This article introduces the main features of analog ICs, their working principle, product classification, market analysis, and the difference with digital ICs.

Ⅰ What is an analog IC?

Analog signals are the source of all information. The physical environment in which we live is characterized by analog quantities, i.e., quantities that vary in a continuous manner rather than in a discrete way, such as temperature, position, light intensity, sound waves, color, texture, etc. These physical quantities are measured asymptotically without limits (e.g. "on and off", "small and large", "black"). When we use graphs to visually represent the values of these analog quantities, the curves become smooth (the most representative is the sine curve). These continuously varying analog quantities constitute the real world and transmit information to the outside world in the form of analog signals, and the integrated circuits used to process them are analog ICs.

Digital signals are the key to the electronic revolution. Although the real world is composed of colorful analog signals, experience has proven that in electrical systems, binary signals bring great convenience and extensibility to the storage, transmission, and processing of information. Therefore, in modern electronic systems, engineers use logic high voltage and logic low voltage (ground) to represent signals 1 and 0, thus converting the mathematical structure of binary into electronic systems, which is the digital signal. Digital signals are widely used in computing, storage, and other fields, and the integrated circuits used to process digital signals are digital ICs.

Ⅱ Working Principle of Analog IC

ICs are composed of transistors (including diodes and transistors) and other passive components, which compress complex functions into a small physical area through miniaturization, and communicate between micro devices and the macro world by means of integration, greatly enriching the portability and extensibility of electronic systems. The difference between analog and digital circuits is mainly reflected in the internal electronic devices, that is, the difference between analog and digital ICs in terms of transistors.

In analog IC, transistors are used to amplify or generate continuously changing signals (bias). When we bias a transistor, we create circuit conditions that allow it to respond correctly to small changes in voltage. Being able to continuously and accurately respond to and amplify analog signals is the main concern of analog ICs. The transistor in an analog IC can be a BJT (bipolar junction diode) or a MOSFET (metal-oxide-semiconductor field-effect transistor).

In digital ICs, the input signal is required to fully turn the transistor on and off, requiring only two values of external output logic high and low. Because of the need for frequent opening and closing, only MOSFETs can meet such performance, so BJTs are generally not applicable in digital ICs. Through complex MOSFET interconnections, Boolean logic-based gate circuits can form complex microprocessors or even general-purpose computing processor units.

Signals go through a process from analog to digital and back again in electronic systems, corresponding to the three stages of information input, processing and storage, and output. The signals from nature are transformed into electrical signals (analog) by sensors and discrete devices. The intermediary of the signal from input to processing to output is done by various analog devices (including digital-analog hybrid circuits). Finally, the analog chip processes the converted digital signal, and the digital IC (processor and memory, etc.) completes the final logic calculation, storage, and other functions.

Ⅲ Types of analog IC products

In the semiconductor industry, downstream products can be divided into OSDs (including sensors, discrete devices, optoelectronic devices, etc.) and integrated circuit ICs. Digital ICs mainly process digital signals, while discrete devices such as analog ICs and sensors process analog signals and convert them with digital signals.

According to the different functions (transmission of weak signals/strong electrical energy), we can generally divide analog IC devices into two categories: signal chain and power chain. The Signal chain mainly refers to the IC used to process signals, while the power chain is mainly used to manage the battery and electrical energy. The signal chain mainly includes comparators, operational amplifiers OPA, AD\DA, interface chips, etc.; the power chain mainly includes PMIC, ADC, DAC, PWM, LDO regulators, and driver ICs, etc. In the high-frequency signal part, RF devices are often discussed in a separate category due to the rapid technology iteration and high shipment volume.

Divided according to the application areas of downstream products, we can also divide analog IC products into System-Level IC SLIC and application-specific standard product ASSP. SLIC is used in different scenarios, the design performance parameters will not be specifically adapted to a certain type of application. By product type, SLIC generally includes five major categories, amplifier Amp in the signal link, signal converter ADC/DAC, general-purpose interface chip, comparators, and voltage regulators in the power supply chain.

