JPH0828629B2 - Differential amplifier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a differential amplifier used for white balance signal processing in a video camera.

[Conventional technology]

FIG. 4 shows a conventional example of a color temperature detection circuit used for signal processing for white balance of a video camera. In the figure, reference numeral 1 is a photometric circuit having a pair of logarithmic amplifiers 2 and 3, and one logarithmic amplifier 2 is The photometric current I _L1 generated by the photodiode 4 that reacts to red light, and the other logarithmic amplifier 3 that is generated by the photodiode 5 that reacts to blue light.
It is configured to logarithmically compress I _L2 and convert it to voltages V ₁ and V ₂ for output. 6 is a differential amplifier for amplifying and outputting the two output differential voltage V _1, V ₂ of the photometry circuit 1, resistors R _1, R _2, made like an operational amplifier 7, resistors R _1,
The gain is set by R ₂ , and its output voltage V ₀ is used as color temperature information.

In the conventional differential amplifier 6 configured as described above, V ₀ = V _r2 + (V ₂ −V ₁ ) × R ₂ / R ₁ (1) is obtained as the output voltage V ₀ . However, V _r2 is the reference voltage.

By the way, the two output voltages V ₁ and V ₂ of the photometric circuit 1 are V _r1
Is the reference voltage, However, V _D1 : Voltage drop of diode D ₁ V _D2 : Voltage drop of diode D ₂ K: Boltzmann constant T: Absolute temperature q: Electron charge I _SD1 : Forward saturation current of diode D ₁ I _SD2 : It becomes the forward saturation current of diode D ₂ , and from this Therefore, when substituting equation (4) into equation (1), Becomes As is clear from the equation (5), the output voltage V ₀ has a portion proportional to the absolute temperature T. Therefore, taking steps such as to have a temperature coefficient proportional to absolute temperature T to a resistance R ₁ of one of the resistor R _1, R ₂ which determines the conventional gain in the differential amplifier 6, the absolute of the output voltage V ₀ The proportion proportional to temperature is canceled out.

[Problems to be solved by the invention]

In the conventional differential amplifier, it is necessary to cancel the temperature dependence of the output voltage by using a special resistor having a temperature coefficient proportional to the absolute temperature as described above, which not only causes an increase in cost but also makes it an IC. However, there is a problem in that it may cause an error in the output voltage, depending on the arrangement of the special resistor.

The present invention has been made to solve such a problem, and it is possible to obtain a differential amplifier which can cancel the temperature dependence of the output voltage without using special parts and can be easily integrated into an IC. It is intended.

[Means for solving problems]

In the differential amplifier according to the present invention, a first constant current source is connected to each of the first electrodes for each emitter of the first and second transistors in which a resistor is connected between the first electrodes. And a pre-stage differential amplifier section that applies an input voltage between the control electrodes of the transistors, and a third,
A second differential current source commonly connected to the first electrodes of the fourth transistors, and an output voltage is obtained from between the second electrodes of the transistors; And a current ratio transmitting section that distributes and transmits two input signals having the same signal ratio as the current ratio flowing on the second electrode side of the first and second transistors to each control electrode of the third and fourth transistors. In addition, the first and second constant current sources are configured such that their current ratio has a temperature characteristic opposite to the input voltage, and the resistance is the first and second constant current sources.
Is sufficiently larger than the internal resistance peculiar to the first electrode of the transistor.

[Action]

In the present invention, the current ratio between the first constant current source and the second constant current source is a parameter that determines the gain of the differential amplifier, and the current ratio is set so as to have a temperature characteristic opposite to the input voltage. Therefore, an output voltage independent of temperature is obtained from the differential amplifier.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of a differential amplifier according to the present invention. In the figure, 8 is a front stage differential amplifier,
The second NPN transistors Q ₁ and Q ₂ and these transistors Q
_{A first} constant current source 9a connected to the emitters of ₁ and Q ₂ ,
And 9b, the transistor Q _1, and a resistor R ₁ connected between the emitters of each of Q _2, the transistors Q _1, Q ₂ of each of the base connected to an input terminal 10a, input from 10b voltages V ₁ , V ₂ is applied.

