Techniques for automatic gain control in a time domain for a signal path for a frequency modulated continuous wave (FMCW) light detection and ranging (LIDAR) system

A light detection and ranging (LIDAR) system includes an automatic gain control (AGC) unit to reduce the dynamic range, reducing processing power and saving circuit area and cost. The system detects a return beam of a light signal transmitted to a target, having a first dynamic range in a time domain. An analog to digital converter (ADC) generates a digital signal based on the return beam. A processor can perform time domain processing on the digital signal, convert the digital signal from the time domain to a frequency domain, and perform frequency domain processing on the digital signal in the frequency domain. The AGC unit can measure a power of the return beam, and apply variable gain in the time domain to reduce a dynamic range of the return beam to a second dynamic range lower than the first dynamic range.

FIELD

Descriptions are generally related to light scanning systems, and more particularly, LIDAR (light detection and ranging) systems.

BACKGROUND

The dynamic range of a frequency modulation continuous wave (FMCW) light detection and ranging (LIDAR) system is the difference between the highest intensity signal and lowest intensity signal received that can be reliably processed. Signals with intensities that are too high can get distorted, which can introduce harmonics and make it difficult for the system to reliably pick the true frequency peak. Signals with intensities that are too low can become indistinguishable from noise sources, which makes the signals difficult to detect.

The dynamic range of an FMCW LIDAR system can be limited by the minimum dynamic range of any individual component in the optical, electrical, and signal processing paths. A system can add bits to analog to digital converters (ADCs) and digital datapaths, which lowers the quantization noise level, and can increase the dynamic range. However, adding bits increases the power, area, and cost of the LIDAR system. Additionally, adding bits may not increase the dynamic range if optical or analog components limit the dynamic range.

Descriptions of certain details and implementations follow, including non-limiting descriptions of the figures, which may depict some or all examples, and well as other potential implementations.

DETAILED DESCRIPTION

As described herein, in accordance with embodiments of the present invention, a light detection and ranging (LIDAR) system can include automatic gain control (AGC). According to some embodiments, AGCs described herein can include one or more signal processors included therein or remotely and/or one or more measuring components. The AGC can adjust the dynamic range of a system while maintaining approximately the same power, area, and cost as a traditional system. One example system is a frequency modulated continuous wave (FMCW) LIDAR system, where the dynamic range of the system is improved by one or more variable gain control elements. The dynamic range of an FMCW LIDAR system can be defined as the difference between the highest intensity and lowest intensity received signal or beat signal that can be reliably processed.

The AGC can control the dynamic range of the system across optical, analog or electrical, or digital paths of the signaling, or a combination of optical, electrical, and digital paths. The AGC provides dynamic range control to reduce signal distortion due to a dynamic range that is too high, and reduce noise interference in peak detection due to dynamic range that is too low.

In one example, AGC can be provided in an optical path. In one example, AGC can be provided in analog or electrical circuitry. In one example, AGC can be provided in digital time domain processing. In one example, AGC is provided in digital frequency domain processing. AGC can be applied in a combination of one or more of the optical circuitry, analog circuitry, digital time domain processing, or digital frequency domain processing.

The system can detect a return beam of a light signal transmitted to a target, having a first dynamic range in a time domain. An analog to digital converter (ADC) can generate a digital signal based on the return beam. A processor can perform time domain processing on the digital signal, convert the digital signal from the time domain to a frequency domain, and perform frequency domain processing on the digital signal in the frequency domain. The AGC unit can measure a power of the return beam, and apply variable gain in the time domain to reduce a dynamic range of the return beam to a second dynamic range lower than the first dynamic range. The AGC unit can measure a power of the digital signal, and apply variable gain in the frequency domain to reduce a dynamic range of the signal to a second dynamic range lower than the first dynamic range.

FIG. 1illustrates an example of automatic gain control (AGC) for dynamic range control in a LIDAR system. System100represents an adjustment to dynamic range based on AGC.

Dynamic range refers to a difference between the largest possible signal power and the smallest possible signal power that needs to be reliably processed. Dynamic range can be a design specification for a LIDAR system, and can be based on the expected signals used, power budget for the system, component performance characteristics, or other factors. Performing signal processing on signals with lower dynamic range can save power, reduce optical component size, thus saving area, and can reduce the system cost (both component cost and operating cost). The LIDAR system can be designed with a datapath having a smaller dynamic range than what is specified for the components. The system can measure the power of a received signal and apply a variable gain to fit the signal within the reduced dynamic range for processing through the datapath.

A variable gain can be applied to any signal to reduce its dynamic range. Variable gain can be applied to gain up weak signals. Variable gain can be applied to attenuate strong signals. Either amplification, or attenuation, or both amplification and attenuation can be applied to adjust the dynamic range.

