JPS62146081A - Matching device for automatic focusing - Google Patents

Abstract

PURPOSE:To realize a component and stable reference frequency component detecting circuit of good performance and high usability by converting a high frequency component into a digital signal and detecting a reference frequency component from the converted digital signal. CONSTITUTION:The high frequency component detected in a high frequency component detecting circuit 7 is converted into a direct current component in a detecting circuit 13, thereafter, and converted into the digital signal by an A/D converter 14. Said signal is converted digital signal and in the change of the digital signal, the reference frequency component is included. The reference frequency component, by constituting the reference frequency component detecting circuit 15 of what is called, a digital filter, can be detected in the same manner as in the case of an analog signal. The detected reference frequency component is converted into the analog signal by a D/A converter 16 and inputted to a synchronization detecting circuit 10. The A/D converter 4, the reference frequency component detecting circuit 15 and the D/A converter 16 constitutes simply an IC of one chip. When a digital circuit is one designed and fabricated, there is no variance, the secular and temperature change and it operation stably.

Description

Detailed Description of the Invention Field of the Invention The present invention relates to an automatic focusing device that drives a lens focusing device so that the high frequency component of an electrical signal obtained from an image sensor of a television camera is maximized. It is.

No. 43-91944. FIG. 7 shows a diagram of an automatic focusing device that operates almost the same as the conventional device. 1 is a lens; 2 is an image sensor that converts the object image formed on the imaging surface into an electrical signal; 3 is a preamplifier that amplifies the electrical signal obtained from the image sensor 2; 4
5 is a process circuit that applies various processing to the output of the preamplifier 3 to produce a television signal; 5 is a synchronization signal generator that supplies blanking signals to the process circuit 4, the image sensor, and the drive circuit 6; and 6 is the image sensor. This is an image sensor drive circuit that drives the image sensor 2. 7 is a high frequency component detection circuit that detects the high frequency component of the electrical signal obtained from the image sensor; for example, the center frequency is 1M;
It consists of a Hz bandpass filter and an amplifier. 8
is a reference frequency component detection circuit for detecting a reference frequency component from the high frequency components, and has a bandpass filter configuration. Reference numeral 9 denotes a reference frequency generator, which supplies the reference frequency to the synchronous detection circuit 1Q and also to the motor drive circuit 11, so that the focusing device of the lens 1 is slightly varied by the motor 12, so that the focus of the lens 1 cannot be detected by the eye. change the degree. Due to the above change, the high frequency component has a reference frequency component. 1o is a synchronous detection circuit that detects the amplitude and phase of the reference frequency component detected by the reference frequency component detection circuit 8 at the reference frequency, applies the detection signal to the motor drive circuit 11, and detects the high frequency component obtained from the image sensor 2. The motor 12 is driven so that the maximum value is reached.

The operation of the conventional automatic focusing device configured as described above will be described below with reference to FIG. 8.

In FIG. 8, the horizontal axis indicates the position of the focusing device of the lens 1, where the near position is a position where a close object is in focus, and the far position is a position where a long distance object is in focus. The vertical axis indicates the amplitude of the high frequency component of the electrical signal obtained from the image sensor 2. Now, assume that the distance to the subject is D. At this time, when the focusing device of the lens 1 is at the position d corresponding to the distance, the focus is aligned and the high frequency component is at its maximum. The component becomes a decreasing mountain-shaped characteristic. Also, 2L1.
1L2 shows the movement of the focusing device due to slight fluctuations in the reference frequency of the motor 12. a shows a slight fluctuation when the focusing device of the lens 1 is closer than the position d, and at this time, the high frequency component is subjected to amplitude modulation such as bl due to the change in focus due to the fine fluctuation. a2
is on the far side, and in this case it receives amplitude modulation like b2.As is clear from the figure, the amplitude modulation of b1 + b2 depends on whether the focusing device is on the near side or far from the in-focus point. The phase is reversed depending on whether it is on the distance side. Therefore, if the signal bl is synchronously detected at the reference frequency and the synchronously detected signal is used to drive the motor 12 in the direction of arrow C1, the signal b2 will drive in the direction of arrow C2, and the high frequency component will always be detected. It becomes stable at the point where is maximum.

