CN116013942A

CN116013942A - Dark current eliminating circuit and visible light sensor

Info

Publication number: CN116013942A
Application number: CN202211588099.2A
Authority: CN
Inventors: 童红杰; 徐建
Original assignee: Ningbo Aixin Microelectronics Co ltd
Current assignee: Ningbo Aixin Microelectronics Co ltd
Priority date: 2022-12-12
Filing date: 2022-12-12
Publication date: 2023-04-25

Abstract

The invention discloses a dark current eliminating circuit, which relates to the technical field of integrated circuits and comprises an MOS tube and a current amplifier, wherein the grid electrode of the MOS tube, the source electrode of the MOS tube and a power supply VDD are connected, and the drain electrode of the MOS tube is connected with the current amplifier as output; the invention also discloses a visible light sensor, which comprises a photosensitive circuit, N-level current amplifying circuits, N dark current counteracting circuits, wherein N is a positive integer greater than or equal to 2, the output end of each level of current amplifying circuit is connected with one dark current counteracting circuit, and the photosensitive circuit and the N-level current amplifying circuits are sequentially connected in series. The invention not only reduces the influence of dark current from the input end, but also eliminates the dark current generated by the circuit step by step in the current amplifying circuit, so that the integral output dark current is far smaller than the initial design, and the static power consumption of the visible light sensor is reduced.

Description

Dark current eliminating circuit and visible light sensor

Technical Field

The present invention relates to the field of integrated circuits, and more particularly, to a dark current eliminating circuit and a visible light sensor.

Background

The visible light sensor is a device that uses visible light as a detection target and converts the visible light into an output electric signal. The visible light sensor is one of the sensors with the highest yield and the highest application at present, and most of visible light sensor products of companies mainly comprise photoresistors, phototriodes, CMOS linear visible light sensors and the like. The visible light sensor can be classified into a middle-low end sensor and a high-end sensor according to the technical content, in the middle-low end sensor, the comprehensive performance of the phototriode is generally superior to that of the photoresistor, and under the influence of factors such as performance, application range and the like, the phototriode gradually replaces the photoresistor by virtue of the good comprehensive performance to become a trend. The high-end sensor is represented by a CMOS linear visible light sensor, adopts a standard semiconductor manufacturing process, integrates a photocurrent amplifier internally, has simple peripheral circuits, can save the manufacturing cost of terminal products, has the advantages of wide backlight adjustment and energy-saving control and the like because of the characteristics of small dark current, high sensitivity, low illumination intensity response, linear change of current along with the enhancement of illumination intensity and the like, is widely applied to products such as televisions, computer monitors, LED backlight, smart phones and the like, and is an important development direction in the future of the visible light sensor.

Existing CMOS linear visible light sensors are capable of providing a linear output current proportional to the intensity of illumination. An optical filter and a current amplifier are built in, and the optical filter and the current amplifier have corresponding characteristics to the visible spectrum, and the response characteristics approximate to the characteristics of human eyes. The visible light sensor circuit converts the output current into voltage by connecting a resistor in series externally, and the dynamic range of luminous flux is determined by the external resistor and a power supply. The dark current of the visible light sensor is extremely small, and thus can provide an output current with high accuracy over the entire temperature range even at low light intensity. Under ideal conditions, no current flows if the MOS transistor in the visible light sensor circuit is turned off. However, two PN junctions are arranged between the drain electrode and the source electrode of the MOS transistor and the substrate, and even if the MOS transistor has no channel, a reverse saturation current exists between the drain electrode and the source electrode, which is called leakage current, and is also called dark current. Due to leakage current, the static power consumption of the whole circuit can be increased. Due to the existence of the gain effect, dark current can be amplified sharply in the voltage rising process, and the dark current has a serious interference effect on signal current.

The patent of 'a photoelectric detector, a dark current suppression circuit and a visible light sensor' (application number: CN 201620159024.6) discloses a photoelectric detector, a dark current suppression circuit and a visible light sensor, wherein an NG injection area is added in a PN junction structure, so that dark current is reduced, photoelectric conversion efficiency is improved, and a visible light sensor with high sensitivity and high linearity is obtained. However, the patent only can offset the dark current from the input photodiode, and cannot eliminate the reverse saturated current (i.e., dark current) between the drain and source of the output MOS transistor, so that the effect of improving the sensitivity is limited.

