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| Differences Between PCB & IC Design |
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- IC design is at the transistor level. (digital ASIC's excepted)
- PCBs stress low component count, chips stress small size.
- IC signal processing is fully differential, PCB tends to be ground referenced.
- ICs emphasize the matching of components (so-called "ratiometric" designs) while tolerating looser absolute values and poorer thermal characteristics.
- Parasitic devices, inherent to fabrication, are a primary issue in IC designs.
- ESD and electromigration are a major issue in chips.
- IC's avoid using large value resistors or capacitors due to area.
- IC's eliminate resistors as much as possible using current mirrors and other circuit design techniques.
- In chips, due to limited externally accessible circuit nodes, design-for-testability issues are much more demanding.
- Due to IC fabrication cycles that take 1-3 months, and high fabrication costs, the "breadboard, measure and adjust" methodology is not viable. Chip design is done totally with SPICE-type simulation tools.
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