JPS60201220A - Detector for illumination light - Google Patents

Abstract

PURPOSE:To obtain an illumination light detection signal which is stable against temperature variation by compensating variation in illumination light detection signal with the temperature of a color filter by varying the reference potential of a differential amplifier. CONSTITUTION:Light from the periphery of an object is converged by a light condenser 25 and converted into an electric signal by the 1st photoelectric converter consisting of color filter glass 26 which allows the transmission of red color light and a photodiode 27 having sensitivity principally to visible light and the 2nd photoelectric converter consisting of color filter glass 28 which allows the transmission of blue light and a photodiode 29 which has sensitivity principally to visible light. Those signals are supplied to the 1st and the 2nd logarithmic compressors 34 and 35 composed of diodes 30 and 31 and operational amplifiers 32 and 33 and then supplied to the differential amplifier 41 consisting of resistors 36-39 and an operational amplifier 40 to output the difference signal 42 between both signals.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an illumination light detection device that can be used in a white balance adjustment device for a color video camera.

Conventional configurations and their problems As is well known, white balance adjustment is one of the essential adjustment functions in a color video camera. Generally, to adjust the white balance, all you have to do is take a picture of a white subject and adjust the balance of the electrical signals of the three primary colors obtained by the camera so that it appears white on the TV receiver.
In order to improve operability, simple color cameras are equipped with a fully automatic adjustment function that constantly detects illumination light and automatically adjusts white balance, eliminating the need for user operations. In order to perform automatic tracking white balance adjustment in response to fluctuations in illumination light, an illumination light sensor that detects the properties of illumination light (light color and ratio of the three primary colors rather than light intensity) is required in addition to the camera's imaging function. Is required.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An illumination light detection device conventionally used for white balance adjustment will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an example of a conventional illumination light detection device. Light around the subject is collected by a light condenser 1 made of a light diffusing plate. The light from the condenser is sent to a photoelectric converter consisting of a red filter 2 and a photodiode 3, and a photoelectric converter also consisting of a blue filter 4 and a photodiode 6, which converts the light from the condenser into a spot original signal IR, etc. is converted to The two current signals are passed through operational amplifiers 8, 9 . diode 10
．． The output signal is supplied to logarithmic compressors 12 and 13, which are configured by 11 and 11.

The relationship between the forward voltage v2 of the diode 10.11 and the forward voltage is generally expressed by the following equation.

8V.

y = engineering s・e 1 can be expressed by the following formulas.

7),=Vs-V,,=Vs---1ogeE-3-@
-Is 1'V, R, V, B: TAIO-1'10111 (7) Forward voltage.

vs: Reference voltage supplied from terminal 16) Both signals 1) R
, 'UB is the operational amplifier 17 and the resistor 18°19.
20.21 is supplied to a differential amplifier 22 configured as shown in FIG.
A difference signal v023 between both signals is output.

If the gain of the differential amplifier is G, the difference signal v0 is expressed by the following formula % (V,: reference potential supplied from terminal 24) difference signal v0
As is clear from the above equation (c), it is a signal that responds to the ratio of the current signals I, , I, and is therefore a signal that is independent of the amount of illumination light and responds to the color of the light. However, with the above configuration as it is, there is no guarantee against temperature changes.

As it is, it is impossible to put it into practical use as an illumination light detection device for a white balance adjustment device. Output signal v023
The causes of temperature changes include (1) temperature changes in the offset voltage and bias current of each operational amplifier, and temperature changes and variations in resistors, (2) temperature characteristics specific to diodes 10 and 11, (3) Temperature changes in the photodiode and color fill can be considered. Regarding the first term, since temperature changes in each element are unavoidable, optimal circuit design must be carried out and care must be taken in selecting components. The second term is the first
As shown in the equation, the problem is that the absolute temperature T appears directly in the output signal, but since this changes linearly with temperature changes, temperature compensation can be performed relatively easily. - As an example, the gain G of the differential amplifier 22 is determined by the resistor 18.19
Since it is determined by the ratio of resistor 20.21, resistor 18.1
If both 9 and 9 are used as a temperature-compensating resistor whose resistance value directly increases as the temperature rises (hereinafter referred to as a temperature-sensitive resistor), the gain G will directly decrease as the temperature rises.
It is possible to offset the temperature change of kT4, and it is possible to stabilize the dullness of the output signal against temperature change.

Next, the third term is the output V caused by temperature changes of the photodiode and color filter. Regarding temperature changes, compensation measures differ depending on the characteristics of the parts, so no clear method has been proposed in the past. In particular, the illumination light detection device for video cameras can detect
Furthermore, it must operate stably under a wide range of temperature conditions and must also ensure durability. Therefore, it is necessary to use a highly reliable colored glass filter even as a single color filter. However, when using colored glass filters, although it is expected that the spectral transmittance will fluctuate due to temperature changes, no compensation method has been shown for this, making it impossible to use the conventional configuration. there were.