Accordingly, those skilled in the art have been working to develop a visible light sensor based on a dark current cancellation circuit.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, the present invention aims to solve the technical problem of eliminating the dark current generated by the MOS transistor as the input end in the amplifying circuit of the visible light sensor, so as to achieve the purpose of reducing the final output dark current and reducing the static power consumption.

The inventor finds that, to eliminate the dark current generated by the input MOS tube, only the dark current generated by the amplifying circuit is needed to be eliminated at the tail end of the current amplifying circuit of the visible light sensor, so that the dark current generated by the current amplifying circuit of the visible light sensor can be further eliminated, and the sensitivity of the chip is greatly improved.

In one embodiment of the invention, a dark current eliminating circuit is provided, which comprises an MOS tube and a current amplifier, wherein the grid electrode of the MOS tube, the source electrode of the MOS tube and a power supply VDD are connected, and the drain electrode of the MOS tube is connected with the current amplifier as output;

the source electrode of the MOS tube is in short circuit with the grid electrode of the MOS tube, the grid source voltage of the MOS tube is equal to 0, the MOS tube is in an cut-off state, the MOS tube only generates dark current, the dark current is output to the current amplifier through the drain electrode of the MOS tube, and the current amplifier amplifies the dark current.

Optionally, in the dark current eliminating circuit in the above embodiment, the MOS transistor is a PMOS.

Optionally, in the dark current eliminating circuit in any of the above embodiments, an amplification factor of the current amplifier is adjustable.

Based on any one of the above embodiments, in another embodiment of the present invention, a visible light sensor is provided, including a photosensitive circuit, N-stage current amplifying circuits, N dark current canceling circuits, N being a positive integer greater than or equal to 2, an output end of each stage of the current amplifying circuits of each stage being connected to one dark current canceling circuit, and an amplification factor of each stage of the current amplifying circuits of each stage being the same as an amplification factor of a current amplifier in a corresponding dark current canceling circuit; the photosensitive circuit and the N-level current amplifying circuit are sequentially connected in series;

the photosensitive circuit in the visible light sensor eliminates dark current generated by the input end at the input end, the photocurrent generated by the visible light sensor circuit enters the N-level current amplifying circuit to be amplified and output, the dark current canceling circuit cancels the dark current of the corresponding current amplifying circuit, and finally the amplified photocurrent is output.

Preferably, in the visible light sensor of the above embodiment, N takes a value of 2.

Optionally, in the visible light sensor of any one of the embodiments, the photosensitive circuit includes PMOS1, PMOS2, a photodiode VD1 and a photodiode VD2, where the exposure of the photodiode VD1 is responsible for sensing the illumination intensity of the external environment, the photodiode VD2 is covered by the light shielding layer and is always in a non-illuminated environment, only the dark current is generated, and the dark current generated by the photodiode VD1 is offset with the dark current generated by the photodiode VD2, so as to achieve the purpose of eliminating the input dark current; the anode of the photodiode VD1 is grounded, the cathode of the photodiode VD1 is connected with the grid electrode of the PMOS1 and the drain electrode of the PMOS1, and the source electrode of the PMOS1 is connected with the power supply VDD; the grid electrode of the PMOS2 is connected with the grid electrode of the PMOS1, the source electrode of the PMOS2 is connected with the power supply VDD, the drain electrode of the PMOS2 is connected with the cathode of the photodiode VD2, the anode of the photodiode VD2 is grounded, and photocurrent is output from between the drain electrode of the PMOS2 and the cathode of the photodiode VD 2.

Further, in the visible light sensor of the above embodiment, the area of the photodiode VD1 is the same as the area of the photodiode VD 2.

Optionally, in the visible light sensor of any one of the embodiments above, the current amplifying circuit of each stage includes 1 PMOS current mirror and 1 NMOS current mirror, the PMOS current mirror includes PMOS3 and PMOS4, and the NMOS current mirror includes NMOS1 and NMOS2; the drain electrode of the PMOS3 is used as the input end of the current amplifying circuit and is connected with the grid electrode of the PMOS3, and the source electrode of the PMOS3 is connected with the power supply VDD; the grid electrode of the PMOS4 is connected with the grid electrode of the PMOS3, the source electrode of the PMOS4 is connected with the power supply VDD, and the drain electrode of the PMOS4 is connected with the drain electrode of the NMOS1 in series; the drain electrode of the NMOS1 is connected with the grid electrode of the NMOS1, and the source electrode of the NMOS1 is grounded; the grid of the NMOS2 is connected with the grid of the NMOS1, the source electrode of the NMOS2 is grounded, and the drain electrode of the NMOS2 outputs current.