Problems to be Solved by the Invention However, although the above configuration has features such as being able to form a closed loop including the focusing device of the lens and not requiring the accuracy of the focusing device, it has the following problems. In general, the current television power system is called an interlaced system, and its frequency components include up to half the vertical scanning frequency. Therefore, the reference frequency is set to 1/4 or less of the vertical scanning frequency. In the case of the NTSC system, the reference frequency is 15H2. Furthermore, the reference frequency component obtained by slightly varying the focusing device of the lens 1 at the reference frequency has a small level tl's/N
It's bad. Therefore, the reference frequency component detection circuit is required to have relatively steep filter characteristics. However, since the reference frequency is low, it is quite difficult to realize this using an analog circuit, and the circuit size is also considerable.

Furthermore, even if a circuit is actually constructed, adjustment is difficult, and many problems remain in practical use when considering the temperature characteristics and variations of the circuit. Recently, I'C technology has advanced and even large-scale devices can be configured in one step, but it is difficult to configure L or large capacity CL in the IC, and it is not suitable for the above-mentioned filter configuration.

In view of the above, it is an object of the present invention to provide a reference frequency component detection circuit that is small, stable, and highly practical, as well as an automatic focusing device.

Means for Solving the Problems The present invention periodically and optically blurs the subject image that is formed by a lens on the imaging surface of an image sensor that converts optical information of the subject image into an electrical signal. A high frequency component of an electric signal or a signal obtained by converting the high frequency component to a low frequency is converted into a digital signal, a signal corresponding to the blur is detected from the digital signal, and the high frequency component is determined based on the phase and amplitude of the detection signal. It is an automatic focusing device that drives the focusing device of the lens to maximize the focus.

Effect of the Invention The present invention realizes a small, stable, high-performance, and highly practical reference frequency component detection circuit for converting a high frequency component into a digital signal and detecting a reference frequency component from the converted digital signal using the above-described configuration. This improves the performance of automatic focusing devices.

Embodiment FIG. 1 shows a block diagram of an automatic focusing device according to a first embodiment of the present invention. In Figure 1, 1
3 is a detection circuit that converts the amplitude of the high frequency component obtained by the high frequency component detection circuit 7 into a DC signal every vertical scanning period, and 14 is an A/D conversion that converts the output of the detection circuit 13 into a digital signal every vertical scanning period. 15 is a reference frequency component detection circuit that detects a reference frequency component from the digital signal, and 16 is a D/A converter that converts the output signal of the reference frequency component detection circuit into an analog signal.

The operation of this embodiment configured as above will be described below.

The high frequency component detected by the high frequency component detection circuit 7 is converted into a DC component by the detection circuit 13, and then converted to a DC component by the A/D converter 14.
is converted into a digital signal. The signal has been converted into a digital signal, and changes in the digital signal include a reference frequency component. The reference frequency component can be detected in exactly the same way as an analog signal by configuring the reference frequency component detection circuit 16 to have a so-called digital filter configuration. The detected reference frequency component is converted into an analog signal by the D/A converter 16 and input to the synchronous detection circuit 10. In this way, this embodiment operates in the same way as the conventional example.

Now, as mentioned above, there has been remarkable progress in ICi technology in recent years, especially in the digital field. Therefore, A/
D converter 14, reference frequency component detection circuit 15, D/
The A converter 16 can easily be made into 10 chips. Moreover, once a digital circuit is designed and manufactured, it operates stably without variations, age, or temperature changes.

As described above, by digitizing the detection of the reference frequency component, it is possible to obtain a reference frequency component detection circuit that is small and operates stably, as well as an automatic focusing device.

