JP2002084461A - Image pickup element drive circuit, image pickup element test unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup element drive circuit that can prevent an overflow voltage given to an image pickup element from being fluctuated. SOLUTION: In the image pickup element drive circuit of a configuration such that a voltage source applies an overflow voltage VOFD to an overflow voltage supply terminal TOFD of an image pickup element 10 through a parallel circuit consisting of a diode D1 and a resistor R1, a regulated current circuit is provided between a common level point and a connection point connecting the diode D1 to the overflow voltage supply terminal, this regulated current circuit supplies a regulated current to the diode D1 and the regulated current stabilizes a forward voltage drop of the diode so as to eliminate fluctuations in the overflow voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention generally relates to a CCD (Ch
The present invention relates to an image sensor driving circuit for maintaining a solid-state image sensor called an “arge couple device” in an operating state, and an image sensor testing apparatus equipped with the image sensor driving circuit.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration of a conventional image sensor driving circuit. In the figure, reference numeral 10 denotes an image pickup device called a CCD or the like, 2
_{Reference numeral} 0 denotes a drive circuit for applying the overflow voltage V _OFD to the image pickup device 10. The image sensor 10 is driven by connecting various drive circuits in addition to the drive circuit 20 for applying the overflow voltage V _OFD. However, since the object of the present invention is the drive circuit 20 for applying the overflow voltage V _OFD . , Only the drive circuit 20 is shown.

[0003] The overflow voltage V _OFD is defined as
When the amount of light input to 0 exceeds a specified value (the input amount of light at this time is referred to as a saturated exposure amount), a voltage that gives a threshold value for discharging excess charges generated in the photoelectric conversion unit to the overflow drain is used. is there. By maintaining this overflow voltage V _OFD at a constant value,
The range of the linear characteristic of the input light-output voltage can be maintained at a constant value. The overflow voltage V _OFD is equal to the voltage source 21
_Is applied to an overflow supply terminal T _OFD of the image sensor 10 through a parallel circuit including a diode D1 and a resistor R1.

Here, the reason why the diode D1 is used will be described. That is, the overflow voltage supply terminal T _OFD
Has an overflow voltage V _OFD and a shutter pulse P
_{CC is} also applied. By the application of the shutter pulse _PCC, the electric charge accumulated in each photoelectric conversion unit is instantaneously released (reset), and immediately after that, the accumulated electric charge is read out according to the input light amount, thereby instantaneously capturing the image. It is aimed at obtaining data. In other words, the shutter mechanism is conceived for the purpose of capturing an instant of a moving object and obtaining an image with less blur of a streamline.

The shutter pulse is supplied from the driver 22
Overflow voltage supply terminal T_OFDMark on
Be added. This shutter pulse is a positive pulse
When no voltage is applied, the output terminal of the driver 22 is at L logic.
Outputs the potential PL, and outputs the pulse
The peak value of the pulse becomes PH giving the H logic potential. Therefore,
Shutter pulse P_CCAt the time of non-output
Pressure supply terminal T_OFDOver a certain voltage from the voltage source 21
-Flow voltage V_OFDIs applied, and the shutter
Luth P_CCAt the time of application of the overflow voltage V_OFDNishi
Shutter pulse P _CCAre added (FIG. 4)
reference). Shutter pulse P_CCIs output when
The node D1 is turned off, and the voltage source 21 is connected to the negative terminal of the driver 22.
Separates from the load and shutters the image sensor 10 with less power
Pulse P_CCDiode D1 is used to apply
ing.

[0006]

The impedance (DC resistance value) as viewed from the overflow voltage supply terminal T _{OFD of the} imaging device 10 is manufactured to be constant regardless of the imaging device 10. . However, although slightly due to manufacturing variations, the impedance seen from the overflow voltage supply terminal T _OFD to the inside is not uniform, and there is variation among the image sensors. Therefore, the operation of the image sensor 10 was tested. Therefore, every time a new image sensor is replaced, the current flowing through the diode D1 fluctuates, and the fluctuation of the current causes a problem that the overflow voltage V _OFD also fluctuates.

In other words, when testing the image pickup device 10 sequentially, when the test of the image pickup device is completed, a new image pickup device 10 is next mounted on the test apparatus, and the newly mounted image pickup device 1 is mounted.
Test for 0. Each time the imaging device 10 is exchanged for this, the value of the resistance value of the current I _c is the imaging device 10 that flows through the overflow voltage supply terminal T _OFD and the diode D1 (internal impedance viewed from the overflow voltage supply terminal T _OFD) And the overflow voltage V _OFD also fluctuates.

This situation will be described with reference to FIG. When the current I _c flowing into the imaging device 10 to be tested were current value I _O corresponding to approximately the midpoint of the on state and off state of the diode D1, the current of the diode D1 - curvature of voltage characteristic curve Will work on the part. In the case of operating with this operating current I _O , if the current I _O fluctuates slightly to + ΔI _O and −ΔI _O due to the variation of the internal resistance of the image sensor 10, the forward voltage drop V _{D1 of the} diode D1 fluctuates greatly. Due to the fluctuation, the overflow voltage V _OFD applied to the image sensor 10 also largely fluctuates.

When the overflow voltage V _OFD applied to the image sensor 10 to be tested varies for each image sensor, the linear range of the photoelectric conversion characteristic varies for each image sensor.
The test is performed in a state where the range of the photoelectric conversion characteristics is different for each image pickup device, and there is a disadvantage that a uniform test cannot be performed. Therefore, conventionally measured in advance an internal impedance of the overflow voltage supply terminal T _OFD every imaging device 10 to be tested, by adjusting the voltage to be set to a voltage source 21 in accordance with the measured internal impedance, the overflow voltage V _OFD is It was necessary to manage the coefficients so as to be constant.

