JPH01241981A - Clip circuit - Google Patents

Abstract

PURPOSE:To obtain an excellent picture signal without limited black level by correcting a clip output voltage waveform by an inter-base difference voltage waveform caused in each collector at the upper and lower part of the clip potential by a constant voltage operating circuit interposed to each collector. CONSTITUTION:A collector of transistors(TRs) 1, 2 is connected to a positive voltage source +Vcc via resistors 4, 6 and a series circuit comprising resistors 5, 7 connected in series to a constant voltage source 29 of voltage V6 in common is connected in parallel with the resistors 4, 6. Then voltage signals V3, V4 caused across the collector of the TRs 1, 2 are led to an adder 9 as a correction voltage waveform signal via coefficient devices 101, 102 multiplying a coefficient alphain common and added to a clip output voltage signal V0 from a common connection emitter and extracted as a clip output voltage signal V5. Thus, a sharp black level clip is attained and an excellent picture signal without limited black level is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a method for converting the base input voltage waveform of one transistor from the emitter of a plurality of transistors, which are grounded through a common constant current source, to the input voltage waveform of the base of one transistor. Concerning a clipping circuit that takes out an output signal with a voltage waveform clipped at a potential, in particular, a circuit that can obtain a corrected, steeply lipped output signal waveform using a voltage waveform formed by inserting a constant voltage operating circuit in the collector. It is.

(Summary of the Invention) The present invention provides an output signal having a voltage waveform obtained by clipping the base input voltage waveform of one transistor with the input potential of another transistor from the emitters of a plurality of transistors that are grounded through a common constant current source. In the clip circuit for extracting the output voltage, the clip output voltage waveform is modified by the difference voltage waveform between the bases generated at each collector above and below the clip potential by a constant voltage and piezo actuated circuit inserted in each collector, so that a steep rip characteristic can be obtained. This is what I did.

(Prior Art) A conventional clipping circuit of this type is configured as shown in FIG. The collectors of transistors 1 and 2 were commonly connected to a positive voltage source +VCC, the input voltage signal Vin was supplied to the base of transistor 1, and the base of transistor 2 was grounded, and the collectors of transistors 1 and 2 were connected in common. The input voltage signal waveform that exceeds the ground potential appearing at the emitter is extracted as a clip output voltage signal.

(Problems to be Solved by the Invention) The input/output characteristics of the conventional clip circuit of this type having the configuration shown in FIG. 6 are as shown by the solid line in FIG. When the base of transistor 2 is grounded, the input/output characteristic curve deviates significantly from the ideal linear characteristic and curves near the clip potential of input voltage OV as shown in the figure. Therefore, when a conventional clipping circuit with such input/output characteristics is used as a black level clipping circuit in an image processing device, for example, the signal level of the clipped output image signal becomes significantly different from the ideal input/output characteristics in the vicinity of the black level which is the clipping potential. The conventional problem has been to solve the problem that the output image signal is so-called crushed black because of the deviation.

(Means for Solving the Problems) It is an object of the present invention to solve the above-mentioned conventional problems, to have linear ideal input/output characteristics, and to solve the conventional black problems that occur when used for black level clipping. An object of the present invention is to provide a clip circuit having input/output characteristics that eliminates crushing and poor lip sharpness.

That is, in the clip circuit of the present invention, the emitters of a pair of transistors are connected to a predetermined voltage source via a predetermined constant current source, and the collectors of the pair of transistors are connected to a common predetermined reverse voltage source via respective resistors. A series circuit of each diode and a common constant voltage source is connected in parallel to each of the resistors, and a predetermined potential is supplied to the base of one of the transistors via the resistor, while the other transistor is connected to the base of the transistor. An input signal is supplied to the base of the input signal, a voltage waveform commonly generated at the emitter is supplied to the adder, and a voltage waveform generated at each of the collectors is supplied to the adder via a coefficient multiplier that respectively multiplies the voltage waveform by a predetermined coefficient. By doing so, the voltage waveform of the input signal is clipped at the predetermined potential, and an output signal having a voltage waveform that is modified and steepened by the voltage waveforms generated at the collectors is taken out from the adder. It is characterized by this.

(Function) Therefore, in the clipping circuit of the present invention, it is possible to perform sharp 6-black level clipping with ideal linear input/output characteristics, and furthermore, it is possible to perform non-additive mixing and non-additive mixing for a large number of input image signals. At the same time, NAM clipping, which clips the maximum amplitude image signal, can be performed with good sharpness.

(Example) The present invention will be described in detail below with reference to the drawings.

An example of the circuit configuration of the clip circuit of the present invention is shown in FIG. In the illustrated circuit configuration, the emitters of a pair of transistors 1 and 2 are commonly connected to a negative voltage source -ν via a constant current source 3.
cc and supplies the input voltage signal v1 to the base of transistor 1, and supplies the ground potential to the base of transistor 2 via resistor 8 as shown, or supplies the required DC potential v2 to the base of transistor 2. do. However, the collectors of transistors 1 and 2 are significantly different from the conventional circuit configuration shown in FIG.
and 6 to a positive voltage source +VCC, and to the resistors 4 and 6, a series circuit in which a constant voltage source 29 of voltage v6 is commonly connected in series to the respective resistors 5 and 7 is connected in parallel.