FIG. 2 shows a specific example of the reference frequency component detection circuit when the reference frequency is 1/4 of the vertical scanning frequency. 1e is a delay circuit that delays the digital signal converted by the A/D converter 14 by twice the vertical scanning period;
17 is the output of the delay circuit 16 and the A/D converter 14
This is a subtracter that subtracts the output of .

The frequency characteristic of the signal obtained with the above configuration is expressed by the following equation, and the amplitude characteristic is illustrated in FIG. 3.

F=2j 6X1) (-j 2πf/fv) sin
(2πf/fv) fv: Vertical scanning frequency As is clear from FIG. 3, the reference frequency component can be easily detected with this configuration. Furthermore, when the cutoff characteristics near the reference frequency are insufficient, it can be improved by cascading this configuration.

FIG. 4 is a schematic diagram of an automatic focusing device showing a second embodiment of the present invention. In the figure, 19 is a reference frequency generator that generates a reference frequency as a digital signal, 2o is a D/A converter that converts the digital reference frequency into an analog signal and supplies it to the motor effective circuit 11, and 21 is a synchronous detection circuit 1.
0, and the reference frequency component detection circuit 1
A multiplier 22 multiplies the reference frequency component obtained in step 5 by the reference frequency fi and detects the phase and amplitude of the reference frequency component; 22 generates a pulse signal whose width changes according to the amplitude detected by the multiplier 21; In the pulse width modulation circuit that supplies the pulses to the motor, for example, the detected amplitude value is set in a counting circuit that subtracts 1 every time a certain basic clock is input, and all pulses are generated until the set value becomes zero. It has become.

The operation of the automatic focusing device of the second embodiment configured as described above will be described below.

This embodiment has almost the same function as the first embodiment; in the first embodiment, the reference frequency component detected by the reference frequency component detection circuit 15 was converted into an analog signal and synchronously detected. The difference is that the phase and amplitude of the digital signal are detected by multiplying the digital reference frequency by the multiplier 21 as a digital signal. However, even though there is a difference between analog and digital, their functions are exactly the same, considering that synchronous detection is analog multiplication. Further, the reference frequency generator 19 is designed to generate a digital reference frequency, but it is supplied to the motor drive circuit 11 after being converted into an analog signal by a D/MU converter 2°, and its function is the same as before. It's the same. The pulse width modulation circuit 22 supplies pulses whose width changes according to the signal amplitude detected by the multiplier 21 to the motor drive circuit 11 to drive the motor 12.
so that the motor 12 is stabilized at the in-focus point.

Now, the A/D converter 14 and the reference frequency component detection circuit 15
, reference frequency generator 19, D/A converter 20, multiplier 21, and pulse width modulation circuit 22 can all be configured on a 1-step IC.

Therefore, this embodiment makes the automatic focusing device even more compact and
It can be made stable. Furthermore, since the motor is driven by pulse width modulation, which is difficult to achieve with analog circuits, the motor responds well and operates without hunting even when the loop gain of the system is set high, making it highly responsive as an automatic focusing device. can be improved.

FIG. 6 is a block diagram of an automatic focusing device showing a third embodiment of the present invention.

In the figure, reference numerals 23 are a reference frequency component detection circuit 15, a reference frequency generator 19, a multiplier 20 . A microcomputer performs software processing in place of the pulse width modulation circuit 22, and receives horizontal synchronization signals and vertical synchronization signals from a synchronization signal generator 6.

The operation of the automatic focusing device of the third embodiment configured as described above will be described below.

The symbol of recent IC technology is the microcomputer.

Microcomputers make it possible to perform complex processing that was traditionally done with hardware using software processing called programs.
Software processing using Ω microcomputers, which can replace a lot of hardware, is highly versatile, easy to apply and change, and also reduces the amount of hardware and makes devices more compact. In this embodiment, by converting processing suitable for digitalization into software using a microcomputer, it is possible to provide an automatic focusing device that is even smaller and more versatile.

FIG. 6 is an example of a flowchart of software processing in this embodiment.

