JPH04310014A - Signal waveform processor - Google Patents

Abstract

PURPOSE:To make the improving characteristic of an unsharpened waveform stable against an ambient temperature change, to set the amplitude of an input signal over a wide range and to realize a processor suitable for a semiconductor integrated circuit. CONSTITUTION:A low pass filter 100 extracts a DC component included in an input signal. A differential amplifier 200 amplifies a difference signal between an DC component extracted by a low pass filter 100 and an original input signal to extract an AC component included in the original input signal. Current mirror circuits 300, 400 extract a signal component corresponding to the falling part of the original input signal from an AC component extracted by the differential amplifier 200. An output circuit 600 subtracts the signal component extracted by the current mirror circuits 300, 400 from the original input signal to obtain a signal in which the unsharpened waveform of the falling part of the original input signal is improved.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a waveform processing device.
In particular, the present invention relates to a waveform processing device for improving waveform distortion in the rising and falling portions of a video signal.

0002

[Background Art] In recent years, VTR (video tape recorder)
With the advancement of signal processing technology in magnetic recording and reproducing devices such as the above, it has become possible to record video signals in a wide frequency band on and reproduce them from recording media. In a magnetic recording and reproducing apparatus that records and reproduces video signals, the video signal is FM-modulated and the FM-modulated video signal is recorded on a magnetic tape. An FM modulated signal (hereinafter simply referred to as an FM signal) is mixed with more noise in a transmission system in which the signal is transmitted, the higher the frequency band. In other words, in a VTR, when an FM-modulated video signal (hereinafter referred to as an FM video signal) is recorded on a magnetic tape and played back from the magnetic tape, the noise mixed into the FM video signal is generated by the FM video signal in the tape head system. The higher the frequency band of the video signal, the more noticeable it becomes.

[0003] Therefore, in such a magnetic recording/reproducing device, a pre-emphasis circuit is installed before the FM modulator to emphasize the high-band components of the video signal by increasing the gain (applying emphasis) to the high-band portions of the FM signal. is provided. As a result, the F
In the video signal obtained by demodulating the M video signal, noise in the high band portion becomes less noticeable.

However, when a video signal is emphasized, sharp overshoots occur in its rising and falling parts. FIG. 7A is a diagram showing an example of a waveform of a video signal in which overshoot has occurred due to emphasis. Referring to FIG. 7(a), overshoot S occurring at the rising edge of the video signal
1, the level of the rising edge of the video signal becomes higher than necessary, destroying the original waveform. Similarly, due to the overshoot S2 occurring in the falling portion of the video signal, the level of the falling portion of the video signal becomes lower than necessary, destroying the original waveform. On the other hand, an FM modulator changes the frequency of a predetermined carrier wave by an amount corresponding to the level of an input signal. Therefore, if the level of the video signal input to the FM modulator changes significantly in the positive or negative direction, in response, the deviation of the output frequency of the FM modulator from the carrier frequency will change to the original level of the video signal. A so-called overmodulation occurs, which is larger than the corresponding one. To prevent such overmodulation, it is necessary to remove the overshoot portion due to emphasis from the video signal output from the pre-emphasis circuit.

