JPH0828615B2 - Temperature compensation circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature compensation circuit in an automatic white balance system with a sensor such as a video camera.

[Conventional technology]

FIG. 4 shows a conventional temperature compensating circuit in this type of auto white balance system. In the figure, 35 is a sensitivity resistor and the potential of the inverting input terminal of the operational amplifier 37 is the same as the temperature characteristic of the potential of the non-inverting input terminal. To the temperature characteristics of
The input signal voltage proportional to the absolute temperature T from the input terminal 34 is amplified and temperature-compensated so that the output voltage of the output terminal 38 does not depend on the temperature.

Here, it will be described below with reference to FIG. 5 that the input signal voltage to the conventional temperature compensation circuit has a proportional relationship with the absolute temperature T.

Fig. 5 shows an auto white balance circuit with a sensor for a video camera. In the figure, 1, 2 and 3 are phyto diodes, 4,5 and 6 are logarithmic compression diodes, and 7, 8 and 9 are operational amplifiers. Similarly, the logarithmic compression type photoelectric conversion circuit is composed of 1,4,7 and 2,5,8,3,6,9, and the output voltage of each can be expressed by the following equation.

Here, V ₀₁ , V ₀₂ , and V ₀₃ are output voltages of each logarithmic compression type photoelectric conversion circuit, k is Boltzmann constant, q is electron charge,
T is the absolute temperature, Is is the reverse saturation current of the logarithmic compression diode, Ip ₁ , Ip ₂ and Ip ₃ are the photocurrents generated in the photodiodes 1, 2 and 3, and E is the voltage of the voltage source 10. ing.

For these output power V ₀₁ , V ₀₂ , V ₀₃ , V _01- V ₀₂ , V ₀₃
Since the subtraction circuits 20 and 21 perform the processing of -V ₀₂ , each subtraction circuit
The output of 20,21 can be expressed by the following equation.

The reverse saturation current Is of the logarithmic compression diodes 4, 5 and 6 is canceled by the processing in the subtraction circuits 20 and 21, and the voltage source E
Is also offset. Therefore, it can be seen that V ₀₁ -V ₀₂ and V ₀₃ -V ₀₂ are outputs proportional to the absolute temperature T. In FIG. 5, reference numerals 31 and 32 are temperature compensating circuits, and the circuit of FIG. 4 is conventionally used for them.

 Next, the operation will be described.

In FIG. 4, the input terminal 34 has the above-mentioned V ₀₁ -V ₀₂ or
Although V ₀₃ -V ₀₂ is input, since the temperature compensation method is the same, V ₀₁ -V ₀₂ will be described as a representative.

Therefore, the resistor 35 is set to have a temperature coefficient proportional to the absolute temperature T. The output of the output terminal 38 can be expressed by the following equation.

Where V _{0 (1)} is the output voltage of output terminal 38 and R ₃₆ is the resistance.
R ₃₅ represents the resistance value of 36, and R ₃₅ represents the resistance value of resistor 35. R ₃₆ / R
₃₅ >> 1 was set.

Since R ₃₆ has a temperature coefficient of zero and R ₃₅ has a temperature coefficient proportional to the absolute temperature T, V _{0 (1)} is given by the following equation.

Here, K is a constant. That is, R ₃₅ = K · T And V _{0 (1)} is temperature compensated.

[Problems to be Solved by the Invention] Since the conventional temperature compensation circuit is configured as described above, it is necessary to set the resistors R ₃₅ and R ₃₆ to R ₃₆ / R ₃₅ >> I. Further, it is necessary to set the resistance value of R ₃₅ to have a temperature coefficient proportional to the absolute temperature T, which causes a problem in temperature compensation accuracy. In addition, when integrated circuit, R ₃₅ , R
There is a problem in that it is necessary to use ₃₆ as an external resistor, which increases the cost.

The present invention has been made to solve the above problems, and a temperature compensation circuit which can be easily integrated into a semiconductor integrated circuit, can be temperature-compensated at low cost, and can be remarkably improved in accuracy. The purpose is to get.

[Means for solving problems]

The temperature compensation circuit according to the present invention utilizes the fact that the relationship between the base-emitter voltage of the transistor and the collector current can be approximated by the following equation, that is, can be expressed in logarithm.
The temperature characteristic of the third constant current source is set to a current independent of the temperature, an input signal current proportional to the absolute temperature T, and a current proportional to the absolute temperature, and the collector current or the emitter of the first, second and third transistors is set. The circuit is configured so that temperature compensation is performed by adding or subtracting the base-emitter voltage of each transistor obtained by setting the current by each of the constant current sources.

