JPH03165609A - Optical current amplifier - Google Patents

Abstract

PURPOSE:To eliminate temperature dependency on an inverted level of a comparator circuit, to attain small size and less effect due to temperature by providing a current mirror circuit to a comparator circuit and connecting a collector of a couple of transistors(TRs) being components of an input stage to a collector of a couple of TRs being components of the current mirror circuit respectively. CONSTITUTION:A current mirror circuit 10 to compare optical current outputs of photodetectors 1, 2 and to eliminate the effect of temperature fluctuation is provided to a comparator circuit 7 in an optical current amplifier provided with the plural photodetectors 1, 2, logarithmic amplifiers 3, 4 amplifying logarithmically the optical current outputs from the photodetectors 1, 2 and the comparator circuit 7 comparing the output voltage with a reference voltage. Then collectors of a couple of TRs Q1, Q2 being components of the input stage of the comparator circuit 7 are connected respectively to collectors of a couple of TRs Q3, Q4 being components the current mirror circuit 10 and different emitter areas of the TRs Q3, Q4 are differentiated. Thus, the optical current amplifier is realized with small size and low cost, in which the temperature compensation is sufficiently implemented.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a photocurrent amplification device that is used in an auto white balance circuit of a video camera with a photodetector and obtains light source information as a digital output. This invention relates to a photocurrent amplification device that does not receive

<Prior Art> A logarithmic amplifier with a wide dynamic range is used to amplify a photocurrent output from a photodetector (photosensor) provided in an auto white balance circuit of a video camera. Since a logarithmic amplifier uses a diode as a current-voltage conversion element, there is a temperature fluctuation due to its thermal constant kT/q. Here, k: Boltzmann constant T: absolute temperature q: charge of electron.

FIG. 5 shows an example of an electric circuit of a conventional photocurrent amplification device. As shown in the figure, the conventional photocurrent amplification device includes a photodetector 1.
2, and a photodetector 1- provided corresponding to the photodetector 1.2.
A logarithmic amplifier 3.4 that logarithmically amplifies the photocurrent output from 2, a differential amplifier 5 that takes the difference between the outputs of the logarithmic amplifiers 3 and 4, a temperature compensation circuit 6 for removing the influence of temperature, and a differential amplifier 5 and a comparison circuit (humparator circuit) 7 for comparing the output voltage of Vre43 with a reference voltage Vre43. In the figure, TRI and TR2 are transistors for logarithmic conversion, R1 is an input resistance of the differential amplifier 5, and R3 is a feedback resistance.

In FIG. 5, the output voltage of the logarithmic amplifier 3 is Vref
1-(kT/q) a Nn(Isc 1/Io
), and the output voltage of the logarithmic amplifier 4 is Vre(1-(kT/q) ・1n(l5c2/I
o). Here, Io:) Reverse saturation current of the diode between the base and emitter of transistors TRI and TR2 l5cl: Photocurrent output from optical sensor 1 l5c2: Photocurrent from optical sensor 2! It is.

Therefore, the output voltage of the differential amplifier 5 is Vref2+
(kT/q)·(Iscl/l5c2>...(1).

As is clear from equation (1), the output voltage of the differential amplifier 5 has temperature fluctuations due to the thermal constant (kT/q) of the diode, so temperature compensation is required to compensate for the thermal constant (kT/q). Circuit 6 is installed.

<Problems to be Solved by the Invention> As mentioned above, the output voltage of the differential amplifier 5 varies depending on the thermal constant of the diode. Temperature compensation is performed using a temperature-sensitive resistor with a temperature coefficient of .

However, since temperature-sensitive resistors such as thermistors are not compatible with integrated circuits, the resistor R1 must be externally attached, which increases the production cost of the photocurrent amplification device and increases the size of the product.

In order to cope with this, a photocurrent amplification device has been proposed which has a temperature compensation method in which a temperature sensitive resistor for temperature compensation is also monolithically formed within an integrated circuit. That is, in this photocurrent amplifier, the input resistor R1 of the differential amplifier 5 is monolithically formed by ion implantation, and the feedback resistor R3 is monolithically formed by base diffusion on the same substrate as the amplifier section, and the input resistor and feedback resistor are Temperature compensation is performed by selecting a temperature coefficient and using the difference to give the gain of the differential amplifier 5 a negative temperature coefficient.