OBJECTS OF THE INVENTION An object of the present invention is to provide an illumination light detection device that makes it possible to obtain an illumination light detection signal that is stable against temperature changes in photodiodes and colored glass filters.

Structure of the Invention The illumination light detection device of the present invention includes a condenser that condenses light around a subject, and a first condenser that converts the light from the condenser into an electrical signal.
a second photoelectric converter; a first and second logarithmic compressor to which output signals of the first and second photoelectric converters are respectively supplied; and output signals of the first and second logarithmic compressors; , a differential amplifier that detects the difference between both signals, and a reference voltage generator that supplies a reference potential signal to the differential amplifier. It is stable against temperature changes by changing the temperature.

This is to obtain an illumination light detection signal responsive to the light color of the average light around the subject.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram showing one embodiment of the present invention. Light around the subject is collected by a condenser 25. The collected light is transmitted through a first photoelectric converter consisting of a color filter glass 26 that transmits red light, a photodiode 27 that is primarily sensitive to visible light, and a color filter glass 28 that transmits blue light. The signal is converted into a spot completion signal by a second photoelectric converter composed of a photodiode 29 that is mainly sensitive to visible light. Photodiode 27
．． The electrical signals of 29 and 29 are connected to diodes 30 and 30, respectively.・3
1. The signal is supplied to first and second logarithmic compressors 34 and 35 which are configured with operational amplifiers 32 and 33. The output signal of the logarithmic compressor is connected to resistors 36 and 37.

38, 39, and a differential amplifier 41 composed of an operational amplifier 4o, which outputs a difference signal 42 between the two signals.

Using the symbols used in the explanation of FIG.
The potential signal supplied from 3 to the V8° reference voltage generator 44
The reference potential signal 45 outputted from Vl, the differential amplifier 4
If the gain of 1 is G, the difference signal 42 can be expressed by the first equation as in the conventional example. Note that the differential amplifier 41 is
Resistors 36 and 37 are temperature sensitive resistors for temperature compensation. The reference voltage generator 44 includes resistors 46 and 47.
A reference potential signal 46 is generated by outputting a potential determined by the resistance ratio of the reference potential signal 46 through an impedance converter constituted by an operational amplifier 48. Note that impedance conversion is performed in order to stabilize the temperature characteristics of the differential amplifier 41, but impedance conversion may not be performed for simplicity.

FIG. 3 shows an example of the spectral sensitivity characteristics of the photodiodes 27 and 29. A photodiode that is primarily sensitive to visible light, or a photodiode that is primarily sensitive to infrared and visible light, such as an ordinary silicon photodiode, is used in combination with an infrared cut filter. FIG. 4 shows an example of the spectral transmittance characteristics (49.50., respectively) of color filter glasses 26.28. As for the red and blue filter characteristics, it is necessary to select a filter with high transmittance, low loss of light amount, and good separation of both characteristics.

In addition, it is preferable to set the light wavelength at the boundary separating blue and red to approximately ssonm ('J), taking into consideration the three primary color separation characteristics of the target video camera. is the light wavelength 55
A sharp cut filter 49 with a transmittance of about 50% near 0 nm is used.

As color filter glass for blue color, mainly 50
A blue filter 50 that transmits light with a short wavelength of 0.011 m or less is used. The first and second photoelectric converters are constructed using the photodiodes and color filters described above.

Here, photodiodes 27.29 and color rays 26.
A detailed study of temperature changes in photodiodes 27 and 28 reveals that photodiodes 27 and 29 experience a shift in the light wavelength at which the spectral sensitivity reaches its peak value as the temperature changes, and also a change in overall sensitivity. , the relative shape change of the spectral sensitivity characteristics is small, and the influence on the output signal 42 can be ignored in many cases. Further, regarding the blue filter, the amount of temperature change in spectral transmittance has little influence because it acts on a relatively low sensitivity portion of the photodiode. On the other hand, the sharp cut filter 49 has a characteristic that the transmission wavelength range shifts in the direction of the arrow in response to a rise in temperature, as shown by the broken line in FIG.

Since the temperature change occurs in the wavelength range where the photodiode has almost the maximum sensitivity, its influence is extremely large.

To explain qualitatively, as the temperature rises, the transmission wavelength range of the sharp cut filter shifts to the longer wavelength side, so the wavelength range that the photodiode 27 receives becomes narrower.
Sensitivity to red light decreases relative to blue light. this is,
As shown in the first equation, the output signal 4 of the illumination light detection device
2I.

is proportional to loge-, and the decrease in IR is proportional to loge- of the output signal.

It appears as an increase. This increase is a relatively linear change in response to temperature changes.

