KR920004228Y1 - Counter light revision circuit for a camera - Google Patents

Abstract

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Description

Backlight Compensation Circuit of Camera

1 is a block diagram of a backlight compensation circuit of a conventional camera.

2 is a block diagram of a backlight correction circuit of a camera according to the present invention.

3 is a detailed circuit diagram illustrating an embodiment of FIG. 2.

* Explanation of symbols for main parts of the drawings

10: aperture control unit 20: reference voltage providing unit

30: reference voltage control unit 40: comparison voltage control unit

50: buffer unit 60: AGC (automatic gain control) control unit

Q1 to Q4: Transistor SW: Backlight Compensation Switch

R1 to R14: resistor VR1: variable resistor

The present invention relates to a backlight compensation circuit of a camera, and more particularly, to a backlight compensation circuit capable of clearly photographing a subject in low light.

In general, the backlight compensation is to prevent the subject from being darkened by opening the iris of the camera when the subject's led is low compared to the ambient illumination. The conventional backlight compensation technique is shown in FIG. An aperture control unit 10 that receives an aperture detection signal and compares the reference voltage to generate an aperture control output, and a reference voltage providing unit 20 that provides a reference voltage to the aperture control unit 10, and a backlight compensation switch. By the reference voltage control section 30 to control the reference voltage by means of the SW (when photographing the subject of the roughness of the back light) by turning on the switch (SW) to raise the reference voltage of the aperture control unit 10 The output of the iris control unit 10 is adjusted, and this output can open the iris to the maximum as a control signal of the iris.

Therefore, only a low-light subject is brought into the shooting range, and the periphery of the subject is outside the shooting range so that the backlight compensation is performed.

However, in the conventional technique, even when the switch is turned on for backlight compensation when the aperture is fully open, the backlight is no longer corrected on the recording screen, and backlight compensation is difficult when the illumination difference between the low-light subject and the surrounding environment is large. Done.

This invention aims to solve this problem, and the purpose of this invention is to open the iris to perform backlight compensation when all the apertures are not open, and to adjust the gain automatically when the subject's illumination is very low when the aperture is fully open. It is to provide a backlight compensation circuit of a camera that can control the circuit to perform backlight compensation.

In order to achieve the above object, the present invention provides an aperture control unit configured to control an aperture by comparing an aperture detection signal and a reference voltage of an output of a main circuit and a reference voltage providing unit that provides a reference voltage to the aperture control unit. A backlight compensation circuit of a camera having a backlight compensation circuit for increasing a reference voltage of an aperture control unit when a backlight compensation switch is turned on, comprising: a comparison voltage controller which is driven when the backlight compensation switch is turned on to generate a control output; A buffer unit which buffers an output signal of the main circuit and is controlled by the control output of the comparison voltage control unit, and an AGC control unit which generates an AGC control signal by comparing a signal by the buffer unit with a predetermined reference voltage. The backlight compensation circuit has its characteristics.

One embodiment of the backlight compensation circuit of another camera in this design is described in detail according to the accompanying drawings.

First, FIG. 2 is a block diagram of a backlight compensation circuit of a camera according to the present invention, and includes an aperture control unit 10, a reference voltage providing unit 20, and a reference voltage controller 30, which are the components of FIG. 1. In one embodiment, a buffer unit for buffering and outputting the output voltages of the comparison voltage control unit 40 and the comparison voltage control unit 40 and the main circuit at the same time to the backlight compensation switch (SW) And an AGC control section 50 for generating an AGC (auto gain control circuit) control signal of the camera in accordance with the control signal input through the buffer section 50. As shown in FIG.

3 shows a detailed circuit of such a backlight correction circuit block.

That is, the aperture control unit 10 includes a comparator OP1 having an inverted input as a detection output of a detector for detecting an aperture signal from a CCD (Charge coulpled Device) output signal transmitted from a camera main circuit. The providing unit 20 is a series connection of the resistor R1, the variable resistor VR1, and the resistor R2 between the power supply Vcc and the ground, so that the divided voltage applied to the variable terminal of the variable resistor VR1 can be obtained. The non-inverting end of the comparator OP1 was applied through a resistor R3.

The reference voltage controller 30 includes a switching transistor Q1 and a resistor R4 for determining whether the non-inverting level of the bias providing resistors R5 and R6 is increased in comparison with the OP1. It is driven by turning on and off the backlight compensation switch SW that applies the driving power to Q1).

