duty factor of the reproducing control signals is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a VTR reproduction control signal waveform shaping circuit.

[0002]

2. Description of the Related Art In recent years, VTRs have been
A method of reading the ratio (hereinafter, referred to as a duty) of the time when the positive pulse and the negative pulse of the signal stored in TR are read to perform the cueing is adopted. VTR
The duty of the signal used for is generally set to 6: 4. Therefore, the only signal used to find the VISS is the duty (6:
4), and set to 8: 2, for example, and stored in the VTR. Therefore, by reading the duty of all the signals stored in the VTR, it is possible to easily find the signal stored in the head of VISS.
It enabled ISS cueing. Hereinafter, reading the duty is referred to as shaping the waveform of the reproduction control signal.

Next, a conventional waveform shaping circuit used for shaping the waveform of the reproduction control signal will be described.

FIG. 5 is a circuit configuration diagram of a conventional waveform shaping circuit. Reference numeral 1 is a reproduction control signal input terminal, 2 is a comparator for reading the rising edge of a positive pulse from the input terminal 1, and 3 is a threshold of the comparator 2. A reference power source (hereinafter, referred to as a positive side threshold value 3) for setting a value is set to a value higher than a bias point (a potential at which a positive pulse and a negative pulse switch is referred to as a bias point). 4 is the input terminal 1
The comparator 5 for reading the rising edge of the negative pulse is a reference power source (hereinafter, referred to as the negative side threshold value 5) for setting the threshold value of the comparator 4, and a value lower than the bias point is set. A flip-flop 6 receives the output of the comparator 2 as a set input and the output of the comparator 4 as a reset input.

The operation of the conventional waveform shaping circuit configured as above will be described. Here, the positive threshold value 3
= 3.0V and the negative threshold value 5 = 2.0V.

As shown in FIG. 6A, when a control signal having an amplitude level larger than the positive threshold value 3 is input to the input terminal 1, the comparator 2 outputs H level,
The flip-flop 6 is set by the comparator 2 and outputs the H level. At this time, it can be read from the output of the waveform shaping circuit that the positive pulse is input to the input terminal 1. Next, when a control signal having an amplitude level larger than the negative side threshold value 5 is input to the input terminal 1, the comparator 4 outputs H level, the flip-flop 6 is reset by the comparator 4, and outputs L level. At this time, it can be read from the output of the waveform shaping circuit that the negative pulse has been input to the input terminal 1. The time when the output of the flip-flop 6 is at the H level corresponds to the time from the input of the positive pulse to the input of the negative pulse. The time when the output of the flip-flop 6 is at the L level corresponds to the time from the input of the negative pulse to the input of the positive pulse.

In this way, the waveform shaping of the reproduction control signal is performed with the sensitivity determined by the positive side threshold value 3 for detecting the positive pulse and the negative side threshold value 5 for detecting the negative pulse. It was

[0008]

However, in the above-described conventional configuration, waveform shaping is accurately performed for an input signal (low frequency) having a small amplitude as shown in FIG. 6A, but FIG. 6B is used. For a signal (high frequency) having a large amplitude as shown in (), there is a problem that the waveform cannot be accurately shaped.

As shown in FIG. 6 (b), when the frequency of the reproduction control signal is relatively high (the amplitude level of the pulse is large), the phenomenon in which the bias point apparently drops occurs. Therefore, the bias point becomes a value lower than the negative side threshold value 5, and if the duty is reproduced by the conventional waveform shaping circuit, the potential of the input signal 1 exceeds the negative side threshold value 5 before the negative pulse rises. Therefore, there was a problem that an error occurred in the duty.

