JPS5937449B2 - Analog-to-digital converter that converts light illuminance into a digital signal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analog-digital converter (hereinafter referred to as an AD converter) that detects light illuminance and converts it into a digital quantity.

Conventionally, there have been many configurations of A-D converters, but all of them often have quite complicated configurations.

For example, an automatic focus adjustment device that detects illuminance information such as screen contrast and adjusts the focus based on this information converts the analog illuminance signal obtained by the light receiving element into a digital signal and processes it. However, it is desirable that the configuration of the A-D converter used here be as simple as possible. On the other hand, in automatic focusing devices, the sensitivity characteristics, wavelength characteristics, shape,
It is necessary to be able to select dimensions, placement, etc. relatively freely. An object of the present invention is to provide an A-D converter that can be realized with a simple configuration and has a large degree of freedom in characteristics, shape, size, and arrangement of light receiving elements.

The A-D converter of the present invention is constructed by connecting in a loop a light receiving element that generates a current according to the light intensity and a logical element whose power consumption and gate propagation delay time change inversely proportionally. An oscillator, means for supplying the current from the light receiving element to the oscillator as a power supply current, and a counter for counting the oscillation frequency of the oscillator; and the output of the counter is configured to obtain a digital signal corresponding to the light illuminance. It is characterized by the following structure.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an example of the configuration of an A-D converter according to the present invention that converts illuminance into a digital signal. Photodiode 1
A current corresponding to the incident light is supplied to the oscillation circuit 2 as a power supply current. The oscillation circuit 2 is constructed using a plurality of logic elements 3 whose power consumption and gate propagation delay time have a relationship as shown in FIG. 2, and whose oscillation frequency and supply current have a relationship as shown in FIG. It's getting old. Therefore, the oscillation frequency will change depending on the light illuminance incident on the photodiode 1, and if this oscillation output is counted by the counter 4, a counted value corresponding to the light illuminance, that is, a digital signal will be obtained. . Of course, the light receiving element is not limited to a photodiode.

Furthermore, as in the usage example described below, it is also possible to provide a plurality of light receiving elements and scan them and convert the illuminance signals obtained one after another into digital signals, but in this case, of course, the counter It is necessary to properly synchronize the gate of No. 4 and the scanning signal. FIG. 4 shows an automatic focus adjustment device constructed using the above-described illuminance-to-digital signal converter of the present invention.

In this example, screen contrast information is obtained based on illuminance signals from light receiving element groups 10 and 11 placed on the light receiving surface, and focus adjustment is performed based on this information. The light-receiving element groups 10 and 11 are composed of a large number of light-receiving elements arranged in a grid as diagrammatically shown in FIG. Here, two types of light-receiving element groups are used: a first light-receiving element group 10 that is roughly arranged as indicated by Δ marks, and a second light-receiving element group 11 that is densely arranged as indicated by ○ marks. The reason will be explained later. To explain the operation, first, the switch 12 switches to the first
The light receiving element drive circuit 13 sequentially scans the light receiving elements of the first light receiving element group 10 to sequentially obtain signals representing the illuminance of each light receiving element. These signals are then sent to the A/D converter 14 of the present invention described in FIG. 1 to become digital signals. Once the scanning of all the light receiving elements is completed, the minimum illuminance detector 15 detects the minimum illuminance among these illuminance signals, and the illuminance signal obtained by the above scanning is used as the dynamic signal of the arithmetic processing section 16, which will be described later. The scanning time of the light-receiving element drive circuit 12 is changed to adjust the level of the illumination signal from the light-receiving element group 10 so that it falls within the range (the number of pits handled). During the second scan, the illuminance signal thus adjusted to an appropriate level is sent to the arithmetic processing unit 16, and the optical system 17 is operated based on the processed result.

The arithmetic processing unit 16 has a configuration as shown in FIG. The illuminance information of the light receiving elements is sequentially outputted in parallel and sent to the local illuminance calculation section 21.