In the connection configuration of the aperture control unit 10, the reference voltage providing unit 20, and the reference voltage control unit 30, a resistor R7 for distributing the power Vcc by the backlight compensation switch SW to provide a bias. And a comparison voltage control unit 40 in which a switching transistor Q2 and a collector resonator R9, which are driven and supplied with a buyer power supply by the resistors R7 and R8, are connected. Transistor Q3, which is switched in accordance with the output of CCP, the divider resistor R10 (R11) and the bypass capacitor C1 which divide the output of this transistor Q3, and the PNP type transistor Q4 which generates the buffer output. The buffer unit 50 is formed of wah to generate an output according to the collector of the transistor Q2 of the comparison voltage control unit 30.

On the other hand, the AGC control unit 60 receives the power supply voltage Vcc by the voltage divider resistors R13 and R14 as the reference voltage, and uses the comparator for the output of the transistor Q2 of the buffer unit 50 as an inverting input ( OP2) to generate AGC control signal. In FIG. 3, C2, which is not described, is a damping capacitor.

The backlight compensation circuit of the camera according to the present invention, which is connected in this manner, is open when the bases of the transistors Q1 and Q2 are open when the backlight compensation switch SW is not turned on.

Therefore, the aperture detection signal is compared according to the reference voltage set by the variable resistor VR1 of the reference voltage controller 20, and the aperture control output is generated in the comparator OP1 to drive the aperture meter. At this time, the output signal of the main circuit is applied to the transistor Q4 through the transistor Q3 of the buffer unit 50 so that the buffer output signal is input to the comparator OP2 of the AGC control unit 60 to generate the AGC control output.

On the other hand, when the backlight compensation switch SW is turned on, the power supply Vcc is applied to the resistors R5 and R6 of the reference voltage controller 30 so that the transistor Q1 is conducted so that the reference voltage of the comparator OP1 is increased. As a result, the aperture control output is increased to increase the aperture, and the backlight is firstly compensated. The backlight is compensated by the resistors R7 and R8 of the comparison voltage controller 40 simultaneously with the operation of the reference voltage controller 30. The power supply Vcc by the correction switch SW is applied to turn on the transistor Q2. The driving of the transistor Q2 causes the base potential of the transistor Q4 of the buffer unit 50 to become a low potential, and thus the signal input of the main circuit applied to the inverting end of the comparator OP2 of the AGC control unit 60. This decreases to increase the AGC control output of the comparator OP2.

As such, when the aperture is not completely opened, the backlight is compensated by opening the aperture further. When the subject is low light even when all the apertures are open, the backlight compensation is performed by controlling the AGC (automatic gain control) circuit.

As described above, according to the backlight compensation apparatus of the camera according to the present invention, the comparison voltage control unit which is driven when the backlight correction switch is turned on to generate a control output, and the output signal of the main circuit are buffered and the control output of the bridge voltage control unit. The buffer unit controlled by the control unit and the AGC control unit generating an AGC control signal by comparing the signal generated by the buffer unit with a predetermined reference voltage, so that the backlight compensation is performed even when the subject is very low illumination (for example, when the sun is turned down). This is done so that the subject is clearly photographed. Therefore, when the subject's illuminance is slightly lower than the surrounding environment, the aperture is largely opened to perform backlight compensation, and when the subject's illuminance becomes very low and backlight compensation is impossible with only the aperture, it is a useful design that controls the automatic gain control circuit to perform backlight compensation .

Claims (2)

The output of the main circuit compares the aperture detection signal with the reference voltage and controls the aperture to control the aperture, and the reference of the aperture control unit when the backlight correction switch is turned on when the reference voltage providing unit provides a reference voltage to the aperture control unit. A backlight compensation circuit of a camera having a reference voltage control unit for raising a voltage to perform backlight compensation, comprising: a comparison voltage controller 40 which is driven when the backlight compensation switch SW is turned on to generate a control output; AGC which buffers the output signal and generates an AGC control signal by comparing the buffer unit 50 controlled by the control output of the comparison voltage controller 40 with the signal by the buffer unit 50 and a predetermined reference voltage. Backlight correction circuit of the camera provided with a control unit (60). 2. The resistors R7 and R8 of claim 1, wherein the comparison voltage controller 40 distributes the power supply Vcc applied by the correction switch SW to provide a bias. The transistor Q2 and the collector resistor R9 are driven by the bias power supplied by R8, and the buffer unit 50 outputs the output of the transistor Q3 driven by the output of the main circuit to the resistor R10. And a transistor Q4 that is divided by R11 and whose output is controlled by the transistor Q2 of the comparison voltage controller 40. The AGC controller 60 is a transistor of the buffer unit 50. The backlight compensation circuit of a camera which becomes a comparator (OP2) which outputs the output of (Q4) by comparing a predetermined reference voltage.