By applying the variable gain, a signal can be made to fit within the dynamic range of the next component in the signal chain or along the datapath. Thus, the variable gain AGC can be applied to fit dynamic range above the noise level and below the distortion level of a component. It will be understood that applying variable gain at a point in the path of the signal, whether in the optical, analog, or digital domain, will adjust the dynamic range for subsequent components in the signal path. Thus, applying a variable gain can reduce the dynamic range requirement of all subsequent signal chain components, resulting in power, area, and cost savings. The earlier AGC is applied in a signal chain, the more savings are possible.

In system100, the difference between signal112with large amplitude and signal114with very small amplitude can be high dynamic range110. System100can apply variable gain to achieve low dynamic range140. To determine the optimal variable gain to apply, system100can measure the input signal level, as represented by device122, which represents a measuring device or measuring apparatus of system100to generate measurement signal124. AGC120represents one or more AGC circuits to apply the variable gain.

AGC120can receive signal124to indicate the measurement of the input signal, determine the desired signal levels to be within a desired dynamic range, and generate control signal126to apply variable gain. Control signal126can set one or more configuration parameters of variable gain130to apply the desired variable gain. The input signal level could be an average level over time or frequency or a peak level, such as instantaneous peak voltage or light intensity or peak frequency component. Variable gain130represents one or more components to apply variable gain to one or more signals to produce low dynamic range140. In system100, the result of the application of variable gain130can be that the high amplitude of signal112has been attenuated to signal142with lower amplitude, and the low amplitude of signal114has been gained or amplified to signal144with higher amplitude.

In one example, either signal112or signal114are adjusted by variable gain130, but not both. For example, signal112can be attenuated and signal114can remain unchanged. Alternatively, signal112can remain unchanged while signal114is gained. The determination to gain or attenuate a signal is made based on the desired lower dynamic range.

Automatic gain control can refer to measuring the input signal level, computing the variable gain or gain range to apply, and controlling the variable gain component. Such operation can minimize the required dynamic range, which also reduces power consumption, circuit area, and cost of the rest of the signal path.

FIG. 2illustrates an example of a LIDAR system that can provide AGC for optical signal processing. System200provides an example of a LIDAR system. Laser210represents a laser transmission system that provides a light signal or optical source for scanning the target. In some implementations, laser210represents an FMCW laser. Optical components220provide the modulation and optics to transmit TX signal212to target230and receive the reflection signal represented by RX signal232.

Photodetector240can receive RX signal232from optical components220from target230, and LO signal214from optical components220from laser210. LO signal214represents a reference signal generated from the laser light signal. LO signal can represent transmission of a first portion of a light signal from laser210toward target230. Photodetector240detects a return beam from target230, where the return beam is the light signal of TX signal212as reflected back from target230.

System200can condition the signal (e.g., the return beam) with ADC250and provide the conditioned signal for digital signal processing260. In one example, digital signal processing260generates point cloud262, which can represent a group of points of estimates of target information. A point cloud can refer to a group of target estimate values that have corresponding coordinate information to spatially map the points relative to each other.

The digital signal processing can include frontend processing270, with time domain processing of the input samples, block samples for frequency transformation (FT), and frequency domain processing. Time domain processing272can apply time domain filters to improve SNR of the signal. Time domain processing272has input samples264as the input, which represent samples generated by ADC250.

Block samples for FT (Fourier Transform)274represents processing on the samples to group them for frequency transformation computations. Time to frequency (FRED) domain276represents the frequency transformation to provide a conversion of the signals into temporal frequency representations. Frontend processing270can include frequency domain processing278to generate a filtered frequency domain waveform282. Frequency domain processing278can perform processing on the digital signal in the frequency domain.

Digital signal processing260can include peak search280of frequency domain waveform282to generate signal detections284or computations of estimates of the points of interest. The points of interest generated can be represented as a point cloud, with point having range and velocity information, associated in a relative spatial mapping.

Along various signal paths of system200, the components can be designed or configured with a dynamic range for operation. In one example, system200applies AGC to adjust the dynamic range of the signal for subsequent components in the signal path. In one example, the AGC measures a power of a signal in the time domain and applies variable gain in the time domain to reduce a dynamic range of the signal to prepare the signal for subsequent components.

There are many possible locations for the application of AGC in system200. In one example, system200can include optical AGC, applying a variable gain to LO signal214prior to photodetector240. In one example, system200can include analog AGC, applying a variable gain to an analog or electrical signal prior to ADC250. In one example, system200can include digital time domain AGC, applying variable gain to a digital signal prior to frequency domain conversion. In one example, system200can include digital frequency domain AGC, applying variable gain to a digital signal after frequency domain conversion. In the case of digital frequency domain AGC, different frequency bands could have different gains applied for further expansion of dynamic range. It should be noted that one or more AGCs described in the present disclosure can be used in combination to achieve advantages described herein.

