JPS6218111B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a blanking device for removing unnecessary signals during a blanking period of a video signal in a device that processes video signals such as a color television camera, and particularly relates to a blanking device for removing unnecessary signals during a blanking period of a video signal in a device that processes video signals such as a color television camera. A semiconductor integrated circuit (hereinafter referred to as
This article relates to a blanking device suitable for IC (abbreviated as IC).

An example of a blanking device in a conventional color television camera is shown in FIG. In Figure 1,
1 is a video signal source such as a color signal, and this video signal source 1
The output terminal of is connected to the base of transistor 3 and the collector of transistor 4 via capacitor 2. At the base of the transistor 4,
The clamp pulse signal input to terminal 5 is applied to resistor 6.
is applied via. The emitter of the transistor 4 is connected to a reference potential circuit 7 having an output reference potential _V7 . The emitter of the transistor 3 is connected to a constant current circuit 8 whose emitter is grounded, and to the collector of a transistor 10 whose emitter is grounded and to the base of a transistor 11 via a resistor 9. and the transistor 1
A blanking signal is input to the base of 0 from a terminal 12 via a resistor 6. transistor 1
4 has its collector and emitter commonly connected to the transistor 11, and the base of the transistor 14 is connected via a resistor 15 to the emitter of a transistor 16 and to a constant current circuit 17 whose one end is grounded. Further, the emitters commonly connected to the transistors 14 and 11 are connected to the input terminal of a constant current circuit 19 with one side grounded, and the output terminal 18 is connected to the connection point between the emitters of the transistors 11 and 14 and the constant current circuit 19. It is derived. Note that transistors 3, 11, 14
A constant DC voltage is applied to the collectors of and 16 from a terminal 20 by a DC power supply.

Now, in the blanking device described above, the DC voltage of the video signal from the video signal source 1 is adjusted to the reference potential V ₇ of the reference potential circuit 7 by the clamp circuit constituted by the capacitor 2, transistor 3, and transistor 4. be clamped. Furthermore, the output of the video signal at the emitter of the transistor 3 is input to the base of the transistor 11 via the resistor 9, but due to the conduction/cutoff switch action of the switching transistor 10 to which the blanking signal is input to the base, During the blanking period, the transistor 10 is turned on and the base potential of the transistor 11 is set to approximately 0V (however, V _CESAT of the switching transistor 10 is ignored), and during the video signal period other than the blanking period, the transistor 10 is cut off. As the base potential of the transistor 11, the output voltage of the video signal at the emitter of the transistor 3 is directly inputted, except for the voltage drop caused by the resistor 9. On the other hand, the reference potential V ₇ is the transistor 1
6 and a resistor 15, it is input to the base of the transistor 14. At this time, the higher base potential input to the bases of the transistors 11 and 14 is outputted to the output 18, and the reference potential V ₇ is applied during the blanking period.
By outputting an amplified video signal during other video signal periods, unnecessary signal components occurring during the blanking period are removed.

When a blanking device using a clamp circuit as described above is integrated into an IC, a total of three terminals are required as the video signal input terminal and the connection terminal for the clamp circuit capacitor 2, but in order to improve the integration degree of the IC, more terminals are required. One possible method is to use negative feedback of the DC potential, which can be realized with a small number of terminals. An example of this will be explained using FIG. 2. First, the output of the video signal source 1 is connected via a resistor 21 to the emitter of a transistor 22 and a resistor 23 that determines the emitter current of the transistor 22.
The collector of the transistor 22 is connected to a DC power supply via a resistor 24, and the video signal amplified by the transistor 22 is input to the base of the transistor 3. On the other hand, the output potential of the emitter of transistor 3 and the reference potential _V7 are
voltage comparator circuit 25 having a clamp pulse signal at
compares the voltage of the other side, and feeds the potential error back to the base of the transistor 22, controls the collector current of the transistor 22, and matches the DC potential of the emitter of the transistor 3 with the reference potential _V7 . . Further, in the same negative feedback, there is provided a capacitor 26 for removing AC components, one end of which is grounded.
The other configurations are almost the same as the mechanism explained in FIG. 1, so the explanation will be omitted.