Therefore, if the value of the negative side threshold value 5 is set to a value further away from the bias point so that it can be used even at high frequencies, there arises a problem that the low frequency duty cannot be measured. For example, the amplitude of the frequency shown in FIG. 6A is in the range of 1.5V to 3.5V. Therefore, if the threshold 3 is set to 4.0V and the threshold 5 is set to 1V, the positive pulse of the input signal cannot exceed the threshold 3,
Also, the negative pulse cannot fall below threshold 5.
That is, the positive-side threshold value 3 and the negative-side threshold value 5 can always be set only to the values included in the amplitude of the low-frequency signal.

As is clear from the above description, there is a limit to the frequency of the reproduction control signal that can be accurately shaped by the conventional waveform shaping circuit.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a waveform shaping circuit in which the reproducibility of the duty of the waveform shaping circuit of the reproduction control signal is improved.

[0013]

In order to achieve this object, a waveform shaping circuit of the present invention has a plurality of waveform shaping circuits having different sensitivities for shaping an input signal, and a plurality of waveform shaping circuits. Switch means for selecting the shaping circuit,
A level detector for detecting the frequency level of the input signal,
Means for controlling the switch means is provided according to the detection result of the level detector.

[0014]

With this configuration, it is possible to select a waveform shaping circuit capable of accurately shaping the waveform from among a plurality of types of waveform shaping circuits having different sensitivities, according to the detection result of the input signal level detector.

[0015]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a waveform shaping circuit according to an embodiment of the present invention. In FIG. 1, 1 is an input terminal of a reproduction control signal, 7 is a first waveform shaping circuit that shapes the reproduction control signal of the input terminal 1 with a first sensitivity, and 8 is a reproduction control signal with a second sensitivity. A second waveform shaping circuit for shaping the waveform, 9 is a level detector for detecting the amplitude level of the reproduction control signal, and 10 is a flag flip-flop set by the level detector 9 (means for raising a flag by the level detector 9). , 11 is a reset input for resetting the flag flip-flop, and 12 is a switch for selectively outputting the output of the first waveform shaping circuit 7 and the output of the second waveform shaping circuit 8. is there.

The operation of the waveform shaping circuit of the above embodiment constructed as above will be described below with reference to FIGS. 1 and 3.

The sensitivity width of the first waveform shaping circuit 7 is narrower than that of the second waveform shaping circuit 8. The sensitivity of the first waveform shaping circuit 7 is 2V to 3V, the sensitivity of the second waveform shaping circuit 8 is 1.5V to 3.5V, the bias point at low pulse is 2.5V, and the apparent at high pulse. The bias point will be described below assuming that it is 1.8V.

In FIG. 1, the reproduction control signal input to the input terminal 1 is first waveform-shaped by the first sensitivity of the first waveform shaping circuit 7, and the duty of the reproduction control signal is reproduced and output. . At the same time, the reproduction control signal is also waveform-shaped by the second sensitivity of the second waveform shaping circuit 8, and the duty of the reproduction control signal is reproduced and output with two types of sensitivity.

The level detector 9 detects the amplitude level of the reproduction control signal, and sets the flag flip-flop 10 according to the amplitude level. When the frequency of the reproduction control signal is high, the flag flip-flop 10 outputs H level, and when the frequency is low, the flag flip-flop 10 outputs L level. Then, while the flag flip-flop 10 outputs the H level, the switch 12 selects the duty reproduction output of the second waveform shaping circuit 8 and while the flag flip-flop 10 outputs the L level. The switch 12 selects the duty reproduction output of the first waveform shaping circuit 7.

Therefore, regardless of whether the reproduction control signal has a high frequency or a low frequency, the switch 12 can output the correct duty as shown in FIG.

Next, regarding the waveform shaping circuit of the above-described embodiment described with reference to FIG. 1, the first waveform shaping circuit 7,
An example of the circuit configuration of the second waveform shaping circuit 8 and the level detector 9 will be described with reference to FIG.

The first waveform shaping circuit 7 comprises a comparator 2, a comparator 4 and a flip-flop 6,
It has the same configuration as the conventional waveform shaping circuit shown in FIG.
Therefore, the same reference numerals are given and the description of the configuration and the operation is omitted.