In one example, system200applies AGC only at one of the identified locations. In an alternative example, system200can apply AGC at multiple locations. In some scenarios, the application of AGC at multiple locations would have benefit if the signal level changes naturally between the previous AGC location and the next, rather than a change due to the application of AGC. Thus, a signal level change due to components or processing can be adjusted by the application of another level of AGC. If there is no natural change in signal level between the LO, ADC, and time domain processing (which could be the case for an example of system200), system200could apply AGC at only one of those locations. Signals in the same frequency range that have not been filtered would not normally see a signal level change. Thus, in typical systems, AGC can be applied at optical, analog, or digital time domain processing. Even with application of AGC at one of these locations, the application of digital frequency domain processing can still be beneficial.

In some scenarios, one or more AGCs can be placed in desirable locations within a given system (e.g., in the signal chain or signal path) based on the costs and benefits to the system. Location292, location,294, location296, and location298represent locations in system200where an AGC can be employed. Location292represents an optical AGC in the optical path. Location294represents an electrical AGC in the analog processing path. Location296represents a digital processing AGC in the time domain processing path. Location298represents a digital processing AGC in the frequency domain processing path.

AGC in the digital frequency domain can be applied to a filtered band of frequencies. There can be benefits to system200by applying digital frequency domain AGC in conjunction with optical, analog, or digital time domain AGC for additional power savings.

FIG. 3illustrates an example of AGC in an LO path of a LIDAR system. System300represents a system in accordance with embodiments of the present disclosure. System300provides an example of a LIDAR system. Laser310represents a laser transmission system that provides a light signal or optical source for scanning the target. In some implementations, laser310represents an FMCW laser. Optical components320provide the modulation and optics to transmit TX signal312to target330and receive the reflection signal or return beam represented by RX signal332.

Photodetector340can receive RX signal332from optical components320from target330, and LO signal314from optical components320from laser310. Photodetector340detects the return beam from target330. System300can condition the signal (e.g., the return beam) with ADC350and provide the conditioned signal for signal processing.

In one example, system300includes an optical AGC360, which controls variable gain of LO signal314in the time domain based on measurement of RX signal332. In system300, optical AGC360can measure RX signal332to determine the signal power and determine whether the dynamic range will be within specifications for subsequent components. Optical AGC360can control variable gain362in the LO path to adjust the beat signal power as needed.

In one example, an attenuated version of the transmit signal can be mixed with the signal received from the target to obtain a beat signal. Beat signal342is illustrated as an output of photodetector340. Photodetector340can receive LO signal314and RX signal332. The more power incident on photodetector340, the more power it consumes. System300can control the LO power. The power consumed by photodetector340gives an estimate of the power of the received signal (RX signal332).

When power consumption of photodetector340increases, optical AGC360can decrease the power of LO signal314with an optical attenuator to keep the overall power consumption constant and ensure the power of beat signal342is within the dynamic range of ADC350. If LO signal314needs to be gained up, system300can use an optical amplifier in the LO path or adjust the split ratio while generating LO signal314from transmit signal312.

Optical components320can include a splitter (not specifically illustrated) to separate TX signal312as a first portion of the light signal generated by laser310and a LO signal314as a second portion of the light signal. In one example, optical AGC360measures RX signal332for comparison against a threshold (e.g., the comparison performed by a signal processor or similar processor described herein). If the threshold is determined to be exceeded, optical AGC360can attenuate LO signal314with an optical attenuator; thus, variable gain362can represent an optical attenuator. If the threshold is determined to not be exceeded, optical AGC360can increase the variable gain.

In one example, optical AGC360compares RX signal332against multiple thresholds. Based on the comparison of RX signal332against the multiple thresholds, optical AGC360can turn one or more optical attenuators off; thus, variable gain362can represent multiple optical attenuators controlled based on multiple threshold levels.

In one example, optical AGC360measures RX signal332for comparison against a threshold, and if the threshold is determined to not be exceeded, optical AGC360can increase an amount of TX signal312relative to LO signal314, for example, by adjustment to gain or attenuation of a splitter in optical components320.

FIG. 4illustrates an example of AGC in an analog processing path of a LIDAR system. System400represents a system in accordance with embodiments of the present disclosure. System400provides an example of a LIDAR system. Laser410represents a laser transmission system that provides a light signal or optical source for scanning the target. In some implementations, laser410represents an FMCW laser. Optical components420provide the modulation and optics to transmit TX signal412to target430and receive the reflection signal or return beam represented by RX signal432. Optical components can include a splitter to separate LO signal414from TX signal412.

Photodetector440can receive RX signal432from optical components420from target430, and LO signal414from optical components420from laser410. Photodetector440detects the return beam from target430. System400can condition the signal (e.g., the return beam) with ADC450and provide the conditioned signal for signal processing. In one example, RX signal432can be mixed with LO signal414to obtain a beat signal. Beat signal442is illustrated as an output of photodetector440.

