JPH0815318B2 - camera - Google Patents

Description

The present invention relates to a camera having an automatic level control circuit such as an AGC circuit.

[Outline of Invention]

The present invention, for example, in an AGC circuit used in a video camera, stabilizes the AGC level set voltage and the reference voltage for clamping in the AGC circuit.
The level does not fluctuate.

[Conventional technology]

For example, the luminance signal system and its AGC in a video camera
The circuit is constructed, for example, as shown in FIG.

That is, in the figure, (1) to (5) indicate a luminance signal system, and (1) is an image pickup device such as an image pickup tube or a CCD. Then, the luminance signal Sy is taken out from this element (1), and this signal Sy is taken out to the terminal (5) through the signal line of the preamplifier (2) → the variable gain amplifier (3) for AGC → the clamp circuit (4). Be done.

Further, the signal Sy from the clamp circuit (4) is supplied to the detection circuit (11), and the detection voltage Vd indicating the level of the signal Sy is extracted. At this time, by selecting a specific number of the resistors R ₁ and R ₂ and the capacitor C ₁ of the detection circuit (11), the detection circuit (11) detection method can be used for peak detection, semi-peem detection and average value detection. And so on.

Then, this electric love Vd is supplied to the level comparison circuit (12) and a reference voltage for setting the output level of the terminal (5) from the variable resistor R ₃ , that is, the setting voltage Vs of the AGC level.
Is supplied to the comparison circuit (12) to compare the output voltage Vd with Vs
Vc is taken out and this voltage Vc is supplied to the variable gain amplifier (3) as its control signal. The variable resistor R
₃ is adjusted and fixed at the manufacturer.

Therefore, when the level of the signal Sy increases, the voltage Vd
Becomes higher and the voltage Vc becomes lower, which causes the amplifier (3)
Since the gain of is reduced, the level of the signal Sy is controlled to be constant.

At this time, a voltage Vr is formed by the voltage dividing resistors R ₄ and R ₅ , and this voltage Vr is supplied to the clamp circuit (4) as a reference voltage for the clamp.

[Problems to be solved by the invention]

However, in such a circuit, Vcc: resistor R ₃ to R to ₅ supply voltage R _31: the variable resistor R ₃ of the hot side of the resistance value R _32: the resistance of the ground side of the variable resistor R ₃ Then, Therefore, the voltages Vs and Vr are affected by the fluctuation of the power supply voltage Vcc due to the resistance decomposition ratio.

Then, in this case, when Vs = Vr ∴R ₃₂ R ₄ = R ₃₁ R ₅ ...... (iii) is established from the equations (i) and (iii), the voltages Vs and Vr change in the power supply voltage V _CC . , The AGC level (the output level of the terminal (5)) does not change.

However, when the equation (iii) is not satisfied, the changes in the voltages Vs and Vr are different with respect to the changes in the power supply voltage Vcc,
The AGC level changes. Particularly in a portable type video camera, since the power supply is a battery, the power supply voltage Vcc decreases as the camera is used, and therefore the AGC level also changes as the camera is used.

Further, even when the expression (iii) is established, if the variable resistor R ₃ is adjusted from that state, the expression (iii) is not established and therefore the AVC level is affected by the power supply voltage Vcc.

Further, even if the equation (iii) is established and the variable resistor R ₃ is fixed, if this circuit is integrated into an IC and is used for general purpose, it is necessary to change the voltage Vr by the detection method of the detection circuit (11). Therefore, as a result, the formula (iii) cannot be satisfied, and the AGC level is affected by the power supply voltage Vcc.

That is, from the above, in the above-mentioned AGC circuit, if the power supply voltage VccNJ fluctuates, the AGC level will change.

The present invention is intended to solve such a problem.

[Means for solving problems]

Therefore, in the present invention, the circuit (3),
(4) and (12) are integrated into an IC, and a constant voltage circuit is also integrated in this IC.
get r.

[Action]

Even if the power supply voltage Vcc fluctuates, the voltages Vs and Vr are stabilized, so that the AGC level does not fluctuate.

〔Example〕

In FIG. 1, (20) indicates an IC, and at least the clamp circuit (4) and the level comparison circuit (12) are connected to the IC (2
0) is integrated into an IC.

Then, the luminance signal Sy from the clamp circuit (4) is taken out to the pin T ₁ at the external terminal, and one input end of the level comparison circuit (12) is connected to the external terminal pin T ₂ and these pins T ₁ and External detection circuit between T ₂ and (11)
Is connected.