If the circuit configuration is as shown in Figure 2 above,
The number of IC terminals in this circuit is the video signal input terminal and 2 capacitors for removing AC components in the negative feedback loop.
6 connection terminals, making a total of 2 terminals. Most of the current blanking devices are integrated circuits, and in order to increase the degree of integration of ICs by reducing the number of IC terminals,
It is necessary to adopt the circuit configuration shown in FIG. 2, which has fewer terminals than the circuit configuration shown in FIG. 1. However, in the circuit configuration shown in FIG. 2, the emitter current (hereinafter abbreviated as I _E ) of the transistor 3 is a constant current (hereinafter abbreviated as I
I ₂₇ ) and the current flowing in the direction of the arrow 28 of the emitter of the transistor 10 when the transistor 10 is in a conductive state (hereinafter referred to as I _ON ) are added (I _E = I ₂₇ + I _ON ), and A case (I _E =I ₂₇ ) in which the transistor 10 is in a cut-off state occurs during a video signal period other than the ranking period. As a result, the potential V _BE between the base and emitter of the transistor 3 is V _BE =V _T L _pge (I _E /I _S ) [However, V _T = KT/q K...Boltzmann's constant, T...Absolute temperature, q...charge, _IS = reverse saturation current of base-emitter diode], and V _BE changes as I _E changes.
Due to this change in V _BE , an error occurs in the DC potential between the blanking period and other signal periods in the output of the output terminal 18 of the blanking circuit, resulting in a white balance deviation in the image. The present invention provides a device that prevents deviations in white balance by providing a circuit for preventing such DC potential errors.

Next, one embodiment of the present invention will be described using FIG. The output of the video signal source 1 is transmitted through a resistor 21,
Emitter of transistor 22 and transistor 2
It is connected to a resistor 23 which determines the emitter current of 2. The collector of the transistor 22 is connected to a DC power supply via a resistor 24,
The video signal amplified by the transistor 22 is input to the base of the transistor 3. On the other hand, the output potential of the emitter of the transistor and the reference potential V ₇ are compared with each other by a voltage comparison circuit 25 having a clamp pulse signal at the terminal 5, and the potential error is applied to the base of the transistor 22 to obtain a negative voltage. Feedback is applied, the collector current of the transistor 22 is controlled, and the DC potential of the emitter of the transistor 3 is matched with the reference potential _V7 . Further, in the negative feedback, there is provided a capacitor 26 for removing an alternating current component, one end of which is grounded, and the above is the same as the circuit shown in FIG. 2 described above. The features of the configuration shown in FIG. 3 will be described below. The emitter output of transistor 3 is connected to the collectors of transistors 31 and 32 via resistors 29 and 30, respectively. On the other hand, a reference potential circuit 7 having a reference potential V ₇
The output terminals of are connected through resistors 33 and 34, respectively.
They are connected to the collectors of transistors 35 and 36, respectively. In particular, transistors 31 and 3
The base of 6 is connected to a blanking signal input terminal 8. Further, the bases of the transistors 32 and 35 are connected to a terminal 8' into which a signal obtained by inverting the blanking signal is input. The emitters of transistors 31 and 35 are connected to a constant current circuit 37.
The emitters of the transistors 32 and 36 are connected to the constant current circuit 38, and the transistors 31 and 35 and the transistor 3
2 and 36 are each connected like a differential amplifier. Note that the collector of the transistor 31 is connected to the base of the transistor 11, the collector of the transistor 35 is connected to the base of the transistor 14, the collectors of the transistors 11 and 14 are connected to the DC power supply, and the emitters of the transistors 11 and 14 are connected to the output terminal 18 and the constant current circuit 19. connected to each input terminal. Now, at the emitter of the transistor 3 which has the output where the video signal is amplified, the emitter current I
_E is either the current flowing in the direction of arrow 39 during the blanking period (hereinafter referred to as I ₃₉ ) or the current flowing in the direction of arrow 40 during the video signal period other than the blanking period (hereinafter referred to as I ₄₀ ). It becomes an electric current. For example, during the blanking period, the transistor 31 as a switch circuit conducts and the transistor 35 as a switch circuit shuts off.
I ₃₉ becomes a constant current (hereinafter referred to as I ₄₂ ) flowing in the direction of arrow 42 by constant current circuit 37. On the other hand, for video signals other than the blanking period, the transistor 32 as a switch circuit conducts and the transistor 36 as a switch circuit shuts off, so I ₄₀ is a constant current (hereinafter referred to as I ₄₃ ) flowing in the direction of arrow 43 by constant current circuit 38. ). This will be explained in detail by dividing it into a blanking period and other video signal periods.