[0005] Therefore, in a VTR or the like, a clip circuit is provided between a pre-emphasis circuit and an FM modulator for correcting the maximum amplitude of an input signal to a predetermined value. The clipping circuit performs white clipping, which removes a portion of the applied video signal having a level equal to or higher than a predetermined reference level, and dark clipping, which removes a portion of the applied video signal having a level lower than a predetermined reference level. FIG. 7(b) is a diagram showing the waveform of a video signal obtained when white clipping and dark clipping are applied to the video signal having the waveform shown in FIG. 7(a). Figure 7 (
Referring to a) and (b), the clipped video signal does not include signal components at a level higher than a certain reference level A and signal components at a level lower than a certain reference level B. Reference levels A and B are called white clip level and dark clip level, respectively. Normally, in magnetic recording and reproducing devices such as VHS VTRs, there are limits to the maximum and minimum values of the FM frequency that can be accurately stored on the magnetic recording medium. The width from the lower reference level B is set narrower than the width from the white level to the upper reference level A. For this reason, signal components in the falling portion of the video signal before FM modulation are likely to be lost. FIG. 8 is a waveform diagram showing how information is lost at the falling edge of a video signal due to clipping. For example, assume that a video signal including a high-level signal component S3 and a low-level signal component S4, which are not caused by overshoot due to emphasis, is input to the clip circuit as shown in FIG. 8(a). In such a case, a portion of the high-level signal component that exceeds the white clip level A is small, whereas a portion of the low-level signal component that exceeds the dark clip level B is large. Clipping therefore removes many of the low level signal components. Then, the clipped video signal (Fig. 8(b))
The waveform of the rising portion of the clipped video signal is not much different from that of the video signal before being clipped, whereas the waveform of the falling portion of the clipped video signal is considerably distorted from that of the video signal before clipping. . Therefore, a waveform processing circuit has conventionally been provided at a subsequent stage of the clipping circuit to improve the dullness of the video signal waveform due to the lack of information that occurs in the falling portion of the video signal due to such clipping.

FIG. 6 is a circuit diagram showing a conventional waveform processing circuit used to improve this type of waveform distortion. Referring to FIG. 6, this waveform processing circuit includes NPN transistors 31 and 32, constant current sources 33 and 34, and resistors 35 and 36, which constitute a differential amplifier. Constant current sources 33 and 34 are connected to transistor 3, respectively.
1 and 32 emitters. transistor 3
The collector of transistor 32 is directly connected to power supply terminal 11, and the collector of transistor 32 is connected to power supply terminal 1 through resistor 36.
Connected to 1. Resistor 35 is connected between the emitter of transistor 31 and the emitter of transistor 32. The waveform processing circuit further includes a series connection of a capacitor 37 and a diode 38 connected in parallel with the resistor 35. The bases of transistors 31 and 32 are biased to a predetermined reference potential Vref by bias voltage sources 21 and 22, respectively. An input signal to this waveform processing circuit is applied to the base of transistor 31, and an output of this waveform processing circuit is taken out from the collector of transistor 32 to output terminal 13. In FIG. 6, it is assumed that the input signal to this waveform processing circuit is output from the AC signal source 12.

When diode 38 is non-conducting,
The difference voltage between the base voltage of the transistor 31 and the base voltage of the transistor 32, that is, the output voltage Vref of the voltage source 22, is the resistance value of the resistor 35 (the impedance between the emitter of the transistor 31 and the emitter of the transistor 32). A signal amplified by an amplification factor determined by the ratio of the resistance value of the resistor 36 and the resistance value of the resistor 36 appears at the collector of the transistor 32. When the base voltage of the transistor 31 is higher than the base voltage of the transistor 32, the current flowing from the emitter of the transistor 31 to the constant current source 34 via the resistor 35 increases as the base voltage of the transistor 31 increases. From power terminal 11 to resistor 3
6 to the collector of transistor 32 decreases. Therefore, the voltage drop across the resistor 36 becomes smaller, and the collector voltage of the transistor 32 becomes higher. Conversely, if the base voltage of transistor 31 is lower than the base voltage of transistor 32, transistor 3
As the base voltage of the transistor 32 decreases, the current supplied from the emitter of the transistor 32 to the constant current source 33 via the resistor 35 increases.
The current flowing into the collector of the transistor 32 via the current increases. Therefore, the voltage drop across the resistor 36 increases, and the collector voltage of the transistor 32 decreases.

When diode 38 is conductive, not only resistor 35 but also capacitor 37 is electrically connected between the emitter of transistor 31 and the emitter of transistor 32. Therefore, the value of the impedance existing between the emitter of transistor 31 and the emitter of transistor 32 is the same as that of resistor 35 and capacitor 3.
This is the impedance value of the 7 parallel connected circuits. The impedance of this parallel connected circuit is smaller than the impedance of the resistor 35 alone. On the other hand, transistor 3
2 collector voltage (output signal voltage of this waveform processing circuit)
The ratio of v1 to the base voltage of transistor 31 (input signal voltage of this waveform processing circuit) v0, that is, the amplification factor v1/v0 of this waveform processing circuit, is the ratio of the resistance value of resistor 36 to the emitter of transistor 31 and transistor 32. It is proportional to the ratio of the impedance present between the emitter and the value. Therefore, the amplification factor of this waveform processing circuit when diode 38 is conducting is greater than when diode 38 is non-conducting.