If the reference potential signal 45 is decreased at the same rate as the temperature rises to compensate for the above fluctuation, the output signal 42
can be stabilized. - For example, if the resistor 46 in FIG. 2 is used as a temperature compensation resistor (II & temperature resistance resistor) whose resistance increases linearly with temperature rise, the reference potential signal 46 will increase linearly with temperature rise. 6 shows another example of the configuration of the reference voltage generator 44.The impedance is composed of a temperature-sensitive resistor 61, resistors 52, 53, and an operational amplifier 64. It is configured to generate a reference potential signal 46 using a converter, and by adding a resistor 62, the temperature compensation characteristic can be designed flexibly. , which shows an example of the configuration of another reference voltage generator, which has multiple configurations including a temperature-sensitive resistor 36 and resistors 56 and 57. By using the resistor 56, it becomes flexible. Circuit design becomes possible.

Note that in the embodiment shown in FIG. 2, the photodiode 27
．． Even when the polarity of the diode 29 is reversed, the polarity of the diode 30.31 is also reversed, and the color filters 26.28 are replaced, the output signal 42 can be similarly expressed by the first equation. The compensation methods shown in FIGS. 2, 4 and 6 can be used. In the embodiment of FIG. 2, if the polarities of photodiodes 27, 29 and diodes 31, 30 are also reversed, the output signal 42 will be 1,5 og 7! - Therefore, the configuration of the reference voltage generator is also the configuration in which the resistors 46 and 47 are exchanged in FIG. 2, and the configuration in which the resistors 63 and 51.52 are exchanged in FIG. , 6th
In the figure, by replacing the resistors 57 and 55 and 56, it is possible to compensate for temperature changes caused by color fog.Furthermore, in the embodiment of FIG. Even if the color filters 26 and 28 are replaced, the same result will occur, so it is sufficient to replace the resistors constituting the -h reference voltage generator 44.In addition, in the reference voltage generator, the resistors 47. 52.53°56.5
If a variable resistor is used for any one of 7, not only temperature compensation but also offset adjustment of the logarithmic compressor 34, 35 and differential amplifier 41 shown in FIG. 2 can be performed at the same time.

Effects of the Invention As explained in detail above, the present invention uses a red filter, a blue filter, and a photodiode to convert illumination light into two parts.
In an illumination light detection device that converts into different types of electrical signals and detects the ratio of both signals using a logarithmic compressor and a differential amplifier, 1
By compensating for changes in the illumination light detection signal caused by temperature changes in the color filter by changing the reference potential of the L differential amplifier, it is possible to obtain an illumination light detection signal that is stable against temperature changes. It is something. Therefore, even when applied to an illumination light detection device for white balance adjustment of a video camera,
It enables very stable adjustment against temperature changes, and has great practical value.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example of an illumination light detection device;
The figure is a circuit diagram showing the configuration of the present invention, Figure 3 is a spectral sensitivity characteristic diagram of a photodiode, Figure 4 is a spectral transmittance characteristic diagram of one color fill, and Figure 6 is a diagram of a reference voltage generator. Circuit Diagram Showing Another Embodiment FIG. 6 is a circuit diagram showing another embodiment of the reference voltage generator. 1.26... Concentrator, 2,26... Red fill, 4,28... Blue fill %3,
5,27゜29...Photodiode, 8,9
, 17, 32° 33.40, 48.54... operational amplifier, 10° 11.30, 31... diode, 36, 37. 46.51,56... Temperature sensitive resistor, 12,13
゜34.35... Logarithmic compressor, 22.41...
. . . Differential amplifier, 23.42 . . . Illumination light detection device output signal. 44... Reference voltage generator, 45... Reference potential signal, 5B, 59... Photoelectric converter. Name of agent: Patent attorney Toshio Nakao (1 person, 4 persons)
8 3rd Bl destination Unq & tnm) Figure 4 light moxibustion (Liu Figure 5 g56

Claims (4)

[Claims] (1) A condenser that condenses light around the subject, and a first condenser that converts the light from the condenser into an electrical signal. a second photoelectric converter;
A first and second logarithmic compressor to which output signals from the first and second photoelectric converters are respectively supplied, and an output signal from the first and second logarithmic compressors to which the difference between the two signals is detected is detected. a differential amplifier;
Detection of illumination light characterized by comprising a reference voltage generator supplying a reference potential signal to the differential amplifier, and obtaining a signal responsive to the average light color of the light surrounding the subject as an output of the differential amplifier. Device. (2) A first photoelectric converter is configured using a color filter glass and a photodiode that mainly transmit blue light, and a second photoelectric converter is configured using a color filter glass and a photodiode that mainly transmits red light. An illumination light detection device according to claim 1, characterized in that the illumination light detection device is configured as follows. (3) The illumination light detection device 0 according to claim 2, wherein the reference voltage generator is configured to change the reference potential signal in response to temperature changes. (4) The reference voltage generator is constructed using a resistor and a temperature compensation resistor whose resistance value increases in response to temperature rise. The illumination light detection device according to item E3. @) Illumination light according to claim 3, characterized in that the reference voltage generator is configured using a resistor, a temperature compensation resistor whose resistance value increases in response to a rise in temperature, and an impedance converter. detection device.