JPH0442691A - White balance control signal generating circuit - Google Patents

Abstract

PURPOSE:To make a circuit scale small and to improve the accuracy by providing plural switches selecting either output voltage of plural optical - voltage conversion circuits and a clamp circuit outputting a ratio signal in response to the ratio of a color component corresponding to a 1st optical - voltage conversion circuit and a 2nd optical - voltage conversion circuit to the generating circuit. CONSTITUTION:A clamp circuit 600 includes a clamp capacitor 29 and the clamp capacitor 29 is charged by a voltage difference between an output voltage of a 1at optical - voltage conversion circuit 100 connecting to the 1at switch 25 among plural optical - voltage conversion circuits and a reference voltage. Moreover, when a 2nd switch among the plural switches is closed, the output voltage of a 2nd optical - voltage conversion circuit 200 connected to the 2nd switch 26 among the plural optical - voltage conversion circuits is outputted via the clamping capacitor 29 to output a ratio signal in response to the ratio of color components corresponding to the 1st optical - voltage conversion circuit 100 and the 2nd optical - voltage conversion circuit 200. Thus, the circuit scale is made small and the accuracy is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used for adjusting the white balance used for photometry of a camera, or used for a color imaging device such as a color video camera or a color electronic camera. The present invention relates to a white balance control signal generation circuit that generates a white balance control signal for use in a computer.

[Conventional technology]

When capturing an image of a subject using, for example, a color video camera, the white balance also changes as the ratio of color components of light irradiating the subject changes. Therefore, in order to obtain high-quality color images in a color video camera, it is necessary to adjust the white balance as the ratio of the color components of the light from the light source changes. To adjust the white balance,
2. Description of the Related Art Auto white balance circuits have been used that measure the ratio of color components of light irradiating a subject separately from an image sensor and automatically adjust white balance based on the measurement results. FIG. 3 is a circuit diagram showing a white balance control signal generation circuit that generates a white balance control signal for adjusting white balance, which constitutes a part of such an auto white balance circuit.

In the figure, 1, 2, and 3 are a red filter, a green filter, and a blue filter, respectively. Reference numeral 4 denotes a red photodiode, the cathode of which is connected to the single input of the operational amplifier 10, and the anode connected to the 10+ input of the operational amplifier and GND. Operational amplifier 10. Logarithmic compression diode 7
The current-voltage conversion circuit 100 is configured by: The output of the operational amplifier 10 is fed back to the output via the logarithmic compression diode 7.

5 and 6 are a green photodiode and a blue photodiode, respectively. Green photodiode 5. Operational amplifier 11. Connection relationship of logarithmic compression diode 8, blue photodiode 6, operational amplifier 12. The connection relationship of the logarithmic compression diode 9 is that of the red photodiode 4 described above. Operational amplifier 10. The connection relationship is the same as that of the logarithmic compression diode 7. Note that the logarithmic compression diode 8 and the operational amplifier 11 constitute a current-voltage conversion circuit 200, and the logarithmic compression diode 9 and the operational amplifier 12 constitute a current-voltage conversion circuit 300, respectively.

The output of the operational amplifier 10 is connected to the operational amplifier 1 through the resistor 17.
The outputs of the operational amplifiers 11 and 3 are respectively connected to the outputs of the operational amplifiers 13 via resistors 15. The output of the operational amplifier 13 is fed back through a resistor 16.

The output of the operational amplifier 12 is connected to the operational amplifier 1 through the resistor 21.
The outputs of the operational amplifiers 11 and 4 are connected to the outputs of the operational amplifiers 14 via resistors 19, respectively. The output of the operational amplifier 14 is fed back through a resistor 20.

Also, a resistor 18. is connected between the inputs of the operational amplifiers 13 and 14.
22 are connected in series, and a common connection point of the resistors 18 and 22 is grounded via a constant voltage source 23. operational amplifier 13
．． A subtraction circuit 400 is configured by resistors 15, 16, 17° 18, and operational amplifiers 14. Resistance 19, 20.21.2
2 constitutes a subtraction circuit 500.

Next, the operation will be explained. The light transmitted through the red filter is converted into photocurrent I by the red photodiode 4. The photocurrent IR is converted into a logarithmic compression voltage A i' o according to the intensity of the red component in the light by a current-voltage conversion circuit 100 consisting of a logarithmic compression diode 7 and an operational amplifier 10.
g I vt (A is a constant). Similarly, the light that has passed through the green filter 2 has a logarithmic compression voltage AIog Ic that corresponds to the intensity of the green component, and the light that has passed through the blue filter 3 has a logarithmic compression voltage A that corresponds to the intensity of the blue component.
1 og I B.

