Back in the 1980s, with the advent of more portable integrated circuits (ICs) and semiconductor devices, and the quickly-improving performance of digital systems, most people of the field thought that analog processing will cease to exist by the 21st century.
However, that was not the case; on the contrary, the demand for electronic systems that can process analog signals efficiently and perform Analog-to-Digital, Digital-to-Analog operations has been on the rise. This can be explained by the improving technologies of sensors, their increased usage, and in parallel, the improving technology of digital processing and digital communication.
Generally speaking, a mixed-signal electronic system is a system that contains both digital and analog signals; such system can be an integrated chip, a PCB product, or a system of components. They all combine together in a hierarchy to come up with a larger device of powerful multi-functionality, like smart phones, for example.
Examples on Mixed-Signal Systems
Nowadays, mixed-signal systems can be found everywhere, especially in consumer electronics that can interact with the outer environment using a variety of sensors. There are no more “only-analog” systems like old radios (with very few exceptions), as these systems has been absorbed within the modern mixed-signal systems.
Here are three examples on mixed-signal systems:
Microcontrollers and SoCs
Microcontrollers has been the backbone of the mixed-signal technologies to follow, with capabilities to contain ADC and DAC functions on-chip, as well as having native support for some inputs, such as capacitive touch buttons. A circuit with a well-selected MCU can save a lot of costs and space, reducing the need for external ICs, like operational amplifiers.
System-on-Chips (SoC), particularly Analog-Mixed-Signal SoCs (AMS-SoC) are even more powerful and usually dedicated to a common function of consumer electronics; such as audio/video processing, as found in most Bluetooth headsets and IP cameras.
For example, below is the block diagram of the ATmega25/45/85, a small 8-pin MCU. As seen in the lower left corner, even this minimal microcontroller, has an ADC (Analog-to-Digital Convertor), which classifies it as a mixed-signal system regarding both design and implementation.
Mobile Phones and Wearables
Whether it was a smart phone or just the legendary Nokia 3310, a mobile phone is necessarily a mixed-signal system that can deal with different types of processing. A mobile phone deals with different analog signals like audio and light inputs and output, in addition to dealing with different transducers (sensors), such as fingerprint scanners, oximeters, heartbeat sensors, and iris scanners. Most modern wearables (smart watches, bracelets, headsets, etc.) share the same functions more or less.
The picture below shows different sensors on the back of a Samsung Galaxy watch.
Digital Multi-Effect Sound Effect Units
An example I like a lot as a person who has worked in the musical industry for several years. Digital SEUs are electronic devices used to add effects on the native sound of an electric musical instrument, before passing this output to amplifiers and audio devices. Digital SEUs will convert the analog signal of your instrument into digital data, processing or storing it, and then convert this digital data to analog signal again. In addition, DSEUs have digital controllers to store and apply user settings, making them mixed-signal systems perfectly.
Below is the Boss ME-80, showing the very diverse functionalities it has.
I hope you have enjoyed this introductionary article! In further articles we will detail the design challenges and remarks for designing a mixed-signal system for engineers, as well as going through the technical details behind these products.
