While vehicles have changed a lot in the past few generations (and most certainly in the past decade), the radio has endured for more than 80 years. You can probably attribute its longevity to the fact that, until relatively recently, it was the only thing in the car that delivered entertainment and information from outside. Today, you can find a simple radio in entry-level vehicles all the way to a feature-rich, high-end audio system (Figure 1) in premium vehicles that integrates navigation, a smartphone-like interface, network connectivity and much more.
Figure 1: A feature-rich, high-end audio system typically found in premium vehicles that integrates navigation, a smartphone-like interface, network connectivity and more.
The “radio” can go by many different names, including stereo, audio system, in-vehicle infotainment system and display audio; however, most automotive designers commonly call it a head unit. There are a wide variety of ways to implement a head unit, which usually depend on the specific requirements of the automaker. Regardless of the implementation, these are the nine basic subsystems that make up a typical head unit:
Let’s dive deeper into the first two subsystems in this list: the off-battery power and the applications processor.
For efficiency, the 12-Volt car battery powers the head unit. As manufacturers add more features to these systems, it is important for the power-conversion circuit to efficiently handle the increase in power consumption. This is especially critical for head units in electric vehicles (EVs) and hybrid EVs (HEVs) because the car battery is the primary power source and has limited capacity.
Most design engineers carefully design circuits in the head unit to be in either standby/sleep mode or a completely off state to conserve power while not in use; they can also design with a power device family that has a range of output capabilities and features with a common package footprint. Such families enable design reuse for different head-unit models, and help minimize the number of changes as requirements evolve during the design cycle.
The primary subsystem of a head unit is the applications processor. It’s not surprising that the processor typically controls all of the interfaces and functions. Depending on the features designed into the head unit, the number of processor interfaces and capabilities will vary, from the low end to the high end. Thus, a processor that can scale with the design maximizes reuse (for both hardware and software) across a fleet of vehicles.
At the printed circuit board (PCB) level, the compatibility of a package footprint is a very important feature for a family of processors. When the design engineer selects a common package, each subsequent design in the platform can use a different processor without changing the PCB. Also, it is possible that design engineers can swap out a higher- or lower-end processor to accommodate more or less features without significantly redesigning the existing hardware and software.
Another aspect of scalability relates to the processor’s internal architecture. Software is an important piece of the head unit, just like it is in many other processor-based systems. The cost of software development and testing is very significant in a project due to increasing complexity and stringent requirements. A scalable architecture will simplify the development and testing processes by allowing the reuse of proven designs utilized as building blocks for a larger design. The tools for testing both software and hardware will also be similar (or the same) to further reduce the cost of implementing changes. This is especially important for a product that has already been certified through a long and costly process.
So the next time you get in a car and turn on the radio, think about how much thought has gone into that design to ensure that it can entertain drivers and passengers in a wide spectrum of vehicles, and with a wide range of features. At the same time, despite all of its upgrades, consider how this entertainment system still serves the same purpose that it did 80 years ago.
If you’re ready to design an automotive head unit system, get started with our Entry Level Head Unit Display Audio with Jacinto™ 6 Entry Reference Design based on TI’s family of scalable Jacinto™ DRAx automotive processors.
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