Integrated Circuits (ICs) are generally classified as digital (i.e., microprocessors) or analog (i.e., operational amplifiers). Mixed-signal ICs are chips that contain both digital and analog circuits on the same chip. This category of chip has grown dramatically with the increased use of 3G cell phones and other portable technologies.
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. Any analog signal (such as an FM radio transmission, a light wave or a sound) can be digitized using a very basic analog-to-digital converter, and the smallest and most energy efficient of these would be in the form of mixed-signal ICs.
Mixed-signal ICs also enable technologies like power over Ethernet. The analog power "signal", in this case a 60 Hz, 120V AC current in the United States, is transmitted alongside a digital data signal (Ethernet) over the same wire. Mixed-signal ICs allow this.
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 would have its digital and analog components share a common power supply. However, as one can imagine, analog and digital components have very different power needs and consumption characteristics that make this a non-trivial goal in chip design.