An object of the present invention is to provide an image pickup device driving circuit which does not need to measure the internal impedance of the overflow voltage supply terminal T _OFD in advance and does not need to change the voltage of the voltage source 21 based on the measurement result. It is an object of the present invention to provide an image sensor test apparatus equipped with the image sensor drive circuit.

[0011]

According to a first aspect of the present invention, there is provided an image sensor having a structure in which an overflow voltage V _OFD is applied to an overflow voltage supply terminal of the image sensor through a diode and a resistor to maintain the image sensor in an operating state. The present invention proposes an image sensor driving circuit having a structure in which a constant current circuit is connected between a connection point between a diode and an overflow voltage supply terminal and a common potential point.

According to a second aspect of the present invention, the imaging device driving circuit according to the first aspect is mounted, and the overflow voltage supplied to the overflow voltage supply terminal maintains a constant value even when the imaging devices under test are sequentially replaced. The present invention proposes an imaging device test apparatus having a structure.

[0013]

According to the configuration of the image pickup device drive circuit proposed in claim 1 of the present invention, the current flowing through the constant current circuit flows through the diode, so that the diode is always maintained in the state where the forward current flows. As a result, the forward voltage drop of the diode maintains a constant value even if the internal impedance of the overflow voltage supply terminal of the image sensor serving as a load fluctuates somewhat. As a result, the overflow voltage V _OFD applied through this diode can maintain a constant value.

According to the imaging device test apparatus proposed in claim 2 of the present invention, the imaging device under test is sequentially replaced, and even if the internal impedance of the overflow voltage supply terminal fluctuates for each replacement, the overflow voltage V _OFD , The forward voltage drop of the diode supplying the constant voltage is maintained at a constant value. As a result, even if the image sensor under test is replaced, the overflow voltage applied to the overflow voltage supply terminal of each image sensor is maintained at a constant value, and the advantage that a test can be performed on the specified photoelectric conversion characteristics is obtained. Can be

[0015]

FIG. 1 shows an embodiment of an image sensor driving circuit according to the present invention. Parts corresponding to those in FIG. 3 are denoted by the same reference numerals. According to claim 1 of the present invention, the voltage source 21
From the imaging device 10 through the diode D1 and the resistor R1
In the imaging device drive circuit 20 having a structure in which the overflow voltage V _OFD is applied to the overflow voltage supply terminal T _OFD of the diode D1 and the overflow voltage supply terminal T _OFD ,
It is characterized in that a constant current circuit 23 is connected between a connection point with the _OFD and a common potential point.

The constant current circuit 23 performs an operation of sucking the constant current I _S from the voltage source 21 through the diode D1.
By sucking the constant current I _S at a constant current circuit 23, the diode D1 operates at an operating point determined by the constant current I _S. The voltage drop V _D2 determined by this operating point is the current I _S
Is maintained at a constant voltage _VD2 as shown in FIG. Further, the diode D
1, a current I _O flowing to the overflow voltage supply terminal T _OFD of the image sensor 10 flows in addition to the constant current I _S. Eventually, the current flowing through the diode D1 is I ₁ = I ₀ + I _S. By comparing the constant current I _S with the current I _O and setting the relationship of I _S > I _O , the current I _O becomes −ΔI ₁ , −Δ
Be varied to I _1, variations of the forward voltage drop V _D2 of the diode D1 can be suppressed to small variations.

[0017]

As described above, according to the present invention, in the image pickup device driving circuit for applying the overflow voltage V _OFD of the image pickup device 10 through the diode D1, the impedance seen from the overflow voltage supply terminal to each image pickup device Each diode has a structure in which a constant current I _S larger than the current I _O flowing to the image sensor 10 flows through the diode by the constant current circuit 23.
Be varied current I _O flowing into the imaging device 10 somewhat, it is possible to suppress the variation of the forward voltage drop V _D2 of the diode D1 to a small value.

Therefore, according to the present invention, a test can be performed in a state where an almost constant value of the overflow voltage V _OFD is _applied to any image pickup device, and the test can be performed in a state where uniform conditions are satisfied. The advantage that can be obtained is obtained. In addition,
Although the case where the image sensor driving circuit according to the present invention is applied to the image sensor testing apparatus has been described above, it can be easily understood that the present invention is not limited to the testing apparatus but can be applied to other apparatuses.

[Brief description of the drawings]

FIG. 1 is a connection diagram for explaining an embodiment of an image sensor driving circuit according to the present invention.

FIG. 2 is a graph for explaining the operation of the main part of the present invention.

FIG. 3 is a connection diagram for explaining a conventional technique.

FIG. 4 is a waveform chart for explaining the operation of FIG. 3;

FIG. 5 is a graph for explaining a drawback of the related art.

[Explanation of symbols]

_{Reference Signs List} 10 Image sensor V _OFD overflow voltage T _OFD overflow voltage supply terminal 20 Image sensor drive circuit 21 Voltage source 22 Driver 23 Constant current circuit D1 Diode R1 Resistor

Claims (2)

[Claims] 1. An image sensor driving circuit having a structure in which an overflow voltage is applied to an overflow voltage supply terminal of an image sensor through a diode and a resistor to maintain the image sensor in an operating state. An image sensor driving circuit having a structure in which a constant current circuit is connected between a connection point and a common potential. 2. An image pickup device driving circuit according to claim 1, wherein the overflow voltage supplied to the overflow voltage supply terminal maintains a constant value even when the image pickup device under test is sequentially replaced. An imaging device test apparatus characterized by the above-mentioned.