From the emitter of transistor 32 to resistor 3
As the current flowing into the constant current source 33 via the constant current source 33 increases, the voltage drop across the transistor 32 increases, and the cathode voltage of the diode 38 decreases due to the coupling of the capacitor 37. As a result, a forward voltage is applied to the diode 38, and the diode 38 becomes conductive. Therefore, transistors 31 and 32 and constant current source 33
The gain of the differential amplifier constituted by the resistors 35 and 34 and the resistors 35 and 36 becomes large only when a signal having a level lower than the reference voltage Vref is input. As a result, the waveform of the falling portion of the signal appearing at the output terminal 13 is the waveform of the falling portion of the output signal of the AC signal source 12 that has been corrected to be sharp.

0010

As described above, a conventional waveform processing circuit for improving the roundness of a signal waveform is constituted by a variable gain amplifier whose gain changes depending on whether a diode is conductive or nonconductive. However, since the conduction resistance of a diode changes with temperature, the characteristics of conventional waveform processing circuits tend to change with temperature and are unstable.

For example, referring to FIG. 6, the amplification factor of the differential amplifier constituting this waveform processing circuit is the transistor 31.
The value of the impedance between the emitter of transistor 32 and the emitter of transistor 32 changes accordingly. Therefore, when the resistance value of the diode 38 changes when it is conductive, the value of the impedance that exists between the emitter of the transistor 31 and the emitter of the transistor 32 changes, so the gain of this differential amplifier is changed when the diode 38 is conductive. It fluctuates over the period of time. As a result, output terminal 13
The degree to which the waveform of the falling portion of the signal appearing in the waveform of the falling portion of the output signal of the AC signal source 12 is sharpened (hereinafter referred to as the waveform rounding improvement characteristic) varies depending on the temperature.

Further, in such a conventional waveform processing circuit, the diode 38 is activated only when the amplitude of the input signal to the base of the transistor 31 in the negative direction is large, that is, when the base voltage of the transistor 31 is equal to the reference voltage Vre.
It conducts only when the voltage drop lower than f and thus created across resistor 35 reaches a forward voltage that can cause diode 38 to conduct. Therefore, in order to reliably improve the roundness of the waveform of the falling portion of the output signal of the signal source 12, the voltage at the falling portion of the input signal to the base of the transistor 31 must be sufficiently lower than the reference voltage Vref. . Therefore, if the voltage at the falling edge of the signal whose waveform rounding is to be improved is not sufficiently lower than the reference voltage Vref in the waveform processing circuit, an amplifier circuit is required at the front stage of the waveform processing circuit. For example, in FIG. 6, this amplifier circuit may be provided between the signal source 12 and the base of the transistor 31. This amplifier circuit increases the amplitude of the output signal of the signal source 12, so that the input signal to the base of the transistor 31 becomes sufficiently lower than the reference voltage Vref at the time of falling.

Furthermore, in order to make the frequency characteristics of such a conventional waveform processing circuit suitable for video signals, the resistance values of the resistors 35 and 36 must be several kΩ, and the capacitance of the capacitor 37 must be must be several tens of pF. On the other hand, when a capacitor is formed within a semiconductor integrated circuit device, it requires a large space. The space required to form a capacitor increases as the capacitance required for the capacitor increases. For this reason, forming a large capacitor in a semiconductor integrated circuit device is
This is not preferable from the viewpoint of improving the degree of integration of semiconductor integrated circuit devices. In fact, the maximum capacitance of a capacitor that can be formed within a semiconductor integrated circuit device is approximately several tens of pF. For this reason, it is difficult to convert a conventional waveform processing circuit for improving the roundness of a signal waveform into a semiconductor integrated circuit device having practical frequency characteristics suitable for video signals. However, with the recent advancements in video equipment such as VTRs and video movies, the circuits used to process video signals tend to be made into semiconductor integrated circuit devices; It is hoped that it will be advantageous to

As described above, in conventional signal waveform processing circuits for improving the rounding of signal waveforms, the waveform rounding improvement characteristics tend to change depending on the temperature, and if the amplitude of the input signal is not appropriate, an extra amplifier circuit is added. This method has problems such as the need to process a semiconductor integrated circuit, and disadvantages in making it into a semiconductor integrated circuit device.