In the clip circuit of the present invention, a clip output voltage signal V is generated from the commonly connected emitters in the circuit configuration described above. The voltage signals v3 and v generated at the collectors of transistors 1 and 2, respectively, are taken out as before.
4 is led to an adder 9 as a correcting voltage waveform signal via coefficient multipliers 101 and 102, respectively, which are commonly multiplied by an appropriate coefficient α, to produce a clipped output voltage signal V from the commonly connected emitter. , and is extracted as the clip output voltage signal v5 of the clip circuit of the present invention.

Thus, in the conventional clip circuit having the configuration shown in FIG. 6, the clip output voltage signal V having the input/output characteristics shown by the solid line in FIG. 7 is generated at the commonly connected emitters. The voltage difference between the voltage and the ideal input/output characteristics shown by the dotted line is the same in the clip circuit of the present invention having the configuration shown in the first figure, but the voltage difference between the input voltage signal V and the ideal input/output characteristics shown in the eighth figure Changes to Therefore, the differential voltage of such voltage waveforms is reversed to form a clipped output voltage signal v0 from the commonly connected emitter.
By adding the above and modifying the output signal voltage waveform, a crimp output voltage signal with a voltage waveform close to ideal input/output characteristics can be obtained.

On the other hand, considering the voltage signal v3 generated at the collector of transistor 1 in the clip circuit of the present invention with the configuration shown in FIG. If the base potential v2, which is defined as Ov, is sufficiently high, the transistor 1 is in the active region and the transistor 2 is in the cutoff region, so that the constant current I of the constant current source 3 flows through the transistor 1. A current approximately equal to that flows through the resistor 4 and diode 5 of the collector circuit.
However, when the voltage across the resistor 4 is large enough to exceed the constant voltage v6 of the constant voltage source 29 and cause the current to flow through the diode 5, the current is divided from the positive voltage source +VCC. The observed collector potential v3 is the constant voltage v6 of the constant voltage source 29.
and the on-voltage V of diode 5 of 0.6 to 0.7■,
It never becomes lower than the sum V6+Vn.

However, the base input signal voltage ν of transistor 1
, is lower than the base potential v2 of transistor 2, transistor 1 is in an operating state close to the cut-off region and transistor 2 is in the active region, so that transistor 1,
Therefore, almost no current flows through the resistor 4 and diode 5. As a result, the voltage across the resistor 4 becomes almost zero, and the diode 5 is turned off, so that the collector potential v3 becomes close to the potential VCC of the positive voltage source.

The collector potential v4 of the other transistor 2 is considered to be almost the same, and therefore the collector potentials v3 and v4 of the transistors 1 and 2 are equal to the potential +VC of the positive voltage source.
With reference to C, as shown in FIG. 2, the input and output characteristics are inversely symmetrical to each other.

FIG. 2 also shows the input/output characteristics of the combined value V3+V4 of the collector potentials of transistors 1 and 2, but this combined input/output characteristic is different from that of the conventional clipped output voltage signal V shown in FIG.
. Although the polarity is opposite to the deviation of the input/output characteristics from the ideal characteristics, they are very similar. Therefore, if the voltage waveforms of the collector potentials v3 and v4 with respect to the ground potential are commonly multiplied by an appropriate coefficient α and added to the clipped output voltage signal v0 from the commonly connected emitter, the ideal input/output characteristics will be approached. If the resistance values of the resistors 4 and 6 in the collector circuit, the constant current value I0 of the constant current source 3, and the constant voltage value v6 of the constant voltage source 29 are appropriately set, as shown in FIG.
A clipped output voltage signal with input/output characteristics much closer to ideal characteristics than the conventional characteristics shown in FIG. 7 can be obtained.

The configuration example of the clip circuit of the present invention shown in FIG. 1 is a basic configuration in principle that is an improved form of the conventional configuration shown in FIG. 6, and the specific configuration actually used is shown in FIG. 4. Fourth
In the specific configuration shown, resistors 11, 12 and 13
The collector potentials v3 and v4 are set to a common resistor emitter output voltage V. is added to obtain the clip output voltage signal V, but the collector potential V3+v4 and the emitter potential V
The means for adding with 0 is not limited to this example. Further, a circuit portion 30 surrounded by a broken line is an example of a specific configuration of the constant voltage source 29, and a circuit portion 31 similarly shown surrounded by a broken line is an example of a specific configuration of the constant current source 3. The configuration is not limited to the two examples shown. Note that in the figure, the transistor 24 and the diode 25 are added to compensate for the temperature characteristics of the diode 5.7 and the constant current source transistor 23, respectively.

The basic configuration of the clip circuit of the present invention shown in FIG. 1 is an improved form of the conventional configuration shown in FIG. For example, the higher input signal voltage v1
It can be thought of as a type of non-additive mixing (NAM) circuit that clips and outputs the signal at the lower input signal voltage v2.