The second waveform shaping circuit 8 includes a comparator 1
3, resistor 14, inverters 17 and 18. The comparator 13 has two inverters 17 and 1
It is connected to the switch 12 via 8. The input terminal 1 is connected to the positive input terminal of the comparator 13, and 1/2 VDD is input to the negative input terminal of the comparator 13 via the resistor 14a. Further, the output of the comparator 13 is fed back to the negative side input terminal via the inverter 17 and the resistor 14b.

The level detector 9 is composed of a comparator 15, the input terminal 1 is connected to the positive side input terminal, and the reference voltage (hereinafter referred to as level detection threshold 1
6) is set. The output of the comparator 15 is input to the setting terminal of the flag flip-flop 10.

In FIG. 2, room temperature, VDD = 5.0V,
VSS = 0.0V, positive side threshold value 3 is 3.0V, negative side threshold value 5 is 2.0V, and the threshold value of the comparator 13 (resistive voltage division by the resistor 14) is H level = 3. 5V,
L level = 1.5V, threshold 16 for level detection is 4.5V, input signal of input terminal 1 is ± 2.5V centered ±
FIG. 4 shows the first waveform shaping circuit 7 and the second waveform shaping circuit 8 and the ideal duty when the amplitude is 2.5 V and the frequency is 2.5 kHz.

With the above set value, the negative side threshold value 5 (= 2.0 V) is exceeded before the rise of the negative pulse, so the output of the first waveform shaping circuit 7 (from the rise of the positive pulse Negative pulse rise time): (Negative pulse rise to positive pulse rise time) = 60: 4
While 0 is an ideal value, for example, (rise time of positive pulse to rise time of negative pulse): (rise time of negative pulse to rise time of positive pulse) = 57: 4
It becomes 3. On the other hand, the output of the second waveform shaping circuit 8 has an ideal value.

Since the input signal has an amplitude of ± 2.5 V centered on 2.5 V, the level detection threshold value 16 (4.5)
V) and the output of the flag flip-flop 10 is H
Become a level. Therefore, the output of the switch 12 at this time is
Since the second waveform shaping circuit 8 is selected, an ideal value can be obtained.

In the above embodiment, the first waveform shaping circuit 7 and the second waveform shaping circuit 8 have different configurations, but waveform shaping can be performed with different sensitivity. If Therefore, the first and second waveform shaping circuits 7 and 8 may have the same circuit configuration by changing only the reference value.

In the above embodiment, the waveform of the input signal is always shaped by the two waveform shaping circuits 7 and 8, but this is not always necessary. For example, the output of the flag flip-flop 10 may be controlled so that the connection between the input terminal 1 and the first waveform shaping circuit 7 is cut off while the switch 12 is selecting the second waveform shaping circuit 8. . In other words, it goes without saying that the same effect can be obtained even if the input signal is shaped by only the waveform shaping circuit selected by the switch 12 and the operation of the unnecessary waveform shaping circuit is stopped.

Further, in the above embodiment, the switch 12 is controlled by using the flag flip-flop 10 according to the detection result of the level detector 9, but this is only an example, and according to the detection result of the level detector 9. There is no problem as long as it can control the switch 12.

In the above embodiment, the positive side threshold and the negative side threshold of the waveform shaping circuit have the same potential difference from the bias point. Specifically, in the first waveform shaping circuit 7,
The difference between the positive side threshold value (3.0V) and the bias point (2.5V) is 0.5V, and similarly, the difference between the negative side threshold value (2.0V) and the bias point (2.5V) is Although it is 0.5 V, it does not necessarily have to be the same.

Further, in the above embodiment, two waveform shaping circuits are provided, but it is needless to say that the same effect can be obtained even if three or more waveform shaping circuits are provided. For example, if three waveform shaping circuits are provided, the input signal
It is needless to say that the degree of freedom in the amplitude of the frequency used for the input signal is improved as compared with the case where two waveform shaping circuits are used, since the waveform shaping can be performed with different types of sensitivity.