Here, V _BE is the base-emitter voltage of the transistor, k is the Boltzmann constant, T is the absolute temperature, q is the electron charge, Ic is the collector current, and Is is the reverse saturation current of the transistor. However, the Ic ≒ I _E, I _E denotes the emitter current.

[Action]

In the temperature compensation circuit according to the present invention, the collector current or the emitter current of the first, second and third transistors is set to the first, first
Temperature compensation is performed because the circuit is configured to add or subtract the base-emitter voltage of each transistor obtained by setting the second and third constant current sources.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a temperature compensating circuit according to an embodiment of the present invention which should be used as the temperature compensating circuits 31 and 32 of the auto white balance circuit of FIG. 5, in which 1 denotes a temperature independent current. The first constant current source 2, 2 is a second constant current source that generates a current proportional to the absolute temperature T according to an input signal, and 3 is a third constant current source that generates a current proportional to the absolute temperature T is there.

Here, the input signal of the second constant current source 2 means the current obtained by passing the output voltage of the logarithmic compression type photoelectric conversion circuit through the voltage / current conversion circuit of FIG.
It is obtained as a current at the terminal 33 in the figure. That is, FIG. 3 shows a general voltage / current conversion circuit.
Since the negative feedback circuit is composed of the transistor 31 and the input terminal voltage of the terminal 29 is generated at the connection point of the emitter of the transistor 31 and the resistor 32, the resistance value of the resistor 32 is R ₃₂ and the input voltage is V ₀₁ −V _{If 02} , the current I _c31 obtained at the terminal 33 can be expressed by the following equation. However, the collector current and the emitter current of the transistor 31 are assumed to be equal, and the direct current amplification factor h _FE of the transistor 31 is set to be sufficiently large.

This is a current proportional to the absolute temperature T. This current I
_c31 becomes the current of the second constant current source 2 which generates a current in response to the input signal.

Further, the first constant current source 1 for generating a current independent of temperature and the third constant current source 3 for generating a current proportional to the absolute temperature T are produced by using the circuit shown in FIG. In FIG. 2, a negative feedback circuit is constituted by the transistors 10, 11, 13 and 14 and the resistor 12, and the current obtained by dividing the difference in V _BE between the transistors 10 and 11 by the resistor 12 is set.

Where k is the Boltzmann constant, T is the absolute temperature, q is the charge of the electron, Is is the reverse saturation current of the transistor, I _CQ11 is the collector current of the transistor 11, and I _CQ10 is the transistor Q _10.
The collector current, the resistance value of R ₁₂ is the resistance 12, I _T is the set current, an output current of terminal 20.

Organize the above formula, This is a current proportional to the absolute temperature T.

Further in FIG. 2, transistors 23, 25, 22 and resistors
The negative feedback circuit is composed of 24
V _BE of 23 divided by resistance 24 sets the current.

Here, V _BEQ23 is a base-emitter voltage of the transistor 23, R ₂₄ is a resistance value of the resistor 24, and Iβ is a collector current of the transistor.

Since this Iβ is a current that depends on V _BE , it has a negative temperature coefficient. Here, using the fact that the energy band gap voltage V _{GO of} silicon is constant, V _GO −V _BE = V
_{If T} is set and V _GO = V _T + V _BE , V _GO = 1.273 [V]
Therefore, since V _BE = 0.6 [V] or V _T = 0.673 [V], if the ratio of V _BE and V _T is taken to be approximately 1: 1, the sum of the currents due to each becomes independent of temperature. Therefore, at this ratio, I _T and I β are output from the terminal 29 as the sum of the two, thereby producing a current I _REF that does not depend on temperature.

In this way, the first, second and third constant current sources 1, 2, 3
Set. In FIG. 1, the constant current of the constant current source 1 is I _REF
, The constant current of the constant current source 2 is I _I = I _C31 (equation), the constant current of the constant current source 3 is I _T (equation), the collector current of the transistor 4 is I _CQ4 , and the emitter current of the transistor 5 is
When I _EQ5 , the emitter current of the transistor 6 are I _EQ6 , and the collector current of the transistor 7 is I _CQ7 , the following equation is established. In FIG. 1, 8 is a load and 9 is a power source.

Here, I _CQ4 is set to the I _REF , that is, a constant current that does not depend on temperature, and I _EQ5 is set to the formula I _C31.
Setting the formula I _T as _EQ6 formula is as follows.

Here, I _REF is a constant current that does not depend on temperature, I _T is expressed by a formula, a current proportional to the absolute temperature T, and I _C31 is expressed by a formula and is a current proportional to the absolute temperature T. Like

From this equation, it can be seen that the absolute temperature T is canceled out, and I _CQ7 does not depend on temperature and becomes constant.