Therefore, it is an object of the present invention to solve the above-mentioned problems, to ensure that the waveform rounding improvement characteristics are stable against temperature changes, and to provide greater freedom in the setting range of the input signal amplitude than in the past. It is an object of the present invention to provide a signal waveform processing device that has high performance and is advantageous for fabrication into a semiconductor integrated circuit device.

[0016]

[Means for Solving the Problems] In order to achieve the above objects, a signal waveform processing device according to the present invention includes a low-frequency component extracting means for extracting a low-frequency component of an input signal, and a low-frequency component extracting means for extracting a low-frequency component of an input signal. A high-frequency component deriving means for deriving a high-frequency component of the input signal based on the input signal and the low-frequency component extracted by the means; a signal component extracting means for extracting only the signal component corresponding to the falling portion or the falling portion; and a waveform shaping means for shaping the waveform of the changing portion of the input signal based on the input signal and the signal component extracted by the signal component extracting means. Equipped with. The waveform shaping means adds the signal component corresponding to the rising portion extracted by the signal component extracting means to the input signal, or the waveform shaping means adds the signal component corresponding to the falling portion extracted by the signal component extracting means to the input signal. and means for subtracting the component from the input signal.

[0017]

[Operation] Since the signal waveform processing device according to the present invention is constructed as described above, the AC component is extracted from the input signal of the signal waveform processing device by the low frequency component extraction means. Since the extracted AC component is subtracted from the original input signal in the high frequency component deriving means, the high frequency component derived by this subtraction becomes the AC component of the original input signal. From this AC component, only a signal component corresponding to either a rising portion or a falling portion of the original input signal is extracted by the signal component extracting means. If the signal component extracted by this corresponds to the rising edge, it is added to the original input signal in the waveform shaping means, so the waveform of the output signal of the waveform shaping means is the same as that of the original input signal. The accent at the rising edge has been improved. Conversely, if the signal component extracted by the signal component extraction means corresponds to the falling part, the extracted signal component is subtracted from the original input signal in the waveform shaping means, so the output of the waveform shaping means The signal waveform becomes one in which the falling part of the original input signal has been improved in its roundness.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing a signal waveform processing circuit according to an embodiment of the present invention. Referring to FIG. 1, this signal waveform processing circuit includes a low-pass filter 100 and a differential amplifier 200.
, current mirror circuits 300 and 400, an input circuit 500, and an output circuit 600. In Figure 1,
The input signal source is represented by an AC signal source 12.

Input circuit 500 includes an NPN transistor 46 having a base biased to a predetermined DC potential by bias voltage source 21 and a constant current source 47. Output circuit 600 includes a series connection circuit of NPN transistor 53 and constant current source 54 connected to power supply terminal 11 . The input signal to this waveform processing circuit (AC signal source 12
) is applied to the base of transistor 46 and also to the base of transistor 53 via resistor 50. The output of this waveform processing circuit is taken out from the emitter of the transistor 53 to the output terminal 13. Therefore, the emitter currents of transistors 46 and 53 exhibit the same waveform as the input signal. Therefore, input circuit 5
The 00 output is taken from the emitter of transistor 46. The output of input circuit 500 is provided to low pass filter 100.

Low-pass filter 100 includes transistor 46
It is constituted by a series connection circuit of a resistor 41 and a capacitor 48, that is, an integrating circuit which is one of the time constant circuits, connected to the emitter of the resistor 41 and the capacitor 48. At the connection point between the resistor 41 and the capacitor 48, only a voltage signal having a waveform obtained by integrating the emitter current waveform of the transistor 46, that is, a DC component of the input signal appears. This DC component is the low-pass filter 1
It is applied to the differential amplifier 200 as an output voltage of 00.