The local illumination calculation unit 21 calculates the change in illuminance, that is, the smoothness of the contrast, for each of the three adjacent light receiving elements, and the results for each of the three adjacent pixels are sent to the cumulative calculation unit 22.
Accumulate with . The local illumination calculation section 21 and the cumulative calculation section 22 perform the following processing. First, local illumination calculation section 2
1, the absolute value Xn of the second order difference in illuminance around the n-th light receiving element is determined based on the illuminance of three adjacent light receiving elements. Xn is calculated for each n, and then the cumulative calculation unit 5 calculates Xn.
(7) Find the sum of n, that is, the sum Y. It is considered that the second-order difference obtained by equation (1) represents the smoothness of the positional change in image illuminance.

For example, if Xn−1, The value of Xn increases to 1 as it deviates from the range.

Therefore, the fact that the sum Y of Xn determined by equation (2) is large means that the positional change in image illuminance is smooth. This shows that this is not the case. In this example, it is assumed that the larger Y is, the better the focus is, and the optical system 17 is automatically operated to maximize this. When this operation is completed, the switch 13 switches the light receiving element group to the second element group 11, determines Y in the same manner as described above, and operates the optical system 17 to maximize this.

The purpose of providing the two light receiving elements 10 and 11 will now be explained with reference to FIG.

FIG. 8 is a graph in which the vertical axis represents the value of Y, and the horizontal axis represents the position of the optical system such as the amount of lens extension. Curve A shows the Y obtained from the second light receiving element group 11, curve B shows the Y obtained from the first light receiving element group 10, and curve B shows the Y obtained from the first light receiving element group 10.
The rate of change is small near 0, making it unsuitable for precise focusing, but the rate of change is relatively large near the out-of-focus position, for example, the position 31, making it suitable for focusing. On the other hand, curve A has a sharp change near the in-focus position 30 and is suitable for precise focusing;
It can be seen that 1 is inappropriate for focusing. That is, it is preferable that the first light-receiving element group 10 be used for coarse focus adjustment, and the second light-receiving element group 11 be used for fine focus adjustment.
Therefore, in this example, two groups of light receiving elements are switched and used as described above. Note that the automatic focus adjustment device described above is only an example, and for example, only one light receiving element group may be provided, or conversely, three or more light receiving element groups may be provided. Further, the adjustment of the light receiving element output by detecting the minimum illuminance is not limited to this, and this adjustment function may be omitted, or another suitable configuration may be used. Further, the calculation algorithm for obtaining the focusing signal Y is not limited to the above example, and other suitable algorithms may be used. Furthermore, the arrangement of the light-receiving elements is not limited to the square lattice shape as in the above example, but various arrangements such as concentric circles can be considered. For example, when arranged in a circle, scanning along the circle can adjust the illuminance in various directions of the image. Changes can be investigated. Since the A-D converter for converting light intensity to digital quantity according to the present invention provides a digital illuminance signal with an extremely simple configuration, the overall configuration of the apparatus using this is simplified.

Furthermore, in the present invention, since the light receiving element and the oscillator are separate bodies, it is possible to combine various light receiving elements and various oscillators, and it is possible to easily realize the optimum combination for various uses. .

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a light illuminance-to-digital signal converter according to the present invention, and FIG. 2 is a diagram showing the relationship between gate propagation delay time and power consumption of the gate used in the above converter. FIG. 3 is a graph showing the relationship between the oscillator in the converter and the input current, FIG. 4 is a diagram showing the overall configuration of an automatic focus adjustment device using the light illuminance-to-digital signal converter according to the present invention, and FIG. Figure 6 is a diagram showing the arrangement of light receiving elements, Figure 6 is a diagram showing the configuration of the arithmetic processing section, Figure 7 is a graph showing an example of the relationship between image illuminance and position, and Figure 8 is a diagram showing different light receiving elements. 3 is a graph showing differences in focusing signals obtained for groups. 1... Photodiode, 2... Oscillation circuit, 3...
- Logic element, 4... counter.

Claims (1)

[Claims] 1. An oscillator configured by connecting a light receiving element that generates a current according to the light intensity, a logic element whose power consumption and gate propagation delay time change in inverse proportion to each other in a loop, and a light receiving element connected to the oscillator. , a counter for counting the oscillation frequency of the oscillator, and a digital signal corresponding to the light illuminance is obtained from the output of the counter. Analog-to-digital converter.