Time-of-flight distance measuring methods and related distance measuring systems
A time-of-flight distance measuring system includes: intermittently transmitting a plurality of first pulses, wherein the plurality of first pulses are reflected by a target to generate a plurality of first reflected signals; using a TOF sensor to selectively perform a first signal sampling or a second signal sampling upon the plurality of first reflected signals respectively to generate a first sampling result, wherein there is a first time difference between a starting time point of the first signal sampling and a transmitting time point of the corresponding first pulse, and the first signal sampling lasts for a first predetermined time, and there is a second time difference between a starting time point of the second signal sampling and a transmitting time point of the corresponding first pulse, and the second signal sampling lasts for second predetermined time, and the first time difference is smaller than the second time difference.
1. A time-of-flight (TOF) distance measuring method, comprising:
intermittently transmitting a plurality of first pulses from a pulse generation unit, wherein the plurality of first pulses are reflected by a target to generate a plurality of first reflected signals;
controlling a TOF sensor to selectively perform a first signal sampling or a second signal sampling upon the plurality of first reflected signals respectively to generate a first sampling result, wherein there is a first time difference between a starting time point of the first signal sampling and a transmitting time point of the first pulse corresponding to the first signal sampling, and the first signal sampling lasts for a first predetermined time, and there is a second time difference between a starting time point of the second signal sampling and a transmitting time point of the first pulse corresponding to the second signal sampling, and the second signal sampling lasts for second predetermined time, and the first time difference is smaller than the second time difference;
detecting TOFs of the plurality of first pulses from the pulse generation unit to the TOF sensor according to the first sampling result; and
determining a distance between the target and a reference position according to the TOFs,
wherein the first predetermined time comprises at least one sampling interval adjacent to the starting time point of the first predetermined time; and the second predetermined time comprises the at least one sampling interval adjacent to the starting time point of the second predetermined time,
wherein a number of the sampling interval in the first predetermined time is greater than a number of the sampling interval in the second predetermined time.
2. The distance measuring method of claim 1 , wherein the sampling interval has a fixed time length.
3. The distance measuring method of claim 2 , wherein the time length of the sampling interval is equal to a pulse length of the first pulse.
4. The distance measuring method of claim 3 , wherein a difference between the second time difference and the first time difference is at least the time length of the sampling interval.
5. The distance measuring method of claim 1 , wherein the step of controlling the TOF sensor to selectively perform the first signal sampling or the second signal sampling upon the plurality of first reflected signals respectively comprises:
assigning each of the plurality of first reflected signals to correspond to the first signal sampling or the second signal sampling according to a predetermined ratio, wherein the number of the plurality of first reflected signals assigned to correspond to the first signal sampling is less than the number of the plurality of first reflected signals assigned to correspond to the second signal sampling.
6. The distance measuring method of claim 1 , wherein the step of controlling the TOF sensor to generate the first sampling result comprises:
sensing each of the plurality of first reflected signals to generate a response signal;
during the sampling interval, selectively using a first readout circuit to receive the response signal according to a first control signal, to generate a first pixel output, and selectively using a second control circuit to receive the response signal according to a second control signal, to generate a second pixel output, wherein the second control signal and the first control signal have different phases; and
sampling the first pixel output and the second pixel output every sampling time interval, so as to generate the first sampling result according to the first pixel output and the second pixel output.
7. The distance measuring method of claim 6 , wherein a phase difference between the first control signal and the second control signal is 180 degrees.
8. The distance measuring method of claim 6 , wherein the sampling time interval is ¼ of the pulse length.
9. The distance measuring method of claim 1 , further comprising:
intermittently transmitting a plurality of second pulses from the pulse generation unit, wherein the plurality of second pulses are reflected by the target to generate a plurality of second reflected signals, and a phase difference between the second pulse and the first pulse is 180 degrees; and
controlling the TOF sensor to selectively perform the first signal sampling or the second signal sampling upon the plurality of second reflected signals respectively to generate a second sampling result, wherein the starting time point of the first signal sampling and the transmitting time point of the second pulse corresponding to the first signal sampling have the first time difference, and the first signal sampling lasts for the first predetermined time, and the starting time point of the second signal sampling and the transmitting time point of the second pulse corresponding to the second signal sampling have the second time difference, and the second signal sampling lasts for the second predetermined time.
