CN111108411A

CN111108411A - Optical sensor, time-of-flight-based ranging system and electronic device

Info

Publication number: CN111108411A
Application number: CN201980004445.8A
Authority: CN
Inventors: 杨孟达
Original assignee: Shenzhen Goodix Technology Co Ltd
Current assignee: Shenzhen Goodix Technology Co Ltd
Priority date: 2019-10-10
Filing date: 2019-10-10
Publication date: 2020-05-05
Anticipated expiration: 2039-10-10
Also published as: CN111108411B; WO2021068156A1

Abstract

The invention discloses a sensor, a ranging system based on flight time and an electronic device. The sensor is used for sensing a reflection signal generated by the reflection of a light pulse signal sent by the light pulse generating unit by a target object, the sensor comprises a pixel array and a plurality of pixels, and each pixel (204) in the plurality of pixels comprises: a Photodiode (PD), a first charge output circuit (2041), a second charge output circuit (2042), and a sampling circuit (2043), the sampling circuit comprising: a first capacitor (C1), a sampling switch (MH), and a second capacitor (C2).

Description

Optical sensor, time-of-flight-based ranging system and electronic device

Technical Field

The present invention relates to an optical sensor, and more particularly, to an optical sensor capable of performing a next exposure operation simultaneously with a readout operation, and a time-of-flight based ranging system and an electronic device related thereto.

Background

In the time of flight (TOF) based distance measurement technology, because there is no storage element inside the pixel of the optical sensor, each exposure operation needs to be performed after the previous readout operation is finished, so that the frame rate cannot be increased. Therefore, an innovative light sensor design is needed to address this problem.

Disclosure of Invention

It is an object of the present application to disclose an optical sensor and a related time-of-flight based distance measuring system and electronic device to solve the above problems.

An embodiment of the present application discloses an optical sensor for sensing a reflected signal generated by a light pulse signal transmitted by a light pulse generating unit being reflected by a target object, the optical sensor including: a pixel array comprising a plurality of pixels, each pixel of the plurality of pixels comprising: a photodiode for sensing the reflected signal to generate charge during an exposure operation; a charge output circuit selectively coupled to the photodiode according to a first charge output signal to generate a first sensing voltage; a second charge output circuit selectively coupled to the photodiode according to a second charge output signal to generate a second sensing voltage, wherein the second charge output signal and the first charge output signal have different phases; and a sampling circuit comprising: a first capacitor, a first end of the first capacitor being coupled to the first charge output circuit and the second charge output circuit, a second end of the first capacitor being coupled to a first voltage; the sampling switch is selectively conducted according to the sampling control signal; and a second capacitor, a first end of the second capacitor being selectively coupled to the first charge output circuit, the second charge output circuit and the first end of the first capacitor through the sampling switch, a second end of the second capacitor being coupled to the first voltage.

Another embodiment of the present application discloses a time-of-flight based ranging system, comprising the light sensor and the light pulse generating unit.

Another embodiment of the present application discloses an electronic device comprising the light sensor.

Another embodiment of the present application discloses an electronic device comprising the time-of-flight based ranging system.

The optical sensor and the related ranging system and electronic device based on the flight time can perform the next exposure operation while performing the reading operation, thereby improving the frame rate to solve the above problems.

Drawings

FIG. 1 is a functional block diagram schematic of an embodiment of a time-of-flight based ranging system of the present application.

FIG. 2 is a diagram of an embodiment of one of the pixels in the pixel array.

FIG. 3 is a flow chart of an embodiment of the operation of a pixel of the light sensor of the present application.

Fig. 4 is a schematic diagram of an embodiment of an electronic device according to the present application.

Detailed Description

Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This specification and the preceding claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. Further, the term "coupled" is used herein to include any direct or indirect electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.

The optical sensor and the time-of-flight based distance measuring system and electronic apparatus disclosed in the present application can perform the next exposure operation at the same time when performing the readout operation by the sampling circuit, and the following description is further made.

