Editing Mixed-signal integrated circuit (section)

== Design and development ==
Typically, mixed-signal 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 [[superluminescent diode|SLED]] [[control logic]] of a [[DVD]] player. Mixed-signal ICs often contain an entire [[system-on-a-chip]]. They may also contain on-chip memory blocks (like [[programmable read-only memory|OTP]]), which complicates the manufacturing compared to analog ICs. A mixed-signal IC minimizes off-chip interconnects between digital and analog functionality in the system—typically reducing size and weight due to minimized packaging and a smaller [[printed circuit board|module substrate]]—and therefore increases the reliability of the system.

Because of the use of both digital signal processing and analog circuitry, mixed-signal ICs are usually designed for a very specific purpose. Their design requires a high level of expertise and careful use of [[computer aided design]] (CAD) tools. There also exists specific design tools (like mixed-signal simulators) or description languages (like [[VHDL-AMS]]). Automated testing of the finished chips can also be challenging. [[Teradyne]], [[Keysight]], and [[Advantest]] are the major suppliers of the test equipment for mixed-signal chips.

There are several particular challenges of mixed-signal circuit manufacturing:
* [[CMOS]] technology is usually optimal for digital performance, while [[Bipolar junction transistor|bipolar junction transistors]] are usually optimal for analog performance. However, until the last decade, it was difficult to combine these cost-effectively or to design both in a single technology without serious performance compromises. The advent of technologies like high performance [[CMOS]], [[BiCMOS]], CMOS [[Silicon on insulator|SOI]], and [[SiGe]] have removed many of these former compromises.
* Testing functional operation of mixed-signal ICs remains complex, expensive, and often is a "one-off" implementation task (meaning a lot of work is necessary for a product with a single, specific use).
* Systematic design methods of analog and mixed-signal circuits are far more primitive than digital circuits. In general, analog circuit design cannot be automated to nearly the extent that digital circuit design can. Combining the two technologies multiplies this complication.
* Fast-changing digital signals send noise to sensitive analog inputs. One path for this noise is [[substrate coupling]]. A variety of techniques are used to attempt to block or cancel this noise coupling, such as [[fully differential amplifier]]s,<ref>{{cite book | chapter-url=https://ieeexplore.ieee.org/document/777869 | doi=10.1109/ISCAS.1999.777869 | chapter=Fully differential current-input CMOS amplifier front-end suppressing mixed signal substrate noise for optoelectronic applications | title=ISCAS'99. Proceedings of the 1999 IEEE International Symposium on Circuits and Systems VLSI (Cat. No.99CH36349) | year=1999 | last1=Chang | first1=J.J. | last2=Myunghee Lee | last3=Sungyong Jung | last4=Brooke | first4=M.A. | last5=Jokerst | first5=N.M. | last6=Wills | first6=D.S. | volume=1 | pages=327–330 | isbn=0-7803-5471-0 | s2cid=206955680 }}</ref> P+ guard-rings,<ref>{{cite book | chapter-url=https://ieeexplore.ieee.org/document/674725 | doi=10.1049/cp:19971128 | chapter=Substrate noise issues in mixed-signal chip designs using Spice | title=International Conference on Electromagnetic Compatibility | year=1997 | last1=Singh | first1=R. | volume=1997 | pages=108–112 | isbn=0-85296-695-4 }}</ref> differential topology, on-chip decoupling, and triple-well isolation.<ref>
[http://electronicdesign.com/Articles/ArticleID/2499/2499.html "Mixed-Signal IC Merges 14-Bit ADC With DSP In 0.18-μm CMOS"]
</ref>

=== Variations ===
Mixed-signal devices are available as standard parts, but sometimes custom-designed [[application-specific integrated circuit]]s (ASICs) are necessary. ASICs are designed for new applications, when new standards emerge, or when new energy source(s){{Clarify|reason=What does "new energy source(s)" mean?|date=August 2022}} are implemented in the system. Due to their specialization, ASICs are usually only developed when production volumes are estimated to be high. The availability of ready-and-tested analog- and mixed-signal [[Semiconductor intellectual property core|IP]] blocks from foundries or dedicated design houses has lowered the gap to realize mixed-signal ASICs. 

There also exist mixed-signal [[FPGA|field-programmable gate array]]s (FPGAs) and [[microcontroller]]s.{{NoteTag|Mixed-signal FPGAs are an extension of [[field-programmable analog arrays]].|name=extension_of_FPAA}} In these, the same chip that handles digital logic may contain mixed-signal structures like analog-to-digital and digital-to-analog converter(s), operational amplifiers, or wireless connectivity blocks.<ref>[https://www.microsemi.com/product-directory/fpgas/1691-fusion "Microsemi Fusion mixed-signal FPGA"]</ref> These mixed-signal FPGAs and microcontrollers are bridging the gap between standard mixed-signal devices, full-custom ASICs, and embedded software; they offer a solution during product development or when product volume is too low to justify an ASIC. However, they can have performance limitations, such as the resolution of the analog-to-digital converters, the speed of digital-to-analog conversion, or a limited number of inputs and outputs. Nevertheless, they can speed up the system architecture design, prototyping, and even production (at small and medium scales). Their usage also can be supported with development boards, development community, and possibly software support.