The voltage and current at specified points in the circuits of analog chips vary continuously in time. In contrast, digital chips only use and create voltages or currents at discrete levels, with no intermediate values. In addition to Transistors, analog chips often have a larger number of passive elements (Inductor/Capacitors/Resistors) than digital chips typically do. Inductors tend to be avoided because of their large size, and a transistor and capacitor together can do the work of an inductor. (When this method is used in a CFL, you get an electronic ballast.)
Analog chips may also contain digital logic elements to replace some analog functions, or to allow the chip to communicate with a microprocessor. For this reason and since logic is commonly implemented using CMOS technology, these chips use BiCMOS processes by companies such as Freescale, Texas Instruments, STMicroelectronics and others. This is known as mixed signal processing and allows a designer to incorporate more functions in the chip. Some of the benefits include load protection, reduced parts count and higher reliability.
Pure analog chips in information processing have been mostly replaced with digital chips. Analog chips are still required for wideband signals on account of sampling rate requirements, high power applications and at the transducer interfaces. Research and industry in the field continues to grow and prosper. Some examples of long-lived and well-known analog chips are the 741 Operational Amplifier, and the 555 timer.
Power supply chips are also considered to be analog chips. Their main purpose is to produce a well-regulated output voltage supply for other chips in the system. Since all electronic systems require electrical power, power supply ICs PMICs are important elements of those systems.
Important basic building blocks of analog chip design include:
All the above circuit building blocks can be implemented using Bipolar technology as well as Metal-Oxide-Silicon(MOS) technology. MOS Band gap references use lateral (poor) bipolar transistors for their functioning.
- Information Freescale website, Mar 28th 2010, About Freescale Analog Products