JPH07336603A - Correction circuit for saturated charge versus temperature characteristic for ccd image sensor - Google Patents

Abstract

PURPOSE:To provide a saturated charge versus temperature characteristic correc tion circuit for a CCD image sensor in which a temperature characteristic to a saturated charge Qs is corrected and its circuit design is simplified. CONSTITUTION:A diode 2 (one or more) and a voltage source 3 without temperature dependency connected in series are inserted between a noninverting input terminal of an operational amplifier 1 and ground GND to provide a negative temperature characteristic to a CCD substrate voltage Vsub. Since the forward bias of the diode 2 has a temperature dependency that it decreases as temperature rises, a voltage inversely proportional to a temperature change is given to the noninverting input terminal of the operational amplifier 1. Thus, a voltage amplified by a multiple of a gain inversely proportional to a temperature change is outputted from an output terminal of the operational amplifier 1. An output voltage of the operational amplifier 1 is provided as an output of a CCD substrate voltage Vsub via a diode 4. A temperature characteristic to a saturated charge Qs of a CCD image sensor is corrected by providing a negative temperature characteristic to the CCD substrate voltage Vsub in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a saturated charge of a CCD image sensor for correcting the temperature characteristic of the saturated charge by giving a negative temperature characteristic of an arbitrary gradient to a CCD substrate voltage supplied to the CCD image sensor. The present invention relates to a temperature characteristic correction circuit.

[0002]

2. Description of the Related Art Conventionally, C given to a CCD image sensor is used.
CD substrate voltage V_subThe output voltage of the op amp
It is generated by performing a card clamp. The CCD substrate
Voltage V s_ubAs shown in FIG. 7 (a) and FIG. 7 (b).
CXD1250 is used for CCD vertical clock driver
Temperature dependence is almost zero, or C
If CXD1267 is used for CD vertical clock driver
In this case, it had a temperature characteristic of +2 mV / ° C. Either
However, CCD substrate voltage V_subAlmost depends on temperature
There is no sex. On the other hand, the saturation voltage of the CCD image sensor
The load Qs is large depending on the temperature as shown in FIG.
Temperature characteristics that change rapidly (CCD substrate voltage V_sub = constant)
In addition to having a CCD substrate as shown in FIG.
Voltage V_subIt has a dependency (temperature T = constant).

[0003]

By the way, in the above-mentioned conventional CCD image sensor, the saturation charge Qs cannot be maintained at a constant value independent of temperature. Therefore, when designing the image sensor, the saturation charge Qs
Therefore, it is necessary to allow the dynamic range of the V resistor and the photodiode to have a margin in consideration of the fluctuation. Therefore, the conventional CCD image sensor has a problem that circuit design becomes very difficult.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a saturation charge temperature characteristic correction circuit for a CCD image sensor which can correct the temperature characteristic of the saturation charge Qs and simplify the circuit design. There is.

[0005]

To achieve the above object, the saturation charge temperature characteristic correction circuit for a CCD image sensor according to the present invention is connected in series in the forward direction to the power supply voltage, and the forward bias increases with temperature. M first diodes having decreasing temperature dependence, a voltage source having no temperature dependence connected in series with the first diode, and a non-inverting input terminal connected to the anode side of the first diode A non-inverting amplifier that multiplies the voltage supplied to the non-inverting input terminal by a predetermined gain and outputs the multiplied voltage as a substrate voltage of the CCD image sensor, and n second forward-connected to the output terminal of the non-inverting amplifier. And a diode of.

Further, in the saturation charge temperature characteristic correction circuit of the CCD image sensor according to the present invention, the voltage source is an electronic volume. In the saturation charge temperature characteristic correction circuit of the CCD image sensor according to the third aspect of the present invention, the number m of the first diodes is m.
When the number n of the second diodes is G, the gain of the non-inverting amplifier is G, and the temperature coefficient of the first and second diodes is k, k × (−G × m + n) <0 is satisfied. It is characterized by

[0007]

In the present invention, the first diode has a temperature dependence in which the forward bias decreases with an increase in temperature, so that the non-inverting input terminal of the non-inverting amplifier has a voltage inversely proportional to the temperature change. Is entered. Therefore, the gain-multiplied voltage inversely proportional to the temperature change is output to the output terminal of the non-inverting amplifier. At the output of the non-inverting amplifier, a second
Is connected to the diode, and the output voltage is
It is output as the substrate voltage via the diode. Therefore, the substrate voltage has a negative temperature characteristic,
The temperature characteristic of the saturated charge of the CCD is corrected.

