As discussed in Tutorial MT-099, there has been much pressure placed on system designers to verify their designs with computer simulations before committing to actual printed circuit board layouts and hardware. Simulating complex digital designs is extremely beneficial, and very often, the prototype phase can be eliminated entirely. However, bypassing the prototype phase in high-speed/high-performance analog or mixed-signal circuit designs can be risky for a number of reasons. The macromodels discussed in MT-099 are only approximations to the actual circuit, and parasitic effects such as package capacitance and inductance and PC board layout are rarely included. The models are simple enough so that circuits using multiple ICs can be simulated in a reasonable amount of computation time and with good certainty of convergence. Consequently, SPICE modeling does not always reproduce the exact performance of a circuit and should always be verified experimentally using a carefully built prototype. Finally, there are certain mixed-signal ICs such as A/D and D/A converters which have no SPICE models, or if they exist, the models do not simulate dynamic performance (signal-to-noise ratio, effective bits, SFDR, etc.). However, recent advances in software (ADIsimADC ™ o
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