However, in this temperature compensation method, the temperature coefficients of the ion-implanted resistor and the base diffused resistor vary depending on external conditions (process conditions) when the resistor is formed, and this variation may result in insufficient temperature compensation.

In view of the above, an object of the present invention is to provide a photocurrent amplification device that is small, low cost, and can perform sufficient temperature compensation.

Means for Solving the Problems The means for solving the problems according to the present invention, as shown in FIGS. a logarithmic amplifier 3.4 for logarithmically amplifying the photocurrent output of each photodetector 1, 2.6-, and the logarithmic amplifier 3;
．． A photocurrent amplification device comprising a comparison circuit 7 for comparing the output voltage of each photodetector 1.2 with a reference voltage, the comparison circuit 7 comparing the photocurrent outputs of each photodetector 1.2 and comparing the effect of temperature fluctuation. A current mirror circuit 10 for removing (temperature compensation) is provided, and a pair of transistors Q1 . The collector of Q2 is a pair of F runnostars Q3 constituting the current mirror circuit 10,
A pair of transistors Q3 . The emitter area of Q4 is different.

Effect> In the above problem solving means, the transistor Q3. Assuming that the emitter area ratio of Q4 is N, the threshold voltage of the comparator circuit 7, that is, the input voltage difference between Q1 and Q2 when the output of the comparator circuit 7 is inverted, is expressed as (kT/q)·lnN.

On the other hand, the output voltage Vo2 of the logarithmic amplifier 3 inputted by the transistor Ql is V, +2 = Vref 1-(kT/q) ・/n(I
sc 1/I. ) Output voltage V of logarithmic amplifier 4. 3
is Vo3 = Vrer 1-(kT/q) ・in(l5
c2/Io).

Therefore, the input difference voltage of the comparator circuit 7 is ~'o2-Vo3 ''(kT/Q)''NnN(Iscl/l5c2>, and the threshold voltage of the comparator circuit 7 (kT/q)・
Between 1r+N, (kT/q) ・NnN(Iscl/l5c2)=(k
T/q) ・NnN --・When (7) is established, the output of the comparator circuit 7 is inverted.

If we transform equation (7) at knee, we get l5c1/l5c2=N...(8) becomes.

In this way, the term (kT/q) also cancels out in equation (8), so when the output of the comparator circuit 7 is inverted, l5
cl/l5c2 has no temperature dependence.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] First, a first embodiment of the present invention will be described based on FIG. 1.

FIG. 1 is an electrical circuit diagram of a photocurrent amplification device according to a first embodiment of the present invention. Note that the same reference numerals are given to the same functional parts as in the prior art.

As shown in the figure, the photocurrent amplification device of this embodiment includes a plurality of photodetectors (photosensors) 1 and 2, and is provided corresponding to each of the photodetectors 1 and 2. A logarithmic amplifier 3.4 that logarithmically amplifies the photocurrent output of the logarithmic amplifier 3.4, a differential amplifier 5 that takes the difference between the outputs of the logarithmic amplifier 3.4, and a comparison circuit that compares the output voltage of the differential amplifier with a reference voltage V ref 2. (comparator circuit) 7.

The comparison circuit 7 is provided with a current mirror circuit 10 for comparing the photocurrent outputs of the respective photodetectors 1 and 2 and for removing the influence of temperature fluctuation (temperature compensation). A pair of transistors Q1. Q
2 collectors are connected to a pair of transistors Q3.2 constituting the current mirror circuit 10. A pair of transistors Q31Q4, which are connected to the collectors of Q4 and constitute the current mirror circuit 10, have different emitter areas.

The photodetector 1.2 uses a 7-diode, and the a/-1' of the photodetector 1.2 is connected to a logarithmic amplifier 3,
4, and their cathodes are respectively connected to the positive logic input terminals of logarithmic amplifier 3.4.

The output terminal of the logarithmic amplifier 3 is connected to the negative logic side input terminal of the differential amplifier 5 via a human resistor R1, and the output terminal of the logarithmic amplifier 4 is connected to the differential amplifier via an input resistor R1. It is connected to the positive logic side terminal of 5. moreover,
The negative logic side input terminals of the logarithmic amplifier 3.4 are connected in negative feedback to the output terminals of the logarithmic amplifier 3.4 via logarithmic conversion transistors TR1 and TR2, respectively. Note that the bases of the 'N number conversion transistors TR1 and TR2 are connected to the positive logic side input terminals of the logarithmic amplifiers 3 and 4.