In one example, system400includes analog AGC460, which represents an analog or electrical AGC. In system400, analog AGC460can measure beat signal442generated by photodetector440to determine average power or peak instantaneous voltage. The measurement enables analog AGC460to determine the amount of variable gain462needed to ensure the resulting signal lies within the dynamic range of ADC450. The application of variable gain462resulting from analog AGC460can enable the use of ADC450in system400with fewer output bits, or lower full-scale voltage, or a combination of lower voltage and fewer output bits. Using fewer bits or lower voltages can save power, area, and cost as compared to a system that does not use AGC in the manner described herein.

In one example, system400includes additional analog circuitry to measure the input signal level, such as an envelope detector. System400can provide variable gain462with, for example, a variable gain amplifier or other electronic circuit.

FIG. 5illustrates an example of AGC in time domain digital processing of a LIDAR system. System500represents a system in accordance with embodiments of the present disclosure. System500does not illustrate the optical components.

System500can detect a return beam signal with photodetector510and condition the signal with ADC520. System500provides the conditioned signal for signal processing by frontend processing530. In one example, frontend processing530includes time domain processing532, time to frequency (FREQ) domain534, and frequency (FREQ) domain processing536. Time domain processing532can perform time domain filtering of the input signal.

Time to frequency domain534represents a frequency transformation to provide a conversion of the signal into a temporal frequency representation. Frequency domain processing536can perform processing or filtering on the digital signal in the frequency domain to generate a frequency domain waveform542. System500can include peak search540of frequency domain waveform542to generate signal detections544or computations of estimates of the points of interest, such as a point cloud.

In one example, system500includes digital time domain AGC550prior to time domain processing532. Digital time domain AGC550can measure the output signal level of ADC520and adjust the signal (e.g., gain the signal or reduce the signal power) prior to further processing. Digital time domain AGC550can control variable gain552to adjust the signal levels.

After application of variable gain552provided by digital time domain AGC550, system500can use fewer data path bits in the signal processing components of frontend processing530, which saves power, area, and costs. Each downstream component (time domain processing532, time to frequency domain534, and frequency domain processing536) can use fewer bits as compared to a traditional system that does not use AGC.

In one example, system500can perform a power measurement of the input signal level from ADC520to frontend processing530such as a sum of squares of input data or simply measuring peak instantaneous input (e.g., max of input data) over a window of samples. In one example, system500can apply variable gain552by choosing a subset of contiguous bits to forward to the rest of the signal chain (the downstream processing components). Thus, certain bits can be selected for processing, and other bits will be ignored for the processing. In one example, system500performs scaling and/or rounding prior to selecting the bits for processing.

In one example, digital time domain AGC550compares the digital signal level to a threshold and adjusts the digital signal with digital multiplication, provided the digital signal is not above the threshold. In one example, the threshold can be multiple thresholds, with different levels of multiplication applied based on different thresholds.

FIG. 6illustrates an example of digital time domain AGC operation. System600illustrates bits selection in accordance with an example of system500. The simplest implementation of digital AGC, whether in the time domain or the frequency domain, is for the processing component(s) to choose a subset of the bits, and only perform processing on the subset of bits. The subset of bits selected should most accurately represent the input signal. Thus, the subset selected should be the subset with the most signal information.

Graph610illustrates two signals, input signal A and input signal B. Graph610represents the range of distortion at the top (the top gray area), and the quantization noise and overall noise floor on the bottom (the bottom gray area). The dynamic range is the range between the distortion and the overall noise floor. Graph610also illustrates AGC threshold612, assuming two different levels of bit selection. As seen to the right of the graph, the signal in the example has 6 bits.

Input signal A has a signal level that is much higher than the noise floor and could potentially be close to the distortion level. Input signal A exceeds AGC threshold612. In one example, the system selects the 4 MSBs (AGC Level 1) out of the 6 available bits. For signals with high input level, the MSBs can be chosen to reduce the chance of distortion.

Input signal B has a signal level that is lower than AGC threshold612, and is relatively close to the noise floor. Thus, choosing the 4 MSBs would bury the signal in the noise. The processing component(s) of system600can select the 4 LSBs (AGC Level 2) for processing of input signal B.

It will be understood that 6 signal bits are illustrated in system600, and a different system can have more or fewer bits. More or fewer than the 4 bits of the example can be selected for processing. In one example, the AGC can include more than two levels. For example, system600could include a second AGC threshold, creating a third AGC level. A third AGC level could allow selection of the 4 middle bits. More levels of AGC bit selection would generally have more associated AGC thresholds.

Graph620illustrates the processing of input signal A, with a new noise floor (bottom gray area) and distortion range (top gray area). Thus, graph620has a different dynamic range for the 4-bit signal as compared to the dynamic range of graph610for the 6-bit signal. Likewise, in graph630, the processing of input signal B illustrates the noise floor (bottom gray area) with a new distortion level (top gray area) and different dynamic range for the 4-bit signal.

System600illustrates selecting a subset of contiguous bits to carry forward to the rest of the data path, which allows shrinking the dynamic range in steps of 6 dB per bit omitted. In one example, system600can perform a digital multiplication (scaling) operation prior to bit selection to achieve less than a 6 dB dynamic range reduction. In one example, system600can perform rounding before discarding LSBs.