Differential amplifier 200 includes PNP transistors 31 and 32, constant current sources 33 and 34, and resistor 35. The output voltage of low-pass filter 100 is applied to the base of transistor 31. On the other hand, the output of the input circuit 500 is connected to the base of the transistor 32 through a resistor 4.
2. Constant current source 33 is transistor 3
1 and the power supply terminal 11. A constant current source 34 connects the emitter of the transistor 32 and the power supply terminal 1.
1. The resistor 35 is connected to the transistor 3
1 and the emitter of transistor 32. Therefore, the base voltage of the transistor 31 and the transistor 32 are connected to the collector of the transistor 32.
A current proportional to the difference between the base voltage and the base voltage flows.

When the base voltage of transistor 31 is lower than the base voltage of transistor 32, transistor 3
As the base voltage of the transistor 31 decreases, the current flowing from the constant current source 34 to the emitter of the transistor 31 via the resistor 35 increases.
The current flowing into the emitter of transistor 32 decreases, resulting in a decrease in the collector current of transistor 32. Conversely, when the base voltage of the transistor 31 is higher than the base voltage of the transistor 32, the current flowing from the constant current source 33 to the emitter of the transistor 31 decreases as the base voltage of the transistor 31 increases. The current flowing from 33 through resistor 35 into the emitter of transistor 32 increases, resulting in an increase in the collector current of transistor 32. Here, the base voltage of the transistor 31 is the output voltage of the low-pass filter 100, which indicates the waveform of the DC component of the input signal to this waveform processing circuit. On the other hand, the base voltage of transistor 32 exhibits the same waveform as the input signal to this waveform processing circuit. Therefore, transistor 3
In the collector current waveform No. 2, only the high frequency components of the input signal to this waveform processing circuit are amplified. The output of differential amplifier 200 is taken out from the collector of transistor 32 and applied to current mirror circuits 300 and 400.

The current mirror circuit 300 includes two NPN transistors 43 and 4 whose bases are connected together.
Contains 4. The collector of transistor 44 is connected to the collector of transistor 32, and the emitter of transistor 44 is grounded. The collector of transistor 43 is connected to power supply terminal 11 via constant current source 45, and the emitter of transistor 43 is grounded. The base and collector of transistor 43 are connected to each other. Similarly to the current mirror circuit 300, the current mirror circuit 400 also includes NPN transistors 51 and 5 whose bases are connected together.
Contains 2. The collector of transistor 51 is connected to the collector of transistor 32, and the emitter of transistor 51 is grounded. The collector of transistor 52 is connected to the base of transistor 53, and the emitter of transistor 52 is grounded. The base and collector of transistor 51 are connected to each other. In this embodiment, the magnitude of the current supplied by the constant current source 45, the constant current source 33
and the magnitude of the current supplied by the constant current source 34
The magnitudes of the currents supplied by are set equal to each other. Therefore, the collector of transistor 44 has
A current of the same magnitude as the current flowing from the constant current source 45 into the collector of the transistor 43 flows. Similarly, a current of the same magnitude as the current flowing into the collector of transistor 51 flows through the collector of transistor 52 .

When the base voltage of the transistor 32 is higher than the base voltage of the transistor 31, that is, when the input signal voltage to this waveform processing circuit is changing in the positive direction around its DC level, the constant current source 34 The collector current of transistor 32 is less than the current supplied by constant current source 34, since most of the current supplied by transistor 31 flows through resistor 35 into transistor 31. On the other hand, a current is supplied to the base of the transistor 44 from the collector of the transistor 43 so that a current having the same magnitude as the current supplied by the constant current source 45 flows into the collector of the transistor 44 . Therefore, the collector current of transistor 32 does not flow into the base and collector of transistor 51, but only into the collector of transistor 44. As a result, in the current mirror circuit 300, the transistor 44 is in a saturated state where the collector current is maximum, while no current flows through either of the transistors 51 and 52 in the current mirror circuit 400.

