CN115396607A - TOF imaging 2-tap pixel modulation resolving method - Google Patents
TOF imaging 2-tap pixel modulation resolving method Download PDFInfo
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Abstract
The invention relates to the technical field of TOF three-dimensional imaging, and aims to provide a TOF three-dimensional imaging modulation method based on a 2-tap pixel structure and a resolving method aiming at the modulation method, so that the problem of background light interference is solved, and meanwhile, new power consumption is not introduced, the invention provides the TOF imaging 2-tap pixel modulation resolving method, emitted light is continuous square wave pulse with a duty ratio of 50%, the emitted light is irradiated to an object to return, and pixels need two frames of integration to complete 4-phase information acquisition; when a modulation signal applied to a specific tap is in a high level, photo-generated charges generated by integration in a photosensitive area of the pixel are transferred to the tap, and a charge signal in the tap is converted into a voltage signal in a reading-out stage for reading. The invention is mainly applied to TOF three-dimensional imaging occasions.
Description
Technical Field
The invention relates to the technical field of TOF three-dimensional imaging, in particular to a modulation calculation method for improving TOF three-dimensional imaging precision.
Background
TOF three-dimensional imaging refers to a technology of non-contact ranging imaging by a Time of flight (TOF), and an imaging device of the TOF three-dimensional imaging mainly comprises an active light source and a TOF image sensor which are matched with a chip. The principle of TOF three-dimensional imaging is that an active light source emits a modulated light pulse of a certain frequency, which is reflected by an object/obstacle to be measured and received by a TOF image sensor, and the distance to the target can be calculated by measuring the time delay between the emitted light pulse and the received light pulse. Based on a continuous wave modulation method, a TOF three-dimensional image sensor for indirectly measuring a distance by resolving a phase difference between a transmitted light pulse and a received light pulse is called an indirect TOF image sensor (I-TOF), and the I-TOF has the advantages of high resolution precision, relatively simple process and the like.
In the conventional method based on continuous square wave modulation and calculation, the waveform of light pulse emitted by an active modulation light source is modulated by adopting square waves with 1/3 and 1/4 duty ratios according to different pixel structures, and a modulation control switch and a charge storage node controlled by the modulation control switch are called tap together. Firstly, for a 1-tap pixel, three and four frames of data are respectively needed to generate a depth map, and the three-dimensional imaging speed is low; secondly, for 3-tap and 4-tap pixels, although the imaging speed can be ensured, the difficulty of design is high due to the complex structure, and the pixel filling factor is low; finally, in the 2tap scheme, a square wave with a 1/4 duty ratio is adopted in the traditional method, and the opening time of a modulation gate cannot cover the whole exposure time during modulation, so that extra leakage tubes are needed for clearing background light, and the power consumption is multiplied.
Disclosure of Invention
Aiming at overcoming the defects of the prior art and solving the problem of power consumption increase caused by background light elimination of a 2-tap TOF pixel modulation scheme, the invention aims to provide a TOF three-dimensional imaging modulation method based on a 2-tap pixel structure. The modulation method adopts square waves with the duty ratio of 1/2, and provides a resolving method aiming at the modulation method, so that the problem of background light interference is solved, and meanwhile, new power consumption is not introduced. Therefore, the technical scheme adopted by the invention is that a TOF imaging 2-tap pixel modulation resolving method is adopted, emitted light is continuous square wave pulse with 50% of duty ratio, the emitted light is irradiated to an object to return, and pixels need two frames of integration to complete 4-phase information acquisition; integrating in a first frame, and modulating the two taps by signals in the same direction and the opposite direction of the emitted modulated light respectively; integrating in a second frame, and modulating two taps by signals with 1/4 period delay in the same direction and 1/4 period delay in the reverse direction of the emitted and modulated light respectively;
when a modulation signal applied to a specific tap is in a high level, photo-generated charges generated by integration in a photosensitive area of the pixel are transferred to the tap, and a charge signal in the tap is converted into a voltage signal in a reading-out stage for reading.
The method comprises the following specific steps:
recording the modulation frequency f of a light source driver circuit driving an active light source to emit modulated light; modulating the two taps by signals in the same direction and the opposite direction of the emitted modulated light, performing first frame photoelectric integration, and recording the difference value output by the two taps after the integration is finished as A;
step two, the light source driver circuit drives the active light source to emit modulated light frequency to be kept unchanged, the two tap modulation frequencies and the duty ratio of the TOF image sensor are kept unchanged, second frame photoelectric integration is carried out, the modulation phases of the two taps at the moment are respectively in the same direction as the emitted modulated light and delayed for 1/4 period, the modulation phases of the two taps are in the opposite direction of the emitted modulated light and delayed for 1/4 period, and the difference of the two tap outputs is marked as B after the integration is finished;
step three, judging the relation between A and zero, if A is more than or equal to 0, judging the relation between B and zero, calculating the phase difference = B/2 (A + B) under the condition that B is more than or equal to 0, and calculating the phase difference = (4A-3B)/2 (A-B) under the condition that B is less than 0; otherwise, if A is less than 0, judging the relation between B and zero, calculating the phase difference (= (2A-B)/2 (A-B) for the condition that B is more than or equal to 0, and calculating the phase difference (= (2A + 3B)/2 (A + B) for the condition that B is less than 0;
step four, calculating the distance of the object to be measured
To resolve the phase difference.