[0008]

First, the principle of the present invention will be briefly described. A. Principle of the Invention The output voltage of the operational amplifier is diode clamped to
When the substrate voltage V _{sub of} D is generated, the CCD substrate voltage V
_{Since the sub} has a positive temperature characteristic, the temperature dependence of the saturated charge Qs in the CCD becomes more remarkable. Therefore, in the present invention, by inserting a diode and a voltage source between the non-inverting input of the operational amplifier and GND, the CCD substrate voltage V
_Sub has a negative temperature characteristic, and the temperature characteristic of the saturated charge Qs is corrected.

B. Basic Configuration Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing the basic configuration of an embodiment of the present invention. In the figure, reference numeral 1 is an operational amplifier, the non-inverting input terminal of which is connected to a power supply V _D via a resistor R and is connected to a ground GND in order to give a negative temperature characteristic to a CCD substrate voltage V _sub . In between, a diode (one or more) 2 and a voltage source 3 having no temperature dependence connected in series are inserted. Since the diode 2 generally has a temperature dependence in which the forward bias decreases with an increase in temperature, a voltage inversely proportional to the temperature change is input to the non-inverting input terminal of the operational amplifier 1. Therefore, a voltage multiplied by a gain that is inversely proportional to the temperature change is output to the output terminal of the operational amplifier 1.

A diode 4 is provided at the output terminal of the operational amplifier 1.
Is connected, and the output voltage is output as the CCD substrate voltage V _sub through the diode 4. Therefore, as the CCD substrate voltage V _sub , a value obtained by subtracting the temperature characteristic of the clamp diode (1 or more) 4 is output. As described above, in the saturated charge temperature characteristic correction circuit shown in FIG. 1, the temperature characteristic of the saturated charge Qs of the CCD image sensor is corrected by giving the CCD substrate voltage V _sub a negative temperature characteristic.

In the above-mentioned structure, the CCD substrate voltage V _sub when the temperature is room temperature RT is changed to the CCD substrate voltage V _sub (R
T) and the CCD substrate voltage V at a certain temperature T
_{If sub} (T), the variation ΔV of the CCD substrate voltage V _sub
sub can be defined as follows. ΔV _sub = V _sub (T) −V _sub (RT) = k (T−RT) × (−G × m + n) where G is the gain of the operational amplifier 1 and m is the diode 2
, N is the number of diodes 4, and k is the temperature coefficient of the diodes 2 and 4 (unit: mV /
C.)> 0.

Next, if the temperature is plotted on the horizontal axis and the variation ΔV _sub is plotted on the vertical axis, the slope of the variation ΔV _sub is k ×
(−G × m + n). Therefore, by appropriately selecting the number m of the diodes 2 and the number n of the diodes 4, it is possible to make the gradient of the variation ΔV _sub negative. Further, the temperature characteristic of the saturated charge Qs is corrected by setting the inclination so as to cancel the temperature characteristic of the saturated charge Qs of the CCD image sensor (keep the saturated charge Qs constant regardless of the temperature).

C. Specific Configuration Example Next, a specific configuration of the saturation charge temperature characteristic correction circuit shown in FIG. 1 will be described. FIG. 2 is a circuit diagram showing a specific configuration of an embodiment of the present invention. The parts corresponding to those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the figure, 10 is an integrated circuit incorporating a non-inverting amplifier using an operational amplifier, and in this embodiment, a product number CXD1.
267N is used. The diodes 2 and 4 are of the same type. Further, numeral 11 is an electronic volume, and in this embodiment, a product number MB88346 (manufactured by Fujitsu) is used, and any other suitable product can be replaced. Also, 1
2 is the CCD substrate voltage V output from the integrated circuit 10.
It is a CCD image sensor supplied with _sub .

