DE10308918B4 - Circuit arrangement for detecting ambient light and ambient light sensor - Google Patents

Abstract

Integrated circuit for detecting ambient light with a phototransistor (T1), wherein - a further transistor (T2) is provided, which is connected to the phototransistor (T1) in Darlington circuit, wherein an internal current feedback from the further transistor (T2) is provided to the phototransistor (T1), - the transistor (T2) has a base terminal (B2), a first main terminal (E2) and a second main terminal (C2) and a further terminal (C3), - for electrical feedback between an electrical connection a base terminal (B1) of the phototransistor (T1) and the further terminal (C3) of the transistor (T2) is provided and - the second main terminal (C2) and the further terminal (C3) of the further transistor (T2) form a current divider, a portion of the signal current flowing at an output (E ') is supplied in anti-phase to the base (B1) of the phototransistor (T1).

Description

The application relates to a circuit arrangement for detecting ambient light according to the preamble of claim 1 and an ambient light sensor.

Ambient light sensors are used to automatically adjust the brightness of displays of any kind to the ambient light. Thus, for example, the brightness of a dashboard in a motor vehicle is adapted to the lighting state in order to be readable in strong ambient light and not to dazzle in the dark. If the motor vehicle drives through a tunnel, the brightness of the dashboard is reduced. If the motor vehicle, however, moved in strong sunshine, the lighting of the dashboard is increased. The same applies to the displays of mobile devices, personal mobile assistants, etc. In addition to the regulation of the brightness of these displays for better readability, the ambient light sensors also contribute to saving energy.

• 1. Die spektrale Empfindlichkeit sollte der Augenempfindlichkeit angepasst werden. Dies ist auch unter dem Begriff „Vλ-Charakteristik” bekannt.
• 2. Das von dem Umgebungslicht-Sensor gelieferte Ausgangssignal muss groß genug sein, um ohne weiteren Verstärker von einem digitalen Signalprozessor (DSP) verarbeitet werden zu können.
• 3. Aufgrund der Verwendung von Umgebungslicht-Sensoren in mobilen, batteriebetriebenen Kleingeräten, wie z. B. den oben genannten Mobilfunkgeräten und Personal Mobil Assistants, sollte der Umgebungslicht-Sensor möglichst klein sein.
• 4. Schließlich soll das Bauelement möglichst kostengünstig sein.

Ambient light sensors must meet essentially the following requirements:

• 1. The spectral sensitivity should be adjusted to the eye sensitivity. This is also known by the term "Vλ characteristic".
• 2. The output signal provided by the ambient light sensor must be large enough to be processed by a digital signal processor (DSP) without further amplification.
• 3. Due to the use of ambient light sensors in mobile, battery-powered small devices, such. As the above-mentioned mobile devices and personal mobile assistants, the ambient light sensor should be as small as possible.
• 4. Finally, the device should be as inexpensive as possible.

These requirements are met by known phototransistors. A disadvantage of these phototransistors is that the output signal has a strong temperature dependence. This is based essentially on the temperature coefficient of the current gain. For single transistors, a value of 0.4% / ° C is typical. In addition, these phototransistors have spectral dependencies of the temperature response. In strongly fluctuating ambient temperature, z. As when used in a motor vehicle, this can lead to misinterpretation by the sensor signal evaluating electronics.

A temperature compensation could for example be done with the aid of operational amplifiers. However, such an ambient light sensor would no longer meet the above size and cost requirements.

From the closest prior art ( US 3,753,433 ), a circuit arrangement is known in which a Darlington transistor together with a photodiode forms an optically coupled data transmission path. The Darlington transistor is externally fed back through a resistor, providing DC stability. In U. Tietze and Ch. Schenk, "semiconductor circuit technology", 11th edition, Springer-Verlag Berlin (1999), p. 114 f. and p. 1305 f. is also known a Darlington circuit and a current negative feedback.

It is an object of the present invention to provide a circuit arrangement for detecting ambient light and an ambient light sensor, which have a minimized temperature response, whereby a cost-effective production should be possible.

This object is achieved by a circuit arrangement having the features of the independent patent claims. Advantageous embodiments and modifications of the invention are the subject of the dependent claims.

An ambient light sensing circuit in accordance with the invention includes a phototransistor and another transistor connected together in a Darlington circuit. In this case, a current feedback from the further transistor to the phototransistor is provided.

The reduction of the temperature sensitivity is based on the fact that a part of the signal current forming the output signal is fed back in opposite phase to the phototransistor. It is therefore an amplifier with internal feedback. The circuit arrangement can be implemented as a discrete component and leads to an excellent linearity of the signal of about 6 orders of magnitude and to a bandwidth which is better by a factor of 10 than with standard transistors. The compensation of the temperature response largely suppresses temperature-related errors. In experiments, temperature transitions were achieved which were more than a factor of 4 lower than ambient light sensors of the prior art. The high gain linearity leads to a very good linearity of the output signal, even at ambient light levels, which otherwise can only be achieved by photodiodes or photo ICs. However, photodiodes have the disadvantage that the signal level of the output signal is low and that a large area is needed. Photo ICs have compared to the circuit arrangement according to the invention significantly higher costs.

