# US 10,371,802 B2 · Systems and methods for optical distance measurement

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 10,371,802 B2
- Document ID: US10371802B2
- Status: Granted
- Kind: B2
- Application number: 15/944,729
- Filed: 2018-04-03
- Published: 2019-01-24
- Granted: 2019-08-06
- Earliest claimed: 2017-07-20
- Assignees: Sz Dji Technology Co., Ltd.
- Applicants: Sz Dji Technology Co., Ltd.
- Inventors: Xiang Liu; Mingming Gao; Xiaoping Hong; Di Wu
- Web page: https://patentgrep.com/patent/US10371802B2

## CPC

- G01S 7/4861: Circuits for detection, sampling, integration or read-out
- G01S 17/10: using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32)
- H03K 5/133: using a chain of active delay devices
- H03K 19/017581: {programmable}
- H03K 5/24: the characteristic being amplitude
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)

## Abstract

Systems and methods for performing optical distance measurement are provided. In one aspect, a system for measuring a distance to an object comprises a light emitter configured to emit an outbound light pulse, and a light sensor configured to receive a returning light pulse reflected from the object and output an analog pulse signal representing the returning light pulse. The system also comprises a field-programmable gate array (FPGA) coupled to the light sensor. The FPGA is configured to convert the analog pulse signal to a plurality of digital signal values, and generate a plurality of time measurements corresponding to the plurality of digital signal values. The system also comprises a controller configured to calculate the distance to the object based on the plurality of digital signal values and the plurality of time measurements.

## Claims

### Claim 1

A system for measuring a distance to an object, the system comprising:
a light emitter configured to emit an outbound light pulse;
a light sensor configured to receive a returning light pulse reflected from the object and output an analog pulse signal representing the returning light pulse;
a field-programmable gate array (FPGA) coupled to the light sensor, wherein the FPGA includes a plurality of delay units and a plurality of latches, wherein the delay units are sequentially coupled to each other, wherein each latch is coupled to a corresponding delay unit of the plurality of delay units, and wherein the FPGA is configured to—
convert the analog pulse signal to a plurality of digital signal values, and
generate a plurality of time measurements corresponding to the plurality of digital signal values by sampling each digital signal value, wherein a time resolution of the sampling is shorter than a clock period of the FPGA, and wherein sampling each digital signal value includes—
transmitting the digital signal value sequentially along the plurality of delay units;
determining a number of the plurality of latches that were triggered during a clock cycle of the FPGA, wherein each latch is configured to be latched in response to the corresponding delay unit receiving the digital signal value; and
calculating a time measurement corresponding to the digital signal value based on the determined number; and
a controller configured to calculate the distance to the object based on the plurality of digital signal values and the plurality of time measurements.

### Claim 2 (depends on 1)

The system of claim 1, wherein the light emitter, light sensor, FPGA, and controller are carried by an unmanned vehicle, an autonomous vehicle, or a robot.

### Claim 3 (depends on 1)

The system of claim 1, wherein the time resolution is at least 5 times shorter than the clock period of the FPGA.

### Claim 4 (depends on 1)

The system of claim 1, wherein the plurality of delay units comprises at least 25 delay units.

### Claim 5 (depends on 1)

The system of claim 1, wherein the plurality of delay units comprises a carry chain or a lookup table (LUT).

### Claim 6 (depends on 1)

The system of claim 1, wherein each of the plurality of delay units is configured to produce a delay within a range from 5 picoseconds to 2000 picoseconds.

### Claim 7 (depends on 1)

The system of claim 1, further comprising a temperature sensor positioned on, in, or near the FPGA, wherein the FPGA is configured to generate the plurality of time measurements by:
receiving a temperature value from the temperature sensor; and
calculating the time measurement based on the temperature value.

### Claim 8 (depends on 1)

The system of claim 1 wherein the field-programmable gate array (FPGA) is configured to convert the analog pulse signal to the plurality of digital signal values by (1) comparing the analog pulse signal to a plurality of threshold values and (2) generating the plurality of digital signal values based on the comparison.

### Claim 9 (depends on 8)

The system of claim 8, wherein the plurality of different threshold values comprises at least 2 different threshold values.

### Claim 10 (depends on 8)

The system of claim 8, wherein the FPGA comprises a plurality of differential input ports, and wherein the FPGA is configured to convert the analog pulse signal using the plurality of differential input ports.

### Claim 11 (depends on 10)

The system of claim 10, wherein each differential input port comprises a low-voltage differential signaling (LVDS) interface or an emitter-coupled logic (ECL) interface.

### Claim 12 (depends on 10)

The system of claim 10, wherein the FPGA is further configured to: receive the analog pulse signal and a threshold value at each of the plurality of differential input ports, wherein each differential input port receives a different threshold value.

### Claim 13 (depends on 8)

The system of claim 8, wherein the controller is configured to calculate the distance by:
inputting the plurality of digital signal values and the plurality of time measurements into a function; and
deriving an estimated time value for the returning light pulse using the function.

### Claim 14 (depends on 13)

The system of claim 13, wherein the function comprises a pulse signal model, and wherein the estimated time value is derived by fitting the plurality of digital signal values and the plurality of time measurements to the pulse signal model.

### Claim 15

A method for measuring a distance to an object, the method comprising:
emitting, by a light emitter, an outbound light pulse;
receiving, at a light sensor, a returning light pulse reflected from the object;
outputting, by the light sensor, an analog pulse signal representing the returning light pulse;
converting, using a field-programmable gate array (FPGA), the analog pulse signal to a plurality of digital signal values;
generating, using the FPGA, a plurality of time measurements corresponding to the plurality of digital signal values by sampling each digital signal value, wherein a time resolution of the sampling is shorter than a clock period of the FPGA, and wherein sampling each digital signal value includes—
transmitting the digital signal value along a plurality of sequentially coupled delay units;
determining a number of a plurality of latches that were triggered during a clock cycle of the FPGA, wherein each latch is coupled to a corresponding delay unit of the plurality of delay units, and wherein each latch is configured to be latched in response to the corresponding delay unit receiving the digital signal value; and
calculating a time measurement corresponding to the digital signal value based on the determined number; and
calculating the distance to the object based on the plurality of digital signal values and the plurality of time measurements.

### Claim 16 (depends on 15)

The method of claim 15, wherein the light emitter, light sensor, and FPGA are carried by an unmanned vehicle, an autonomous vehicle, or a robot.

### Claim 17 (depends on 15)

The method of claim 15, wherein generating the plurality of time measurements comprises:
receiving a temperature value from a temperature sensor positioned on, in, or near the FPGA; and
calculating the time measurement based on the temperature value.

### Claim 18 (depends on 15)

The method of claim 15 wherein converting the analog pulse signal to the plurality of digital signal values includes (1) comparing the analog pulse value to a plurality of threshold values and (2) generating the plurality of digital signal values based on the comparison.

### Claim 19 (depends on 18)

The method of claim 18, wherein the FPGA comprises a plurality of differential input ports, and wherein the converting step is performed using the plurality of differential input ports.

### Claim 20 (depends on 19)

The method of claim 19, further comprising: receiving the analog pulse signal and a threshold value at each of the plurality of differential input ports, wherein each differential input port receives a different threshold value.

### Claim 21 (depends on 20)

The method of claim 20, wherein the analog pulse signal is received at a first pin of each differential input port and the threshold value is received at a second pin of each differential input port.

### Claim 22 (depends on 21)

The method of claim 21, further comprising applying an adjustment voltage to the second pin of each differential input port, wherein the adjustment voltage is configured to compensate for an offset voltage between the first and second pins of the differential input port.