Amixed-signal integrated circuit is anyintegrated circuit that has bothanalog circuits anddigital circuits on a singlesemiconductor die.[1][2][3][4] Their usage has grown dramatically with the increased use ofcell phones,telecommunications, portable electronics, and automobiles with electronics anddigital sensors.
Integrated circuits (ICs) are generally classified as digital (e.g. amicroprocessor) or analog (e.g. anoperational amplifier). Mixed-signal ICs contain both digital and analog circuitry on the same chip, and sometimesembedded software. Mixed-signal ICs process both analog and digital signals together. For example, ananalog-to-digital converter (ADC) is a typical mixed-signal circuit.
Mixed-signal ICs are often used to convert analog signals to digital signals so that digital devices can process them. For example, mixed-signal ICs are essential components for FM tuners in digital products such as media players, which have digital amplifiers. Anyanalog signal can be digitized using a very basic ADC, and the smallest and most energy efficient of these are mixed-signal ICs.
Mixed-signal ICs are more difficult to design and manufacture than analog-only or digital-only integrated circuits. For example, an efficient mixed-signal IC may have its digital and analog components share a common power supply. However, analog and digital components have very different power needs and consumption characteristics, which makes this a non-trivial goal in chip design.
Mixed-signal functionality involves both traditional active elements (liketransistors) and well-performing passive elements (likecoils,capacitors, andresistors) on the same chip. This requires additional modelling understanding and options from manufacturing technologies. High voltage transistors might be needed in the power management functions on a chip with digital functionality, possibly with a low-powerCMOS processor system. Some advanced mixed-signal technologies may enable combining analog sensor elements (like pressure sensors or imaging diodes) on the same chip with an ADC.
Typically, mixed-signal ICs do not necessarily need the fastest digital performance. Instead, they need more mature models of active and passive elements for more accurate simulations and verification, such as for testability planning and reliability estimations. Therefore, mixed-signal circuits are typically realized with larger line widths than the highest speed and densest digital logic, and the implementation technologies can be two to fourgenerations behind the latest digital-only implementation technologies. Additionally, mixed signal processing may need passive elements like resistors, capacitors, and coils, which may require specialized metal, dielectric layers, or similar adaptations of standard fabrication processes. Because of these specific requirements, mixed-signal ICs and digital ICs can have different manufacturers (known asfoundries).
There are numerous applications of mixed-signal integrated circuits, such as inmobile phones, modernradio andtelecommunication systems,sensor systems with on-chip standardized digital interfaces (includingI2C,UART, SPI, or CAN), voice-related signal processing, aerospace and space electronics, theInternet of things (IoT),unmanned aerial vehicles (UAVs), and automotive and other electrical vehicles. Mixed-signal circuits or systems are typically cost-effective solutions, such as for building modernconsumer electronics and in industrial, medical, measurement, and space applications.
Examples of mixed-signal integrated circuits include data converters usingdelta-sigma modulation,analog-to-digital converters anddigital-to-analog converters usingerror detection and correction, anddigital radio chips. Digitally controlledsound chips are also mixed-signal circuits. With the advent of cellular and network technology, this category now includescellular telephone,software radio, andLAN andWANrouter integrated circuits.
Typically, mixed-signal chips perform some whole function or sub-function in a larger assembly, such as the radio subsystem of acell phone, or the read data path and laserSLEDcontrol logic of aDVD player. Mixed-signal ICs often contain an entiresystem-on-a-chip. They may also contain on-chip memory blocks (likeOTP), 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 smallermodule 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 ofcomputer aided design (CAD) tools. There also exists specific design tools (like mixed-signal simulators) or description languages (likeVHDL-AMS). Automated testing of the finished chips can also be challenging.Teradyne,Keysight, andAdvantest are the major suppliers of the test equipment for mixed-signal chips.
There are several particular challenges of mixed-signal circuit manufacturing:
Mixed-signal devices are available as standard parts, but sometimes custom-designedapplication-specific integrated circuits (ASICs) are necessary. ASICs are designed for new applications, when new standards emerge, or when new energy source(s)[clarification needed] 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-signalIP blocks from foundries or dedicated design houses has lowered the gap to realize mixed-signal ASICs.