Conversely, if the base voltage of transistor 32 is lower than the base voltage of transistor 31, that is,
When the input signal voltage to this waveform processing circuit is changing in the negative direction around its DC level, the transistor 32
The collector current of the transistor 32 is supplied by the constant current source 34 because the current supplied by the constant current source 33 as well as the current supplied by the constant current source 34 flows into the emitter of the transistor 32 through the resistor 35. More than current. Therefore, in this case, only a portion of the collector current of the transistor 32 having the same magnitude as the current supplied by the constant current source 45 flows into the collector of the transistor 44, and the rest is supplied to the collector and base of the transistor 51. . Therefore, current flows not only through transistor 44 but also through transistors 51 and 52.

In this way, when the input signal to the input circuit 500 rises, no current flows through either of the transistors 51 and 52 in the current mirror circuit 400, and when the input signal falls, no current flows in the current mirror circuit 400. Current flows through transistors 51 and 52. Since the collector current of transistor 52 flows through resistor 50,
The base voltage of the transistor 53 is reduced by a voltage corresponding to the product of the resistance value of the resistor 50 and the collector current of the transistor 52 due to the collector current generated in the transistor 52 . On the other hand, the base of the transistor 53 is connected to the output of the current mirror circuit 400 (transistor 5
2) as well as the input signal to this waveform processing circuit via a resistor 50. Therefore, a voltage appears at the base of the transistor 53, which is obtained by subtracting the voltage drop across the resistor 50 due to the collector current of the transistor 52 from the input signal voltage to the waveform processing circuit. As a result, the signal waveform appearing at the base of the transistor 53 is the one in which the waveform of the falling portion of the input signal to the base of the transistor 46 is corrected to be sharp. In other words, the waveform distortion of the falling portion of the input signal is improved. Since the transistor 53 operates as an emitter follower, a signal appears at the emitter of the transistor 53, and has a waveform similar to the signal appearing at the base of the transistor 53, with the rounding of the falling portion improved.

As described above, in this embodiment, the DC component contained in the input signal is extracted by the low-pass filter 100, and the original input signal is converted by the differential amplifier 200 that receives the extracted DC component and the original input signal. AC components contained in the input signal are extracted. The extracted AC components are half-wave rectified by current mirror circuits 300 and 400,
A portion having an amplitude in the positive direction (rising portion) is removed. Only the AC component from which the rising portion has been removed, that is, the portion (falling portion) having an amplitude in the negative direction among the extracted AC components, has its polarity inverted, and the transistor 5
3 with the original input signal. As a result, a signal is obtained from the emitter of the transistor 53 in which the waveform rounding of the falling portion of the original input signal is improved.

Next, the operation of this waveform processing circuit will be described, taking as an example a case where a rectangular wave with a rounded falling portion is input to this waveform processing circuit. Refer to FIG. 2 for the explanation. FIG. 2 is a diagram showing signal waveforms appearing in major parts of the waveform processing circuit when such a rectangular wave is input to the waveform processing circuit.