Expanding this concept, the circuit configuration shown in FIG. 5, in which n combination circuits each consisting of a transistor 1, a resistor 4, and a diode 5 are connected in parallel, is configured as an N circuit having n input voltage signals.
It can be considered as an AM clip circuit. In the configuration example shown in FIG. 5, a clipping operation exhibiting the same input/output characteristics as shown in FIG. 3 is obtained, and the input signal voltage on the horizontal axis in the input/output characteristics shown in FIG. If it is considered as the difference voltage between the highest input signal voltage and the next highest input signal voltage, the highest input signal voltage is clipped by the next highest input signal voltage and extracted as a clipped output voltage signal.

(Effects of the Invention) As is clear from the above description, according to the present invention, a clip circuit having almost ideal input/output characteristics as a clip circuit can be obtained, and can be used for black level clipping to provide a sharp black level. - Clipping can be performed, and a high-quality processed output image signal without black clutter, which is produced by conventional clipping circuits, can be obtained.

In a conventional image signal processing device using a clip circuit, the signal amplitude of the input image signal is increased in order to compensate for the deviation of the input/output characteristics of the clip circuit from the ideal characteristics and reduce black clutter. According to the present invention, there is no need to particularly increase the signal amplitude of the input image signal, and therefore there is no need to particularly increase the power supply voltage used for the clip circuit, and it is possible to share the voltage power supply with other image signal processing circuits. At the same time, the special effect of reducing the power consumption of the voltage power source can also be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of the basic configuration of the clip circuit of the present invention, Fig. 2 is a characteristic curve diagram showing the input/output characteristics of the collector potential of the clip circuit, and Fig. 3 is the input/output characteristic of the clip circuit. FIG. 4 is a circuit diagram showing an example of a specific configuration of the clip circuit, FIG. 5 is a circuit diagram showing an example of the configuration of the clip circuit as a NAM clip circuit, and FIG. 6 is a characteristic curve diagram showing the characteristics. A circuit diagram showing the configuration of a conventional clip circuit, Fig. 7 is a characteristic curve diagram showing the input/output characteristics of the clip circuit, and Fig. 8 is a characteristic curve showing the deviation of the input/output characteristics of the clip circuit from the ideal characteristics. It is a curve diagram. 1, 2.23.24.71-74...transistor 3.31...constant current source 4.6, 8.11-21.41-44...resistor 5,
7.25.51-54...Diode 9...Adder 10, 101-104...Coefficient unit 29, 30...Constant voltage source Patent applicant Japan Broadcasting Association Figure 1 Tomeiwarip rotation g - one unit reto structure - Vcc Fig. 7 A Shiba rice υ g I rub supination -
, / −θo5 7oo5 θl
Procedural amendment 1. Display of the case Patent Application No. 68272 filed in 1988 2, Title of the invention Rib circuit 3, Person making the amendment Relationship to the case Patent applicant (435) Japan Broadcasting Corporation 4, Agent 5, Subject of the amendment 1. Specification page 15 line 5 r 10.101-104
. . . coefficient unit" is corrected to "101-104 . . . coefficient unit". 2. In the drawings, Figure 5 is corrected as shown in the attached correction diagram.

Claims (1)

[Claims] 1. The emitters of a pair of transistors are connected to a predetermined voltage source via a predetermined constant current source, and the collectors of the pair of transistors are connected to a common predetermined reverse voltage source via respective resistors. A series circuit of each diode and a common constant voltage source is connected in parallel to each of the resistors, and a predetermined potential is supplied to the base of one of the transistors via the resistor, while the other transistor is connected to the base of the transistor. An input signal is supplied to the base of the input signal, a voltage waveform commonly generated at the emitter is supplied to the adder, and a voltage waveform generated at each of the collectors is supplied to the adder via a coefficient multiplier that respectively multiplies the voltage waveform by a predetermined coefficient. By doing so, the voltage waveform of the input signal is clipped at the predetermined potential, and an output signal having a voltage waveform that is modified and steepened by the voltage waveforms generated at the collectors is taken out from the adder. A clip circuit characterized by: 2. The emitters of the plurality of transistors are connected to a predetermined voltage source via a predetermined constant current source, and the collectors of the plurality of transistors are commonly connected to a predetermined reverse voltage source via respective resistors. A series circuit of each diode and a common constant voltage source is connected in parallel to each of the resistors, each input signal is supplied to the bases of the plurality of transistors, and the voltage waveforms commonly generated at the emitters are added. The voltage waveforms of the respective input signals are subjected to non-additive mixing (N
AM), clip the voltage waveform having the highest voltage level at the voltage level of the voltage waveform having the voltage level following the highest voltage level, and modify the voltage waveforms respectively generated at the collectors to make the voltage waveform steeper. 1. A NAM clipping circuit, wherein an output signal having a voltage waveform of 0.05 to 1.0 is taken out from the adder.