ASSPs, on the other hand, are standardized according to dedicated application scenarios and generally integrate digital as well as analog ICs with a higher degree of complexity and integration, sometimes called mixed-signal ICs. Typical ASSP products include RF devices in cell phones, physical layer interface chips in switches, battery management chips and industrial power control chips, etc. ASSPs are generally divided into five categories according to downstream application scenarios, including automotive electronics, consumer electronics, computer, communication, and industrial markets.

Ⅳ Analog IC vs digital IC

Digital ICs are the core of the semiconductor industry, while analog ICs are the cornerstone of the semiconductor industry and the link between the real world and electronic systems. Due to the different types of signals that need to be processed, we can see that there are major differences between analog ICs and digital ICs in terms of the product life cycle, production process, design threshold, and related auxiliary tools.

Long product life cycle and slow iteration. Digital ICs emphasize the ratio of computing speed to cost. The core of Moore's Law is that designers pursue a more cost-effective computing rate, so new processes and new algorithms are emerging, and the life cycle is only 1-2 years. Analog ICs, on the contrary, emphasize a high signal-to-noise ratio, low distortion, low power consumption, and stability, so once the product is launched, it often has a longer life cycle, and the iteration cycle is longer, and the price will be reduced year by year.

The CMOS process has become the mainstream of digital ICs due to its complete development and shrinking process. However, analog ICs often require high voltage, low distortion, and high signal-to-noise ratio, and the CMOS process has poor drive capability, making it difficult to meet the needs of analog circuits.

Analog ICs early use Bipolar process, but the Bipolar process power consumption is high, so there is BiCMOS process, combining the advantages of both Bipolar process and CMOS process. There is also the CD process, which combines the CMOS process with the DMOS process. The BCD process combines the advantages of Bipolar, CMOS, and DMOS processes. In the high frequency field there are also SiGe and GaAS processes. These special processes need the cooperation of foundries and also need designers to be familiar with them, so most of the general analog IC factories still use the IDM model.

Close relationship with electronic components, design matching layout complex. Analog IC's low noise, low distortion needs in the design layout to consider the structure and components parameters match each other mode. Common resistive and capacitive sensing components can produce distortion, while in the digital IC design process, due to the binary characteristics, there is no need to consider the related impact. In the high-frequency range, the performance of certain RF ICs is also closely related to the wiring, so the designer of analog ICs needs to be familiar with most of the electronic component characteristics, and the design threshold is high.

Few auxiliary tools and high experience knowledge requirements. Since analog IC design requires familiarity with most of the component characteristics and different manufacturing packaging processes, which makes analog IC practitioners have a higher barrier to entry, and the accumulation of experience time is often more than 10 years. Analog ICs are often not very versatile in different scenarios. More performance indicators are involved, and the stability and certification cycle is more factory, which leads to a smaller number of EDA tools that can be used, and higher requirements for the designer's own experience. Therefore, in the analog IC industry, rich design experience (or also called Know-how) is more important.

Ⅴ Analog IC market analysis

Reviewing the market size and growth rate of each segment of the semiconductor industry in the past 15 years, we find that the analog IC market is stable in size and is not affected by short-term fluctuations in certain downstream markets, and the market fluctuations are small. Analog chips are also the barometer of the global semiconductor industry, closely related to macroeconomic changes, and relatively weak cyclical changes.

After continuous development since the 1950s, analog ICs have become a global industry of nearly $60 billion. According to WSTS and Statista data statistics and forecasts, the global analog IC market size reached $55.7 billion in 2020, an increase of 3.3% compared to 2019, the annual semiconductor industry size of $440.4 billion, analog IC market share of 12.6%.

With the global epidemic gradually under control, the semiconductor industry has also ushered in a recovery, in which 5G communications, automotive electronics and other application scenarios will accelerate the development of the analog IC market. It is expected that the analog chip market size can reach $64 billion in 2021, an increase of 15.1% year-on-year, higher than the overall growth rate of the semiconductor industry. Considering the stable development of analog chip track, less affected by the downstream boom, the future will become a segment of the semiconductor industry gold track.