JPS6042665B2 - Video signal processing circuit - Google Patents

Description

[Detailed description of the invention] Color television camera (hereinafter referred to as television)
(abbreviated as ), the output signal of the image pickup tube is linearly amplified in a preamplifier and then supplied to a process amplifier. A blanking signal is mixed in to remove distortion, a setup level is established by the clipping effect of a linear clipper, the amplitude of the video signal is limited by a white emitter, and a gamma correction circuit is used to control the image reception. The gamma characteristics of the tube are corrected.

If the various signal processing in the process amplifier described above is not performed stably, the operation of the color T camera will become unstable.
Linear clippers, white emitters, gamma correction circuits, etc. are each individually configured with sufficiently high performance and high temperature stability.
This results in a large device with a complex circuit configuration that requires a large number of parts, and a large amount of power consumption. I had no choice but to do so.

On the other hand, in the case of simple color T-cameras, which are particularly desired to be smaller and lighter, it is necessary to use signal processing circuits with high performance, high temperature stability, and low power consumption. Like before. If we use a circuit that performs temperature compensation for each individual signal processing circuit,
It was impossible to construct a color TV camera that was compact and lightweight, and furthermore, the signal processing circuit, which was constructed with a complicated temperature compensation circuit for each circuit, was not suitable for mass production. There was a need to complete a video signal processing circuit that has a simple configuration, is suitable for mass production, performs signal processing well, has high stability, and consumes low power.

The present invention has been made for the purpose of providing a small, high-performance video signal processing circuit that is well suited to small color TV cameras, has high stability, consumes little power, and is suitable for mass production. The contents thereof will be explained in detail below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram of one embodiment of the video signal processing circuit of the present invention, and the circuit in the frame A1 surrounded by the broken line in FIG. This is a video signal processing circuit that performs a linear clip operation.

The video signal processing circuit A1 has a transistor Q1 to which a video signal including a DC component is applied to the base, an emitter connected to the collector of this transistor Q1, and a bias voltage V for a linear clipper to the base.

, a diode D1 for providing a blanking signal, a resistor R2 connected between the collector of the transistor Q1 and the electric current Cc,
A resistor R1 is connected between the emitter of the transistor Q1 and ground, the collector of the transistor Q2 and the power supply Vcc.
The resistor connected between. It is composed of etc. In FIG. 1, block B is a pulse clamp circuit that reinserts a DC component into the video signal, and the DC component is inserted into the base of the transistor Q1 of the video signal processing circuit A1 by the aforementioned pulse clamp circuit A reinserted video signal is provided.

A blanking signal is applied to a connection line between the collector of the transistor Q1 and the emitter of the transistor Q2 via a diode D1.

The transistor Q1 amplifies the input video signal supplied to its base by constant current operation, and an output signal having a signal level approximately R2lRl times the input video signal appears on its collector side.

The waveform Sc shown by the dotted line in FIG. 2 is the waveform Sc shown by the collector of the transistor Q1 when the input video signal to the base of the transistor Q1 is a triangular wave and the emitter of the transistor Q2 is not connected to the collector of the transistor Q1. 3 shows an example of the waveform of the output signal wedge appearing in the figure.

A bias voltage VClVc for linear clipper is applied to the base of transistor Q2 whose emitter is connected to the collector of transistor Q1.
is the base-emitter voltage of transistor Q2), the potential of the emitter of transistor Q2 is fixed to L1 when transistor Q2 is in a conductive state, and at this time, the potential of the collector of transistor Q1 is also It is fixed in the position.

That is, when the transistor Q2 is in a conductive state, the emitter of the transistor Q2 operates in the constant voltage operation region, so all of the constant current AC component appearing at the collector of the transistor Q1 at this time is transferred to the transistor Q2. Flows into the collector load resistance R3 of Q2,
The signal level of the output signal from transistor Q2 at this time is R3lRl times the input signal.

The signal waveform indicated by Sa in FIG. 2 is the output signal waveform of transistor Q2 when transistor Q2 is in a conductive state, and as can be seen from this waveform Sa, the signal appearing at the collector of transistor Q1 Sc is output as a signal Sa from the collector of the transistor Q2 when the transistor Q2 is in a conductive state, and the signal Sa output from the collector of the transistor Q2 is good at the potential L of the emitter of the transistor Q2. It is said to be linearly clipped to the As mentioned above, when the transistor Q2 is in a conductive state, the emitter of the transistor Q2 operates in the constant voltage operation region, so a constant voltage drive circuit is used as the base voltage source of the transistor Q2. No need and easy. It is also sufficient to provide the base bias voltage by means of a voltage divider circuit consisting of a resistor network.

