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The common questions in analog layout

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Presentation on theme: "The common questions in analog layout"— Presentation transcript:

1 The common questions in analog layout
Author:Jerry Zhao

2 Content Why!!! Why need match Why need same length
Why need unit width to replicate Why need dummy Why need shielding Why care parasitic Why need seal ring Why top metal is immune to antenna effect Know how is not enough, we need know Why!!!

3 Why need match we need accurate. We are same! You are too fat! NO!
Oh, my god! My head is missing! OP Current mirror

4 Why need match (1) Why unit elements (2)Why common central
Many errors source --we only discuss system error oxide and doping gradients error Gate shadow Bird beak effect (LOCOS) Short channel effect lateral etching Oxide gradients

5 Why need same length Short channel effect (need same λ)
The current mirror and OP’s input transistor need same length, not just only same W/L Short channel effect (need same λ) Leff =L - △L △L/L= λVds (one order approximately) Where △L=2LD

6 Why need unit Width to replicate
The multiple current mirrors need unit current cell to repeat Bird beak effect (LOCOS) Narrow channel effect

7 Why need Dummy The lateral etch affect outsides device
The environment effect Lateral etch Same environment And ion distribution Notice Ions distribution

8 Why need shielding Critical signal need shielding
Crosstalk interference Electronic field interference Noise disturbance I don’t like Cross-talk Critical signal Clock line Too many noise! I want to be quiet! Charge affinity sensitive signal Strong signal Hi, The guys arrest us

9 Why care parasitic Rp Affect R-DAC accuracy. Rp Affect circuit speed
Cp Affect circuit speed Cp increase signal couple P. Inductor increase noise ∆V=L*dI/dt Current change abrupt lead to large voltage variety Parasitic Resistor Increase loading Parasitic Capacitor Limit current

10 Why need seal ring Avoid mobile ion enter die when wafer saw
Na+ can move in oxide It affects MOS threshold voltage No way !! The passivation is lacerated! Let’s go!

11 Why top metal is immune to antenna effect
Top metal almost connect diffusion region in geometry (discharge the electrostatic charge.) Dry, HV, long conductor , A lots of Static charges Dangerous!!! Jumper Few charges Safe

12 Summary Must ask why. Attitude is most important! Thanks!!!


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