The microcomputer updates data and generates a reference frequency every time a horizontal synchronizing signal is input or every time it is input several times. The signal is converted into an analog signal by the D/A converter 20 and supplied to the motor drive circuit 11. Also, based on the horizontal synchronization signal, the value set in the memory area is subtracted by the amplitude of the detected reference frequency component. , when it becomes zero, the motor will stop driving. This replaces the pulse width modulation circuit 22. Next, when the vertical synchronization signal is input, the output of the MU/D converter 14 is taken in and the amplitude of the high frequency component is detected. Captured mu/D
A reference frequency component is detected from the output of converter 14. This is obtained by sequentially storing the captured values in a memory area and subtracting them from the value captured two vertical scanning periods ago. Furthermore, although the phase and amplitude of the reference frequency component are detected, since the microcomputer itself generates the reference frequency component, the detection is easy. When the amplitude is detected, the corresponding value is set in the memory area as described above, and the motor starts driving.

As described above, according to this embodiment, conventional hardware can be replaced by a program running on a microcomputer, and its effects are significant due to its versatility and ease of application and modification. , in the first embodiment, the reference frequency component detection circuit 1
Although the configuration shown in FIG. 2 is used as a specific example of No. 6, this configuration is not applicable as long as the reference frequency component can be detected. ! ! In the third embodiment, the A/D converter 14, the microcomputer 23, and the D/A converter 2
0 has a different configuration, but recently many microcomputers have incorporated peripheral devices.
'i may also be included. Needless to say, in this case, the system becomes smaller. Further, although FIG. 6 is shown as an example of a flowchart of a microcomputer, it is not obvious that other flowcharts may be used.

The present invention periodically and periodically images the subject image formed by the lens.
The method of optically blurring is not the method described in the main text.

As described in detail, according to the present invention, it is possible to provide an automatic focusing device that is small and operates stably, and has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an automatic focusing device according to an embodiment of the present invention, FIG. 2 is a block diagram of a specific example of a reference frequency component detection circuit, and FIG. 3 is an amplitude characteristic of the reference frequency component detection circuit with respect to frequency. 4 is a block diagram of an automatic focusing device according to another embodiment of the present invention, FIG. 6 is a block diagram of an automatic focusing device according to another embodiment of the present invention, and FIG. 6 is a flowchart of a microcomputer. , FIG. 7 is a block diagram of a conventional automatic focusing device, and FIG. 8 is a characteristic diagram for explaining the operation of the device shown in FIG. 1...Lens, 2...Image sensor, 5.
... Synchronization signal generator, 7 ... High frequency component detection circuit, 9 ... Reference frequency generator, 1o ...
...Synchronous detection circuit, 13...Detection circuit, 1
4...A/D converter, 16...Reference frequency component detection circuit, 16...D/A converter 0 Name of agent Patent attorney Toshio Nakao et al. 1 person Figure 2 Figure 3 Circumference 5 Number of skins Figure 5 Figure 6 Figure 7 Figure 8

Claims (3)

[Claims] (1) The image of the subject that is formed by a lens on the imaging surface of the image sensor that converts the optical information of the subject image into an electrical signal.
Periodically and optically blur, convert the high frequency component of the electric signal or a signal obtained by converting the high frequency component to a low frequency into a digital signal, detect a signal corresponding to the blur from the digital signal, and generate the detected signal. The automatic focusing device is characterized in that the focusing device of the lens is driven so that the high frequency component is maximized according to the phase and amplitude of. (2) A method of detecting a signal corresponding to blur from a digital signal is a method of adding and subtracting a converted digital signal and a signal converted at an integral multiple of the vertical scanning frequency of the image sensor. An automatic focusing device according to scope 1. (3) The digital signal is imported into the microcomputer, and the software processing of the microcomputer detects the signal corresponding to the blur, and based on the phase and amplitude of the detected signal,
2. The automatic focusing device according to claim 1, wherein the focusing device of the lens is driven so that a high frequency component is maximized.