The common questions The common questions in analog in analog layoutlayout

AuthorAuthor ：： Jerry ZhaoJerry Zhao

ContentContent Why need matchWhy need match Why need same lengthWhy need same length Why need unit width to replicateWhy need unit width to replicate Why need dummyWhy need dummy Why need shieldingWhy need shielding Why care parasiticWhy care parasitic Why need seal ringWhy need seal ring Why top metal is immune to antenna effectWhy top metal is immune to antenna effect Know how is not enough, we need know Know how is not enough, we need know

Why!!!Why!!!

Why need matchWhy need match we need accurate.we need accurate.

Oh, my god! My head is missing!

OP

We are same! NO!

You are too fat!

Current mirror

Why need matchWhy need match(1) Why unit elements(1) Why unit elements(2)Why common central(2)Why common central

Many errors sourceMany errors source

----we only discuss system errorwe only discuss system error oxide and doping gradients erroroxide and doping gradients error Gate shadowGate shadow Bird beak effect (LOCOS)Bird beak effect (LOCOS) Short channel effectShort channel effect lateral etching lateral etching

Oxide gradients

Why need same lengthWhy need same length The current mirror and OP’s input transistor The current mirror and OP’s input transistor

need same length, not just only same W/Lneed same length, not just only same W/L

Short channel effect (need same Short channel effect (need same λλ))

LLeff =eff =LL - - △△L L △△L/L= L/L= λλVVdsds

(one order (one order approximatelyapproximately) Where ) Where △△L=2L=2LLDD

Why need unit Width to replicateWhy need unit Width to replicate The multiple current mirrors need The multiple current mirrors need

unit current cell to repeatunit current cell to repeat

Bird beak effect (LOCOS)Bird beak effect (LOCOS) Narrow channel effectNarrow channel effect

Why need DummyWhy need Dummy The lateral etch affect outsides The lateral etch affect outsides

devicedevice The environment effectThe environment effect

Lateral etch

Same environment

And ion distributionNotice Ions distribution

Why need shieldingWhy need shielding Critical signal need shieldingCritical signal need shielding Crosstalk interferenceCrosstalk interference Electronic field interferenceElectronic field interference Noise disturbanceNoise disturbance

Too many noise!

I want to be quiet!

I don’t like

Cross-talk

Charge affinity

sensitive signal

Strong signal

Clock line

Critical signal

Hi, The guys arrest us

Why care parasiticWhy care parasitic RRp p Affect R-DAC accuracy.Affect R-DAC accuracy. RRp p Affect circuit speedAffect circuit speed CCp p Affect circuit speedAffect circuit speed CCp p increase signal coupleincrease signal couple P. Inductor increase noiseP. Inductor increase noise

Parasitic

Resistor

Parasitic

Capacitor

Limit current

Increase loading

∆ V=L*dI/dt

Current change abrupt lead to large voltage variety

Why need seal ringWhy need seal ring

Avoid mobile ion enter die when wafer sawAvoid mobile ion enter die when wafer saw

Na+ can move in oxideNa+ can move in oxide

It affects MOS threshold voltageIt affects MOS threshold voltage

The passivation is lacerated!

Let’s go!

No way !!

Why top metal is immune to Why top metal is immune to antenna effectantenna effect

Top metal almost connect diffusion Top metal almost connect diffusion region in geometry (discharge the region in geometry (discharge the electrostatic charge.)electrostatic charge.)

Dry, HV, long conductor ,

A lots of

Static charges

Dangerous!!!

Jumper

Few charges

Safe

SummarySummary

Must ask why.Must ask why. Attitude is most important!Attitude is most important!

Thanks!!!Thanks!!!