Further, in the visible light sensor of the above embodiment, the PMOS current mirror changes the ratio of the widths of PMOS3 and PMOS4 in the case that the PMOS3 and PMOS4 are the same in length, and the amplification factor of the PMOS current mirror is the ratio of the widths of PMOS4 and PMOS 3.

Further, in the visible light sensor of the above embodiment, when the NMOS current mirror is the same in length as the NMOS1 and the NMOS2, the ratio of the widths of the NMOS1 and the NMOS2 is changed, and the amplification factor of the NMOS current mirror is the ratio of the widths of the NMOS2 and the NMOS 1.

Further, in the visible light sensor of the above embodiment, the amplification factor of the current amplifying circuit of each stage is a product of the PMOS current mirror and the NMOS current mirror amplification factor.

Further, in the visible light sensor of the above embodiment, the total amplification factor of the N-stage current amplification circuits is the product of the amplification factors of the current amplification circuits of each stage.

Alternatively, in the visible light sensor of any of the above embodiments, the structure and composition of the current amplifying circuit of each of the N stages of the current amplifying circuits are the same.

Alternatively, in the visible light sensor in any of the above embodiments, the length and width of the PMOS in the dark current canceling circuit are the same as the length and width of the PMOS3 in the current amplifying circuit to which it is connected.

The invention improves the circuit of the visible light sensor in the prior art, increases the design of eliminating the dark current, not only reduces the influence of the dark current from the input end, but also eliminates the dark current generated by the circuit step by step in the current amplifying circuit, so that the integral output dark current is far smaller than the initial design, and reduces the static power consumption of the visible light sensor. The current eliminating circuit can be flexibly increased and decreased along with the increase and decrease of the current amplification stage number, so that the actual application of the circuit is more flexible.

The conception, specific structure, and technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, features, and effects of the present invention.

Drawings

Fig. 1 is a schematic diagram illustrating a structure of a dark current eliminating circuit according to an exemplary embodiment;

fig. 2 is a schematic diagram illustrating a structure of a visible light sensor according to an exemplary embodiment;

fig. 3 is a schematic diagram illustrating a structure of a photosensitive circuit according to an exemplary embodiment

Fig. 4 is a schematic diagram illustrating a structure of a current amplifying circuit according to an exemplary embodiment.

Detailed Description

The following description of the preferred embodiments of the present invention refers to the accompanying drawings, which make the technical contents thereof more clear and easy to understand. The present invention may be embodied in many different forms of embodiments and the scope of the present invention is not limited to only the embodiments described herein.

In the drawings, like structural elements are referred to by like reference numerals and components having similar structure or function are referred to by like reference numerals. The dimensions and thickness of each component shown in the drawings are arbitrarily shown, and the present invention is not limited to the dimensions and thickness of each component. The thickness of the components is schematically and appropriately exaggerated in some places in the drawings for clarity of illustration.

The inventor designs a dark current eliminating circuit, as shown in figure 1, which comprises an MOS tube and a current amplifier, wherein the grid electrode of the MOS tube, the source electrode of the MOS tube and a power supply VDD are connected, and the drain electrode of the MOS tube is connected with the current amplifier as output; the source electrode of the MOS tube is in short circuit with the grid electrode of the MOS tube, the grid source voltage of the MOS tube is equal to 0, the MOS tube is in an cut-off state, the MOS tube only generates dark current, the dark current is output to the current amplifier through the drain electrode of the MOS tube, and the current amplifier amplifies the dark current; the MOS tube adopts PMOS, and the amplification factor of the current amplifier is adjustable.