FIG. 1 is a functional block diagram schematic of an embodiment of a time-of-flight based ranging system of the present application. Time-of-flight based ranging system 100 may be used to detect the distance between object 101 and ranging system 100, noting that the distance between object 101 and ranging system 100 should be less than or equal to the maximum measured distance of ranging system 100. By way of example, and not limitation, the ranging system 100 may be a three-dimensional imaging system that may employ time-of-flight to measure the distance to surrounding targets to obtain depth of field and three-dimensional image information. In this embodiment, ranging system 100 may be implemented as a time-of-flight based optical ranging system.

The ranging system 100 may include, but is not limited to, a light pulse generating unit 102 and a light sensor 103. The light pulse generating unit 102 may be implemented by a light emitting unit to generate the light pulse signal EL. The optical pulse signal EL may comprise a plurality of optical pulses. The optical pulse generating unit 102 may be, but is not limited to, a Laser Diode (LD), a Light Emitting Diode (LED), or other light emitting unit capable of generating optical pulses. Specifically, the optical pulse signal EL generated by the optical pulse generating unit 102 may include optical pulses with different phases, and in this embodiment, the optical pulse signal EL generated by the optical pulse generating unit 102 sequentially includes N optical pulses with a first phase, N optical pulses with a second phase, N optical pulses with a third phase, and N optical pulses with a fourth phase, and repeatedly cycles, where N is an integer greater than 0. In one embodiment, the first phase is 0 degrees, the second phase is 90 degrees, the second phase is 180 degrees, and the third phase is 270 degrees.

The optical sensor 103 is used for sampling a reflection signal RL generated by the target 101 reflecting the optical pulse signal EL to detect a distance between the ranging system 100 (or the time-of-flight optical sensor 130) and the target 101. Specifically, the light sensor 103 performs an exposure operation, a sampling operation, and a readout operation for every N light pulse signals EL having the first phase, the second phase, the third phase, and the fourth phase, which will be described in detail below.

The light sensor 103 includes, but is not limited to, a pixel array 104 and a read circuit 105. The pixel array 104 includes a plurality of pixels (not shown in fig. 1), the readout circuit 105 is coupled to the pixel array 104, and in the present embodiment, the readout circuit 105 may include an amplifier 106, an analog-to-digital converter 108, and an operational circuit 110. FIG. 2 is a diagram of an embodiment of one of the pixels in the ith row in the pixel array 104. As shown in fig. 2, the photodiode PD of the pixel 204 is used to sense the reflection signal RL to generate electric charges during the exposure operation.

The first charge output circuit 2041 of the pixel 204 is configured to control the switch MT1 according to the first charge output signal TX1 to selectively couple the first charge output circuit 2041 to the photodiode PD, and when the first charge output signal TX1 controls the switch MT1 to be turned on, charges of the photodiode PD flow into the floating diffusion region FDN1 of the first charge output circuit 2041, and are driven by the source follower transistor MF1 to generate the first sensing voltage at the source output SFO1 of the source follower transistor MF 1. The switch MT1 is coupled between the gate of the source follower transistor MF1 and the photodiode PD. The first charge output circuit 2041 further includes a reset transistor MR1 and a select transistor MS1, a source of the reset transistor MR1 is coupled to the gate of the source follower transistor MF1, the reset transistor MR1 selectively resets the floating diffusion FDN1 and the source output SFO1 of the first charge output circuit 2041 according to a reset signal R1 to reset the first sensing voltage, drains of the reset transistor MR1 and the source follower transistor MF1 are both coupled to the second voltage V2, a drain of the select transistor MS1 is coupled to the drain of the source follower transistor MF1, a drain of the select transistor MS1 is coupled to the sampling circuit 2043, and the select transistor MS1 selectively transfers the source output SFO1, i.e., the first sensing voltage, to the sampling circuit 2043 according to a first select control signal FD 1.

The second charge output circuit 2042 of the pixel 204 is configured to control the switch MT2 according to the second charge output signal TX2 to selectively couple the second charge output circuit 2042 to the photodiode PD, and when the second charge output signal TX2 controls the switch MT2 to be turned on, charges of the photodiode PD flow into the floating diffusion region FDN2 of the second charge output circuit 2042, and are driven by the source follower transistor MF2 to generate the second sensing voltage at the source output SFO2 of the source follower transistor MF 2. The switch MT2 is coupled between the gate of the source follower transistor MF2 and the photodiode PD. The second charge output circuit 2042 further includes a reset transistor MR2 and a select transistor MS2, a source of the reset transistor MR2 is coupled to the gate of the source follower transistor MF2, the reset transistor MR2 selectively resets the floating diffusion region FDN2 and the source output SFO2 of the second charge output circuit 2042 according to a reset signal R2 to reset the second sensing voltage, and drains of the reset transistor MR2 and the source follower transistor MF2 are both coupled to the second voltage V2. The drain of the select transistor MS2 is coupled to the drain of the source follower transistor MF2, the drain of the select transistor MS2 is coupled to the sampling circuit 2043, and the select transistor MS2 selectively transmits the source output SFO1, i.e., the second sensing voltage, to the sampling circuit 2043 according to the second select control signal FD 2.