The output terminal of the differential amplifier 5 is connected to the base of one side transistor Q1 that constitutes the input stage of the comparison circuit M, and Vrer2 is connected to the base of the observation transistor Q2 that constitutes the input stage of the comparison circuit 7. ing. Further, the negative logic side input terminal of the differential amplifier 5 is connected in negative feedback to the output terminal of the differential amplifier 5 via a feedback resistor R3.

The comparator circuit 7 has an emitter that has the same constant current vJ in common,
Transistor Q1 connected to Q11 and forming an input stage
, Q2, a current mirror circuit 10 which compares the photocurrent output of the photodetector 1.2 and is used as a temperature compensation circuit, a switching transistor Q5 and a resistor R5.
It is composed of.

The current mirror circuit 10 includes transistors Q3. Q
The bases of transistors Q 1 and Q 3 are connected in common, and a bypass path is provided between the midpoint between the collectors of transistors Q 1 and Q 3 and the midpoint between the bases of transistor Q 3 and IQ 4, and the collectors of transistors Q 2 and Q 4 are connected. The base of switching transistor Q5 is connected to the intermediate point.

In the above configuration, if the emitter area ratio of the transistors Q 3 and Q 4 constituting the current mirror circuit 10 in the comparator circuit 7 is N, then the threshold voltage of the comparator circuit 7, that is, when the output of the comparator circuit 7 is inverted, is Q
The input voltage difference between I and R2 is expressed as (kT/q)·1nN.

On the other hand, the output voltage of the differential amplifier 5 input to the F transistor 1 and the V ref 2 input to the transistor Q2
The input voltage difference between the two is expressed as (R3/Rl)·1n(Iscl/l5c2). Here, l5cl: photocurrent output of optical sensor l; l5c2: photocurrent output of optical sensor 2;

As a result, (R3/R1)・(kT/q)・Nn(rscl/l5
c2)=(kT/q)1nN (2) When it becomes, the output of the comparator circuit 7 is inverted.

Here, equation (2) is transformed into (Iscl/l5c2)R1=N@6 (3).

In equation (3), the thermal constant (kT/q) is canceled by the left and right sides, and when the comparator circuit 7 is busy, (Isc1/l
It can be seen that the value of 5c2) is not affected by temperature fluctuations.

That is, the output voltage Vol of the differential amplifier (5) is 'v
'o 1 = Vref 2 + (R3/R1)・(kT/q)・Nn(Iscl/l
5c2).

On the other hand, the transistor Ql constituting the input stage of the comparator circuit 7
o1 at the base of transistor Q2, and Vr at the base of transistor Q2.
ef2 is input. This makes the Ql of the transistor
The input voltage difference between the base and the base of F transistor Q2 is (R3/R1)・(kT/q)Jn(Iscl/l5c
2)...(4)

Since the transistor Q3 to which the collector of the transistor Q1 is connected and the transistor Q4 to which the collector of the transistor Q2 is connected constitute a current mirror circuit 10, the transistor Q3. When the emitter areas of Q4 are not the same, for example 1:N, the emitter area of transistor Q3 is A3, and the emitter area of transistor Q4 is A4, then A 3 / A 4 = 1
/N, when the input terminal difference between the base of the transistor Q1 and the base of the transistor Q2 becomes (kT/q)·NnN, the output of the comparison circuit 7 is inverted.

That is, (kT/q)·anN becomes the threshold voltage of the comparator circuit 7.

Therefore, (4) upstream (R3/R1)・(kT/q)・No(Iscl/l5
c2)=(kT/q)·anN (5) When the following holds true, the output of the comparison circuit 7 is inverted.

In Uni, when formula (5) is transformed, it becomes l5cl/l5c2=NFr 6 & -(G).

From equation (6), the ratio l5cl/l5c2 of the photocurrent output of optical sensor 1 and the photocurrent output of optical sensor L2 is N r'-l
When this is satisfied, inversion of the comparator circuit 7 occurs.

At this time, it can be seen that there is no term (kT/q) in equation (6), and the inversion level of the comparator circuit 7 has no temperature dependence.

Therefore, it is not necessary to set the input resistance in consideration of the temperature coefficient as in the past, and a resistor that is compatible with integrated circuits can be used as the input resistance, making it possible to reduce the size and cost of the photocurrent amplification device. Moreover, temperature compensation can be sufficiently performed.

[Second Embodiment 1 Next, a second embodiment of the present invention will be described based on FIG. 2.