FIG. 7illustrates an example of AGC in frequency domain digital processing of a LIDAR system. System700represents a system in accordance with embodiments of the present disclosure. System700does not illustrate the optical components.

System700can detect a return beam signal with photodetector710and condition the signal with ADC720. System700provides the conditioned signal for signal processing by frontend processing730. In one example, frontend processing730includes time domain processing732, time to frequency (FREQ) domain734, and frequency (FREQ) domain processing736. Time domain processing732can perform time domain filtering of the input signal.

Time to frequency domain734represents a frequency transformation to provide a conversion of the signal into a temporal frequency representation. Frequency domain processing736can perform processing or filtering on the digital signal in the frequency domain to generate a frequency domain waveform742. System700can include peak search740of frequency domain waveform742to generate signal detections744or computations of estimates of the points of interest, such as a point cloud.

In one example, system700includes digital frequency domain AGC750prior to frequency domain processing736, after the conversion of the time domain signal to the frequency domain. After the signal is converted to the frequency domain, frequency domain AGC750can measure the signal and apply variable gain752based on the signal measurement, to reduce the dynamic range for frequency domain processing. In one example, system700can divide the signal into multiple frequency bands, with the signal level in each band measured separately. In one example, a different variable gain can be applied to each band. The number of frequency bands and band boundaries can be decided a-priori or dynamically.

The digital implementation of the digital frequency domain AGC can be the same as the digital time domain AGC described with respect to system500and system600. In one example, digital frequency domain AGC750compares the digital signal level to a threshold and adjusts the digital signal with digital multiplication, provided the digital signal is not above the threshold. In one example, the threshold can be multiple thresholds, with different levels of multiplication applied based on different thresholds.

FIG. 8illustrates an example of digital frequency domain AGC operation. Diagram800illustrates signal processing with digital frequency domain AGC in accordance with an example of system700.

In diagram800, the signal for Target1is in Band1, and Gain1is applied to the signal for processing. The signal for Target2is in Band2, and Gain2is applied to the signal for processing. Gain1and Gain2can be different levels of gain. Such an AGC can preserve a large dynamic range over the full frequency band, while saving power by significantly limiting the dynamic range in a single band.

It will be understood that 2 targets with large differences in intensity within a single frequency band could generally not be simultaneously detected. Signals for targets in different bands can be detected, even with large differences in signal intensity.

FIG. 9illustrates an example of digital frequency domain AGC operation in multiple frequency bands. System900illustrates multi-band signal processing with digital frequency domain AGC in accordance with an example of system700. System900illustrates digital frequency domain AGC and variable gain as part of the digital frequency processing.

System900illustrates time to frequency conversion, followed by full band DSP (digital signal processing)922. Time to frequency conversion (time to FREQ)910represents a digital processing component to perform a frequency conversion on a time domain digital signal. Frequency domain processing920represents digital processing in the frequency domain of the signal output of time to frequency conversion910. Frequency domain processing920includes full band DSP922to apply filtering and/or processing on the signal across all frequency bands.

In one example, after full band processing by full band DSP922, frequency domain processing920can split the signals into different bands, applying variable gains to the different bands. The gain to each band can be separately controlled to allow different gains for different bands. System900illustrates the different band processing as band DSP930[1:N], collectively band DSPs930. System900can apply variable gain932[1:N] (collectively variable gains932), respectively, to band DSP930[1:N] prior to the band DSP. System900can apply variable gain934[1:N] (collectively variable gains934), collectively, to band DSP930[1:N] after band DSP. Separating the input signals into different frequency bands allows the system to reduce the power consumption for processing, circuit area, and system cost (operating cost as well as component cost) by processing on signals in lower dynamic ranges. By separating the signals into different bands, each band can be processed at a lower dynamic range, while preserving the overall large dynamic range of the entire frequency band. The splitting into different bands can allow processing on significantly limited dynamic ranges, then recombining restores the dynamic range of the signal for further processing. The processing on the entire band can be simpler because of the processing performed per band, thus minimizing the processing needed on a signal of large dynamic range.

Digital frequency (FRED) domain AGC936can control the application of variable gains932and the application of variable gains934. In one example, variable gains932apply signal gain or signal attenuation to process a signal with band DSPs930, and then variable gains934provide gain normalization to return the separate bands to a normalized range for recombining after processing. In one example, during the normalization, any other variable gains applied by optical, analog, or time domain AGC can also be normalized. The normalization can be performed, for example, by padding bits in the MSBs or LSBs, depending on the gain applied, to have signals with information bits aligned to the proper bit range.

After recombining the full band signal, system900can apply additional full band DSP924to complete the frequency domain processing920. Frequency domain processing920can send its signal output to peak search950for peak processing to generate detections952. It should be noted that, according to some embodiments, frequency domain processing920can be performed serially using one band DSP and one set of variable gain components and thus not limited to the depiction inFIG. 9.

