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The common questions in analog layout

The common questions in analog layout. Author ： Jerry Zhao. Content. 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

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The common questions in analog layout

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  1. The common questions in analog layout Author：Jerry Zhao

  2. Content 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 are same! • we need accurate. NO! You are too fat! 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 • 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 I don’t like Cross-talk • Critical signal need shielding • Crosstalk interference • Electronic field interference • Noise disturbance 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 ∆V=L*dI/dt Current change abrupt lead to large voltage variety • Rp Affect R-DAC accuracy. • Rp Affect circuit speed • Cp Affect circuit speed • Cp increase signal couple • P. Inductor increase noise 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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