The common questions in analog layout AuthorJerry Zhao
- Slides: 12
The common questions in analog layout Author：Jerry Zhao
Content n n n n n 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!!!
Why need match n we need accurate. Oh, my god! My head is missing! We are same! NO! You are too fat! OP Current mirror
Why need match (1) Why unit elements (2)Why common central n Ø Ø Ø 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
Why need same length n Ø 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= (one order approximately) Where △L=2 LD λVds
Why need unit Width to replicate n Ø Ø The multiple current mirrors need unit current cell to repeat Bird beak effect (LOCOS) Narrow channel effect
Why need Dummy n n The lateral etch affect outsides device The environment effect Lateral etch Same environment And ion distribution Notice Ions distribution
Why need shielding n Ø Ø Ø Critical signal need shielding Crosstalk interference Electronic field interference Noise disturbance Charge affinity I don’t like Cross-talk Clock line Critical signal Too many noise! I want to be quiet! Strong signal Hi, The guys arrest us sensitive signal
Why care parasitic n n n Rp Affect R-DAC accuracy. Rp Affect circuit speed Cp increase signal couple P. Inductor increase noise Parasitic Increase loading Resistor Limit current Parasitic Capacitor ∆V=L*d. I/dt Current change abrupt lead to large voltage variety
Why need seal ring n Avoid mobile ion enter die when wafer saw Na+ can move in oxide It affects MOS threshold voltage The passivation is lacerated! Let’s go! No way !!
Why top metal is immune to antenna effect n Top metal almost connect diffusion region in geometry (discharge the electrostatic charge. ) Dry, HV, long conductor , Jumper A lots of Few charges Static charges Dangerous!!! Safe
Summary n n Must ask why. Attitude is most important! Thanks!!!