First, during the blanking period, the blanking signal is input to the bases of the transistors 31 and 36 from the terminal 8, so the transistors 31 and 36 become conductive. is input, so there is no input signal, and transistors 32 and 3
5 is in a cut-off state. Therefore, the emitter current I _E of transistor 3 is I ₄₂ (however, I ₄₂ = α ₁・I ₃₉ and α
₁ flows as the current amplification factor of transistors 31 and 35). Furthermore, the base potential (hereinafter referred to as V _B-11 ) of the transistor 11 connected between the collector of the transistor 31 and the resistor 29 (hereinafter referred to as R ₂₉ ) is V, where the emitter potential of the transistor 3 is V _E . _B-11 = V _E −I ₃₉・R ₂₉ . On the other hand, the base potential (hereinafter referred to as V _B-14 ) of the transistor 14 connected between the collector of the transistor 35 and the resistor 33 (hereinafter referred to as R ₃₃ ) is in the direction of arrow 41 because the transistor 35 is in the cut-off state. The current (hereinafter referred to as I ₄₁ ) becomes zero, and V _B-14 becomes the reference potential V ₇
becomes the same as Therefore, the output of the output terminal 18 is the reference potential from the transistor 14 whose base potential is high.
The level corresponds to V ₇ .

Next, video signal periods other than the blanking period will be explained. During the video signal period other than the blanking period, the blanking signal is not input to the terminal 8, so the transistors 31 and 36 are cut off, while the terminal 8', to which the inverted signal is input, just receives the level voltage of the blanking signal. Therefore, transistors 32 and 35 become conductive. Therefore, the emitter current I _E of the transistor 3 flows as I ₄₃ (where I ₄₃ =α ₂ ·I ₄₀ , where α ₂ is the current amplification factor of the transistors 32 and 35). Also, the base potential V _B-11 of transistor 11 is I ₃₉
is zero, so V _B-11 = V _E , and on the other hand, the base potential V _B-14 of the transistor 14 becomes V _B-14 = V ₇ - I ₄₁ · R _{33, assuming that the resistor 33 is R 33 ,} and the output terminal 18
A video signal from the transistor 11 having a high base potential is output.

As described above, the emitter current I _E of the transistor 3 flows as a constant current I 42 through the transistor 31 during the blanking period, and as a constant current I ₄₂ through the transistor 32 during the video signal period other than the blanking period.
It runs as I ₄₃ . Here, if the constant current circuit 37 and the constant current circuit 38 are set so that I ₄₂ =I ₄₃ for both the blanking period and the other video signal periods, the emitter current I _E of the transistor 3 becomes blank. It flows constantly during the ranking period and other video signal periods, and there is no change in the emitter current I _E in the transistor 3.
As a result, it is possible to prevent white balance deviations in images. Also, the circuit configuration in Figure 3 is
When integrated into an IC, the error in V _BE can be sufficiently reduced to 1 mV or less even if variations in the manufacturing process are considered, and the error voltage range of 2 to 3 mV can be satisfied to allow for deviations in the white balance of the video signal. can.

