December Thesis Presentation

8/9/2019 December Thesis Presentation

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High Speed Sigma-delta

ADC for CMOS ImageSensor

Rohish Kumar Reddy Mitta(r0!"#$

%romoter - &eorges &ielen

Super'isor -hai Ha )e


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Outline

Introdu*tion to CMOS image sensors ypes of A+D *on'erters

In*remental , *on'erter

In*remental , ADC

.eed for MASH stru*ture for high order *onsideration


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! read out

4 he 6asi* ! pi3el ar*hite*ture*onsists

A pinned diode *onfiguration

A reset transistor

A transfer gate to mo'e

*harge from the photodiode tothe floating diffusion sense

node

A sour*e follo5er transistor

A ro5 sele*t transistor

5i8ipedia


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# read out4 #- A%S pi3el in*ludes a reset transistor a sour*e follo5er transistor to

isolate the sense node from thelarge *olumn 6us *apa*itan*e

a ro5 sele*t transistor he *urrent sour*e *omponent of

the follo5er amplifier is shared 6y a

*olumn of pi3els9 Readout is performed one ro5 at a

time9 7a*h ro5 of pi3els is reset

after it is read out to the *olumn

*apa*itors

'ia the ro5 a**ess transistors and

*olumn amplifiers9

5i8ipedia


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! is most *ommonly used pi3el *onfiguration

4 he pi3el uses CDS (Correlated Dou6le Sampling$4 A method to measure ele*tri*al 'alues su*h as 'oltages or

*urrents that allo5s remo'ing an undesired offset9 It is

used often 5hen measuring sensor outputs9

4 he output of the sensor is measured t5i*e/ on*e in a8no5n *ondition and on*e in an un8no5n *ondition9 he

'alue measured from the 8no5n *ondition is then

su6tra*ted from the un8no5n *ondition to generate a 'alue

5ith a 8no5n relation to the physi*al :uantity 6eing

measured9

http://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Voltage


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;hy 5e need CDS for the image sensors

4 Read out *ir*uit of the image sensors


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7l gamal


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ADC ypes

4 here are many 'ariations of ADCs 5hi*h *an 6e 6roughtdo5n to

o Single Sampling e9g9


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Single Sampling ADC


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Single sampling ADC


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In*remental Sigma Delta ADC


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In*remental Sigma delta

4 here are t5o types of in*remental sigma delta*onfigurationo


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uanti=er signal is *omplete dependent on the 'alue of the ?9


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Designing the digital filter

4 he resolution of the ad* depends on the Computing more samples

More orders

he order ADC output at se*ond integrator

4


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he input

4 -?ref@?@?ref

4 -@?in@

4 hus 6y this inferen*e the resolution in*reases 6y theimplementation 9

4

M


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o in*rease the resolution of the ADC

4 he resolution of the ad* ar*hite*ture in*reases 6yo In*reasing the num6er of samples

o In*reasing the order of the ADC

hus 5e *ome to introdu*e the MASH ar*hite*ture for thedesign of high resolution ad*

h MASH hit t


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he MASH ar*hite*ture

Σ ∫ ∫ Σ

DAC

Σ ∫ ∫ Σ

DAC

Σ

-

-

-

--

<

<

Σ

dB

dB


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%ro6lems 5ith MASH ADC

4 Mismat*h in the analog loops and the digital loopmat*hing9

4 A different analysis is re:uired in assigning the *onstantsfor the sta6ility of the system

4 SMASH(sturdy MASH$ ar*hite*ture is re:uired


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Documents

December Thesis Presentation