a time error correction method applied to high-precision aer asynchronous cmos image sensor...

A Time Error Correction Method Applied to High-Precision AER Asynchronous CMOS Image Sensor

李东盛

Introduction

• Low redundancy• High time resolutionNo frame

• High DR• Digital

Time-domain

• Real-time visual sensory

• Intelligent

Autonomous

Categories

Light intensity change

• Tracking for high-speed particle

Light intensity

• Video monitoring

Color change

• Robotics vision

Event AER Process

Working principle of AER

Address Event Representation

Pixel structure Two PDs Three stages in

CD Reset control EM

Pixel Array Pixel → Row arbiter →

Row address encoder → pixel → Column arbiter → Column address encoder → external → pixel

Because the time-stamping of the AER asynchronous image sensors is made in the external, so the time of making time-stamping is not the accurate time when the pixel generates pulse events.

0,0

0,1

0,n 1,n

1,1

1,0 n,0

n,1

n,n

a,b

Row

Add

ress

Enc

ode

Row

Arb

iter

Tre

e

Colum Address Encode

Colum Arbiter Tree

AER[0:x]

REQ

ACK

The Arbiterreq0

req1

ack0

ack1

req2

req3

ack2

ack3

req(n-1)

req(n)

ack(n-1)

ack(n)

treq

treq

tack

tack

tack-ME

tsw

treq

MEackackreqab ttitiT )1(

Time Error Analysis

outaercolabpixaerrowabdelay TTTTT

Time Error Analysis Single event

Two events(in an 8×8 pixel array)

Tp1 is the delay of external processing and acknowledgment(Mainly determined by the external processing speed)

Tdelay2

outaercolabpixaerrowabdelay TTTTT MEackackreqrowab ttntnT )1(

MEackackreqcolab ttntnT )1(

MEackackreqoutaerpixaerdelayerror tttTTTT 25711

2112 delaypdelayerror TTTT

(a) (b) (c)

If the two events are in the different rows

In Fig. 5 Trowab Tdelay2

(a)

(b)

(c)

acksw tt outaerpixaerMEackreqacksw TTtttt 44

ackswreq ttt 2 outaerpixaerMEackreqacksw TTtttt 55

ackswreq ttt 32 outaerpixaerMEackreqacksw TTtttt 66

(a) (b) (c) (d)

If the two events are in the same row

In Fig 6 Tcolab Tdelay2

(a)

(b)

(c)

(d)

acksw tt outaeracksw Ttt

ackswreq ttt 2 outaerackswreq Tttt 2



more than two pixels sending requests at the same time

When an event is being processed and some other events are waiting for being processed, another event occurs:

1

1

)(m

idelaympidelayierrorm TTTT

mn

m

nidelaympidelayierrorm tTTTT

1

)(

Time Error Analysis Main factors

The complexity of the pixel array The event rate Processing speed of the external circuit

Error on image

The more the light intensity is, the worse the error on image is.

%100__

hl

errorherrorl

tt

tt

ph

PDthhl I

CVTtt

int

Correct method

Recording the time error from red to green can be achieved.

Pixel and pixel array with correction

Change Detector

Exploration Measure

Counter

Rst

RR

RA

RS

CS

RH RL AH AL

C

0,0

0,1

0,n 1,n

1,1

1,0 n,0

n,1

n,n

a,b

Row

Add

ress

Enc

ode

Row

Arb

iter

Tre

e

Colum Address Encode

Colum Arbiter Tree

REQ

ACK

Cou

nter

Rea

dout

Cir

cuit

Cou

nter

Con

trol

Cir

cuit

Mod

ifie

d V

alue

Row

and

Col

um A

ddre

ss

Timer

CorrectTime-stamping Processing

External

Simulation in Matlab

All the simulation was based on the global reset mode.

Mainly based on an 8×8 pixel array.

Light intensity

10 100 1000 10000 100000

line 1 0.0001 0.0006 0.0043 0.0415 0.2789

line 2 0.000001 0 0.0001 0.0005 0.0031

2.50%

7.50%

12.50%

17.50%

22.50%

27.50%

Simulation condition: All the pixels with the same input signal. Speed: 100MHz

Collision events

Number

of

collision

events

Without

correctionWith correction

Error

rangeAverage

Error

rangeAverage

64

0.033%

~7.933

%

4.154% 0. 033% 0. 033%

32

0.200%

~4.100

%

2.111%0~0.033

%0. 017%

16

0.142%

~2.062

%

0.996%0~0.041

%0.023%

Simulation condition: Speed:100MHz Light:

5000~10000Lux

Processing Speed

9000

9500

10000

10500

11000

11500

9000

9500

10000

10500

11000

11500

9000

9500

10000

10500

11000

11500

9000

9500

10000

10500

11000

11500

(a) Input illumination

(b) Results with 50MHz speed

(c) Results with 100MHz speed

(d) Results with 200MHz speed

9000

9500

10000

10500

11000

11500

9000

9500

10000

10500

11000

11500

9000

9500

10000

10500

11000

11500

Uncorrected Corrected

uncorrected corrected0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

2.92%

0.53%

1.85%

0.24%

1.22%

0.16%

50MHz 100MHz 200MHz

Simulation condition: Light: 10000~11000Lux

Scale of the pixel array

Simulation condition: Light: 3000~4000Lux Speed: 100MHz

Simulation in Specture

Signals in CD unit

Simulation results for the array

THANK YOU~

a time error correction method applied to high-precision aer asynchronous cmos image sensor...

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