Mixed-signal

Definition

Mixed-signal ICs are integrated circuits that contain both analog and digital circuitry on one chip.

An analog signal is a continuous time-varying signal, and a digital signal is a noncontinuous signal that takes on only a finite number of values. Mixed signal ICs make use of both of these types of signals. Mixed-signal ICs are used in a wide variety of applications and application-specific integrated circuits (ASICs).

Analog signals

As an example, a building block of analog circuit design is the op amp, which is a high-gain amplifier. An op amp can take a continuous signal and output another, higher-valued, continuous signal. An op amp can also be used to make a comparator, which is a circuit that compares two input voltages and outputs a binary signal indicating which is larger. Since the output of the comparator is digital, this is an example of a mixed-signal circuit.

Digital signals

Where analog signals are continuous, digital signals are discrete, meaning that they take on a finite number of values. An example is a square wave, where a signal alternates between values in steps, ideally instantaneously. Another example is a binary signal, which can have two possible values (such as 0/1 or on/off) and is used in logic gates such as AND/NAND gates or in D flip flops.

ADCs and DACs

The two clearest examples of mixed-signal ICs are analog to digital converters (ADCs) and digital to analog converters (DACs). Since these convert analog to digital or digital to analog, they must contain circuitry for both.