FIG. 10illustrates an example LIDAR system that can implement AGC as described herein. LIDAR system1000includes one or more of each of a number of components, but may include fewer or additional components than what is illustrated. One or more of the components depicted in LIDAR system1000can be implemented on a photonics chip, according to some examples.

As shown, LIDAR system1000includes optical circuits1012implemented on a photonics chip. In one example, optical circuits1012include active optical components. In one example, optical circuits include passive optical components. In one example, optical circuits1012include a combination of active optical components and passive optical components. Active optical components refer to components that can generate, amplify, or detect optical signals, or perform a combination of generate, amplify, or detect. In some examples, the active optical component performs operations on optical beams at different wavelengths, and includes one or more optical amplifiers, one or more optical detectors, or other components to perform operations on the light signal.

Free space optics1032refers to one or more components that can carry optical signals and route and manipulate optical signals between appropriate input or output ports of the optical circuit and the components of the optical circuit. In one example, free space optics1032includes one or more optical components such as taps, wavelength division multiplexers (WDM), splitters/combiners, polarization beam splitters (PBS), collimators, couplers, or other components to direct an optical signal. In some examples, free space optics1032includes components to transform the polarization state and direct received polarized light, for example, to optical detectors using a PBS. In one example, free space optics1032includes a diffractive element to deflect optical beams having different frequencies at different angles along an axis (e.g., a fast axis).

In some examples, LIDAR system1000includes optical scanner1042that includes one or more scanning mirrors that are rotatable along an axis (e.g., a slow axis) that is orthogonal or substantially orthogonal to the fast axis of the diffractive element. Optical scanner1042can steer optical signals to scan an environment according to a scanning pattern. For instance, the scanning mirrors can be rotatable by one or more galvanometers. Incident light from a source optical signal tends to scatter off objects in a target environment, generating a return optical beam or a target return signal. Optical scanner1042can collect the return optical beam or the target return signal and provide the return signal for processing. Optical scanner1042can return the signal to passive optical circuit components or active optical circuit components of optical circuits1012. For example, free space optics1032can direct a signal to an optical detector via a polarization beam splitter. In addition to mirrors and galvanometers, examples of optical scanner1042can include components such as a quarter-wave plate, lens, anti-reflective coated window, or other component to receive an optical signal.

To control and support optical circuits1012and optical scanner1042, LIDAR system1000includes LIDAR control system1020. LIDAR control system1020includes a signal processor, control component, or other device to process control operations for LIDAR system1000. The signal processor represents a processing device to control the operation of LIDAR system1000. The signal processor can be or include, for example, one or more general-purpose processing devices such as a microprocessor, central processing unit, processing component, or other controller/processor. The signal processor can be, for example, a complex instruction set computing (CISC) microprocessor, a reduced instruction set computer (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets, or processors implementing a combination of instruction sets. In one example, the signal processor can be or include one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or other computation component.

In some examples, LIDAR control system1020includes signal processing unit1022. Signal processing unit1022represents a processing device specific for perform signal computations. For example, signal processing unit1022can be a DSP. LIDAR control system1020can be configured to output digital control signals to control optical drivers1014. In some examples, the digital control signals can be converted to analog signals through signal conversion unit1016. For example, signal conversion unit1016can include a digital-to-analog converter (DAC). Optical drivers1014can provide drive signals to active optical components of optical circuits1012to drive optical sources such as lasers and amplifiers. In some examples, several optical drivers1014and signal conversion units1016can be provided to drive multiple optical sources.

LIDAR control system1020can be configured to output digital control signals for optical scanner1042. Motion control system1050can control galvanometers or other movable components of optical scanner1042based on control signals received from LIDAR control system1020. For example, a DAC can convert coordinate routing information from LIDAR control system1020to signals interpretable by galvanometers in optical scanner1042. In some examples, motion control system1050can return information to LIDAR control system1020about the position or operation of components of optical scanner1042. For example, an analog-to-digital converter (ADC) can convert information about a galvanometer's position to a signal interpretable by LIDAR control system1020.

LIDAR control system1020can be configured to analyze incoming digital signals. In this regard, LIDAR system1000includes free optical receivers1034to measure one or more beams received by free space optics1032, which can also be passed to optical circuits1012. For example, a reference beam receiver can measure the amplitude of a reference beam from an active optical component, and an ADC converts signals from the reference receiver to signals interpretable by LIDAR control system1020. Target receivers measure the optical signal that carries information about the range and velocity of a target in the form of a beat frequency, modulated optical signal. The reflected beam can be mixed with a signal from a local oscillator. Optical receivers1034can include a high-speed ADC to convert signals from the target receiver to signals interpretable by LIDAR control system1020. In some examples, signal conditioning unit1036can perform signal conditioning on signals from optical receivers1034prior to receipt by LIDAR control system1020. For example, the signals from optical receivers1034can be provided to an operational amplifier (op-amp) for amplification of the return signals and the amplified signals can be provided to LIDAR control system1020.