FIG. 2 is an electrical circuit diagram of a photocurrent amplification device according to a second embodiment of the present invention.

As shown in the figure, the photocurrent amplification device of this embodiment uses the logarithmic amplifiers 3 and 4 without using the differential amplifier 5 that takes the difference between the logarithmic amplifiers 3 and 4.
The output terminal of the logarithmic amplifier 3 is connected to the base of the transistor Q1 on one side constituting the input stage of the comparator circuit 7, without providing the input resistor R1 and the feedback resistor R3, so that the output of the logarithmic amplifier 3 is directly input to the comparator circuit 7. The output terminal of the logarithmic amplifier 4 is connected to the comparison circuit 7
The configuration of this pond is the same as that of the first embodiment.

In the above configuration, the logarithmic amplifier 3 does not pass through the differential amplifier 5.
, 4 are input to the comparison circuit 7, the output voltage Vo2 of the logarithmic amplifier 3 is V, 2=Vrefl (
kT/q)Jn(Iscl/Io) Output voltage V of logarithmic amplifier 4. 3 is Vo3 = Vref 1-(kT/q) ・1n(l5
c2/1. ) 6 Therefore, the input difference voltage of the comparator circuit 7 is Vo3-Vo2 = (kT/q) ・&n(Isc 1 / l5c2
), and the threshold voltage (kT
/q)・ρnN, (kT/q)・nn (Tsc'l / I sc
2)=(kT/q)@1nN (7) When (7) is established, the output of the comparator circuit 7 is inverted.

Here, if we transform equation (7), we get ■sc1/l5c2=N...(8) becomes.

In this way, the term (kT/q) also cancels out in equation (8), so when the output of the comparator circuit 7 is inverted, l5
cl/l5c2 has no temperature dependence.

[Third Embodiment 1] Next, a third embodiment of the present invention will be described based on FIG.

FIG. 3 is an electrical circuit diagram of a photocurrent amplification device according to a third embodiment of the present invention.

As shown in the figure, the photocurrent amplification device of this embodiment has a comparator circuit 7.
has a first current mirror circuit 10 and a second current mirror circuit 20, the first current mirror circuit 10 and the second current mirror circuit 20 are cross-connected, and a transistor Q constitutes each current mirror circuit 10°20.
3, Q4 and Q6, Q7 have different emitter areas.

The first current mirror circuit 10 is composed of transistors Q 3 and Q 4 whose bases are commonly connected, and the second current mirror circuit 20 is composed of transistors Q 6 . It consists of Q7. The collector of the one-side transistor Q3 constituting the first current mirror circuit 10 is connected to the collector of the one-side transistor Q1 constituting the input stage of the comparator circuit 7,
The collector of the other side transistor Q7 forming the second current mirror circuit 20 is connected to the collector of the other side transistor Q2 forming the input stage of the comparison circuit 7. Further, the other side transistor Q4 configuring the first current mirror circuit 1( ) is cross-connected to the collector of the other side transistor Q2 configuring the input stage of the comparison circuit 7, and the transistor Q6 configuring the second current mirror circuit 20 is connected to the collector of one side transistor Q1 constituting the human power stage of the comparator circuit 7.

In addition, in the figure, 21 is a constant current source, and Q8 to Q15 are transistors.

In the above configuration, the comparison circuit 7 has hysteresis because the current mirror circuits 10 and 20 are cross-connected.

That is, transistor Q3. The emitter area ratio of Q4 is 1:N (N>1), and the transistor Q6. If the emitter area ratio of Q7 is 1:M (M>1.N>M), the input voltage difference between transistors Ql and Q2 is (R3/R1)・(
kT/q)・nn(Iscl/l5c2)=(kT/
q)·ρnN (9) When the following holds true, the output of the comparator circuit 7 is inverted.

On the other hand, the input voltage difference between transistors Ql and Q2 is (R3/R1)・(kT/q)・&n(Iscla/
l5c2a)=(kT/q)·11M (10) When the output of the comparator circuit 7 which had been inverted returns to the original state. Here, l5cl, l5c2: photocurrent outputs of the optical sensors 1 and 2 when the comparator circuit 7 is inverted l5cla, l5c2a: photocurrent outputs when the output of the comparator circuit 7 that has been inverted returns to the original position.

l5cl/l5c2a=M”.

becomes.

Therefore, if N>M, the comparator circuit 7 becomes a circuit with hysteresis.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described based on FIG. 4.