Wherein the second charge output signal TX2 and the first charge output signal TX1 are turned on at different times, for example, the second charge output signal TX2 and the first charge output signal TX1 have different phases, for example, the second charge output signal TX2 and the first charge output signal TX1 are 180 degrees out of phase.

In the present embodiment, the pixel 204 may further include a first reset transistor MP, but the present application is not limited thereto, the first reset transistor MP is coupled between the photodiode PD and the second voltage V2, and the first reset transistor MP is used for selectively resetting the photodiode PD according to a reset signal TXB to reduce the chance of accumulating the charges generated by the non-reflected signal RL.

The sampling circuit 2043 of the pixel 204 includes a bias transistor MV, a first capacitor C1, a second capacitor C2, a sampling switch MH, a source follower transistor MF, and a row select transistor MS. The sampling circuit 2043 is used for storing the first sensing voltage and the second sensing voltage in the second capacitor C2 and the first capacitor C1 during a sampling operation. The drain of the bias transistor MV is coupled to the source of the select transistor MS1 and the source of the select transistor MS2 and to a first terminal of the first capacitor C1. The source of the bias transistor MV is coupled to the first voltage V1, and the bias transistor MV is selectively turned on according to the bias signal VB to provide a current to the sampling circuit 2043. The second terminal of the first capacitor C1 is coupled to the first voltage and the source of the sampling switch MH, the drain of the sampling switch MH is coupled to the first terminal of the second capacitor C2, and the second terminal of the second capacitor C2 is coupled to the first voltage V1. The sampling switch MH is selectively turned on according to the sampling control signal SH, such that the first terminal of the second capacitor C2 is selectively coupled to one of the drains of the selection transistor MS1 or the selection transistor MS 2.

The sampling circuit 2043 further includes a source follower transistor MF and a row selection transistor MS, a gate of the source follower transistor MF is coupled to the first terminal of the second capacitor C2, a drain of the source follower transistor MF is coupled to the second voltage V2, a drain of the source follower transistor MF is coupled to a drain of the row selection transistor MS, and the row selection transistor MS is selectively turned on according to the row selection signal S.

In the embodiment, the transistors are all N-type transistors, and the second voltage V2 is greater than the first voltage V1, i.e., the polarities of all the transistors in the pixel 204 are the same in the embodiment of fig. 2. However, the present application is not limited thereto, and in some embodiments, the transistors in the pixel 204 may be P-type transistors, and the magnitude relationship between the first voltage V1 and the second voltage V2 may be adjusted correspondingly. In some embodiments, the transistors in the pixel 204 may have both N-type transistors and P-type transistors.

Fig. 3 is a flow chart of an embodiment of the operation of the pixel 204 of the light sensor 103 of the present application. As shown in fig. 3, at the beginning of the exposure operation, the reset signal R1 and the reset signal R2 cause the source output SFO1 (i.e., the first sensing voltage) of the first charge output circuit 2041 and the source output SFO2 (i.e., the second sensing voltage) of the second charge output circuit 2042 to be reset, and then, in the remaining exposure operation, the light pulse signal EL of the light pulse generating unit 110 will include N light pulses, and the first and second charge output signals TX1 and TX2 respectively turn on the switch MT1 and the switch MT2 corresponding to each of the N optical pulses, to introduce the charges of the photodiode PD by the reflection signal RL into the first charge output circuit 2041 and the second charge output circuit 2042, and are accumulated into the first sensing voltage and the second sensing voltage, that is, N light pulses correspond to N first charge output signals TX1 and N second charge output signals TX 1. In this embodiment, the switch MT2 is turned on after the switch MT1, and the switch MT1 and the switch MT2 are not turned on simultaneously, or the on-times of the switch MT1 and the switch MT2 are staggered.