D. Procedure for setting CCD substrate voltage V _sub Next, the CCD in the saturation charge temperature characteristic correction circuit shown in FIG.
The procedure for setting the substrate voltage V _sub will be described. First, C
The following are known as preconditions for setting the CD substrate voltage V _sub . D-1. Prerequisites-Analog output characteristic of electronic volume 11 FIGS. 3A and 3B are characteristic diagrams showing an analog output-sink current characteristic and an analog output-source current characteristic of the electronic volume 11, respectively. As shown in FIG. 3A, the analog output-sink current characteristic shows that the sink current is up to about 27.5 μA and 3.7 when data #FF is output.
5V constant, 1.25V constant when data # 00 is output. Also, the analog output-source current characteristics are shown in FIG.
As shown in (b), the source current is up to about 1000 μA, the data #FF is constant at 3.75 V at the time of output, the data #
At the time of the output of 00, it becomes 1.25V constant. The temperature characteristic of the gain (× 440) of the operational amplifier incorporated in the integrated circuit 10 (CXD1267N) is hardly observed. -In general, the forward bias of diode 2 decreases with increasing temperature. If the forward bias drop due to the diode at a certain temperature T is V _F (T) and the forward bias drop due to the diode at room temperature RT is V _F (RT), then V _F (T) −V _F
(RT) =-k (T-RT). Where k is the temperature coefficient, and for Si (silicon) diodes, 2 m
V / ° C. About this, Donald L. Schilling,
Charles Belove: Electronic Circuits Discrete and
Integrated Second Edition, McGraw-Hill, New York,
See 1985.

D-2. Comparison of fluctuations ΔV _{sub When} the output of the electronic volume 11 is directly input to the DCIN terminal of the integrated circuit 10 as in the conventional technique, V _sub (T) = DCOUT−V _F (T) × n V _{sub (RT) = DCOUT-V F} (RT) is a × n. Now, assuming that ΔV _sub = V _sub (T) −V _sub (RT), ΔV _sub = (V _F (RT) −V _F (T)) × n = k (T−RT) × n. ……………………………………… (1).

On the other hand, when the output of the electronic volume 11 + the diode 2 is input to the DCIN terminal of the integrated circuit 10 as in this embodiment shown in FIG. 2, when the output of the electronic volume 11 is V ₀ , V _sub (T) = 4.4 (V ₀ + V _F (T) × m) −V _F (T) × n V _sub (RT) = 4.4 (V ₀ + V _F (RT) × m) −V _F ( RT)
× n _{Thus, △ V sub = 4.4 (V} F (T) -V F (RT)) × m + (V F (RT) -V F (T)) × n = -4.4k (T-RT ) × m + k (T−RT) × n = k (T−RT) × {−4.4 × m + n} …………………… (2).

D-3. Comparison of Gradients of Variation ΔV _sub Based on Equations (1) and (2) Next, the gradients of the variation V _sub expressed by the equations (1) and (2) are compared. If the temperature is plotted on the horizontal axis and the variation ΔV _sub is plotted on the vertical axis, the gradient of the variation ΔV _sub is: slope of equation (1): k × n> 0 slope of equation (2): k × {− It becomes 4.4 * m + n}. The slope of the equation (1) is always positive, but the slope of the equation (2) is the number m of the diodes 2 and the number n of the diodes 4.
Can be made negative by appropriately selecting. Moreover, the value can be set arbitrarily (discretely changed). Here, in FIGS. 4 and 5 show a variation △ V _sub of the prior art, the temperature characteristics of the variation △ V _sub of the present embodiment. FIG. 4 shows the characteristics when the CCD substrate voltage V _sub is constant at 5 V, and FIG. 5 shows the CCD substrate voltage V _sub .
_This is a characteristic when _sub is kept constant at 12.75V. As shown in FIGS. 4 and 5, the variation ΔV _sub according to the present embodiment.
It can be seen that the slope of has a negative characteristic with respect to temperature.

D-4. Setting method (1) A variation Δ so as to cancel the saturation charge Qs-temperature T (V _sub = constant) characteristic of the CCD image sensor 12, that is, to keep the saturation charge Qs constant regardless of the temperature T. Select the slope of V _sub . (2) The number m of the diodes 2 and the number n of the diodes 4 are set so as to realize the inclination determined in the step (1).
After determining, adjust the input of the electronic volume 11 and
The CD substrate voltage V _sub is set.