Next, the linear clipping operation in the video signal processing circuit shown in the first diagram described above depends on the temperature characteristics of the base-emitter voltage VBE of the transistor Q2. So, let's think about how things are affected.

Now, the base-emitter voltage VBE of transistor Q2
changes in accordance with temperature changes, and the emitter potential when transistor Q2 is conductive changes from L1 to L in Figure 12.
2, the voltage of the signal Sc appearing at the collector of the transistor Q1 becomes L2.
Since conduction begins when the transistor Q2 reaches , the output signal waveform appearing on the collector side of the transistor Q2 at this time becomes as shown by the waveform Sb in FIG.

That is, in the circuit shown in the first diagram, the transistor Q2
The collector waveform of the transistor Q1 in the off state (a state in which a base bias is applied to the transistor Q2 so that the transistor Q2 is always off) is a waveform Sc shown by a dotted line in FIG. In this state, if the base bias of transistor Q2 is set so that the emitter potential of transistor Q2 becomes L1 (the emitter potential of transistor Q2 + the voltage between the base and emitter of transistor Q2), the emitter of transistor Q2 will be at a constant voltage. , the collector potential of transistor Q1 becomes the same as the constant emitter potential of transistor Q2.

On the other hand, the change in the collector current of the transistor Q1, that is, the signal current, is output as the collector current of the transistor Q2 in the on state.
is shown.

Next, considering the case where the emitter potential of transistor Q2 changes as shown in FIG.
1, that is, the waveform Sc of the collector current of the transistor Q2 output as a signal current.
The part above L2 in FIG. 2 remains in the state shown by the dotted line, and the part below it becomes fixed at the level.

Then, in the part below L2 in FIG.
2 is turned on, the collector current of the transistor Q2 flows through the resistor R2, and a signal having a waveform as shown by the signal Sb in FIG. 2 is output.

What should be noted here is that the P-P of the signal Sa mentioned above
Even though a change in potential larger than the value (signal Sa(7) P-P value is smaller than the difference between L1 and !) was applied to the emitter of transistor Q2, the emitter potential of transistor Q2 but! This means that the signal Sb can be obtained even when the value changes to .

That is, in the video signal processing circuit of the present invention, a change in the emitter potential of transistor Q2
This means that the change in the emitter potential of the transistor appears in a reduced state in the output signal of the transistor, which is completely different from the conventional circuit described above, in which a change in the emitter potential of the transistor appears in a one-to-one state in the output signal of the transistor. In the video signal processing circuit of the present invention, as is clear from FIG. 2, the emitter potential of transistor Q2 is ! Even if the voltage drops below the lowest potential of the signal Sa, an output can be obtained.

When the emitter potential of transistor Q2 changes from low to low, the clip level is 1:1 with the above change.
From les in response to! The signal Sc in Fig. 2 changes to
Even if the emitter potential of transistor Q2 changes from L to L2, the required output signal is the signal S shown in FIG.
The signal only changes from signal a to signal SY), and the change is smaller than the above-mentioned change in the conventional circuit. Figure 11 shows the transistor Q
The signal S that is finally obtained on the collector side of transistor Q2 when the emitter potential of Q2 changes from L1 to L2.
a″, Sb″, and the signal S shown in FIG.
This is a waveform diagram for comparing and explaining the signals Sa, Sb, and Sc in FIG. 11, and the signals Sa, Sb, and Sc shown in FIG. There are things.

As is clear from the correspondence between the signals Sa'' and Sb'' obtained on the collector side of the transistor Q2 and the signals Sa and Sb shown in FIG. 11, when the potential of the emitter of the transistor Q2 is L1, However, even in the case of L2, the potential appearing on the collector side of transistor Q2 corresponding to the emitter potentials Ll and L2 is the power supply voltage ■C
c.

As can be easily understood from the signal waveform diagram shown in FIG. 11, in the video signal processing circuit of the present invention, even if the potential of the emitter of transistor Q2 changes widely, the The effect of this on the final signal is extremely small.