11 is a differential amplifier in the latter stage, which is common to the emitters of the third and fourth NPN transistors Q ₃ and Q ₄ whose emitters are connected to each other and whose bases are input parts, and these transistors Q ₃ and Q _4. And a second constant current source 12 connected thereto, and the collectors of the transistors Q ₃ and Q ₄ are connected to the power supply voltage terminal 13 via resistors R ₂ and R ₂ , respectively, and these transistors Q ₃ and Q ₄ are connected. Output voltage from output terminals 14a and 14b connected to the collector of
It is configured to take out V ₀₁ and V ₀₂ .

Reference numeral 15 denotes the first and second transistors Q ₁ of the front stage differential amplification section 8,
It is a current ratio transmission unit that transmits an input signal to the bases of the third and fourth transistors Q ₃ and Q ₄ of the post-stage differential amplification unit 11 corresponding to the collector current of Q ₂ , and the collector is the power supply terminal 13
The emitter is connected to the collector of the first transistor Q ₁ and the third
5th transistor connected to the base of transistor Q ₃ of
NPN transistor Q ₅ and a sixth NPN transistor Q ₆ whose collector is connected to the power supply voltage terminal 13 and whose emitter is connected to the collector of the _second transistor Q _{2 and} the base of the fourth transistor Q ₄ , respectively. 5th and 6th transistor Q
₅ , V ₆ Base voltage V _B to turn these on
A first and second transistor having a power supply 16 for applying
Two inputs having the same signal ratio as the current ratio of Q ₁ and Q ₂ are applied to the bases of the third and fourth transistors Q ₃ and Q ₄ , respectively.
The constant current I ₂ of the second constant current source 12 in the above is distributed to the third transistor Q ₃ and the fourth transistor Q ₄ at the above current ratio and is made to flow. And the above-mentioned first
The constant current sources 9a, 9b and the second constant current source 12 are assembled so that the current ratio I ₂ / I _{1 of} these constant currents I ₁ and I ₂ is inversely proportional to the absolute temperature T, as will be described later. ing.

FIG. 2 shows the first constant current sources 9a, 9 in the embodiment of FIG.
3 is a circuit showing a specific example of b and the second constant current source 12.
However, for convenience of illustration, only the output current I ₁ corresponding to one of the first constant current sources 9a and 9b is shown, but the other is also the same. The first constant current source 9a, 9b is the emitter area ratio of 1: a current mirror constituted by the transistors Q _7, Q ₈ which is n, the transistor Q ₉ and another transistor Q ₁₀ to Q ₁₃
It consists of a current mirror and so on. In addition, the second constant current source 12 includes a transistor Q ₁₅ and another transistor Q _15.
It comprises a current mirror formed between ₁₆ and Q ₁₇ , a constant current source 17 for supplying a constant current I, a transistor Q ₁₈ connected in series to the constant current source 17, and the like.

 Next, the operation of the differential amplifier will be described.

In FIG. 1, the input voltage V _in between the input terminals 10a and 10b is V _in =
Each unit of current when V ₁ -V ₂ is input to the I _A ~I _E, the resistance R ₁ to inherent internal resistance emitter resistance i.e. the emitter of transistor Q _1, Q ₂ is assumed sufficiently large , V _in = R ₁ I _E (6) I _A + I _B = 2I ₁ (7) I _E + I _B = I ₁ (8) Substituting this into equation (7) with I _A / I _B = g, Becomes Substituting equation (9) into equation (8) And from now on Holds. Then substituting equation (11) into equation (6) Becomes

