Lidar system with multiple comparators and time-to-digital converters
A lidar system includes a transmitter that encodes successive transmit pulses with different pulse characteristics and a receiver that detects the pulse characteristics of each received (scattered or reflected) pulse and that distinguishes between the received pulses based on the detected pulse characteristics. The lidar system thus resolves range ambiguities by encoding pulses of scan positions in the same or different scan periods to have different pulse characteristics, such as different pulse widths or different pulse envelope shapes. The receiver includes a pulse decoder configured to detect the relevant pulse characteristics of the received pulse and a resolver that determines if the pulse characteristics of the received pulse matches the pulse characteristics of the current scan position or that of a previous scan position.
1. A lidar system, comprising:
a light source configured to emit pulses of light;
a scanner configured to scan the emitted pulses of light across a field of regard of the lidar system and direct one or more of the emitted pulses of light towards a remote target; and
a receiver configured to detect a received pulse of light comprising light from one of the emitted pulses of light that is scattered by the remote target, wherein the receiver comprises:
a light detector element configured to produce an electrical-current signal that corresponds to the received pulse of light; and
an application specific integrated circuit (ASIC) comprising an electronic amplifier coupled to a plurality of amplitude detection circuits, at least one of the plurality of amplitude detection circuits comprising a comparator and a time-to-digital converter (TDC) coupled to the comparator, wherein:
the electronic amplifier is configured to receive the electrical-current signal from the light detector element and produce a voltage signal corresponding to the received electrical-current signal;
the comparator is configured to receive the voltage signal from the electronic amplifier and produce an electrical-edge signal when an amplitude of the received voltage signal rises above or falls below a particular threshold voltage; and
the TDC is configured to receive the electrical-edge signal from the comparator and produce a time delay value corresponding to an interval of time between (i) emission of the one of the emitted pulses of light by the light source and (ii) receipt of the electrical-edge signal by the TDC.
2. The lidar system of claim 1 , wherein the receiver further comprises an envelope detector coupled to a plurality of TDCs including the TDC, wherein the envelope detector is configured to determine an amplitude envelope of the received pulse of light based at least in part on (i) two or more time delay values produced by at least a portion of the plurality of TDCs and (ii) the particular threshold voltage associated with each of the two or more time delay values.
3. The lidar system of claim 2 , wherein the envelope detector is further configured to determine an amplitude of the received pulse of light.
4. The lidar system of claim 3 , wherein the amplitude of the received pulse of light is determined based at least in part on (i) a highest particular threshold voltage of the particular threshold voltages associated with each of the two or more time delay values or (ii) a curve fitting routine.
5. The lidar system of claim 2 , wherein the envelope detector is further configured to determine a width of the received pulse of light based at least in part on a rising edge and a falling edge of the amplitude envelope of the received pulse of light.
6. The lidar system of claim 1 , wherein the receiver further comprises an envelope detector coupled to a plurality of TDCs including the TDC, wherein the envelope detector is configured to determine a center of the received pulse of light based at least in part on (i) two or more time delay values produced by at least a portion of the plurality of TDCs and (ii) the particular threshold voltages associated with each of the two or more time delay values.
7. The lidar system of claim 6 , further comprising a range detector configured to determine a distance to the remote target based at least in part on the determined center of the received pulse of light.
8. The lidar system of claim 1 , wherein the TDC is configured to receive a timing initialization signal corresponding to a time of the emission of the one of the emitted pulses of light by the light source.
9. The lidar system of claim 8 , wherein the timing initialization signal is an electrical signal provided by (i) a controller that controls the light source or (ii) a sensor that senses when the one of the emitted pulses of light is emitted by the light source.
10. The lidar system of claim 1 , wherein the receiver further comprises:
a range detector configured to determine a distance to the remote target; and
an intensity detector configured to:
determine an intensity of the received pulse of light based on one or more of: a maximum amplitude of the received pulse of light, a width of the received pulse of light, a power of the received pulse of light, and an energy of the received pulse of light; and
determine a reflectivity of the remote target based at least in part on the distance to the remote target and the intensity of the received pulse of light.
11. The lidar system of claim 10 , wherein, in response to the reflectivity of the remote target being determined to be greater than 100%, the lidar system is configured to disregard the reflectivity and attribute the reflectivity to light received from a source of light external to the lidar system.
12. The lidar system of claim 1 , wherein the light source comprises a current-modulated laser diode.
13. The lidar system of claim 1 , wherein the scanner comprises:
a scanning mirror configured to scan the emitted pulses of light in a first scan direction across the field of regard; and
a polygon mirror configured to scan the emitted pulses of light in a second scan direction substantially orthogonal to the first scan direction.
14. The lidar system of claim 1 , wherein the light detector element comprises a linear-mode avalanche photodiode.
15. The lidar system of claim 1 , wherein the light detector element is disposed on the ASIC.
16. The lidar system of claim 1 , wherein the light detector element is bump bonded to the ASIC.
17. The lidar system of claim 1 , wherein the electronic amplifier comprises a transimpedance amplifier configured to receive the electrical-current signal and produce an output voltage signal that corresponds to the received electrical-current signal.
18. The lidar system of claim 17 , wherein the electronic amplifier further comprises a gain circuit configured to amplify the output voltage signal to produce the voltage signal that is supplied to the comparator of the amplitude detection circuits.
19. A lidar system, comprising:
a light source configured to emit pulses of light;
a scanner configured to scan the emitted pulses of light across a field of regard of the lidar system and direct one or more of the emitted pulses of light towards a remote target; and
a receiver configured to detect a received pulse of light comprising light from one of the emitted pulses of light that is scattered by the remote target, wherein the receiver comprises:
a light detector element configured to produce an electrical-current signal that corresponds to the received pulse of light; and
an electronic amplifier coupled to a plurality of amplitude detection circuits, at least one of the plurality of amplitude detection circuits comprising a comparator and a time-to-digital converter (TDC) coupled to the comparator, wherein:
the electronic amplifier is configured to receive the electrical-current signal from the light detector element and produce a voltage signal corresponding to the received electrical-current signal;
the comparator is configured to receive the voltage signal from the electronic amplifier and produce an electrical-edge signal when an amplitude of the received voltage signal rises above or falls below a particular threshold voltage; and
the TDC is configured to receive the electrical-edge signal from the comparator and produce a time delay value corresponding to an interval of time between (i) emission of the one of the emitted pulses of light by the light source and (ii) receipt of the electrical-edge signal by the TDC.
20. A lidar system, comprising:
a light source configured to emit pulses of light;
a scanner configured to scan the emitted pulses of light across a field of regard of the lidar system and direct one or more of the emitted pulses of light towards a remote target; and
a receiver configured to detect a received pulse of light comprising light from one of the emitted pulses of light that is scattered by the remote target, wherein the receiver comprises:
a light detector element configured to produce an electrical-current signal that corresponds to the received pulse of light; and
an electronic amplifier coupled to a plurality of amplitude detection circuits, each of the plurality of amplitude detection circuits comprising a corresponding comparator and a corresponding time-to-digital converter (TDC) coupled to the comparator, wherein:
the electronic amplifier is configured to receive the electrical-current signal from the light detector element and produce a voltage signal corresponding to the received electrical-current signal;
the corresponding comparator is configured to receive the voltage signal from the electronic amplifier and produce an electrical-edge signal when an amplitude of the received voltage signal rises above or falls below a particular threshold voltage; and
the corresponding TDC is configured to receive the electrical-edge signal from the comparator and produce a time delay value corresponding to an interval of time between (i) emission of the one of the emitted pulses of light by the light source and (ii) receipt of the electrical-edge signal by the corresponding TDC.