The subtraction circuit 400 calculates voltage A, Q og I c and voltage (
The subtraction circuit 500 calculates a signal representing the ratio of red and green components, that is, v + αl (Afog (IR/IG) 1ref') by taking the difference between the voltages A and Q og By taking the difference between I c and the voltage (V + A, QoglB), ref' is a signal representing the ratio of green and blue components, that is, V +
a2 (ANogl (IB/IG) 1
Output each ef. Here, V is the er voltage value of the constant voltage source 23, α1 is the gain determined by the resistance values of the resistors 15.16 and 17.18, and α2 is the resistor 19°20.21
．． The gain is determined by the resistance value of 22.

The outputs of the subtraction circuits 400 and 500 are given to a white balance adjustment circuit (not shown) as a white balance control signal, and the white balance adjustment circuit adjusts the white balance according to the white balance control signal.

[Problem to be solved by the invention]

The conventional white balance control signal generation circuit is configured as described above, and since it uses two subtraction circuits 400 and 500, the circuit scale becomes large and the characteristics of each subtraction circuit vary (resistors 15 to 400). There was a problem in that accuracy deteriorated due to variations in resistance values of 22, etc.).

The present invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide a white balance control signal generation circuit with a small circuit scale and high accuracy.

[Means to solve the problem]

The white balance control signal generation circuit according to the present invention includes:
A plurality of light-to-voltage conversion circuits that convert a specific color component contained in the irradiated light into a logarithmically compressed voltage according to its intensity; a plurality of switches that selectively output any one of the output voltages of the plurality of light-voltage conversion circuits by selectively turning on/off, and a clamping capacitor; When the switch is turned on, the voltage difference between the output voltage of the first light-voltage conversion circuit connected to the first switch among the plurality of light-voltage conversion circuits and the reference voltage causes the clamping capacitor to When the battery is charged and a second switch among the plurality of switches is turned on, the output voltage of the second light-voltage conversion circuit connected to the second switch among the plurality of light-voltage conversion circuits is a clamp circuit that outputs a ratio signal according to a ratio of corresponding color components to the first light-voltage conversion circuit and the second light-voltage conversion circuit by outputting through the clamp capacitor; We are prepared.

[Effect]

The clamp circuit according to the present invention includes a clamping capacitor, and when a first switch among the plurality of switches is turned on, the first light-voltage conversion circuit connected to the first switch among the plurality of light-voltage conversion circuits. The clamp capacitor is charged by the difference voltage between the output voltage of the voltage conversion circuit and the reference voltage, and the second switch among the plurality of switches is turned on/off.
In the case of a plurality of light-voltage conversion circuits, the output voltage of the second light-voltage conversion circuit connected to the second switch is outputted via the clamping capacitor.
A ratio signal corresponding to the ratio of the corresponding color components is output to the first light-voltage conversion circuit and the second light-voltage conversion circuit. Therefore, there is no need to provide two subtraction circuits as in the conventional case.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of a white balance control signal generation circuit according to the present invention. In the figure, the third
The difference from the conventional circuit shown in the figure is the subtraction circuit 4CI0.
500 and newly provided a switch 25°26.27, a clamp circuit 600, and a voltage follower 30. Switches 25, 26, and 27 are connected to the outputs of current-voltage conversion circuits 100, 200, and 300, respectively. The switches 25, 26, and 27 are controlled to be selectively turned on, so that the current voltage conversion circuit 100°200
．． 300 output voltages are selectively output.

The clamp circuit 600 is connected to the switches 25, 26 and 27, and the output of the clamp circuit 600 is outputted via the voltage follower 30. The clamp circuit 600 includes a constant voltage source 23. Switch 28 and clamp capacitor 29
Consists of. The clamp capacitor 29 is connected to the switch 25,
It is connected between the node X, which is a common connection point of 26 and 27, and the voltage follower 30. voltage follower 3
A series circuit of a switch 28 and a constant voltage source 23 is connected between the common connection point of the clamp capacitor 29 and GND. The other configurations are the same as the conventional circuit.