Next, assuming that the base-emitter voltages of the transistors Q ₅ and Q ₆ are V _BE5 and V _BE6 , the base potentials V _B3 and V _B4 of the transistors Q ₃ and Q ₄ are respectively However, I _S1 : Saturation current of transistors Q ₅ and Q ₆ , Holds. On the other hand, since V _B3 −V _BE3 = V _B4 −V _BE4 (16) holds, However, I _{S2 is} the saturation current of transistors Q ₃ and Q ₄ . From equation (17) Considering that I _A / I _B = g holds, from these equations (18) and (15), Becomes When the input voltage V _in = 0 is _{I C = I D = I 2} /2, this time, the output terminal 14a, the output voltage V ₀₁ of 14b, V ₀₂ are equal. Therefore, with reference to the case of input voltage V _in = 0,
_Obtaining the change v ₀₁ of the output voltage V ₀₁ , Since, and I _C + I _D = I ₂ (21), from (19) and (21), Is obtained, substituting equation (22) into equation (20) Holds. When the input voltage V _in = 0, based on, since the variation v ₀₂ of variation v ₀₁ and the output voltage V ₀₂ of the output voltage V ₀₁ is in a relation of opposite phase in the same amount, after all, the output terminal 14a, The output voltage V _out = V ₀₁ −V ₀₂ obtained between 14b is Becomes Therefore, the gain G of this differential amplifier is (1
From equations 2) and (24), Becomes That is, in this differential amplifier, constant currents I ₁ , I ₂
The input voltage v _in is amplified by the gain G including the current ratio I ₂ / I _{1 of the above} and is taken _out as the output voltage v _out .

On the other hand, the first constant current source 9a as shown in FIG. 2, the 9b, assuming that the temperature characteristics of the resistor R can be neglected, a current mirror formed by transistors Q _10, Q _11, the emitter area ratio With a current mirror composed of transistors Q ₇ and Q ₈ with 1: n A constant current I ₁ proportional to the absolute temperature T is obtained.

Further, in the second constant current source 12, a constant base-emitter voltage V _BE18 is generated in the transistor Q ₁₈ by the current flowing from the constant current source 17 into the transistor Q ₁₈ , and based on this, the constant current I flows in the resistor R _{4. 3} flows.

By the way, since the base-emitter voltage V _BE18 of the transistor Q ₁₈ has a negative temperature characteristic, that is, a temperature coefficient inversely proportional to the absolute temperature T, the constant current I ₃ also has a negative temperature characteristic. Then, the second constant current source 12, a constant current I ₃ which is the first constant current source 9a, since obtaining a constant current I ₂ as the sum of the constant current I ₁ from 9b, a constant current I ₁ The positive temperature characteristic of I and the negative temperature characteristic of the constant current I ₃ are canceled, and the constant current I ₂ having substantially no temperature dependence is taken out.

From the above, the above current ratio I ₂ / I ₁ has a negative temperature characteristic inversely proportional to the absolute temperature. Therefore, in the differential amplifier shown in FIG. 1, when the input voltage v _in having the positive temperature characteristic is input, the temperature characteristic is canceled by the negative temperature characteristic of the gain G, which is substantially the same. Therefore, the output voltage V _out having no temperature dependence can be obtained.

FIG. 3 is a circuit diagram showing another embodiment in which the output stage of the post-stage differential amplifier section 11 has a different configuration. Instead of the resistors R ₂ and R ₂ in the embodiment shown in FIG. A transistor Q ₂₀ is inserted between the transistor Q _{3 of 3} and the power supply terminal 13, and a current mirror is formed by this transistor Q ₂₀ and another transistor Q ₂₁ , while between the fourth transistor Q ₄ and the power supply terminal 13. also inserted through the transistor Q _22, this transistor Q ₂₂
And another transistor Q ₂₃ form a current mirror so that a current equal to the current I _C flowing through the third transistor Q ₃ flows through the transistor Q ₂₁ , and the fourth transistor Q ₄
It is configured to pass a current equal to the current I _D flowing through the transistor Q ₂₃ . Then, one transistor Q ₂₄ and transistor Q _{21 of the} current mirror composed of another pair of transistors Q ₂₄ and Q ₂₅ , and the other transistor Q ₂₅ and transistor Q ₂₃ are connected in series,
Connect a series circuit of bias power supply 18 and resistor R ₅ and output terminal 19 to the connection point of transistor Q _{23 and} transistor Q ₂₅ ,
The output terminal 19 is configured to obtain an output voltage corresponding to the difference between the currents I _C and I _D of the third and fourth transistors Q ₃ and Q ₄ . The other structure is similar to that of the previous embodiment, and the description thereof is omitted.

