Seamless MicrosystemsD i g i t i z i n g Yo u r W o r l d S e a m l e s s l y

Augustine Kuo

VP Engineering

ADCs for

Autonomous Driving

Seamless Microsystems Background

Consumer

Medical Imaging

Wireless and

Wireline Comm.

SM40M SM80M SM45MSM250M SM250M SM250M SM400M

LiDAR and RADAR in

cars

2

3

Silicon Valley Traffic

4

Tesla Autopilot! Available now!

5

Works most of the time, but…

Range – needs to be 300m for freeway speeds

Range/angular resolution – needs to be in cm for object identification

Works in bad weather – rain/snow/etc.

Works in dark

Works in bright light

Radial velocity – determining speed of objects moving toward or away

from car

Color/contrast – recognize signs, lane markers, signal lights

6

Important Capabilities for Automotive Sensors

Sensor RADAR Camera/Vision LIDAR

Range

Range resolution

Angular resolution

Works in bad weather

Works in dark

Works in bright light

Radial velocity

Color/contrast

7

Comparison of sensors in various environments

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Why Tesla’s autopilot might be failing?

Tesla’s autopilot only uses radar and cameras for sensing

High resolution RADAR

Sensor RADAR Camera/Vision LIDAR

Range

Range resolution

Angular resolution

Works in bad weather

Works in dark

Works in bright light

Radial velocity

Color/contrast

9

Comparison of sensors in various environments

10

Comparison of RADAR vs LiDAR

High resolution RADAR LiDAR

12 feet? 17 feet

11

Most autonomous cars now use all three sensors

LiDAR

Camera

RADAR(usually mounted behind body

panels)

Laser

PIN

APD

SPAD

array

A ADC Detection Estimation

TDC Estimation

3-D Point

Cloud

3-D Point

Cloud

Full waveform capture LiDAR Rx

Geiger/Single-Photon LiDAR Rx

OPTICAL ANALOG DIGITAL

12Gb/s 300Mb/s

Time-of-Flight LiDAR Systems

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LiDAR

Receiver Technique

Geiger

Mode

Full-Waveform

Capture

Processing simplicity/power consumption

Cost

Range/Resolution

Quick Object Classification (reflectance data)

Multi-return echo detection (ie foliage, poles/wires)

Error-free from other LiDARs (interference)

Comparison of LiDAR receiver techniques

13

Current LiDAR solutions are expensive

$1600 for ADCs alone (8 channels)

ADC ADC ADC ADC

ADC ADC ADC ADC

Digital

14

ADCs in LiDAR Are Bulky and Expensive

Very hard to build

Large footprint

ADC ADC ADC ADC

ADC ADC ADC ADC

Digital

Speed Resolution

> 0.5 GHz 10-bits

Power/ch.

~1W

15

LiDAR Receive Pulse Digitization

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ADC

RX Chain

Time domain

Pulse + Noise

Frequency domain

LiDAR

Received

Pulse

4ns

Sampling speed > 0.5GHz

Resolution > 10-bits

LiDAR ADC Requirements

Bandwidth > 250MHz

LPF

Problem 1: Power Hungry LPF

ADCLPF

LiDAR

Pulse

Significant SNR degradation due

to noise aliasing

Requires expensive LPF to

minimize noise aliasing

• 8th order LPF

• 4x AD8099 chips @ $14

• 600mW 0 2.5 5 7.5 10 15

Frequency Hz 108

-40

-35

-30

-25

-20

-15

-10

-5

0

Am

plitu

de

dB

Nyquist

Band

Alias

Band 1

Alias

Band 2

Alias

Band 3

Alias

Band 4

Alias

Band 5

Analog LPF

Power hungry (600mW/ch.) and expensive ($14/ch)17

Problem 2: Poor Jitter Tolerance

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ADCLPF

LiDAR

Pulse

CLOCK

Very accurate clock source requirement for ADC sampling

<300fs rms jitter requirement for LiDAR ADCs

Expensive

• On-board clock generators: TI LMK61A2-100M00SIAT ~ $7.00

• On-chip (inside ADC) clock generators

- Large Silicon area

- Large cost

Switched-capacitor input interface is hard to drive

• Needs power hungry buffer

ADC input driver ~ 20% ADC power consumption

Problem 3: Power-Hungry ADC Input Driver

LogicVREF

SAR 1

SAR 2

SAR N

ADC

RX Chain

LPF

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Best ADCs for LiDAR: Continuous-time DS ADCs

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High speed sigma delta ADCs

• Enabled by SMI’s patented technology

Inherent over-sampling

• No requirement for anti-alias filter

Resistive input impedance

• Low power ADC driver

Low-pass filtering using integrators before sampling

Simple digital calibration

ò ò òSM4-bit SM

ADC

4-bit

SCDAC

Merged SMOA-RC

Integrator-ADC

-VINCalibration

& Filtering

ANALOG DIGITAL

DOUT+

12-bit

Seamless’ Continuous-Time DS ADCs

All products have to be safety certified

• Design management certifications – ISO 9001/IATF 16949

• ISO 26262- IP/Chips have to be AEC Q100 certified

ESD testing

Latch-up

Long term high temperature operation (1000 hour bake)

Need production versions of chips – at least 3600 units

- IP/Chips have to detect, report and self-correct a fault

In real time to enable work-around

- IP/Chips need to have hooks to protect the system above itself

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Other Automotive ADC Requirements

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ADC Testing Requirements in ISO 26262

SMSP CT

SD ADC

+

-IN

DOUT

12-bits

500MS/s

FCLK = 3GHz

SMSP CT

SD ADC

+

-IN

DOUT

12-bits

500MS/s

FCLK = 3GHz

SMSP CT

SD ADC

+

-IN

DOUT

12-bits

500MS/s

FCLK = 3GHz

SMSP CT

SD ADC

+

-IN

DOUT

12-bits

500MS/s

FCLK = 3GHz

SMSP CT

SD ADC

+

-IN

DOUT

12-bits

500MS/s

FCLK = 3GHz

SM250M

4 channel ADC

With 1 redundant

testing channel

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DIGITAL

ADC ADC ADC ADC ADC

IP or Chiplets?

• Digital will be a large portion of the SoC

• Done in lower CMOS nodes for

power/cost savings

• ADCs as chiplets

• Does not need to be in same

process as digital

• Can be ISO 26262 qualified

independently to reduce time-to-

market

• ADCs as IP

• Lower power

• Easier packaging

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Conclusions

• For autonomous driving sensors, high bandwidth and high

resolution ADCs will be needed

• LiDAR/RADAR will definitely be used

• Full-waveform capture needed for long range

• Automotive components have long lead time

• Products need to be done quickly so exhaustive tests can

begin sooner

• ISO 26262 compliance is easier if every component is

already qualified

[1] 2015 study released by the Auto Insurance Center

[2] Synopsys white paper – “Data converters IP for Automotive SoCs”

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References