The difference making method of the two tap outputs in the first step and the second step is realized by adopting a differential reading circuit;
the invention has the characteristics and beneficial effects that:
compared with the traditional 1/4 duty ratio square wave modulation mode, the signal duty ratio applied to the modulation grid is 1/2, and the opening time of the modulation grid covers the whole exposure time in 2-tap pixel application, so that the interference of background light is eliminated and no extra power consumption is brought.
Description of the drawings:
FIG. 1 is a timing diagram of a TOF imaging 2-tap pixel modulation resolving method of the invention.
FIG. 2 is a flow chart of a TOF imaging 2-tap pixel modulation resolving method.
Figure 3 shows a detailed pulse diagram of the reflected light situation that may occur in the present invention.
Detailed Description
The invention discloses a TOF three-dimensional imaging modulation resolving method based on a 2-tap pixel structure, aiming at a TOF image sensor. The invention is realized by the following technical scheme:
the TOF imaging-based 2-tap pixel modulation method is shown in figure 1: the emitted light is continuous square wave pulse with the duty ratio of 50%, the emitted light irradiates to the object to return, and the pixels need two frames of integration to complete 4-phase information acquisition. Integrating in a first frame, and modulating the two taps by signals in the same direction and the opposite direction of the emitted modulated light respectively; during the second frame integration, the two taps are modulated by signals which are delayed by 1/4 period in the same direction and 1/4 period in the opposite direction of the emitted modulated light respectively.
Furthermore, tap in the pixel structure refers to a storage node and a control switch thereof for generating charges through pixel photoelectric integration, when a modulation signal applied to a specific tap is in a high level, photo-generated charges generated through integration in a photosensitive area of the pixel are transferred to the tap, and a charge signal in the tap is converted into a voltage signal in a reading stage for reading;
the flow chart of the 2-tap pixel calculating method based on TOF imaging is shown in FIG. 2:
recording the modulation frequency of a light source driver circuit driving an active light source to emit modulated light as f (modulation period T = 1/f); the two taps are modulated by signals in the same direction and the opposite direction of the emission modulated light, and the photoelectric integration of the first frame is carried out. After the integration is finished, recording the difference value output by the two taps as A;
and step two, the light source driver circuit drives the active light source to emit modulated light frequency to be kept unchanged, the two tap modulation frequencies and the duty ratio of the TOF image sensor are kept unchanged, and second frame photoelectric integration is carried out. At the moment, the modulation phases of the two taps are respectively 1/4 period delay in the same direction as the emitted modulated light and 1/4 period delay in the opposite direction of the emitted modulated light, and the difference of the two tap outputs is recorded as B after the integration is finished;
step three, judging the relation between A and zero, if A is more than or equal to 0, judging the relation between B and zero, calculating the phase difference = B/2 (A + B) under the condition that B is more than or equal to 0, and calculating the phase difference = (4A-3B)/2 (A-B) under the condition that B is less than 0; otherwise, if A is less than 0, judging the relation between B and zero, calculating the phase difference (= (2A-B)/2 (A-B) for the condition that B is more than or equal to 0, and calculating the phase difference (= (2A + 3B)/2 (A + B) for the condition that B is less than 0;
step four, calculating the distance of the object to be measured
To resolve the phase difference.
Furthermore, the difference making method for the two tap outputs in the first step and the second step can be realized by adopting a differential reading circuit.
The technical scheme of the invention is further clearly and completely described below by combining the attached drawings in the invention:
the specific implementation flow chart of the TOF three-dimensional imaging resolving method based on the 2-tap pixel structure is shown in FIG. 2, and FIG. 3 is a specific description of a possible reflected light situation. The specific implementation mode comprises the following steps:
the method comprises the following steps:
the light source driver circuit drives the active light source to emit square wave modulated light with the modulation frequency f; two different taps of the TOF image sensor use mutually-inverted signals with the frequency f and the duty ratio 1/2 as modulation signals to carry out first-frame photoelectric integration.
When the emitting light modulation pulse period is T, T =1/f, and the rising edge time of the emitting light pulse is recorded as 0, the charges generated by photoelectric conversion of the photosensitive area of the pixel are stored in tap1 within 0-T/2, and the output is recorded as Q1 after the charges are converted by voltage during reading; and in the time from T/2 to T, the charges generated by photoelectric conversion of the photosensitive area of the pixel are stored in tap2, and the charges are subjected to charge-voltage conversion during reading, and then the output is recorded as Q2. Finally, the output signals of the two taps are read out in a differential form, resulting in the first frame output a = Q1-Q2.