FIG. 4 is an electrical circuit diagram of an optical @flow amplifying device according to a fourth embodiment of the present invention.

As shown in the figure, the photocurrent amplification device of this embodiment is provided with a level shift circuit 30 between the differential amplifier 5 and the comparison circuit 7 for adjusting the threshold of the comparison circuit 7.

The level shift circuit 30 has a function of level shifting the output voltage of the differential amplifier 5 or the reference voltage Vref2 of the comparator circuit 7, and includes a pair of transistors Q16. The emitters of Q17 are commonly connected to each other and connected to a constant current source 31,
The collector is connected to a pair of transistors Q18 . Connected to Q19. The transistor 018 . The emitter area of Ql9 is
are set up differently.

In the figure, Q20 is a transistor, R6 and R7 are resistors, and the other configurations are the same as in the first embodiment.

In the above configuration, Ql constituting the input stage of the comparator circuit 7
The input voltage of is Vref2+ (R3/R1)・(kT/q)・1n(Iscl/l5
c2).

On the other hand, the input voltage of the transistor Q2 is Vref2+ΔVSFT, where the shift voltage of the level shift circuit 30 is ΔVSET. The emitter area ratio of Ql9 is 1:
When L (L>1), ΔVSFT=(1+R6/R7)”(kT/q)&nL
becomes.

The input voltage difference of the comparison circuit 7 is (R3/R1)・(kT/q)・#n(Iscl/l5
c2) - (1+R6/R?) ・(kT/q) ・Extinction
Since it is a blind IL and the threshold F' voltage of the comparator circuit 7 is (kT/q)・lnN, (R3/R1)・(kT/qL!n(Iscl/l5c)
2) (1+R6/R7)・(kT/q)・1nL=(k
T/q).11N (11), the output of the comparison circuit 7 is inverted.

Here, formula (11) is (Isel/l5c2)""(L")・N...(
12).

In equation (12), the term (kT/q) is canceled out, so l5cl/l5c2, where the output of the comparator circuit 7 is inverted, has no temperature dependence.

Therefore, by making resistors R6 and R7 variable resistors,
It can be used to adjust the output inversion level of the comparator circuit 7.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

<Effects of the Invention> As is clear from the above description, according to the present invention, the comparison circuit includes a current mirror circuit for comparing the logarithmically amplified outputs of each photodetector and removing the influence of temperature fluctuation (temperature compensation). The collectors of the pair of transistors forming the input stage of the comparison circuit are connected to the collectors of the pair of transistors forming the current mirror circuit, respectively, and the emitter areas of the pair of transistors forming the current mirror circuit are set differently. Therefore, the inversion level of the comparator circuit has no temperature dependence.

Therefore, it is not necessary to set the input resistance in consideration of the temperature coefficient as in the past, and a resistor that is compatible with integrated circuits can be used as a human resistance, making it possible to downsize and reduce the cost of the photocurrent amplification device. Moreover, it has excellent effects such as sufficient temperature compensation.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a photocurrent amplifying device according to a first embodiment of the present invention, FIG. 2 is an electric circuit diagram of a photocurrent amplifying device according to a second embodiment of the present invention, and FIG. 3 is an electrical circuit diagram of a photocurrent amplifying device according to a second embodiment of the present invention. FIG. 4 is an electric circuit diagram of a photocurrent amplification device according to a fourth embodiment of the present invention, and FIG. 5 is an electric circuit diagram of a conventional photocurrent amplification device. ■, 2: Photodetector, 3, 4: Logarithmic amplifier, 5: Differential amplifier, 7: Comparison circuit, 10, 20: Current mirror circuit,
30 level shift circuit, Q]~Q20: Transistor. Applicant Sharp Corporation

Claims (1)

[Claims] a plurality of photodetectors, a logarithmic amplifier provided corresponding to each photodetector to logarithmically amplify the photocurrent output from each photodetector, and a comparison circuit to compare the output voltage of the logarithmic amplifier with a reference voltage. The comparison circuit is provided with a current mirror circuit for comparing the logarithmically amplified output of each photodetector and removing the influence of temperature fluctuation (temperature compensation), and the comparison circuit The collectors of the pair of transistors forming the input stage are connected to the collectors of the pair of transistors forming the current mirror circuit, and the emitter areas of the pair of transistors forming the current mirror circuit are different. Photocurrent amplifier.