In some applications, LIDAR system1000includes one or more imaging devices1060configured to capture images of the environment, global positioning system (GPS)1080configured to provide a geographic location of the system, or other sensor inputs. Image processing system1070represents one or more components configured to receive the images from imaging devices1060or geographic location from GPS1080and prepare the information for receipt and use by LIDAR control system1020or other system connected to LIDAR system1000. For example, image information can be pre-processed for use by LIDAR control system1020. In another example, location information can be formatted for use by LIDAR system1000.

In some examples, the scanning process begins with optical drivers1014and LIDAR control system1020. LIDAR control system1020can instruct optical drivers1014to independently modulate one or more optical beams, and these modulated signals propagate through the optical circuit to a collimator. The collimator directs the light at the optical scanning system that scans the environment over a preprogrammed pattern defined by motion control system1050. Optical circuits1012can include a polarization wave plate (PWP) to transform the polarization of the light as it leaves optical circuits1012. In some examples, the polarization wave plate can be a quarter-wave plate or a half-wave plate. A portion of the polarized light can be reflected back to optical circuits1012. For example, lensing or collimating systems used in LIDAR system1000can have natural reflective properties or a reflective coating to reflect a portion of the light back to optical circuits1012.

Optical signals reflected back from the environment pass through optical circuits1012to the receivers. If the polarization of the light has been transformed, it can be reflected by a polarization beam splitter (PBS) along with the portion of polarized light that was reflected back to optical circuits1012. Accordingly, rather than returning to the same fiber or waveguide as an optical source, the reflected light can be reflected to separate optical receivers. These signals interfere with one another and generate a combined signal. Each beam signal that returns from the target produces a time-shifted waveform. The temporal phase difference between the two waveforms generates a beat frequency measured on the optical receivers (photodetectors). The combined signal can then be reflected to optical receivers1034.

Optical receivers1034can apply ADCs to convert the analog signals from optical receivers to digital signals. The digital signals are then sent to LIDAR control system1020. Signal processing unit1022can receive the digital signals and interpret them. In some examples, signal processing unit1022also receives position data from motion control system1050and galvanometers (not shown) as well as image data from image processing system1070. Signal processing unit1022can then generate a 3D point cloud with information about range and velocity of points in the environment as optical scanner1042scans additional points. Signal processing unit1022can also overlay a 3D point cloud data with the image data to determine velocity and distance of objects in the surrounding area. In one example, LIDAR system1000processes satellite-based navigation location data to provide a precise global location.

In operation according to some examples, LIDAR system1000can be configured to provide AGC. The AGC can be applied anywhere in the signal path, in accordance with any example provided. In one example, the AGC can be applied to an optical signal in an optical time domain signal path. In one example, the AGC can be applied to an electrical signal in an analog time domain signal path. In one example, the AGC can be applied to a digital signal in a time domain signal path. In one example, the AGC can be applied to a digital signal in a frequency domain signal path. AGC can be applied at more than one location in a signal path.

FIG. 11represents a time-frequency diagram illustrating an example of LIDAR waveform detection and processing. Diagram1100represents a time-frequency diagram of an FMCW scanning signal1110that can be used by a LIDAR system in accordance with embodiments of the present disclosure to scan a target environment according to some examples. In one example, the scanning waveform1110, labeled as fFM(t), can be a sawtooth waveform (sawtooth “chirp”) with a chirp bandwidth ΔfCand a chirp period TC.

The slope of the sawtooth is given as k=(ΔfC/TC). Diagram1100also depicts target return signal1120according to some examples. Target return signal1120, labeled as fFM(t−Δt), is a time-delayed version of scanning signal1110, where Δt is the roundtrip time to and from a target illuminated by scanning signal1110. The roundtrip time can be given as Δt=11R/v, where R is the target range, and v is the velocity of the optical beam, which can be the speed of light c. The target range, R, can therefore be calculated as R=c(Δt/2).

When return signal1120is optically mixed with scanning signal1110, a range-dependent difference frequency, referred to as the beat frequency, ΔfR(t) can be generated. The beat frequency ΔfR(t) can be linearly related to the time delay, Δt, by the slope of the sawtooth k. Thus, ΔfR(t)=kΔt. Since the target range R is proportional to Δt, the target range R can be calculated as R=(c/2)(ΔfR(t)/k). Thus, the range R is linearly related to the beat frequency ΔfR(t).

The beat frequency ΔfR(t) can be generated, for example, as an analog signal in optical receivers1034of system1000. The beat frequency can then be digitized by an ADC, for example, in a signal conditioning unit such as signal conditioning unit1036in LIDAR system1000. The digitized beat frequency signal can then be digitally processed, for example, in a signal processing unit, such as signal processing unit1022in system1000.