From signal source 12 to transistors 46 and 5
When a signal with a waveform as shown in FIG. 2(a) is applied to the base of transistor 3, the base voltage of transistor 32 becomes higher than the base voltage of transistor 31 at the rising edge of the input signal (FIG. 2(a)). Therefore, the base voltage of the transistor 31 becomes lower than the base voltage of the transistor 31 when the input signal falls. Therefore, the collector current of the transistor 32 temporarily decreases at the rising edge of the input signal, as shown in FIG. 2(b).
Temporarily increases when the input signal falls. In other words, the collector current of the transistor 32 becomes less than or equal to the current supplied by the constant current source 34 when the input signal rises, and becomes greater than or equal to the current supplied by the constant current source 34 when the input signal falls. Therefore, the collector current flows through the transistor 52 only when the input signal falls. Since a current corresponding to the difference between the collector current of the transistor 32 and the current supplied by the constant current source 34 flows through the collector of the transistor 52, the collector current waveform of the transistor 52 is as shown in FIG. 2(c). As shown in FIG. 2, only the portion C of the collector current waveform of the transistor 32 (FIG. 2(b)) having an amplitude in the positive direction is extracted. Therefore, the voltage generated across the resistor 50 by the collector current of the transistor 52 exhibits a sharp pulse waveform that reaches its maximum at the falling edge of the input signal, as shown in FIG. 2(d). The base voltage of the transistor 53 is lower than the base voltage of the transistor 46, which is the input signal, by the voltage across the resistor 50, so the base voltage waveform of the transistor 53 is as shown in FIG. 2(e). , by inverting the polarity of the signal waveform shown in Figure 2(d) to the input signal waveform (shown by the dashed line) (shown by the dashed line).
The superimposed one, that is, the signal with the waveform of FIG. 2(d) subtracted from the signal with the waveform of FIG. 2(a) (shown by the solid line)
becomes. That is, the signal waveform appearing at the base and emitter of the transistor 53 has an improved roundness in the falling portion D of the input signal waveform.

FIG. 3 is a circuit diagram showing the configuration of a signal waveform processing circuit according to another embodiment of the present invention. In the above embodiment, the signal applied to the output circuit 600 as an input signal to the waveform processing circuit is taken out from the base of the transistor 46 in the input circuit 500, but it may be taken out from the emitter of the transistor 46. Specifically, at the base of the transistor 53 in the output circuit 600, the current mirror circuit 3
When it is desired to extract the signal to be added to the falling portion of the signal extracted by 00 and 400 from the emitter of the transistor 46 in the input circuit 500, the input circuit 5
00 and output circuit 600 may be connected between the emitter of transistor 46 and the base of transistor 53, as shown in FIG.

FIG. 4 is a circuit diagram showing the configuration of a signal processing circuit according to still another embodiment of the present invention. According to the embodiments shown in FIGS. 1 and 3, the dullness of the falling part of the input signal waveform is improved, but the dullness of the rising part of the input signal waveform is improved using a circuit with a similar functional configuration. It is also possible to do so. For example, as shown in Figure 4,
Contrary to the case of the signal waveform processing circuit in Figure 1, the low-pass filter 1
If the output of 00 is applied to the base of transistor 32, the emitter output of transistor 46 is applied to the base of transistor 31, and the current mirror circuit 700 is added between the output terminal of current mirror circuit 400 and the base of transistor 53, It is possible to improve the roundness of the waveform at the rising edge of the input signal.

Referring to FIG. 4, in this signal waveform processing circuit, the DC component extracted from the input signal is applied to the base of transistor 32, and the original input signal is applied to the base of transistor 31. 32
Contrary to the previous embodiment, the collector current increases when the input signal rises and decreases when the input signal falls. Therefore, the collector current of transistor 52 flows only at the rising edge of the input signal. On the other hand, current mirror circuit 7
00 includes a PNP type transistor 55 connected between the power supply terminal 11 and the collector of the transistor 52, and a PNP type transistor 56 connected between the power supply terminal 11 and the base of the transistor 53. transistor 5
The gates of transistors 5 and 56 are connected to each other, and the base and collector of transistor 55 are connected to each other. Therefore, the collector current flowing through the transistor 52 causes a current to flow from the collector of the transistor 56 to the resistor 50. In this way, according to this embodiment,
As the collector current flows through the transistor 52, a current flows through the resistor 50 in the opposite direction to that in the previous embodiment.
3's base voltage rises temporarily.