In the circuit arrangement according to the invention, the transistor has a base terminal, a first and second main terminal and another connection on. For current feedback, an electrical connection between a base terminal of the phototransistor and the further terminal of the transistor is provided. The second main terminal and the further terminal of the transistor form a current divider, wherein a portion of the current flowing at an output signal current is supplied in opposite phase to the base of the phototransistor.

• – ein Phototransistor mit einer an die erste Hauptseite grenzenden ersten Wanne vom zweiten Leitfähigkeitstyp und einem in der ersten Wanne gelegenen, an die erste Hauptseite angrenzenden ersten Bereich vom ersten Leitfähigkeitstyp und
• – ein weiterer Transistor mit einer an die erste Hauptseite grenzenden zweiten Wanne vom zweiten Leitfähigkeitstyp und einem in der zweiten Wanne gelegenen, an die erste Hauptseite angrenzenden zweiten Bereich vom ersten Leitfähigkeitstyp, wobei zwischen dem ersten Bereich und der zweiten Wanne eine elektrische Verbindung besteht und wobei in der zweiten Wanne ein dritter Bereich zur Stromrückkopplung vorgesehen ist.

An ambient light sensor according to the invention comprises a layer of the first conductivity type with a first main side, wherein in the layer are integrated:

• A phototransistor having a first well of the second conductivity type adjoining the first main side and a first region of the first conductivity type located in the first well and adjoining the first main side
• A further transistor having a second conductivity type second well adjacent the first main side and a first conductivity type second region adjacent the first main side, wherein there is an electrical connection between the first region and the second well; a third region for current feedback is provided in the second well.

According to the invention, a third region is provided in a photo Darlington transistor, which forms a current divider with the collector of the Darlington transistor. The third region is diffused into the second well of the further transistor. Thus, no additional process steps are required for the production. The ambient light sensor according to the invention can be realized only by small changes in the layout during the mask production. The distance between the second and third region in the second well of the further transistor allows the feedback to occur. It is particularly preferred if the second and the third region have a small distance, measured in relation to the width of the second trough.

Advantageously, a second region corresponding to the conductivity of the emitter is thus diffused in the immediate vicinity of the emitter of the further transistor. This area, referred to as the third area, then forms the desired current divider with the Darlington collector, which minimizes the temperature variation of the ambient light sensor.

While the gain of the interconnected according to the Darlington principle phototransistor and the further transistor is adjusted in a conventional manner by diffusion of the emitter and the associated reduction in the base width, the feedback according to the invention alone by the geometric distance between the second and third region of the other transistor To be defined. This makes it possible to largely optimize the component properties of the ambient light sensor.

Since neither additional process steps are required and four slightly larger footprints (compared to a standard Darlington transistor) can easily be compensated by the feedback by a slightly higher gain, the ambient light sensor can be manufactured at the cost of a standard phototransistor.

An embodiment of the circuit arrangement according to the invention and of the ambient light sensor as well as further advantages will become apparent from the following with reference to FIGS 1 to 3 illustrated embodiment.

Show it:

1 a circuit for detecting ambient light,

2 a schematic cross-sectional view of a physical structure of the in 1 shown ambient light sensor with npn transistors, and

3 a schematic cross-sectional view of an alternative physical structure of the in 1 shown ambient light sensor with npn transistors.

1 shows a schematic diagram of the circuit for detecting ambient light. The circuit arrangement comprises two transistors T1, T2. For example only, the transistors are implemented as npn transistors. The transistors are each bipolar transistors having a base terminal B1, B2, a collector terminal C1, C2 and an emitter terminal E1, E2. The transistors T1, T2 are interconnected in Darlington circuit. Accordingly, the collector terminals C1, C2 are connected to each other and constitute the collector terminal C 'of the Darlington transistor. The emitter terminal E1 of the transistor T1 is connected to the base terminal B2 of the transistor T2. The emitter terminal E2 of the transistor T2 forms the emitter terminal E of the Darlington transistor. The base terminal B1 forms the base terminal B 'of the Darlington transistor.

Between the base terminal B1 and the collector terminal C1 of the transistor T1, a diode D is connected. The transistor T1 together with the diode D forms a phototransistor.

Transistor T2 has another terminal C3, which is a collector. The collector terminal C3 is connected to the base terminal B1 of the transistor T1. The collector terminals C2, C3 of the transistor T2 form a current divider, wherein a part of the signal current is fed back in phase opposition to the base terminal B1 of the transistor T1 through the connection between the collector terminal C3 and the base terminal B1. The circuit arrangement results in an amplifier with internal feedback of the.