The reset signal TXB resets the photodiode PD at a time other than when the first and second charge output signals TX1 and TX2 turn on the switches MT1 and MT2, so as to reduce the chance of accumulating the charges generated by the non-reflected signal RL. During the exposure operation, the bias transistor MV is turned off by the bias signal VB in the sampling circuit 2043, and the sampling circuit 2043 does not perform sampling. Then, in the sampling operation, the bias signal VB turns on the bias transistor MV, the first selection control signal FD1 turns on the selection transistor MS1, and the sampling control signal SH _ i (SH _ i represents the sampling control signal SH of the ith row) turns on the sampling switch MH, so that the first sensing voltage can be output to the first capacitor C1 and the second capacitor C2, and the first capacitor C1 and the second capacitor C2 both have the first sensing voltage. Then, the second selection control signal FD2 turns on the selection transistor MS2, and the sampling control signal SH _ i turns off the sampling switch MH, so that the second sensing voltage is outputted to the first capacitor C1 and not to the second capacitor C2, only the first capacitor C1 has the second sensing voltage, and the second capacitor C2 holds the first sensing voltage.

In the readout operation, the bias transistor MV is first turned off by the bias signal VB, and then the row selection transistor MS is turned on by the row selection signal S, so as to read out the first sensing voltage from the second capacitor C2 to the reading circuit 105. Next, the sampling control signal SH _ i is turned on, and since the selection transistor MS1 and the selection transistor MS2 are not turned on by the first selection control signal FD1 and the second selection control signal FD2, the voltages of the first capacitor C1 and the second capacitor C2 are balanced to an average value of the first sensing voltage and the second sensing voltage and are read out to the reading circuit 105.

In this embodiment, the sensing results of each row of pixels of the pixel array 104 are read out in a row-by-row manner during the readout operation, and therefore, fig. 3 illustrates the sampling control signal SH _ i +1 of the i +1 th row and the sampling control signal SH _ i +2 of the i +2 th row, which are only exemplary, so the sampling control signals of the remaining rows are not shown in fig. 3. Since each column of pixels shares one readout circuit 105, the operation of controlling the outputs of the first capacitor C1 and the second capacitor C2 by the sampling control signal of each row cannot be performed simultaneously, that is, the sampling control signal SH _ i of the ith row, the sampling control signal SH _ i +1 of the ith +1 th row, the sampling control signal SH _ i +2 of the ith +2 th row, and the sampling control signals of the other rows are staggered, and the time point when the sampling control signal of each row makes the sampling switch MH end to be turned on and the time point when the sampling control signal of the next row makes the sampling switch MH start to be turned on are at least separated by a time long enough for the first sensing voltage to be output.

As shown in fig. 3, since the sampling circuit 2043 temporarily stores the first sensing voltage and the second sensing voltage, the readout operation is not affected by the next exposure operation, so that the readout operation can be performed simultaneously with the next exposure operation, in other words, the exposure operation can also be performed simultaneously with the previous readout operation. Additional read-out operation time may be saved as compared to the operation of conventional photosensors.

After the reading circuit 105 reads out the first sensing voltage and the average value of the first sensing voltage and the second sensing voltage from the second capacitor C2 successively, a reading result is generated in response to the difference between the first sensing voltage and the average value of the first sensing voltage and the second sensing voltage, i.e. the first sensing voltage- (the first sensing voltage + the second sensing voltage)/2, i.e. (the first sensing voltage-the second sensing voltage)/2. Referring to fig. 1, the reading circuit 105 includes an amplifier 106, an analog-to-digital converter 108, and an operation unit 110. In this embodiment, the amplifier 106 may be configured to enhance the reading of the first sensing voltage and the average value of the first sensing voltage and the second sensing voltage sequentially, the analog-to-digital converter 108 is configured to perform analog-to-digital conversion on the first sensing voltage enhanced by the amplifier 106 and the average value of the first sensing voltage and the second sensing voltage, and the operation unit 110 is configured to perform a difference operation on the enhanced first sensing voltage and the average value of the first sensing voltage and the second sensing voltage after analog-to-digital conversion.