According to the temperature compensating circuit of the present embodiment as described above, since the temperature sensitive resistor as in the conventional case is not required, the temperature can be accurately compensated at low cost, and the external resistor is not required, so that the semiconductor integrated circuit can be easily formed. can do.

Although the present invention has been described above by using the circuit configuration example of FIG. 1, the present invention is not limited to this, and a constant current source as shown in another embodiment of the present invention of FIG. 1,2,3
Is connected to each collector of each transistor 4,5,6, or constant current sources 1,2,3 are connected to each transistor 4,5,6 as shown in another embodiment of the present invention in FIG. 1 may be configured to be connected to each emitter, or, although FIG. 1 is an example thereof, it may be configured to arbitrarily connect to the collector side and the emitter side.

Further, as still another embodiment of the present invention constructed based on the above-mentioned concept, FIG. 8, FIG. 9, FIG. 10, FIG.
Those shown in FIGS. 12, 13, and 14 are considered. As described above, the structure is based on the above concept, and at the same time, a resistor for applying a bias voltage to the transistors 5 and 6 is provided (FIGS. 8 and 9).
50, 51 (Fig. 10), operational amplifiers 71-74 with high input resistance and a differential amplifier circuit (Figs. 13, 14) to reduce errors due to base current, and MOS input circuit It is possible to propose a large number of circuits, such as a circuit configuration in which is used, or a circuit configuration in which the Early effect of a transistor is compensated is adopted.

As described above, according to the present invention, the relationship between the base-emitter voltage of the transistor and the collector current or the emitter current is used by using the current source proportional to the absolute temperature T and the current source independent of the temperature. Since the circuit is configured so that the temperature can be compensated for, the temperature adjustment parts such as temperature sensitive resistors are not particularly required, and the device can be inexpensive especially when configured as an integrated circuit, and adjustment is not required, and accuracy can be improved. There is an effect that a high price can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a temperature compensation circuit according to an embodiment of the present invention, and FIG. 2 is a diagram showing a circuit example for producing a current proportional to an absolute temperature T and a current independent of temperature.
FIG. 4 is a diagram showing an example of a circuit for converting a voltage into a current, FIG. 4 is a diagram showing an example of a conventional temperature compensation circuit, and FIG. 5 is an auto white balance circuit with a sensor for a video camera, which is a logarithmic compression type photoelectric conversion. FIG. 6 is a block diagram showing a simple circuit composed of a circuit, a subtraction circuit, and a temperature compensation circuit. FIG. 6 is a temperature compensation circuit according to another embodiment of the present invention, in which collector currents of respective transistors are set. FIG. 7 is a diagram showing another example of the present invention in which the emitter current of each transistor is set, and FIG. 8 is an example in which the collector current of each transistor is set similarly to FIG. FIG. 9 is a diagram showing another embodiment of the present invention. In particular, the transistor 4 sets the collector current and the transistors 5 and 6 set the emitter current. FIG. 10 shows another example of the present invention. In the example, the level is set to the transistors 4 and FIG. 11 is a diagram showing an example in which transistor transistors 5 and 6 for switching are provided respectively, and FIG. 11 shows an example in which the emitters of transistors 4 and 7 are commonly connected and grounded via a resistor in another embodiment of the present invention. FIGS. 12 and 13 show another embodiment of the present invention in which transistors 4 and 7 are of PNP type,
FIG. 6 is a diagram showing an example configured in NPN type, FIGS. 13 and 14 are other examples of the present invention, respectively, in order to reduce the base current error of each transistor by using an operational amplifier with a high input resistance. It is a figure which shows the comprised example. 1, 2, 3 are first, second, and third constant current sources, 4,5, 6, 7 are transistors, 8 is a load, and 9 is a power supply. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. The temperature characteristics of the first and second constant current sources are set such that one of them is a current that does not depend on temperature and the other is an input signal current that is proportional to the absolute temperature T. The temperature characteristic is set to a current proportional to the absolute temperature T, the first constant current source is connected to the collector or the emitter of the first transistor, and the current is used as the collector current or the emitter current. The second constant current source is connected to the collector or the emitter of the second transistor, and the third constant current source is connected to the collector or the emitter of the third transistor, and the current is used as the collector current or the emitter current. An added voltage of the base-emitter voltage of the transistor and the base-emitter voltage of the second transistor is created, and the third transistor is added from the added voltage. Voltage is generated by subtracting the base-emitter voltage of the fourth transistor, the subtracted voltage is applied between the base-emitter of the fourth transistor, and the collector current of the fourth transistor is obtained as an output. Characteristic temperature compensation circuit.