[0034]

According to the present invention, the waveform shaping circuit capable of accurately shaping the waveform can be selected from the waveform shaping circuit outputs having a plurality of types of sensitivity according to the detection result of the level detector of the input signal. The reproducibility of the duty of can be improved.

Therefore, by adopting the waveform shaping circuit of the present invention to reproduce the duty of the control signal, the frequency range in which the duty can be accurately reproduced is expanded. Therefore, since a high-frequency control signal can be used as an input signal when performing VISS cueing,
It is possible to speed up VISS cueing.

[Brief description of the drawings]

FIG. 1 is a block diagram of a waveform shaping circuit according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a waveform shaping circuit according to an embodiment of the present invention.

FIG. 3 is a time chart of the waveform shaping circuit according to the embodiment of the present invention.

FIG. 4 is a schematic diagram of a measured output waveform of a waveform shaping circuit according to an embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of a conventional waveform shaping circuit.

FIG. 6 is a schematic diagram of a measured output waveform of a conventional waveform shaping circuit.

[Explanation of symbols]

 1 Input Terminal 7 First Wave Shaping Circuit 8 Second Wave Shaping Circuit 9 Level Detector 10 Flag Flip Flop 11 Reset Input 12 Switch 13 Comparator 14 Resistor 15 Comparator 16 Level Detection Threshold 17 Inverter 18 Inverter

Claims (5)

[Claims] 1. A plurality of waveform shaping circuits having different sensitivities for shaping an input signal, and one of the plurality of waveform shaping circuits.
A waveform shaping circuit comprising switch means for selecting one of the waveform shaping circuits, a level detector for detecting the frequency level of the input signal, and means for controlling the switch means according to the detection result of the level detector. 2. The waveform shaping circuit according to claim 1, wherein the means for controlling the switch means is constituted by a flip-flop. 3. A first waveform shaping circuit for shaping the waveform of an input signal, a second waveform shaping circuit for shaping the waveform of the input signal, and a first waveform shaping circuit or a second waveform shaping circuit. Switch means for selecting either one, and a level detector for detecting the frequency level of the input signal,
A waveform shaping circuit comprising means for controlling the switch means according to a detection result of the level detector, wherein the first waveform shaping circuit and the second waveform shaping circuit have different sensitivities. 4. A first waveform shaping circuit having a sensitivity formed by a first positive side threshold value and a first negative side threshold value, for shaping the waveform of an input signal, and a second positive side shaping circuit. A second waveform shaping circuit having a sensitivity formed by a side threshold value and a second negative side threshold value, and shaping the waveform of an input signal, and the first waveform shaping circuit or the second waveform. When the switching means for selecting one of the shaping circuits, the level detector for detecting the amplitude of the input signal, and the detection result of the amplitude of the input signal by the level detector is narrower than a reference value, the first waveform When the shaping circuit is selected and is wider than the reference value, a means for controlling the switch means is selected so as to select the second waveform shaping circuit, and the first negative side threshold value is set to the second negative side. A waveform shaping circuit characterized by being higher than a threshold value. 5. A first waveform shaping circuit having a sensitivity formed by a first positive side threshold value and a first negative side threshold value and shaping the waveform of an input signal, and a second positive side shaping circuit. A second waveform shaping circuit having a sensitivity formed by a side threshold value and a second negative side threshold value, and shaping the waveform of an input signal, and the first waveform shaping circuit or the second waveform. A switch means for selecting one of the shaping circuits, a level detector for detecting the amplitude of the input signal, and when the detection result of the level detector is narrower than a reference value, the first waveform shaping circuit is selected. , A means for controlling the switch means to select the second waveform shaping circuit when the value is wider than a reference value, and the first negative side threshold value is higher than the second negative side threshold value. , A wave characterized in that the first positive threshold is lower than the second positive threshold Shape shaping circuit.