It will be understood that target return signal1120will, in general, also include a frequency offset (Doppler shift) if the target has a velocity relative to the LIDAR system. The Doppler shift can be determined separately, and used to correct the frequency of the return signal, so the Doppler shift is not shown in diagram1100for simplicity and ease of explanation. It should also be noted that the sampling frequency of the ADC will determine the highest beat frequency that can be processed by the system without aliasing. In general, the highest frequency that can be processed is one-half of the sampling frequency (i.e., the “Nyquist limit”).

In one example, and without limitation, if the sampling frequency of the ADC is 1 gigahertz, then the highest beat frequency that can be processed without aliasing (ΔfRmax) is 500 megahertz. This limit in turn determines the maximum range of the system as Rmax=(c/2)(ΔfRmax/k) which can be adjusted by changing the chirp slope k. In one example, while the data samples from the ADC may be continuous, the subsequent digital processing described below may be partitioned into “time segments” that can be associated with some periodicity in the LIDAR system. In one example, and without limitation, a time segment might correspond to a predetermined number of chirp periods T, or a number of full rotations in azimuth by the optical scanner.

FIG. 12illustrates an example of a LIDAR system that provides AGC for a LIDAR signal. System1200represents a system in accordance with embodiments of the present disclosure. System1200includes LIDAR1210, which represents a LIDAR system in accordance with any example herein.

In one example, LIDAR1210represents an optical chip, which can be coupled to a processor device or processor chip and a memory device or memory chip. In one example, system1200can be a single device with LIDAR, processing, and memory components in a single device or device package. In one example, LIDAR1210can be one of multiple LIDAR components coupled to a processing device.

LIDAR1210includes laser1220to provide an optical signal. Optical circuit1230includes one or more optical circuit components or elements to provide modulation, reference signaling, optical combining or other optical manipulation of an optical signal, amplification or attenuation, or other operation on an optical signal for system1200. The modulation can be active or passive. Optical circuit1730provides the modulation and optics to transmit TX signal1222to target1240and receive the reflection signal represented by RX signal1242.

Photodetector1250can receive RX signal1242from optical circuit1230from target1240, and LO signal1224from optical circuit1230from laser1220. System1200can condition the signal with one or more circuit components, represented by circuit1260. In one example, circuit1260includes an ADC component. Circuit1260can condition the received signal detected by photodetector1250.

Processor1270represents a processor device or processing unit. Processor1270can be a standalone component or be integrated in a computer system. Processor1270can provide time domain and frequency domain processing. Processor1270can compute or determine a target range value for target1240and/or a target velocity value for target1240based on the optical signal scanning and detected reflection signals.

The values generated can be part of a point cloud of information to map an environment of target1240. In one example, system1200includes memory1280coupled to processor1270to store information computed by processor1270, and to provide data for computation by processor1270. In one example, memory1280stores point cloud1282, to represent the information gathered by scanning target1240with LIDAR1210. Point cloud1282can be or include estimates or values computed by processor1270based on scanning target1240.

In one example, system1200includes AGC. Various AGC elements are represented in system1200. In one example, system1200includes more than one of an optical AGC at LO path1226, an analog AGC at path1252, a time domain AGC (one example of AGC1272in processor1270), or a frequency domain AGC (another example of AGC1272in processor1270).

In one example, system1200includes an AGC at LO path1226. Such an AGC can be referred to as an optical AGC, to provide variable gain to a light signal. The variable gain can increase the gain when the signal is lower than a threshold, and the variable gain can attenuate the signal to fit within a smaller dynamic range of subsequent processing elements. In one example, system1200includes an AGC at path1252, between photodetector1250and circuit1260. In one example, the AGC can be considered part of circuit1260. The AGC at path1252can be referred to as an analog AGC. The analog AGC can provide variable gain to an electrical signal generated from a detected return beam. The variable gain can increase the gain when the signal is lower than a threshold, and the variable gain can attenuate the signal to fit within a smaller dynamic range of subsequent processing elements.

In one example, processor1270includes AGC1272. In one example, AGC1272can represent a time domain AGC or digital time domain AGC in a digital processing path of the signal received from LIDAR1210. The digital time domain AGC can provide variable gain to a digital signal within processor1270. The variable gain can increase the gain when the signal is lower than a threshold, and the variable gain can attenuate the signal to fit within a smaller dynamic range for subsequent processing.

In one example, AGC1272can represent a frequency domain AGC or digital frequency domain AGC in a digital processing path of the signal received from LIDAR1210. The digital frequency domain AGC can provide variable gain to a frequency signal within processor1270. The variable gain can increase the gain when the signal is lower than a threshold, and the variable gain can attenuate the signal to fit within a smaller dynamic range for subsequent processing.

Besides what is described herein, various modifications can be made to the disclosed embodiments and implementations of the invention without departing from their scope. Therefore, the illustrations and examples herein should be construed in an illustrative, and not a restrictive sense.