Next, another embodiment of the present invention will be described using FIG. The output terminal of the video signal source 1 is connected via a resistor 21 to the emitter of a transistor 22' and to a resistor 23 whose one end is grounded. The base of the transistor 22' is connected to a resistor 44, one end of which is connected to a DC power source, and a resistor 45, one end of which is grounded. Further, the base of a transistor 46 is connected to the collector of the transistor 22', the collector of the transistor 46 is connected to a DC power supply, and the emitter of the transistor 46 is applied with a clamp pulse signal to the base of the transistor 3'. transistor 4
7 and a constant current circuit 8'. The collector of the transistor 3' is connected to a DC power supply, and the emitter of the transistor 47 is connected to the base of a transistor 48 whose collector is connected to the DC power supply, and to a capacitor 49 whose one end is grounded. Note that the transistor 3'
The emitter of the transistor 48 and the emitter of the transistor 48 are
They are connected to points A and B of the circuit surrounded by dashed-dotted lines, respectively. Here, the circuit surrounded by the dashed-dotted line is the same as the circuit surrounded by the dashed-dotted line in FIG. 3, and points A and B in FIG. 4 are the same as points A and B in FIG. 3. . Now, in FIG. 4, the reference potential is the blanking period potential of the video signal, transistor 47, transistor 4.
8 and a capacitor 49, and is obtained by holding the gate until the next gate period. In particular, the transistor 3'
This corresponds to the transistor 3 explained using the figure, and I _E of the transistor 3' is connected to the point A only by the current in the direction of the arrow 50.
Since the contents are the same as explained using the figure, there is no variation in V _BE of the transistor 3'. As a result, it is possible to prevent deviations in white balance in images. Furthermore, when the circuit configuration shown in Fig. 4 is integrated into an IC, even if variations in the manufacturing process are considered, V _BE
The error can be sufficiently reduced to 1 mV or less, and satisfies the error voltage range of 2 to 3 mV in which white balance deviation in images can be tolerated.

As described above, the present invention solves the problem of the white balance deviation of the image that occurs between the blanking period and other signal periods when using the configuration circuit shown in FIG. 2 that is suitable for IC implementation. In particular, the circuit configuration of the present invention is suitable for IC implementation because it does not require adjustment, and has the effect of improving the degree of integration of the IC by reducing the number of input/output terminals.

In addition to the embodiments described above, the switch circuit may be configured using a method other than a differential amplifier, or a circuit that obtains the same reference potential as the blanking period potential or average value potential of the video signal may be used. Of course it's a good thing.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional blanking device, Fig. 2 is a circuit diagram showing an example of a blanking device suitable for IC implementation, and Fig. 3 is a circuit diagram showing an embodiment of the present invention. 4 are circuit diagrams showing other embodiments of the present invention. 1...Video signal source, 3...Transistor, 7...
...Reference potential circuit, 11, 14, 31, 32, 35
and 36...transistor, 37 and 38...constant current circuit.

Claims (1)

[Claims] 1. A video signal input circuit, a reference potential circuit having the same output potential as the blanking period potential or average value potential of the video signal from the video signal input circuit, and a resistor connected to the output end of the video signal input circuit, respectively. first and second switch circuits whose input terminals are connected to the reference potential circuit, third and fourth switch circuits whose input terminals are respectively connected to the output terminal of the reference potential circuit via a resistor; 1. A first constant current circuit connected to the output terminal of the third switch circuit, and a current amount equal to that of the first constant current circuit connected to the output terminals of the second and fourth switch circuits. The second constant current circuit and the first and fourth switch circuits are made conductive during the blanking period, and the second and third switch circuits are cut off during the blanking period. a driving means for driving the second and third switch circuits to be in a conducting state and driving the first and fourth switch circuits to be in a cut-off state during the video signal period; The first potential is compared with a third potential at the input terminal of the third switch circuit, and a signal corresponding to the output of the video signal input circuit is generated at the output terminal during a period in which the first potential is higher than the third potential. and a comparison output circuit which causes a signal corresponding to the output of the reference potential circuit to be generated at the output terminal during a period in which the third potential is higher than the first potential.