In the differential amplifier of this embodiment, as described above, a current equal to the current I _C flowing through the third transistor Q ₃ flows into the transistor Q ₂₁ , and a current equal to the current I _D flows through the fourth transistor Q ₄ as a transistor. While current flows through Q ₂₃ , currents that are equal to each other always flow between transistors Q ₂₄ and Q _25. Therefore, when I _C <I _D , the increment ΔI _D with respect to I _C flows to the bias power supply 18 through the resistor R ₅ and the output as the reference voltage a power supply voltage V _r3 of the bias power supply 18 to the terminal 19, the output voltage _{V out = V r3 + ΔI D} × R 5 ... (27) is taken out. In the case of I _C> I _D is, I for I _{C D}
(-ΔI _D ) from the bias power supply 18 flows through the resistor R ₅ to the transistor Q ₂₅ , the output voltage V _out is V _out = V _r3 −ΔI _D × R ₅ … (28) When the input voltage v _{in is} taken out and the output voltage v _out is V
It becomes _r3 . Therefore, by adjusting the voltage V _r3 ,
It is possible to freely set the output voltage V _{out when there} is no signal. The temperature characteristic is the same as that of the circuit of FIG.

In the above embodiment, the first and second constant current sources 9a, 9b, 12 are configured so that the current ratio I ₂ / I _{1 which} is a parameter of the gain G has a negative temperature characteristic, and the positive and negative current sources 9a, 9b, 12 are positive. The case where the output voltage v _out having no temperature dependence is obtained with respect to the input voltage V _in having the temperature characteristic has been described, but the present invention is not limited to this, and the input voltage V in
When the temperature characteristic of v _in is negative, conversely, the current ratio I ₂ / I ₁ has a positive temperature characteristic, so that the first and second potential source 9a are connected according to the temperature characteristic of the input voltage v _in. Of course, it is possible to deal with the input voltage V _in having various temperature characteristics by setting the characteristics of 9b, 9b and 12.

〔The invention's effect〕

As described above, according to the present invention, since the current ratio of the first and second constant current sources, which is a parameter for determining the gain of the differential amplifier, has the temperature characteristic opposite to the input voltage,
The temperature dependence of the output voltage can be canceled without the use of special parts, and the effect of facilitating IC integration can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a differential amplifier according to the present invention, FIG. 2 is a circuit diagram showing a concrete configuration of a constant current source of the differential amplifier, and FIG. 3 is a differential amplifier according to the present invention. FIG. 4 is a circuit diagram showing another embodiment of FIG. 4, and FIG. 4 is a circuit diagram showing a conventional differential amplifier. In the figure, 8 is a front stage differential amplification section, 9a and 9b are first constant current sources, 11 is a rear stage differential amplification section, 12 is a second constant current source, 15 is a current ratio transmission section, and Q1 is a _first constant current source. 1 is a transistor, Q ₂ is a second transistor, Q ₃ is a third transistor, and Q ₄ is a fourth transistor. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first and a first resistor in which a resistor is connected between the respective first electrodes.
For the second transistor, a first constant current source is connected to each of the first electrodes, and an input voltage is applied between the control electrodes of each of the first and second transistors. The amplifier section and the second electrodes on the first electrodes of the third and fourth transistors, respectively.
A constant differential current source is commonly connected to obtain an output voltage from between the second electrodes of the third and fourth transistors, and a first differential amplifier of the first and second transistors. And a current ratio transmitting section for transmitting two input signals having the same signal ratio as the current ratio of the current flowing on the second electrode side to the respective control electrodes of the third and fourth transistors. The second constant current source is configured such that these current ratios have temperature characteristics opposite to those of the input voltage, and the resistance is unique to the first electrodes of the first and second transistors. A differential amplifier characterized by being made sufficiently larger than the internal resistance.