Based on any one of the above embodiments, in another embodiment of the present invention, there is provided a visible light sensor, as shown in fig. 2, including a light sensing circuit, N-stage current amplifying circuits, N dark current canceling circuits, preferably n=2, specifically, 2-stage current amplifying circuits including a current amplifying circuit 1 and a current amplifying circuit 2, and 2 dark current canceling circuits including a dark current canceling circuit 1 and a dark current canceling circuit 2; the output end of the current amplifying circuit of each stage is connected with a dark current counteracting circuit, the amplification factor of the current amplifying circuit of each stage is the same as that of a current amplifier in the corresponding dark current counteracting circuit, namely, the output end of the current amplifying circuit 1 is connected with the dark current counteracting circuit 1, the amplification factor of the current amplifying circuit 1 is the same as that of the current amplifier in the dark current counteracting circuit 1, the output end of the current amplifying circuit 2 is connected with the dark current counteracting circuit 2, the amplification factor of the current amplifying circuit 2 is the same as that of the current amplifier in the dark current counteracting circuit 2, and the photosensitive circuit, the current amplifying circuit 1 and the current amplifying circuit 2 are sequentially connected in series;

as shown in fig. 3, the photosensitive circuit includes PMOS1, PMOS2, photodiode VD1 and photodiode VD2, where the exposure of photodiode VD1 is responsible for sensing the illumination intensity of the external environment, and the coverage of photodiode VD2 by the light shielding layer is always in a non-illuminated environment, so that only the dark current is generated, and the dark current generated by photodiode VD1 is offset with the dark current generated by photodiode VD2, so as to achieve the purpose of eliminating the input dark current; the anode of the photodiode VD1 is grounded, the cathode of the photodiode VD1 is connected with the grid electrode of the PMOS1 and the drain electrode of the PMOS1, and the source electrode of the PMOS1 is connected with the power supply VDD; the grid electrode of the PMOS2 is connected with the grid electrode of the PMOS1, the source electrode of the PMOS2 is connected with the power supply VDD, the drain electrode of the PMOS2 is connected with the cathode of the photodiode VD2, the anode of the photodiode VD2 is grounded, and photocurrent is output from between the drain electrode of the PMOS2 and the cathode of the photodiode VD 2; the area of the photodiode VD1 is the same as that of the photodiode VD 2;

as shown in fig. 4, the current amplifying circuits of each stage of the 2-stage current amplifying circuit have the same structure and composition, that is, the current amplifying circuit 1 and the current amplifying circuit 2 have the same structure and composition, the current amplifying circuit 1 comprises 1 PMOS current mirror and 1 NMOS current mirror, the PMOS current mirror comprises PMOS3 and PMOS4, and the NMOS current mirror comprises NMOS1 and NMOS2; the drain electrode of the PMOS3 is used as the input end of the current amplifying circuit and is connected with the grid electrode of the PMOS3, and the source electrode of the PMOS3 is connected with the power supply VDD; the grid electrode of the PMOS4 is connected with the grid electrode of the PMOS3, the source electrode of the PMOS4 is connected with the power supply VDD, and the drain electrode of the PMOS4 is connected with the drain electrode of the NMOS1 in series; the drain electrode of the NMOS1 is connected with the grid electrode of the NMOS1, and the source electrode of the NMOS1 is grounded; the grid electrode of the NMOS2 is connected with the grid electrode of the NMOS1, the source electrode of the NMOS2 is grounded, and the drain electrode of the NMOS2 outputs current; under the condition that the length of the PMOS3 is the same as that of the PMOS4, changing the width ratio of the PMOS3 to the PMOS4, wherein the amplification factor of the PMOS current mirror is the width ratio of the PMOS4 to the PMOS 3; under the condition that the length of the NMOS1 is the same as that of the NMOS2, the NMOS current mirror changes the width ratio of the NMOS1 to the NMOS2, and the amplification factor of the NMOS current mirror is the width ratio of the NMOS2 to the NMOS 1; the amplification factor of the current amplification circuit 1 is the product of the amplification factors of the PMOS current mirror and the NMOS current mirror, and the total amplification factor of the 2-stage current amplification circuit is the product of the amplification factors of the current amplification circuits of each stage, namely the product of the amplification factors of the current amplification circuit 1 and the current amplification circuit 2;

the length and width of the PMOS in the dark current canceling circuit are the same as the length and width of the PMOS3 in the current amplifying circuit connected thereto, i.e., the length and width of the PMOS in the dark current canceling circuit 1 are the same as the length and width of the PMOS3 in the current amplifying circuit 1 connected thereto, and the length and width of the PMOS in the dark current canceling circuit 2 are the same as the length and width of the PMOS3 in the current amplifying circuit 2 connected thereto;

the photosensitive circuit in the visible light sensor eliminates dark current generated by the input end at the input end, the photocurrent output by the photosensitive circuit enters the current amplifying circuit 1 and the current amplifying circuit 2 to be amplified and output, the dark current canceling circuit cancels the dark current of the corresponding current amplifying circuit, namely, the dark current canceling circuit 1 cancels the dark current of the current amplifying circuit 1, the dark current canceling circuit 2 cancels the dark current of the current amplifying circuit 2, and finally, the amplified photocurrent is output.