Further, the IC (20) is integrated with a constant voltage circuit (21) using, for example, a built-in potential, and its input terminal and output terminal are connected to the external terminal pins T ₃ and T ₄ , respectively. Then, between pin T ₄ and ground, a variable resistor R ₃
Is externally connected, and the voltage Vs obtained from the variable resistor R ₃ is supplied to the other input terminal of the comparison circuit (12) as an AGC level setting voltage through the external terminal pin T ₅ .

Further, the IC (20) is also integrated with the dividing resistors R ₄ and R ₅ , and its series circuit is connected to the output terminal of the constant voltage circuit (21) and obtained from the resistors ₄ and R _5. The voltage Vr is supplied to the clamp circuit (4) as a reference voltage.

Further, outside the IC (20), the voltage Vcc is supplied from the DC power supply (31) such as a battery to the pin T ₃ and also to other necessary circuits (not shown).

According to this structure, even if the power supply voltage Vcc fluctuates, the voltage supplied to the resistor R ₃ to R ₅ is a constant voltage circuit (2
The voltage Vr, Vs is the power supply voltage because it is kept constant by 1).
Even if Vcc fluctuates, it is held at a predetermined constant value, and therefore the AGC level does not change with the power supply voltage Vcc.

Thus, according to the present invention, the set voltage V of the AGC level is
Since the s and the reference voltage of the clamp are stabilized by the constant voltage circuit (21), the AGC level does not change even if the power supply voltage Vcc changes. Moreover, in that case, the constant voltage circuit (21) is integrated with the circuits (3), (4) and (12) in the IC (2
0), the constant voltage output is mainly supplied only to the resistors R _{3 to} R ₅ , and a small current is sufficient. Therefore, the constant voltage characteristic of the constant voltage circuit (21) should be improved. Therefore, the AGC level becomes extremely stable with respect to the fluctuation of the power supply voltage Vcc.

Further, the detection circuit (11) and the variable resistor R ₃ are connected to the IC (2
Since it is externally attached to 0), the detection method can be arbitrarily selected and the AGC level can be freely adjusted or set.

Although the above is the case of the AGC level circuit, it is also effective for an automatic diaphragm circuit of a video camera, for example, in which case the diaphragm may be controlled by the voltage Vc to control the level of the signal Sy.

〔The invention's effect〕

According to the present invention, since the set voltage Vs of the AGC level and the reference voltage of the clamp are stabilized by the constant voltage circuit (21), the AGC level does not change even if the power supply voltage Vcc changes. Moreover, in that case, the constant voltage circuit (21)
The circuit (3), (4), together with the integrally formed in IC (20), the constant voltage output is not supplied only to the predominantly resistor R ₃ to R _5, a small current (12) Since it is good, the constant voltage characteristic of the constant voltage circuit (21) can be improved,
Therefore, the AGC level becomes extremely stable with respect to fluctuations in the power supply voltage Vcc.

Further, the detection circuit (11) and the variable resistor R ₃ are connected to the IC (2
Since it is externally attached to 0), the detection method can be arbitrarily selected and the AGC level can be freely adjusted or set.

[Brief description of drawings]

FIG. 1 is a connection diagram of an example of the present invention, and FIG. 2 is a diagram for explaining it. (3) is a variable gain amplifier, (4) is a clamp circuit, (11) is a detection circuit, (12) is a level comparison circuit, (20) is an IC, and (21) a constant voltage circuit.

Claims (1)

[Claims] 1. A DC voltage source, a video signal supply means, a clamp circuit for clamping the supplied luminance signal, a level comparison circuit, a constant voltage circuit, and a constant voltage output of the constant voltage circuit. , An integrated circuit in which a voltage dividing resistor to be supplied to the clamp circuit as a clamp reference voltage is integrated, and a luminance signal from the clamp circuit is detected, and its detection output is supplied to the level comparison circuit. From the voltage output of the circuit and the constant voltage circuit,
A level setting voltage is formed and an AGC voltage setting circuit for supplying the setting voltage to the level comparison circuit is provided, and the integrated circuit outputs the comparison output of the level comparison circuit to a signal of a luminance signal supplied to the clamp circuit. A camera having an automatic level setting circuit, which is supplied as a control signal to a system and takes out a luminance signal of a level set by the set voltage from the clamp circuit.