Phase anti-aliasing using spread-spectrum techniques in an optical distance measurement system
A three dimensional time of flight (TOF) camera includes a transmitter and a receiver. The transmitter is configured to generate an electrical transmit signal at a plurality of frequencies over an integration time period and generate a transmit optical waveform corresponding with the electrical transmit signal. The receiver is configured to receive a reflected optical waveform that is the transmit optical waveform reflected off of an object, integrate the reflected optical waveform over the integration time period, and determine a distance to the target object based on a TOF of the optical waveform. The integration time period includes exposure time periods. A length of each of the exposure time periods corresponds to one of the frequencies. The TOF is determined based on a correlation of the electrical transmit signal and the return optical waveform utilizing a correlation function with respect to the integration time period.
1. A three dimensional (3D) time of flight (TOF) system, comprising:
a transmitter configured to:
generate an electrical transmit signal at a plurality of frequencies over an integration time period; and
generate a transmit optical waveform corresponding with the electrical transmit signal; and
a receiver configured to:
receive a reflected optical waveform that is the transmit optical waveform reflected off of a target object;
integrate the reflected optical waveform over the integration time period, the integration time period including a plurality of exposure time periods, wherein each exposure time period in the plurality of exposure time periods is different from the other exposure time periods; and
determine a distance to the target object based on a TOF of the transmit optical waveform from the transmitter to the target object and back to the receiver as the reflected optical waveform, the TOF determined based on a correlation of the electrical transmit signal and the reflected optical waveform utilizing a correlation function with respect to the integration time period.
2. The 3D TOF system of claim 1 , wherein the electrical transmit signal includes a plurality of discrete electrical signals, each at a different frequency.
3. The 3D TOF system of claim 1 , wherein the electrical transmit signal includes a single tone electrical signal that continuously changes frequency over the integration time period.
4. A transmitter for an optical distance measuring system, comprising:
a signal generator configured to generate an electrical transmit signal at a plurality of frequencies over an integration time period, each of the plurality of frequencies corresponding with a length of one of a plurality of exposure time periods of a receiver, wherein each exposure time period in the plurality of exposure time periods is different from the other exposure time periods;
a light source configured to generate a transmit optical waveform corresponding with the electrical transmit signal; and
an illumination driver coupled to the signal generator and the light source, the illumination driver configured to drive the light source.
5. The transmitter of claim 4 , wherein the signal generator includes a first phased-lock loop (PLL), a second PLL, a frequency sequencer, and a multiplexer.
6. The transmitter of claim 4 , wherein the signal generator includes a phased-lock loop (PLL) and a chirp generator.
7. The transmitter of claim 6 , wherein the PLL is configured, based on a signal from the chirp generator, to generate an analog electrical transmit signal with a continuously varying frequency.
8. A method of determining a distance to an object, comprising:
receiving, by a receiver, a reflected optical waveform that is a transmitted optical waveform reflected off of a target object;
integrating the reflected optical waveform over an integration time period, the integration time period including a plurality of exposure time periods, wherein each exposure time period in the plurality of exposure time periods is different from the other exposure time periods; and
determining a distance to the target object based on a time of flight (TOF) of the transmitted optical waveform from a transmitter to the target object and back to the receiver as the reflected optical waveform, the TOF determined based on a correlation of an electrical transmit signal and the return optical waveform utilizing a correlation function with respect to the integration time period.
9. The method of claim 8 , further comprising:
generating the electrical transmit signal at the plurality of frequencies over the integration time period; and
generating the transmit optical waveform corresponding with the electrical transmit signal.
10. The method of claim 9 , wherein the electrical transmit signal includes a plurality of discrete electrical signals, each at a different frequency.
11. The 3D TOF system of claim 1 , wherein the plurality of exposure time periods includes a first exposure time period corresponding to the first frequency, a second exposure time period corresponding to the second frequency, and a center exposure time period corresponding to the center frequency.
12. The 3D TOF system of claim 11 , wherein the center exposure time period is greater than the first exposure time period and the second exposure time period.
13. The 3D TOF camera of claim 12 , wherein each of the plurality of exposure time periods corresponds with spectral power of the transmit optical waveform at a point in time within the integration time period.
14. The 3D TOF system of claim 13 , wherein the spectral power of the transmit optical waveform during the integration time period approximates a sinc raised to an n power function, wherein n is a real number.
15. A three dimensional (3D) time of flight (TOF) system, comprising:
a receiver configured to:
receive a reflected optical waveform that is the transmit optical waveform reflected off of a target object;
integrate the reflected optical waveform over the integration time period, the integration time period including a plurality of exposure time periods, wherein each exposure time period in the plurality of exposure time periods is different from the other exposure time periods; and
determine a distance to the target object based on a TOF of the transmit optical waveform from the transmitter to the target object and back to the receiver as the reflected optical waveform, the TOF determined based on a correlation of the electrical transmit signal and the reflected optical waveform utilizing a correlation function with respect to the integration time period.
16. The 3D TOF system of claim 15 , wherein the electrical transmit signal includes a plurality of discrete electrical signals, each at a different frequency.
17. The 3D TOF system of claim 15 , wherein the electrical transmit signal includes a single tone electrical signal that continuously changes frequency over the integration time period.
18. The 3D TOF system of claim 15 , wherein the plurality of exposure time periods includes a first exposure time period corresponding to the first frequency, a second exposure time period corresponding to the second frequency, and a center exposure time period corresponding to the center frequency.
19. The 3D TOF system of claim 18 , wherein the center exposure time period is greater than the first exposure time period and the second exposure time period.
20. The 3D TOF system of claim 19 , wherein each of the plurality of exposure time periods corresponds with spectral power of the transmit optical waveform at a point in time within the integration time period.
21. The 3D TOF system of claim 20 , wherein the spectral power of the transmit optical waveform during the integration time period approximates a sinc raised to an n power function, wherein n is a real number.