In the linear clipping operation in the video signal processing circuit of the present invention, even if the base bias voltage of the transistor Q2 changes, the clipping level with respect to the signal varies little, and in this respect, it is shown in FIG. The operation of a linear clipper in a conventional video signal processing circuit is completely different from the operation when the anode-cathode voltage of the linear clipping diode Db in Fig. 3 changes in response to temperature changes. .
To explain the conventional example circuit shown in the third figure including this point, in the circuit shown in the third figure, when the voltage between the anode and cathode of the diode Db changes with temperature change,
Since the clip level changes as it is, in the conventional circuit, it is necessary to separately provide a diode Da for compensating the temperature characteristics of the diode Db. In order to perform this, it is necessary to supply a bias voltage to the diode Db from a voltage source having a low output impedance. Furthermore, since the reproducibility of the small signal portion of the linear coupler in the circuit shown in FIG. It is difficult to obtain signal reproducibility.

(As is well known, "linear clipping circuits for video signals are generally used to set the black level, but since a non-linear element is used as the element that performs the clipping operation, the area near the clip level becomes non-linear. The reproducibility of signals near the black level becomes poor.This is usually referred to as gradation reproducibility at 1 small signal, J.r. small signal reproducibility, 1 dark gamma characteristic, etc. However, in the specification of the present application, the reproducibility of one small signal is a term used in the usual meaning as described above.In contrast, the linear clipping operation in the video signal processing circuit of the present invention In,
As mentioned above, the change in the base bias voltage of the transistor Q2 does not result in a change in the clip level as it is, and it also shows extremely excellent small signal reproducibility.

That is, in the circuit of the present invention shown in Figure 1, when a small signal is applied to the emitter of transistor Q2, the conduction impedance of transistor Q2 increases, and as a result, a small signal is applied to the emitter of transistor Q2 from the collector side of transistor Q1. Since the AC signal being received has a large amplitude and the transistor Q2 immediately becomes conductive, the circuit of the present invention has excellent reproducibility of small signal portions.

The degree of improvement in the reproducibility of the small signal part by the circuit shown in Figure 1 is as follows:
Since it is determined by the ratio of R3lRl and R2lRl, the degree of improvement is as follows: degree of improvement = (R2/R1)/(R3/R1) = R2
As can be seen from the formula /R3, the ratio R2/R3 of the resistor R2 and the resistor R3 determines the degree of improvement in the reproducibility of the small signal portion, and
This shows the degree of improvement in the clip bias voltage stability described above.

To give an example of the degree of improvement described above, when the base bias voltage of transistor Q1 in FIG. R3 is R1=560Ω, R2=
Assuming 6.8kΩ and R3=560Ω, the improvement is about 22C
Becomes IB.

As can be seen from the comparison with the conventional circuit shown in FIG. 3, the video signal processing circuit of the present invention described above has a simple circuit configuration with a small number of parts, but it can produce good signal. It has processing capabilities and good stability of operation.

FIG. 4 shows an embodiment of the video signal processing circuit of the present invention in which a white limiter circuit is added to the video signal processing circuit of the present invention shown in FIG.
is a white emitter diode connected between the collector of the transistor Q1 and the bias power source 1, and R4 is a resistor connected between the collector of the transistor Q1 and the emitter of the transistor Q2.

In order to connect the diode D2 for the white emitter to the circuit shown in the first diagram, it is conceivable to connect the diode D2 to the collector side of the transistor Q2, but as already mentioned, in the circuit shown in the first diagram, Since the degree of improvement is indicated by R2lR3, it is good. Resistance R3 to get improvement
is required to have a low resistance value.

If the resistor R3 has a low resistance value, even if the diode D2 for a white emitter is connected to the collector circuit of the transistor Q2, the diode D2 will have a good white emitter. A business operator would immediately understand that it is not possible to perform limiter operation. Therefore,
In the present invention, a resistor R4 is connected between the collector of the transistor Q1 and the emitter of the transistor Q2, and a diode D2 for a white limiter is connected to the collector of the transistor Q1 to perform a good white limit operation. I made it possible to do so. In the video signal processing circuit shown in FIG. 4, when the transistor Q2 is in a conductive state, the emitter potential of the transistor Q2 is fixed to the clip bias voltage, and the collector voltage of the transistor Q1 is fixed to the white limiter voltage. Since the bias voltage can be fixed by the transmitter diode D2, the circuit shown in FIG. All of the alternating current signal current appearing at the collector flows to the white emitter diode D2, allowing a good white emitter operation to be performed.