Fig. 4 is a schematic diagram of an embodiment of an electronic device according to the present application. Electronic device 400 is configured to perform ranging, and electronic device 400 includes time-of-flight based ranging system 100, in some embodiments. The electronic device 400 may be any electronic device such as a smart phone, a personal digital assistant, a handheld computer system, or a tablet computer.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An optical sensor for sensing a reflected signal generated by a light pulse signal transmitted from a light pulse generating unit being reflected by a target object, the optical sensor comprising:

a pixel array comprising a plurality of pixels, each pixel of the plurality of pixels comprising:

a photodiode for sensing the reflection signal to generate charge during an exposure operation;

a first charge output circuit selectively coupled to the photodiode according to a first charge output signal to generate a first sensing voltage;

a second charge output circuit selectively coupled to the photodiode according to a second charge output signal to generate a second sensing voltage, wherein the second charge output signal and the first charge output signal have different phases; and

a sampling circuit, comprising:

a first capacitor, a first end of the first capacitor being coupled to the first charge output circuit and the second charge output circuit, a second end of the first capacitor being coupled to a first voltage;

the sampling switch is selectively conducted according to the sampling control signal; and

a second capacitor, a first end of the second capacitor being selectively coupled to the first charge output circuit, the second charge output circuit and the first end of the first capacitor through the sampling switch, a second end of the second capacitor being coupled to the first voltage.

2. The light sensor of claim 1, wherein during a sampling operation, the voltage of the second capacitance is the first sensing voltage and the voltage of the first capacitance is the second sensing voltage.

3. The light sensor of claim 2, wherein the first charge output circuit and the second charge output circuit each comprise a select transistor, the select transistor of the first charge output circuit selectively coupling the first sense voltage to the sampling circuit in accordance with a first select control signal; the select transistor of the second charge output circuit selectively couples the second sense voltage to the sampling circuit in accordance with a second select control signal.

4. The photosensor of claim 3, wherein in the sampling operation, the select transistor of the first charge output circuit is conductive, the select transistor of the second charge output circuit is non-conductive, and the sampling switch is conductive, such that the first capacitance and the second capacitance both have the first sensing voltage.

5. The light sensor of claim 4, wherein during the sampling operation, when the first capacitance and the second capacitance both have the first sensing voltage, the select transistor of the first charge output circuit is non-conductive, the select transistor of the second charge output circuit is conductive, and the sampling switch is non-conductive, causing the first capacitance to have the second sensing voltage.

6. The light sensor of claim 5, wherein the sampling circuit further comprises a row select transistor for outputting the first sensing voltage during a readout operation.

7. The light sensor of claim 6, wherein in the readout operation, when the first and second capacitances have the second and first sensing voltages, respectively, the sampling switch is turned on so that the first and second capacitances each have an average of the first and second sensing voltages.

8. The light sensor of claim 7, wherein the row select transistor of the sampling circuit is further configured to output an average of the first sensing voltage and the second sensing voltage during the readout operation.

9. The light sensor of claim 8, wherein the first charge output circuit and the second charge output circuit each further comprise:

a switch for selectively turning on according to the first charge output signal; and

a source follower transistor having a gate selectively coupled to the photodiode through the switch, a source/drain of the source follower transistor being selectively coupled to the sampling circuit through the selection transistor.

10. The light sensor of claim 1, wherein each of the plurality of pixels further comprises a first reset transistor coupled between the photodiode and a second voltage for selectively resetting the photodiode.

11. The light sensor of claim 9, wherein the sampling circuit further comprises:

a source follower transistor having a gate coupled to the first terminal of the second capacitor.

12. The light sensor of claim 2, wherein the light sensor further comprises:

a reading circuit coupled to the pixel array for generating a reading result in response to the first sensing voltage and a difference between average values of the first sensing voltage and the second sensing voltage in the readout operation.

13. The photosensor of claim 1, wherein the first charge output signal and the second charge output signal are 180 degrees out of phase.

14. A time-of-flight based ranging system, comprising:

the light sensor of any one of claims 1-13; and

the light pulse generating unit.

15. An electronic device, comprising:

the light sensor of any one of claims 1-13.

16. An electronic device, comprising:

the time-of-flight based ranging system of claim 14.