Step two:
and the light source driver circuit drives the active light source to emit modulated light frequency to be kept unchanged, the two tap modulation frequencies and the duty ratio of the TOF image sensor are kept unchanged, and second frame photoelectric integration is carried out.
At the moment, the rising edge time of the emitted light pulse is still recorded as 0, the charges generated by photoelectric conversion of the photosensitive area of the pixel are stored in tap1 within the time of T/4-3T/4, and the output is recorded as Q3 after the charges are subjected to voltage conversion during reading; and storing the charges generated by photoelectric conversion of the photosensitive area of the pixel in tap2 in 0-T/4 and 3T/4-T time, converting the charges by voltage during reading, and then outputting Q4. Finally, the output signals of the two taps are read out in a differential form, resulting in a second frame output B = Q3-Q4. (ii) a
Step three:
when the phase delay of the reflected light pulse is between 0 and T/4, namely the reflected light pulse (case one) in FIG. 3, A is greater than or equal to 0 and B is greater than or equal to 0, Q1-Q2 is greater than or equal to 0 and Q3-Q4 is greater than or equal to 0, according to the formula
Calculating delay information;
when the phase delay of the reflected light pulse is between T/4 and T/2, namely the reflected light pulse (case two) in FIG. 3, A is less than 0 and B is more than or equal to 0, Q1-Q2 is less than 0 and Q3-Q4 is more than or equal to 0, according to the formula
Calculating delay information;
when the phase delay of the reflected light pulse is between T/2 and 3T/4, i.e. the reflected light pulse (case three) in FIG. 3, where A < 0 and B < 0, Q1-Q2 < 0 and Q3-Q4 < 0, according to the formula
Calculating delay information;
when the phase delay of the reflected light pulse is between 3T/4 and T, namely the reflected light pulse (case four) in FIG. 3, A is greater than or equal to 0 and B is less than 0, Q1-Q2 is greater than or equal to 0 and Q3-Q4 is less than 0, according to the formula
Calculating delay information;
step four:
calculating the distance of the object to be measured according to the phase difference obtained by the calculation in the third step
The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (3)
1. A TOF imaging 2-tap pixel modulation resolving method is characterized in that emitted light is continuous square wave pulses with a duty ratio of 50%, the continuous square wave pulses irradiate an object and return, and pixels need two frames of integration to complete 4-phase information acquisition; integrating in a first frame, and modulating two taps by signals in the same direction and the opposite direction of the emitted modulated light respectively; integrating in a second frame, and modulating two taps by signals with 1/4 period delay in the same direction and 1/4 period delay in the reverse direction of the emitted and modulated light respectively;
the tap in the pixel structure refers to a storage node of charges generated by photoelectric integration of the pixel and a control switch thereof, when a modulation signal applied to a specific tap is in a high level, the photogenerated charges generated by integration in a photosensitive area of the pixel are transferred to the tap, and a charge signal in the tap is converted into a voltage signal for reading in a reading-out stage.
2. The TOF imaging 2-tap pixel modulation solution method according to claim 1, characterized by the specific steps of:
recording the modulation frequency f of a light source driver circuit driving an active light source to emit modulated light; modulating the two taps by signals in the same direction and the opposite direction of the emitted modulated light, performing first frame photoelectric integration, and recording the difference value output by the two taps after the integration is finished as A;
step two, the light source driver circuit drives the active light source to emit modulated light frequency to be kept unchanged, the two tap modulation frequencies and the duty ratio of the TOF image sensor are kept unchanged, second frame photoelectric integration is carried out, the modulation phases of the two taps at the moment are respectively in the same direction as the emitted modulated light and delayed for 1/4 period, the modulation phases of the two taps are in the opposite direction of the emitted modulated light and delayed for 1/4 period, and the difference of the two tap outputs is marked as B after the integration is finished;
step three, judging the relation between A and zero, if A is more than or equal to 0, judging the relation between B and zero, calculating the phase difference = B/2 (A + B) under the condition that B is more than or equal to 0, and calculating the phase difference = (4A-3B)/2 (A-B) under the condition that B is less than 0; otherwise, if A is less than 0, judging the relation between B and zero, calculating the phase difference (= (2A-B)/2 (A-B) for the condition that B is more than or equal to 0, and calculating the phase difference (= (2A + 3B)/2 (A + B) for the condition that B is less than 0;
step four, calculating the distance of the object to be measured
To resolve the phase difference.
3. The TOF imaging 2-tap pixel modulation resolving method according to claim 1, wherein the difference making method for the two tap outputs in the first step and the second step is implemented by using a differential readout circuit.
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| CN109814083A (en) * | 2018-11-14 | 2019-05-28 | 深圳市光微科技有限公司 | The sub- Demodulation Type pixel unit of electric current fill-in light, back side illumination image sensor chip, imaging system, forming method and measuring method |
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