10. The distance measuring method of claim 9 , wherein the step of detecting the TOFs of the plurality of first pulses from the pulse generation unit to the TOF sensor according to the first sampling result comprises:
detecting the TOFs according to the first sampling result and the second sampling result.
11. A time-of-flight (TOF) distance measuring system, comprising:
a pulse generation unit;
a control circuit, coupled to the pulse generation unit and configured to control the pulse generation unit to intermittently transmit a plurality of first pulses, wherein the plurality of first pulses are reflected by a target to generate a plurality of first reflected signals; and
a TOF sensor, controlled by the control circuit and configured to selectively perform a first signal sampling or a second signal sampling upon the plurality of first reflected signals respectively to generate a first sampling result, wherein there is a first time difference between a starting time point of the first signal sampling and a transmitting time point of the first pulse corresponding to the first signal sampling, and the first signal sampling lasts for a first predetermined time, and there is a second time difference between a starting time point of the second signal sampling and a transmitting time point of the first pulse corresponding to the second signal sampling, and the first time difference is smaller than the second time difference, and the second signal sampling lasts for second predetermined time, and detecting TOFs of the plurality of first pulses from the pulse generation unit to the TOF sensor according to the first sampling result, and determining a distance between the target and a reference position according to the TOFs,
wherein the first predetermined time comprises at least one sampling interval adjacent to the starting time point of the first predetermined time; and the second predetermined time comprises the at least one sampling interval adjacent to the starting time point of the second predetermined time,
wherein a number of the sampling interval in the first predetermined time is greater than a number of the sampling interval in the second predetermined time.
12. The distance measuring system of claim 11 , wherein the sampling interval has a fixed time length.
13. The distance measuring system of claim 12 , wherein the time length of the sampling interval is equal to a pulse length of the first pulse, and a difference between the second time difference and the first time difference is at least the time length of the sampling interval.
14. The distance measuring system of claim 12 , wherein the TOF sensor comprises:
a pixel array, comprising a plurality of pixels, wherein each pixel comprises:
a photo sensor, configured to sense the plurality of first reflected signals respectively to generate a response signal;
a first readout circuit, configured to selectively transmit the response signal to generate a first pixel output according to a first control signal generated by the control circuit during the sampling interval; and
a second readout circuit, configured to selectively transmit the response signal to generate a second pixel output according to a second control signal generated by the control circuit during the sampling interval, wherein a phase difference between the first control signal and the second control signal is 180 degrees; and
a processing circuit, coupled to the pixel array and the control circuit and configured to sample the first pixel output and the second pixel output every sampling time interval according to a sampling control signal generated by the control circuit, so as to generate the first sampling result according to the first pixel output and the second pixel output.
15. The distance measuring system of claim 14 , wherein the sampling time interval is ¼ of the pulse length.
16. The distance measuring system of claim 11 , wherein:
the control circuit further controls the pulse generation unit to intermittently transmit a plurality of second pulses, wherein the plurality of second pulses are reflected by the target to generate a plurality of second reflected signals, and a phase difference between the second pulse and the first pulse is 180 degrees; and
the TOF sensor is further configured to selectively perform the first signal sampling or the second signal sampling upon the plurality of second reflected signals respectively to generate a second sampling result, wherein the starting time point of the first signal sampling and the transmitting time point of the second pulse corresponding to the first signal sampling have the first time difference, and the first signal sampling lasts for the first predetermined time, and the starting time point of the second signal sampling and the transmitting time point of the second pulse corresponding to the second signal sampling have the second time difference, and the second signal sampling lasts for the second predetermined time, and the TOF sensor is further configured to detect the TOFs according to the first sampling result and the second sampling result.
17. A time-of-flight (TOF) distance measuring method, comprising:
intermittently transmitting a plurality of pulse sets from a pulse generation unit, wherein each pulse set includes a first pulse and a second pulse, the intensity of the first pulse and the intensity of the second pulse are different, and the plurality of pulse sets are reflected by a target to generate a plurality of reflected signal sets, wherein the first pulse and the second pulse have the same pulse length, and a transmitting time of the second pulse falls behind the first pulse in the same pulse set by at least the pulse length;
controlling a TOF sensor to perform signal sampling upon the plurality of reflected signal sets respectively to generate a sampling result, wherein the signal sampling lasts for a predetermined time;
detecting TOFs of the plurality of pulse sets from the pulse generation unit to the TOF sensor according to the sampling result; and
measuring the distance between the target and a reference position according to the TOFs.