Time varying gain in an optical detector operating in a lidar system
To decrease the likelihood of a false detection when detecting light from light pulses scattered by remote targets in a lidar system, a receiver in the lidar system includes a photodetector and a pulse-detection circuit having a gain circuit with a varying amount of gain over time. The gain circuit operates in a low-gain mode for a time period T 1 beginning with time t 0 when a light pulse is emitted to prevent the receiver from detecting return light pulses during the threshold time period T 1 . Upon expiration of the threshold time period T 1 , the gain circuit operates in a high-gain mode to begin detecting return light pulses until a subsequent light pulse is emitted.
1. A lidar system comprising:
a light source configured to emit a light pulse; and
a receiver configured to detect light from the light pulse scattered by a remote target, the receiver including:
a photodetector that detects an optical signal corresponding to the light; and
a light pulse-detection circuit configured to convert the optical signal to an electrical signal and to detect whether the converted electrical signal is indicative of the light pulse scattered by the remote target, the light pulse-detection circuit including:
a gain circuit configured to amplify the converted electrical signal by a predetermined amplification amount that varies according to an amount of time that has elapsed since the light pulse has been emitted, wherein the gain circuit switches from a first gain mode to a second gain mode after a threshold time period T 1 since the light pulse has been emitted, and wherein the threshold time period T 1 is dynamically adjusted based on one or more characteristics of the detected optical signal, and
a comparison circuit configured to compare the amplified electrical signal to a threshold amount to determine whether the amplified electrical signal is indicative of the light pulse scattered by the remote target.
2. The lidar system of claim 1 , wherein within the threshold time period T 1 since the light pulse has been emitted the gain circuit operates in a low-gain mode having the predetermined amplification amount below a threshold value, and within a threshold time period T 2 after the threshold time period T 1 has elapsed, the gain circuit switches to a high-gain mode having the predetermined amplification amount at or above the threshold value.
3. The lidar system of claim 2 , wherein:
the light pulse is a first light pulse;
after the second threshold time period has elapsed, the gain circuit switches back to the low-gain mode; and
the light source emits a second light pulse.
4. The lidar system of claim 2 , further comprising a controller configured to:
initialize a clock for identifying the first and second threshold time periods based on at least one of: determining the light pulse has been emitted or determining light from the light pulse has been detected; and
provide a control signal to the gain circuit indicative of the predetermined amplification amount.
5. The lidar system of claim 4 , wherein the controller determines that the light pulse has been emitted in response to the controller providing a control signal to the light source to transmit the light pulse.
6. The lidar system of claim 4 , wherein the controller determines that the light pulse has been emitted and initializes the clock in response to receiving an indication from the photodetector that light from the light pulse has been detected as the light pulse is emitted.
7. The lidar system of claim 1 , wherein the predetermined amplification amount in the gain circuit increases in relation to the amount of time that has elapsed since the light pulse has been emitted until a second threshold time period has elapsed or a maximum predetermined gain is reached.
8. The lidar system of claim 1 , further comprising:
a scanner configured to scan a field of regard of the lidar system including direct light pulses toward different points within the field of regard.
9. A method for dynamically varying gain in a lidar system, the method comprising:
emitting a light pulse by a light source in a lidar system;
detecting, by a receiver in the lidar system, light from the light pulse scattered by a remote target to identify a return light pulse, including detecting an optical signal corresponding to the light;
converting, by a light pulse-detection circuit in the lidar system, the optical signal to an electrical signal;
amplifying, by the light pulse-detection circuit, the electrical signal by a predetermined amplification amount that varies according to an amount of time that has elapsed since the light pulse has been emitted, wherein the light pulse-detection circuit switches from a first gain mode to a second gain mode after a threshold time period T 1 since the light pulse has been emitted, and wherein the threshold time period T 1 is dynamically adjusted based on one or more characteristics of the detected optical signal; and
comparing, by the light pulse-detection circuit, the amplified electrical signal to a threshold amount to determine whether the amplified electrical signal is indicative of the light pulse scattered by the remote target.
10. The method of claim 9 , wherein within the threshold time period T 1 since the light pulse has been emitted the light pulse-detection circuit operates in a low-gain mode having the predetermined amplification amount below a threshold value, and within a threshold time period T 2 after the threshold time period T 1 has elapsed, the light pulse-detection circuit switches to a high-gain mode having the predetermined amplification amount at or above the threshold value.
11. The method of claim 10 , wherein:
the light pulse is a first light pulse;
after the second threshold time period has elapsed, the light pulse-detection circuit switches back to the low-gain mode; and
the light source emits a second light pulse.
12. The method of claim 10 , further comprising:
initializing a clock for identifying the first and second threshold time periods based on at least one of: determining the light pulse has been emitted or determining light from the light pulse has been detected; and
providing a control signal to the light pulse-detection circuit indicative of the predetermined amplification amount.
13. The method of claim 12 , further comprising providing a control signal to the light source to transmit the light pulse, wherein determining that the light pulse has been emitted includes determining that the light pulse has been emitted in response to providing the control signal to the light source to transmit the light pulse.
14. The method of claim 12 , wherein determining that the light pulse has been emitted and initializing the clock includes receiving an indication from the receiver that light from the light pulse has been detected as the light pulse is emitted.
15. The method of claim 9 , wherein the predetermined amplification amount increases in relation to the amount of time that has elapsed since the light pulse has been emitted until a second threshold time period has elapsed or a maximum predetermined gain is reached.
16. The method of claim 9 , further comprising:
scanning, by a scanner in the lidar system, a field of regard of the lidar system, including directing light pulses toward different points within the field of regard to illuminate a field of view of the light source.
17. A controller in a lidar system comprising:
one or more processors; and
a non-transitory computer-readable memory coupled to the one or more processors and storing instructions thereon that, when executed by the one or more processors, cause the controller to:
provide a control signal to a light source to emit a light pulse;
initialize a clock based on at least one of: determining the light pulse has been emitted or determining light from the light pulse has been detected; and
provide a control signal to a light pulse-detection circuit indicative of a predetermined amplification amount at which to amplify an electrical signal converted from an optical signal corresponding to light from the light pulse scattered by a remote target, wherein the predetermined amplification amount is based on an amount of time that has elapsed since the light pulse has been emitted, and wherein:
the instructions cause the controller to provide a control signal to the light pulse-detection circuit to switch from a first gain mode to a second gain mode after a threshold time period T 1 since the light pulse has been emitted, and
the instructions cause the controller to dynamically adjust the threshold time period T 1 based on one or more characteristics of the detected optical signal.
18. The controller of claim 17 , wherein:
within the threshold time period T 1 since the light pulse has been emitted, the instructions cause the controller to provide a control signal to the light pulse-detection circuit to operate in a low-gain mode having the predetermined amplification amount below a threshold value; and
within a threshold time period T 2 after the threshold time period T 1 has elapsed, the instructions cause the controller to provide a control signal to the light pulse-detection circuit to switch to a high-gain mode having the predetermined amplification amount at or above the threshold value.
19. The controller of claim 18 , wherein:
the light pulse is a first light pulse; and
after the second threshold time period has elapsed, the instructions cause the controller to provide a control signal to the light pulse-detection circuit to switch back to the low-gain mode and provide a control signal to the light source to emit a second light pulse.
20. The controller of claim 17 , where the instructions cause the controller to initialize a clock for determining the amount of time that has elapsed since the light pulse has been emitted in response to receiving an indication from a photodetector that light from the light pulse has been detected as the light pulse is emitted.