Analog and mixed-signal ICs are chips that connect electronics to the physical world. IC stands for integrated circuit, another name for a chip. The real world is analog: temperature, pressure, sound, light and voltage change smoothly, with no steps. Computers work only with numbers. So an analog chip must turn real-world signals into numbers, and numbers back into signals. The page on analog and digital explains this idea in general.
There are three main kinds. An analog-to-digital converter (ADC) measures a voltage many times a second and gives each measurement a number. A digital-to-analog converter (DAC) does the reverse: it turns numbers back into a voltage, for example to drive the speaker in your earphones. An amplifier strengthens a weak signal, such as the few thousandths of a volt from a sensor, so that it can be measured accurately. A mixed-signal chip has analog circuits and digital circuits on the same die, the single piece of silicon inside the package.
Two numbers describe a converter. The sample rate is how many times a second it measures. The resolution is how finely it measures, given in bits. A 12-bit converter divides its range into 4,096 steps. A 24-bit converter divides it into about 1.7 crore steps, fine enough to see a change of a millionth of a volt.
Consider a smart electricity meter on the wall of a flat in Indore. Inside it, a metering chip measures the voltage of the supply, about 230 volts, and the current going into the flat. The current passes through a tiny resistor. The voltage across that resistor is only a few thousandths of a volt, so an amplifier strengthens it first. Two 24-bit converters then measure the voltage and the current about 4,000 times a second each. The chip multiplies each pair of numbers to get the power at that instant, and adds up the results to get the energy used, in kilowatt-hours (kWh). When the family runs a 1.5 kW geyser for 20 minutes, the meter adds 0.5 kWh. At fixed intervals, often every 15 or 30 minutes, the smart meter's microcontroller sends the readings over the metering network to the electricity distribution company.
Analog chips are hard to design. Electrical noise, heat and tiny differences between transistors all change the result. Much of the design is still done by hand, by experienced engineers, many of them in Bengaluru and Hyderabad. Each design is checked on the bench with oscilloscopes and test instruments. Machine learning tools that tune circuit designs, described on AI for chip design, are now starting to help. Most analog chips do not need the smallest transistors, so their makers often make them in their own factories, on older and cheaper production lines. A good analog chip sells for years, often decades, once a customer has chosen it, which the industry calls a design win. The signals it converts usually come from sensor chips.