December Thesis Presentation
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Transcript of 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
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-
-
--
<
<
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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