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A mixed-signal integrated circuit combines analog and digital circuitry on a single semiconductor die.
Typically, these chips perform some whole function or sub-function in a larger assembly such as the radio subsystem of a cell phone, or the read data path and laser sled control logic of a DVD player. They often contain an entire system-on-a-chip.
Because of their use of both digital logic and analog circuitry, mixed-signal ICs are usually designed for a very specific purpose and their design requires a high level of expertise and careful use of the ECAD design automation tools. Automated testing of the finished chips can also be challenging. Teradyne and Agilent are the major suppliers of the test equipment for mixed-signal chips.
Until the mid-1990s, "mixed-signal" usually meant ADC, DAC, modem, electronic power supply, or digital buffer integrated circuits. Digitally controlled sound chips are also mixed-signal circuits. With the advent of cellular technology and network technology this category now includes cellular telephone, software radio, LAN and WAN router integrated circuits.
The particular challenges of mixed signal include:
- CMOS technology is usually optimal for digital performance and scaling while bipolar transistors are usually optimal for analog performance, yet until the last decade it has been difficult to either combine these cost-effectively or to design both analog and digital in a single technology without serious performance compromises. The advent of technologies like high performance CMOS, CMOS SOI and SiGe have removed many of the compromises that previously had to be made.
- Testing functional operation of mixed-signal ICs remains complex, expensive and often a "one-off" implementation task
- Systematic design methodologies comparable to digital design methods are far more primitve in the analog and mixed-signal arena. Analog circuit design can not generally be automated to nearly the extent that digital circuit design can. Combining the two technologies multiplies this complication.
Commercial examples
"Mixed-signal integrated circuit"