FIG. 5 shows a video signal processing circuit of the present invention in which a gamma correction circuit is added to the collector circuit of the transistor Q2 in the video signal processing circuit of the present invention shown in FIG.

In FIG. 5, a high resistance resistor R8 is connected between the collector of the transistor Q2 and the ground, and a diode D and a resistor R5 are connected between the collector of the transistor Q2 and the power supply Vcc. and a series connection circuit of resistor R6 and diode D4 are connected, and further between the connection point of resistor R5 and diode D3 and the connection point of resistor R6 and diode D4. A resistor R7 is connected to the resistor R7, and the configuration is such that an output signal can be taken out from any point of the resistor R7.Figures 6 to 9 explain the problems of the conventional gamma compensation circuit. First, FIG. 6 shows the basic circuit of a gamma compensation circuit consisting of a bridge circuit of a diode and a resistor.

If the gamma values for each of the three systems (red, blue, and green) are relatively uniform, such as in a three-tube color T camera, the gamma compensation circuit will adjust the gamma values for each of the three systems. Since the amount of gamma compensation to be applied is constant, even if the gamma value or signal level of the circuit changes, this will not cause white balance fluctuations.

However, in color TV cameras that use antimony trisulfide-based vidicon and single-tube color TV cameras that obtain color multiplexed signals as output signals, the red, blue, and green signals obtained from them are Since the gamma values of the three signals are different, the gamma value settings in the circuit system will be different. Therefore, in this case, unless the stability of the gamma correction circuit is improved, the gamma value fluctuations will occur. This will cause the white balance to collapse.

To explain this point with respect to the conventional example circuit shown in FIG. R5
and diode D3, resistor R6 and diode D
11 constant currents always flow in each of the circuits 4 and 4.

The output current is taken out through an emitter follower stage consisting of transistors Tr3 and Tr4, respectively, so as not to affect the bridge circuit.
Variable resistor VR connected between each emitter of r3 and Tr4
An arbitrary gamma value can be obtained by

In the conventional circuit shown in FIG. 6 described above, the transistor T
A signal whose gamma is 1 and whose signal level does not fluctuate is always obtained from r4, but a signal whose output fluctuates as the temperature of the diode voltage vs. current 1 characteristic changes as shown in Figure 7 is obtained from transistor Tr3. appears.

In Fig. 7, ■1 is the output voltage at temperature T1, V
2 is the output voltage at temperature T2, and thus,
As the output voltage changes depending on the temperature, the set value of the gamma value changes, and the white balance changes depending on the temperature change. FIG. 8 shows an example of a gamma compensation circuit that has been proposed in the past to alleviate the drawbacks of the conventional circuit shown in FIG. 6. The gamma compensation circuit shown in FIG. By connecting a resistor R8 between the two and allowing a bias current to flow through the diode bridge circuit, fluctuations in white balance due to changes in the characteristics of the gamma compensation circuit are reduced.

That is, the operation of the gamma compensation circuit shown in FIG.
To explain with reference to the characteristic curve shown in the figure, first, if the resistor R8 does not exist in the circuit, an output of V''1 is obtained at temperature T1, and an output of V''2 is obtained at temperature T2. ″
1-■''2=ΔV'' is the worst white balance fluctuation.

However, when the resistor R8 is connected in the circuit and a bias current of 1 is passed through the circuit, and if the collector current of the transistor Tr5 is I, the current flowing through each branch of the bridge circuit is 112 at the minimum, Also, since it becomes a drop at the maximum temperature, an output of ■1 can be obtained at a temperature of T1, and
At a temperature of 2, an output of V2 is obtained. The worst white balance fluctuation at this time is V1-V2=ΔV1-Δ■2, which is considerably reduced compared to the white balance fluctuation of ΔV1 described above. However, in general, the temperature characteristics of the voltage versus current of a diode have large fluctuations for small currents and small fluctuations for large currents, so the above-mentioned Δ
V1 and Δ■2 are not equal, so even if the bias current is made to flow through the diode bridge circuit through the resistor R8 as in the proposed circuit shown in Fig. 8, the result is sufficiently satisfied. You won't get the desired results. FIG. 10 shows a gamma compensation circuit which is a further improvement of the gamma compensation circuit shown in FIG. In the gamma compensation circuit shown in Figure 10, the resistor R and the diode D
In order to adjust the signal level of the signal appearing at the connection point with 3, a resistor is connected between the connection point of diode D4 and resistor R6 and the connection point of diode D3 and resistor R5. , the signal current that changes depending on the temperature change is shunted through this resistor R7, and the signal current flowing through the resistor R5 is changed. If the above-mentioned resistor R7 in the circuit shown in FIG. 10 is made into a variable resistor, it is possible to configure a circuit that serves both as a variable circuit for setting the gamma value and as a circuit for stabilizing white balance.