2 shows a sectional view of the physical structure of the ambient light sensor according to the invention. In an epitaxial layer 20 , the n-type and on a p-type substrate layer 10 is arranged, a first well, to a first main page I adjacent, arranged. The well is p-type and forms the base of the transistor T1. In the first well B1, an n-type region B1 is arranged, which represents the emitter of the transistor T1. Collector C1 is penetrated by one in the epitaxial layer 20 arranged region which is highly n-type.

In a corresponding manner, the transistor T2 is constructed. In a p-type well B2 (base), an n-type region E2 (emitter) is arranged. The collector C2 of the transistor T2 is also in the epitaxial layer 20 arranged and strongly n-type.

The current feedback is produced by the introduction of a second lateral collector C3 in the transistor T2. This is formed by an n-type region in the p-type well B2. The collector C3 is electrically connected to the first well B1 of the transistor T1.

Diode D is through the pn junction between first well B1 and epitaxial layer 20 educated. Since it is in the 2 is a schematic representation, the actually greater extent of the first tub B1 compared to the second B2 is not shown correctly.

The degree of feedback is freely adjustable by the choice of the distance between the emitter E2 and the collector C3. This is independent of the actual current gain of the Darlington transistor. Preferably, the collector C3 is arranged in the immediate vicinity of the emitter E2, so that there is a strong feedback. The farther the collector C3 is spaced from the emitter E2, the more the feedback decreases.

The base B2 of the second transistor T2 is electrically connected to the emitter E1 of the phototransistor T1. The base B1 of the phototransistor T1 can be contacted via the base terminal B 'from the outside. In a corresponding manner, the emitter E2 of the second transistor T2 can be contacted via the emitter terminal E 'from the outside. This also applies to the collectors C1, T2, which have an electrical connection outside the substrate and are connected to the collector terminal C '.

In a modification, it is also possible and also customary in practice to connect the ambient light sensor via a second main side II, which lies opposite the first main side and forms the rear side of the semiconductor chip. This means that the substrate 10 forms the common collector and is connected to the collector terminal C '. A corresponding physical structure is in 3 shown. In this case, those in the epitaxial layer 20 trained areas C1 and C2 not necessary.

LIST OF REFERENCE NUMBERS

T1

phototransistor

T2

transistor

B1

Base / Base Connection

C1

Collector / collector terminal

E1

Emitter / emitter terminal

B2

Base / Base Connection

C2

Collector / collector terminal

E2

Emitter / emitter terminal

C3

Collector / collector terminal

B '

basic Rate Interface

C '

collector connection

e '

emitter terminal

D

diode

I

first main page

II

second main page

10

substratum

20

epitaxial layer

Claims (9)

Integrated circuit for detecting ambient light with a phototransistor (T1), wherein - a further transistor (T2) is provided, which is connected to the phototransistor (T1) in Darlington circuit, wherein an internal current feedback from the further transistor (T2) is provided to the phototransistor (T1), - the transistor (T2) has a base terminal (B2), a first main terminal (E2) and a second main terminal (C2) and a further terminal (C3), - for electrical feedback between an electrical connection a base terminal (B1) of the phototransistor (T1) and the further terminal (C3) of the transistor (T2) is provided and - the second main terminal (C2) and the further terminal (C3) of the further transistor (T2) form a current divider, a portion of the signal current flowing at an output (E ') in antiphase is supplied to the base (B1) of the phototransistor (T1). Circuit arrangement according to the preceding claim, wherein one of the main terminals of the phototransistor (T1) is connected to the base terminal (B2) of the second transistor (T2). Ambient light sensor having a first main side (I) layer ( 20 ) of the first conductivity type, in which are integrated: a phototransistor (T1) with a first well (B1) of the second conductivity type adjacent to the first main side (I) and to the first main side (B1) in the first well (B1) I) adjacent first region (E1) of the first conductivity type, and - another transistor (T2) with a second side of the first main side (I) second well (B2) of the second conductivity type and one located in the second trough (B2), to the first main side (I) of the first conductivity type adjacent second region (E2), wherein there is an electrical connection between the first region (E1) and the second well (B2) and in the second well (B2) a third region (C3) Current feedback is provided. Ambient light sensor according to claim 3, wherein the third region (C3) is applied to the main side of the layer (C3). 20 ) adjoins. Ambient light sensor according to claim 3 or 4, wherein the third region (C3) has an electrical connection to the first well. An ambient light sensor according to any one of claims 3 to 5, wherein the third region (C3) is of the first conductivity type. Ambient light sensor according to one of claims 3 to 6, wherein the feedback is adjustable by the distance between the second and third region (E2, C3). An ambient light sensor according to any one of claims 3 to 7, wherein the second and third regions (E2, C3) have a small distance measured in proportion to the width of the second well (B2). Use of the circuit arrangement according to one of claims 1 or 2 as ambient light sensor.

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