JPH0410782A - Automatic light quantity control device - Google Patents

Abstract

PURPOSE:To suppress the influence of offset of a braking circuit by separating the low frequency component of the braking circuit and negatively feeding back the separated component. CONSTITUTION:The control device is provided with an optical system 1 for forming the image of a subject on an image pickup element 3, an iris 2 for adjusting the quantity of light made incident upon the element 3, an integrating circuit 22 for integrating the output of the element 3, an iris driving circuit 8 for driving the iris 2 in accordance with the output of the circuit 22, a speed detecting circuit 11 for detecting the speed of the iris 2, the braking circuit 12 for negatively feeding back the output of the circuit 11 to the circuit 8, a separator circuit 22 for separating the low frequency component of the output of the circuit 12, and a negative feedback circuit 25 for negatively feeding back the output of the circuit 22 to the circuit 12. Namely, the low frequency component of the output of the circuit 12 is detected and negatively fed back to the circuit 8. Consequently, the quantity of light can be controlled without being influenced by the offset of the braking circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic light amount control device suitable for use in a video camera.

[Prior Art] FIG. 6 is a block diagram showing the configuration of an example of a conventional automatic light amount control device disclosed in Japanese Patent Laid-Open No. 62-38084.

After the light incident from the imaging lens 1 has its sight adjusted by the aperture 2, it is imaged on an imaging device 3 such as a CCD.

The output of the image sensor 3 is sent to a camera circuit 5 via a preamplifier 4.
is input. The signal processed in the camera circuit 5 is output as a video signal to a circuit (not shown).

The output of the preamplifier 4 is input to an integrating circuit 6, where it is integrated. The output of the integrating circuit 6 is sent to the drive circuit 8 via the adder 7.
is input. The drive circuit 8 compares the input signal with a predetermined reference voltage V1, and drives the drive coil 9 in accordance with the error signal. As a result, the aperture 2 is driven.

That is, when the output level of the image sensor 3 is larger than the reference voltage V1 (when it is bright), the diaphragm 2 can be fully driven in the closed direction, and when it is small (when it is dark), the diaphragm 2 can be fully driven in the open direction.

In this way, the amount of light is automatically controlled to an appropriate value.

On the other hand, a magnet 10 is connected to the diaphragm 2, so that when the diaphragm 2 is driven, the magnets l-1 and l-0 can be rotated in synchronization with each other. The braking coil 11 detects the rotation of the magnet 10 and outputs a detection signal corresponding to the driving speed to the braking circuit 12. The braking circuit 12 compares the level of this detection signal with the reference voltage 2, and feeds back the error voltage negatively to the drive circuit 8 via the adder 7.

The rotational position of the magnet 10 (the open state of the aperture 2) is detected by the detection circuit 13, and the detection signal is sent to the braking circuit 1.
2 is input. The braking circuit 12 has a voltage control term 1llii
It is composed of a VCA (VCA) and controls the amount of negative feedback of the output of the braking coil 11 in accordance with the output of the detection circuit 13.

That is, when the aperture 2 is in the open position (when it is very dark), the gain of the voltage controlled amplifier is completely reduced, and when it is in the closed position (the gain is increased when it is bright). When the diaphragm 2 is close to the closed state, the response speed of the diaphragm 2 becomes faster.Also, when the diaphragm 2 is close to the closed state,
Braking is applied, the driving speed of aperture 2 becomes slow, and aperture 2
can be driven stably.

[Problems to be Solved by the Invention] However, the conventional circuit has a problem in that when an offset occurs in the braking circuit 12, it is directly fed back negatively to the drive circuit 8, and the amount of drive of the aperture 2 changes. Ta.

The present invention has been made in view of this situation, and is intended to suppress the influence of offset.

1. Means for Solving Problems] The automatic light amount control device of the present invention includes an optical system that forms a subject image on an image sensor, an aperture that adjusts the amount of light incident on the image sensor, and an output power of the image sensor. an aperture drive circuit that drives an aperture in response to the output of the integrator circuit;
A speed detection circuit that detects the speed of the aperture, a braking circuit that negatively feeds back the output of the speed detection circuit to the aperture drive circuit, a separation circuit that separates the low frequency component of the output of the braking circuit, and a braking circuit that uses the output of the separation circuit. and a negative feedback circuit that provides negative feedback.

[Function] In the automatic light amount control circuit configured as described above, the low frequency component of the output of the braking circuit is detected and negatively fed back to the aperture drive circuit.

Therefore, the sight can be controlled without being affected by the offset of the braking circuit.

[Embodiment] FIG. 1 is a block diagram showing the configuration of an embodiment of the automatic light amount control device of the present invention. Parts corresponding to those in FIG. is repetitive, so it will be omitted as appropriate.

