I. Analog Integrated Circuits
Analog integrated circuits (ICs) are integrated circuits composed of capacitors, resistors, transistors, and other analog circuits used to process analog signals. There are many types of analog ICs, such as operational amplifiers, analog multipliers, phase-locked loops (PLLs), and power management chips. The main components of an analog IC include amplifiers, filters, feedback circuits, reference source circuits, and switched-capacitor circuits. Analog IC design is primarily achieved through manual circuit debugging and simulation by experienced designers. In contrast, digital IC design is mostly generated automatically through synthesis using hardware description languages under the control of EDA software.
In 1958, Jack Kilby implemented a simple oscillator circuit using five components on germanium, creating the world's first integrated circuit. This invention ushered in the 20th-century information revolution and marked the arrival of the electronic age. With the increasingly widespread application of high-tech products, represented by computers and communication technologies, in defense technology, industrial production, and daily life, the microelectronics industry, represented by integrated circuits, has also entered an unprecedented stage of development.
Integrated circuits (ICs) can be broadly classified into two categories based on their function and structure: digital ICs and analog ICs. Digital ICs are circuits used to generate, amplify, and process various digital signals (signals that vary discretely in time and amplitude, such as audio and video signals played on VCDs and DVDs). Analog ICs are circuits used to generate, amplify, and process various analog signals (signals whose amplitude varies continuously over time). They are one of the core technologies of microelectronics, capable of acquiring, amplifying, comparing, converting, and modulating analog quantities such as voltage or current.
II. Three Stages for Analog Integrated Circuit Design Beginners
A scenario: You're new to this field, with only a general understanding of PMOS/NMOS/BJTs, and you're not very clear on the characteristics of various devices. You don't have much idea about what kind of circuits to design. Your circuit diagrams are mainly based on articles in domestic journals or existing circuits in textbooks, and you always feel that what they say makes sense. The circuits you make are mainly small-scale modules, doing simulations of differential op-amps or bandgap references, and you're calculating to publish papers, afraid of not having enough papers to fill. In general, you're still intimidated by op-amps. You think SPICE is a very difficult and strange thing to use.
Stage Two: You begin to understand circuit design, spending your days frantically calculating on scratch paper while holding a textbook. You also frequently mention technical parameters like Vdsat, lambda, early voltage, GWB, and ft. Sometimes the circuit seems close to the hand-calculated result, while other times the difference is significant. You start paying attention to variations in voltage, temperature, and manufacturing processes, such as low-voltage, low-power systems, or ultra-high-speed, high-precision technologies. You occasionally mention these things as well. When designing circuits, you begin planning to tape out, although tape out still seems quite distant. During this stage, you find SPICE powerful, but often get frustrated by incorrect AC simulation results.
Stage Three: You've been struggling with PVT for a while now, but overall you haven't had many successful design experiences. You find it really difficult to design truly usable circuits, and you're eager to build your confidence, but you don't know how. You start reading JSSC papers or doctoral dissertations, but you feel that what they say is one thing, and the actual chip is another. You feel that metrics like Vdsat are not precise enough, and the default settings of the simulator don't meet your requirements, so you try adjusting the simulator parameters or trying a different simulator, but the results are still sometimes accurate and sometimes inaccurate. You go to forums, hoping to get guidance from experts. But their explanations are vague, and what they say is sometimes right and sometimes wrong. At this stage, you feel that while SPICE is good, its help manual is too unclear.