As described above, in this embodiment, the operational amplifier 1
(Or integrated circuit 10) non-inverting input (input end DCI
N) and GND, the diode 2 and the voltage source 3 (or the electronic volume 11) are inserted, and the number m of the diodes 2 and the number n of the diodes 4 are set appropriately, thereby the CCD
The substrate voltage V _sub can have negative temperature characteristics with various slopes. Therefore, the temperature characteristic of the saturated charge Qs can be corrected according to the characteristic of each CCD image sensor 12. As a result, the saturated charge Qs does not depend on the temperature and is kept constant, so that it is not necessary to allow a margin in the design of the V resistor and the photodiode. That is, CC
The design of D can be simplified as compared with the conventional one, and the degree of freedom of design can be expanded. Then, as this problem is solved, it is possible to focus on the improvement of other characteristics.

E. Modified Example Next, a modified example of the present embodiment will be described. It is not always necessary to use the electronic volume 11 for the input of the operational amplifier 1 shown in FIG. 1 or the integrated circuit 10 shown in FIG. For example, even in the resistance division method shown in FIG. 6 which is an example of the conventional technique, a resistor connected in series to the diode 2
That is, if elements having considerably small temperature characteristics are used for the resistor 30 and the variable resistor 31, the variation ΔV _sub can have negative temperature characteristics. Therefore, if an element satisfying the above conditions can be easily obtained, the circuit can be configured more easily.

[0021]

As described above, according to the saturation charge temperature characteristic correction circuit of the CCD image sensor according to the present invention, the temperature dependence in which the forward bias is connected in series in the forward direction and the forward bias decreases as the temperature rises. A first non-inverting input terminal is connected to the anode side of the first diode, the non-inverting input terminal is connected to the anode side of the first diode, A non-inverting amplifier that multiplies the voltage supplied to the end by a predetermined gain and outputs the result as a substrate voltage of the CCD image sensor, and n second second ends connected in the forward direction to the output end of the non-inverting amplifier.
Therefore, the CCD substrate voltage can have negative temperature characteristics with various gradients. Therefore, by appropriately selecting the numbers of the first diode and the second diode, the temperature characteristic of the saturated charge can be corrected according to the characteristic of each CCD. As a result, the saturated charge remains constant, independent of temperature,
There is no need to allow a margin in the design of the V resistor and the photodiode. That is, the CCD design can be simplified as compared with the conventional one, and the degree of freedom in design can be expanded. Then, as this problem is solved, it is possible to focus on the improvement of other characteristics.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a basic configuration of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration in the embodiment.

FIG. 3 is a characteristic diagram showing an analog output-sink current characteristic and an analog output-source current characteristic of the electronic volume in the embodiment.

FIG. 4 is a characteristic diagram showing temperature characteristics of a variation ΔV _{sub in} the related art and this embodiment.

FIG. 5 is a characteristic diagram showing temperature characteristics of a variation ΔV _{sub in} the related art and this embodiment.

FIG. 6 is a circuit diagram showing a configuration of a modified example when the present invention is applied to a resistance division method.

FIG. 7 is a characteristic diagram showing temperature characteristics of CCD substrate voltage.

FIG. 8 is a characteristic diagram showing a temperature characteristic of a saturated charge Qs and a CCD substrate voltage V _sub dependency of a CCD image sensor.

[Explanation of symbols]

 1 operational amplifier (non-inverting amplifier) 2 diode (first diode) 3 voltage source 4 diode (second diode) 10 integrated circuit (non-inverting amplifier) 11 electronic volume 12 CCD image sensor

Claims (3)

[Claims] 1. A number m of first diodes connected in series to a power supply voltage in a forward direction and having a temperature dependence of a forward bias decreasing with an increase in temperature, and a temperature dependence connected in series to the first diode. A non-inverting input terminal connected to the anode side of the first diode, and a non-inverting amplifier for multiplying the voltage supplied to the non-inverting input terminal by a predetermined gain and outputting it as the substrate voltage of the CCD image sensor. And n second diodes connected in the forward direction to the output terminal of the non-inverting amplifier.
Saturation charge temperature characteristic correction circuit for image sensor. 2. The saturation charge temperature characteristic correction circuit for a CCD image sensor according to claim 1, wherein the voltage source is an electronic volume. 3. The number m of the first diodes and the number n of the second diodes are such that when the gain of the non-inverting amplifier is G and the temperature coefficients of the first and second diodes are k, A saturated charge temperature characteristic correction circuit for a CCD image sensor, wherein k × (−G × m + n) <0 is satisfied.