In the embodiment shown in FIG.
(separation circuit) and a comparator circuit 25 (
negative feedback circuit).

The output of the calibration circuit 25 is the braking coil 11 (speed detection circuit)
The signal is input to an adder 26 inserted between the brake circuit 12 and the brake circuit 12, and is fed back negatively to the brake circuit 12.

The other configurations are the same as in FIG. 6.

Next, its operation will be explained.

As in the case described above, a part of the signal output from the image sensor 3 on which the subject image is formed via the photographing lens 1 (optical system) is integrated by the integrating circuit 6, and then sent to the drive circuit via the adder 7. 8 (aperture drive circuit), and a drive coil 9 is driven. This drives the diaphragm 2, and its driving speed is detected by the braking coil 11 (speed detection circuit).

The output of the braking coil 11 is input to the braking circuit 12, where it is compared with a reference voltage (2), and its error signal is negatively fed back to the drive circuit 8 via the adder 7.

For example, as shown in Fig. 2, the output of the braking circuit 2 becomes a signal that changes in the positive range when the diaphragm 2 (magnet 10) rotates in the positive direction, and changes in the negative range when the diaphragm 2 (magnet 10) rotates in the negative direction. The signal changes at . A part of this signal is input to the integrating circuit 22, and its envelope component (low frequency component) is separated.

This low frequency component is applied to the reference voltage ■2 in the comparator circuit 25.
compared to Comparison circuit 25 outputs an error signal between the low frequency component and the reference voltage to adder 26 . The adder 26 adds this error signal to the reference voltage V2 and outputs the result to the braking circuit 12.

For example, when a positive offset (low frequency component) occurs in the braking circuit 12, the comparator circuit 25 generates a negative error signal. This error signal is added by the adder 26 to the reference voltage (2) that can be supplied to the braking circuit 12. Similarly, when, for example, a negative offset 1~ (low frequency component) occurs in the braking circuit 12, the comparator circuit 25 generates a positive error signal. This error signal is added to the reference voltage V2 supplied to the braking circuit 12 by an adder 26. In this way, the braking circuit 12
A negative feedback servo is applied so that the offset output by the diaphragm 2 becomes zero (so that the output of the braking circuit becomes equal to the reference voltage V2 when the diaphragm 2 is not rotating).

FIG. 3 shows a more detailed configuration of a part of the circuit of the embodiment shown in FIG.

In this embodiment, a predetermined voltage V is applied to the resistors 31 and 3.
2 and is outputted as a reference voltage V2 via a slow (φi amplifier 33).

Further, a buffer amplifier 44 having a gain of 1 as an inverting amplifier is connected to the rear stage of the comparator circuit 25 and is made up of resistors 4, 42 and an operational amplifier 43.

Roughly speaking, the adder 26 is constituted by an operational amplifier 48 having resistors 45 to 47.

The embodiment shown in FIG. 3 has a single power supply configuration, but if positive and negative power supplies are used, as shown in FIG. The terminals can be individually grounded.

Furthermore, in the above embodiment, the operational amplifier 21 is shared by the integrating circuit 22 and the comparing circuit 25;
As shown in FIG.
3 and an operational amplifier 21 having a capacitor 54, and the two can be made into independent circuits.

[Effect of the invention] As described above, the automatic sight system of the present invention (according to the wholesale device,
Since the low frequency component of the braking circuit is separated and negative feedback is provided, the influence of the set of the braking circuit can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the automatic light amount control device of the present invention, FIG. 2 is a waveform diagram explaining the operation of FIG. 1, and FIG. 3 is a part of the circuit in FIG. 1. 4 and 5 are block diagrams showing the structure of other embodiments of the automatic light amount control device of the present invention,
FIG. 6 is a block diagram showing the configuration of an example of a conventional automatic light control device. 1...Photographing lens (optical system), 2...Aperture, 3...
Image sensor, 8 - Drive circuit (aperture drive circuit), 9 - Drive coil, 10... Magnet, 11... Braking coil (
speed detection circuit), 12...braking circuit, 13...detection circuit, 22...integration circuit, 25...comparison circuit. Patent applicant Japan Victor Co., Ltd. Representative Patent attorney Yoshimu Inagi 1 [-p

Claims (1)

[Scope of Claims] An optical system that forms a subject image on an image sensor, an aperture that adjusts the amount of light incident on the image sensor, an integration circuit that integrates the output of the image sensor, and an output of the integration circuit. an aperture drive circuit that drives the aperture in response to the aperture; a speed detection circuit that detects the speed of the aperture; a braking circuit that negatively feeds back the output of the speed detection circuit to the aperture drive circuit; and an output of the braking circuit. An automatic light amount control device comprising: a separation circuit that separates a low frequency component of the separation circuit; and a negative feedback circuit that provides negative feedback of the output of the separation circuit to the braking circuit.