There also exist mixed-signalfield-programmable gate arrays (FPGAs) andmicrocontrollers.[note 1] 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.[8] 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.
TheMOSFET was invented at Bell Labs between 1955 and 1960, after Frosch and Derick discovered and used surface passivation by silicon dioxide to create the first planar transistors, the first in which drain and source were adjacent at the same surface.[9][10][11][12][13]Robert Noyce andJack Kilby invention of the silicon integrated circuit was enabled by theplanar process developed by Jean Hoerni.[14] In turn, Hoerni's planar process was inspired by thesurface passivation method developed atBell Labs by Carl Frosch and Lincoln Derick in 1955 and 1957.[15][16][17][18][19][20][21]
MOS technology eventually became practical fortelephony applications with the MOS mixed-signalintegrated circuit, which combines analog anddigital signal processing on a single chip, developed by former Bell engineerDavid A. Hodges with Paul R. Gray atUC Berkeley in the early 1970s.[22] In 1974, Hodges and Gray worked with R.E. Suarez to develop MOSswitched capacitor (SC) circuit technology, which they used to develop adigital-to-analog converter (DAC) chip, usingMOS capacitors and MOSFET switches for data conversion.[22] MOSanalog-to-digital converter (ADC) and DAC chips were commercialized by 1974.[23]
MOS SC circuits led to the development ofpulse-code modulation (PCM) codec-filter chips in the late 1970s.[22][24] Thesilicon-gateCMOS (complementary MOS) PCM codec-filter chip, developed by Hodges and W.C. Black in 1980,[22] has since been the industry standard fordigital telephony.[22][24] By the 1990s,telecommunication networks such as thepublic switched telephone network (PSTN) had been largely digitized withvery-large-scale integration (VLSI) CMOS PCM codec-filters, widely used inelectronic switching systems fortelephone exchanges,private branch exchanges (PBX), andkey telephone systems (KTS); user-endmodems;data transmission applications such asdigital loop carriers,pair gainmultiplexers, telephoneloop extenders,integrated services digital network (ISDN) terminals, digitalcordless telephones, and digitalcell phones; and applications such asspeech recognition equipment, voicedata storage,voice mail, and digital tapelessanswering machines.[24] The bandwidth of digital telecommunication networks has been rapidly increasing at an exponential rate, as observed byEdholm's law,[25] largely driven by therapid scaling andminiaturization of MOS technology.[26][22]
While working atBell Labs in the early 1980s, Pakistani engineerAsad Abidi worked on the development ofsub-micronMOSFET (metal–oxide–semiconductor field-effect transistor)VLSI (verylarge-scale integration) technology at the Advanced LSI Development Lab, along with Marty Lepselter,George E. Smith, and Harry Bol. As one of the fewcircuit designers at the lab, Abidi demonstrated the potential of sub-micronNMOSintegrated circuit technology in high-speedcommunication circuits, and developed the firstMOSamplifiers forGb/s data rates inoptical fiber receivers. Abidi's work was initially met with skepticism from proponents ofgallium arsenide andbipolar junction transistors, the dominant technologies for high-speed circuits at the time. In 1985, he joinedUCLA, where he pioneeredRF CMOS technology in the late 1980s. His work changed the way in whichradio-frequency (RF) circuits would be designed, away from discretebipolar transistors and towards CMOSintegrated circuits.[27]
Abidi was researching analogCMOS circuits forsignal processing andcommunications during the late 1980s to early 1990s. In the mid-1990s, the RF CMOS technology that he pioneered was widely adopted inwireless networking, asmobile phones began entering widespread use. As of 2008, theradio transceivers in all wireless networking devices and modern mobile phones are mass-produced as RF CMOS devices.[27]
Thebaseband processors[28][29] and radio transceivers in all modernwireless networking devices andmobile phones are mass-produced using RF CMOS devices.[27] RF CMOS circuits are widely used to transmit and receive wireless signals in a variety of applications, such assatellite technology (such asGPS),Bluetooth,Wi-Fi,near-field communication (NFC),mobile networks (such as3G,4G, and5G),terrestrialbroadcast, andautomotiveradar applications, among other uses.[30] RF CMOS technology is crucial to modern wireless communications, including wireless networks andmobile communication devices.[31]
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