The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.

Claims

1. The dark current eliminating circuit is characterized by comprising an MOS tube and a current amplifier, wherein the grid electrode of the MOS tube, the source electrode of the MOS tube and a power supply VDD are connected, and the drain electrode of the MOS tube is connected with the current amplifier as output;

2. The dark current elimination circuit of claim 1, wherein said MOS transistor is PMOS.

3. The dark current cancellation circuit of claim 2, wherein the current amplifier is adjustable in amplification factor.

4. A visible light sensor using the dark current eliminating circuit according to any one of claims 1 to 3, comprising a photosensitive circuit, N stages of current amplifying circuits, N being a positive integer greater than or equal to 2, an output end of the current amplifying circuit of each stage being connected to one of the dark current eliminating circuits, and a magnification factor of the current amplifying circuit of each stage being the same as that of the current amplifier in the corresponding dark current eliminating circuit; the photosensitive circuit and the N-level current amplifying circuit are sequentially connected in series;

the visible light sensor circuit eliminates the dark current generated by the visible light sensor circuit to offset, eliminates the input dark current, the photocurrent generated by the visible light sensor circuit enters the N-level current amplifying circuit to be amplified and output, the dark current offset circuit offsets the dark current of the corresponding current amplifying circuit, and finally outputs the amplified photocurrent.

5. The visible light sensor of claim 4, wherein N has a value of 2.

6. The visible light sensor as claimed in claim 4, wherein the photosensitive circuit comprises a PMOS1, a PMOS2, a photodiode VD1 and a photodiode VD2, wherein the exposure of the photodiode VD1 is responsible for sensing the illumination intensity of the external environment, the photodiode VD2 is covered by a light shielding layer and is always in a non-illuminated environment, only generates the dark current, and the dark current generated by the photodiode VD1 and the dark current generated by the photodiode VD2 are offset to achieve the purpose of eliminating the input dark current; the anode of the photodiode VD1 is grounded, the cathode of the photodiode VD1 is connected with the grid electrode of the PMOS1 and the drain electrode of the PMOS1, and the source electrode of the PMOS1 is connected with the power supply VDD; the grid electrode of the PMOS2 is connected with the grid electrode of the PMOS1, the source electrode of the PMOS2 is connected with the power supply VDD, the drain electrode of the PMOS2 is connected with the cathode of the photodiode VD2, the anode of the photodiode VD2 is grounded, and photocurrent is output from between the drain electrode of the PMOS2 and the cathode of the photodiode VD 2.

7. The visible light sensor of claim 6, wherein the area of the photodiode VD1 is the same as the area of the photodiode VD 2.

8. The visible light sensor of claim 4, wherein the current amplifying circuit of each stage comprises 1 PMOS current mirror and 1 NMOS current mirror, the PMOS current mirrors comprising PMOS3 and PMOS4, the NMOS current mirrors comprising NMOS1 and NMOS2; the drain electrode of the PMOS3 is used as the input end of the current amplifying circuit and is connected with the grid electrode of the PMOS3, and the source electrode of the PMOS3 is connected with the power supply VDD; the grid electrode of the PMOS4 is connected with the grid electrode of the PMOS3, the source electrode of the PMOS4 is connected with the power supply VDD, and the drain electrode of the PMOS4 is connected with the drain electrode of the NMOS1 in series; the drain electrode of the NMOS1 is connected with the grid electrode of the NMOS1, and the source electrode of the NMOS1 is grounded; the grid electrode of the NMOS2 is connected with the grid electrode of the NMOS1, the source electrode of the NMOS2 is grounded, and the drain electrode of the NMOS2 outputs current.

9. The visible light sensor of claim 4, wherein the current amplifying circuits of each of the N stages are identical in structure and composition.

10. The visible light sensor of claim 9, wherein the length and width of PMOS in the dark current canceling circuit are the same as the length and width of PMOS3 in the current amplifying circuit to which it is connected.