In the gamma compensation circuit shown in FIG. 10, the maximum white balance variation −(ΔV1−ΔV
All that is required is to shunt the signal corresponding to 2) through the resistor R7.At room temperature, the two branches are balanced and the current shunted through the resistor R7 becomes zero, and the temperature characteristics of the diode are approximately 2. Since it is .3mv/CO,
The current Δi to be shunted for a temperature change of ΔTO of 1 degree is 1SiJ\■$2.3n1V×ΔTR7.

If a resistor R7 that satisfies the above equation is used, variations in the white balance with respect to temperature with respect to the gamma value set in the gamma compensation circuit can be well compensated for.

The video signal processing circuit of the present invention shown in FIG. 5, which has a configuration in which the gamma compensation circuit shown in FIG. 10 described above is connected to the video signal processing circuit shown in FIG. Equipped with a linear clip function, gamma compensation function, etc., it is possible to perform good signal processing on video signals with high stability.

Moreover, the current used in the circuit flows in series through the bridge circuit in the gamma compensation circuit and transistors Q2, Ql, etc., and the emitter current of transistor Q1 becomes the total current consumption, so video signal processing with extremely low power consumption is possible. The circuit can be realized. As is clear from the detailed explanation above, the video signal processing circuit of the present invention is configured as a simple circuit with a small number of parts, has low power consumption and high stability, and has improved basic performance. According to the video signal processing circuit of the present invention, a compact, lightweight and simple color TV can be realized.
The present invention can greatly contribute to making cameras with low power consumption, no adjustment required, and available at a low price.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 3 to 5 are circuit diagrams of different embodiments of the video signal processing circuit of the present invention, FIGS. 2 and 11 are waveform diagrams for explaining the operation, and FIGS. 6 and 8 are conventional circuit diagrams of gamma compensation circuits, FIGS. 7 and 9 are characteristic curve examples, and FIG. 10 is a circuit diagram of the gamma compensation circuit.

B...Pulse clamp circuit, Ql, Q2, Tr
l~Tr5...transistor, R1~R8...
...Resistance, D1 to D4, Da, Db...Diode.

Claims (1)

[Scope of Claims] 1. A resistor is connected to the collector and emitter of the first transistor to which a video signal including a DC component is applied to the base, and a blanking signal for mixing is connected to the collector of the first transistor. A blanking signal is applied through the semiconductor element, and the collector of the first transistor is connected to the emitter of the second transistor, and the base of the second transistor is connected to a linear clipper. A video signal processing circuit which applies a bias voltage and further includes a load resistor connected to the collector of the second transistor. 2. A resistor is connected to the collector and emitter of the first transistor to which a video signal including a DC component is applied to the base, and a semiconductor element for mixing a blanking signal and a white limiter are connected to the collector of the first transistor. and the first semiconductor element described above.
The collector of the transistor is connected to the emitter of the second transistor via a resistor, and a bias voltage for a linear clipper is applied to the base of the second transistor, and the collector of the second transistor is connected to the emitter of the second transistor. is a video signal processing circuit that is connected to a load resistor. 3. A resistor is connected to the collector and emitter of the first transistor to which a video signal including a DC component is applied to the base, and a semiconductor element for mixing a blanking signal is connected to the collector of the first transistor as a white limiter. In addition to connecting the semiconductor element for the first
The collector of the transistor is connected to the emitter of the second transistor via a resistor, and a bias voltage for a linear clipper is applied to the base of the second transistor. A resistor having a high resistance value is connected between the collector and ground, and a series connection circuit of a resistor and a diode is connected between the collector of the second transistor and the power supply, and the resistor is connected to the collector side. Connecting a series connection circuit of a diode and a resistor with a diode connected to the side, and connecting a resistor between the connection points of the diode and the resistor in the two series connection circuits consisting of the diode and the resistor, A video signal processing circuit configured to take out an output from any point in the resistor connected between the connection points described above.