Next, the operation will be explained using FIG. 2. The current-voltage conversion circuits 100, 200, and 300 each have a logarithm compression voltage Al.
)ogI, AJ! ogl'+ Ai'ogl
The operation up to outputting BRG is the same as the conventional one. As shown in FIG. 2, the switches 26, 25, and 27 are turned on in this order.
Output voltage A of current-voltage conversion circuit 200, 100°300
J2ogl, AI2ogl, Ai)G
RoglB is selectively output. In other words, switch 26
When switch 25 is turned on, the voltage at node Voltage according to intensity A 1 og I
When the switch 27 is turned on, the voltage at the node X becomes a voltage A corresponding to the intensity of the blue component contained in the emitted light.
It becomes fl og I o.

Switch 28 is temporarily turned on when switch 26 is turned on. Now, the voltage Vrer of the constant voltage source 23 is the voltage AI
If it is larger than oglc, when the sun pin 26.28 is turned on, the clamping capacitor 29 will be V A
Charged to 1 og Ic. Well, switch 26.28 turned on, and then Sui Sochi 2
8 is off, the clamp capacitor 29 is V
Since the node Y, which is the output of the voltage follower 30, is charged to A1ogIg, during the period when the voltage at the node
The voltage of is V.

ref Next, when the switch 25 is turned on, the voltage at the node X is A f
'og I R. Since the clamping capacitor 29 is charged with V A log I c, the voltage at the ref node Y is V, 8r+A! f! Og(IR/IG)(-Allog
l+(V-Aj!oglG))Rref, and a voltage Y1 representing the ratio of the red component to the green component is obtained.

Next, when the switch 27 is turned on, the voltage at the node X is A,
Q og I n. Since the clamp capacitor 29 is charged with V A fl og I c, the voltage at the ref node Y is V + A j! og (1/Ic)er
B (-Afogl + (V, 8r-Aj!oglG)
), and the voltage Y2 represents the ratio of the blue component to the green component.
is obtained.

White balance adjustment is performed by applying voltages Y2 and Y2 as white balance control signals to a white balance adjustment circuit (not shown).

According to this embodiment, the clamp capacitor 29 is used to obtain a ratio signal (white balance control signal) between color components without providing two subtraction circuits as in the conventional case, so the circuit size is reduced. As the size becomes smaller, the accuracy improves.

In the above embodiment, the timing of turning on the switch 28 is the same as the timing of turning on the switch 26, but the timing may be the same as that of the switch 25 or the switch 27.

〔Effect of the invention〕

As described above, according to the present invention, when the first switch of the plurality of switches including the clamping capacitor is turned on, the first switch of the plurality of light-voltage conversion circuits connected to the first switch When the clamp capacitor is charged by the difference voltage between the output voltage of the light-voltage conversion circuit and the reference voltage, and the second switch of the plurality of switches is turned on, the second of the plurality of light-voltage conversion circuits is turned on. By outputting the output voltage of the second light-voltage conversion circuit connected to the switch via the clamp capacitor, the first
Since a clamp circuit that outputs a ratio signal according to the ratio of the corresponding color components is provided in the light-to-voltage conversion circuit and the second light-to-voltage conversion circuit, it is no longer necessary to provide two subtraction circuits as in the conventional method. It disappears. As a result, the circuit scale is reduced and accuracy is improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the white balance control signal generation circuit according to the present invention, FIG. 2 is a diagram for explaining the operation of the circuit shown in FIG. 1, and FIG. FIG. 3 is a diagram showing a balance control signal generation circuit. In the figure, 1 is a red filter, 2 is a green filter, and 3 is a red filter.
is a blue filter, 4 is a red photodiode, 5 is a green photodiode, 6 is a blue photodiode,
23 is a constant voltage source, 25, 26, 27 and 28 are switches, 29 is a clamp capacitor, 100, 200 and 3
00 is a current-voltage conversion circuit, and 600 is a clamp circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A plurality of light-to-voltage conversion circuits that convert a specific color component contained in the irradiated light into a logarithmically compressed voltage according to its intensity; and a connection to the output of each of the plurality of light-to-voltage conversion circuits. is,
a plurality of switches that selectively output any one of the output voltages of the plurality of light-voltage conversion circuits by selectively turning on/off; and a clamping capacitor; When the switch is turned on, the voltage difference between the output voltage of the first light-voltage conversion circuit connected to the first switch among the plurality of light-voltage conversion circuits and the reference voltage causes the clamping capacitor to be turned on. is charged and a second switch among the plurality of switches is turned on, the output voltage of a second light-voltage conversion circuit connected to the second switch among the plurality of light-voltage conversion circuits. a clamp circuit that outputs a ratio signal according to a ratio of corresponding color components to the first light-voltage conversion circuit and the second light-voltage conversion circuit by outputting the signal through the clamp capacitor; White balance control signal generation circuit.