FIG. 5 shows that when a signal with a waveform rounding at the rising edge is input to this waveform processing circuit, the voltages between the collector of the transistor 32, the collector of the transistor 56, both ends of the resistor 50, and the base of the transistor 53 are input to the waveform processing circuit. It is a figure which shows the signal waveform which appears in each. When a rectangular wave with a rounded rising edge as shown in FIG. 5(a) is input to this waveform processing circuit, the collector current waveform of the transistor 32 and the collector current waveform of the transistor 52 are respectively changed as shown in FIG. 5(b). ) and (c), the part corresponding to the rising edge and the part corresponding to the falling edge of the input signal in FIGS. 2(b) and 2(c) are interchanged. The collector current of transistor 52 has its polarity reversed by current mirror circuit 700 and is supplied to resistor 50 . As a result, the base voltage waveform of the transistor 53 is the sum of the original input signal waveform (indicated by a broken line) and the voltage waveform appearing at the resistor 50 (indicated by a dashed-dotted line), as shown in FIG. 5(e). As a result, the dullness of the rising portion of the input signal waveform is improved. The voltage waveform across the resistor 50 reaches its maximum in response to the rise of the input signal, as shown in FIG. 5(d).

Of course, in the circuit shown in FIG.
A resistor 50 may be provided between the emitter of transistor 46 and the base of transistor 53.

As described above, in any of the above embodiments, the waveform of the input signal is changed by using a time constant circuit including a resistor and a capacitor, a differential amplifier, and a current mirror circuit in combination. The accent is improved. Therefore, unlike conventional signal waveform processing circuits for improving the roundness of signal waveforms, elements such as diodes, which are significantly affected by ambient temperature changes, are no longer required.
It becomes possible to stably improve the roundness of the input signal waveform without being affected by temperature changes. Furthermore, a signal (transistor 5
The pulse signal appearing at the collector of No. 2) is obtained by amplifying the voltage difference between the input signal and the DC component extracted from this input signal. It is not created based on differential voltage. Therefore, regardless of the amplitude of the input signal, the roundness of the waveform of the input signal is reliably improved. Furthermore, since the capacitance of the capacitor 48 only needs to be set to a value that removes only the high-frequency components of the input signal,
Even when a video signal is used as an input signal, there is no need to use a capacitor 48 with a large capacity as in the conventional case. For this reason, the waveform processing circuits of any of the above embodiments are advantageous for fabrication into semiconductor integrated circuit devices.

[0036]

As described above, according to the present invention, there is provided a signal waveform processing device that improves the roundness of a signal waveform using a method completely different from the conventional method. As a result, it is possible to reliably improve the roundness of the signal waveform regardless of changes in ambient temperature or the voltage level or type of the input signal whose waveform is to be improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a signal waveform processing circuit according to an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the signal waveform processing circuit shown in FIG. 1;

FIG. 3 is a circuit diagram showing the configuration of a signal waveform processing circuit according to another embodiment of the present invention.

FIG. 4 is a circuit diagram showing the configuration of a signal waveform processing circuit according to still another embodiment of the present invention.

FIG. 5 is a waveform diagram for explaining the operation of the signal waveform processing circuit shown in FIG. 4;

FIG. 6 is a circuit diagram showing the configuration of a conventional signal waveform processing circuit for improving the rounding of the falling portion of a signal waveform.

FIG. 7 is a waveform diagram for explaining the function of a clip circuit in video signal processing.

FIG. 8 is a waveform diagram for explaining the reason why a circuit for improving the rounding in the falling portion of a signal waveform is required in video signal processing.

[Explanation of symbols]

100 Low-pass filter 200 Differential amplifier 300, 400, 700 Current mirror circuit 500
Input circuit 600 Output circuit In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. A signal waveform processing device for improving the roundness of a waveform of a changing portion of an input signal, comprising: a low-frequency component extracting means for extracting a low-frequency component of the input signal; and the low-frequency component extracting means. a high-frequency component deriving means for deriving a high-frequency component of the input signal based on the low-frequency component extracted by the input signal and the input signal; a signal component extraction means for extracting only the signal component corresponding to the changing portion of the input signal; and a waveform of the changing portion of the input signal based on the signal component extracted by the signal component extracting means and the input signal. A signal waveform processing device comprising means for shaping. 2. The changing portion is a falling portion of the input signal, and the waveform shaping means includes means for subtracting the signal component extracted by the signal component extraction means from the input signal. 2. The signal waveform processing device according to item 1. 3. The changing portion is a rising portion of the input signal, and the waveform shaping means includes means for adding the signal component extracted by the signal component extraction means to the input signal. 2. The signal waveform processing device according to item 1.