Audio amplifier selection for car audio host system
Cars of all models and prices are providing more and more entertainment and information to enhance driving and ride experience. Today's factory-installed hosts typically integrate entertainment, multimedia and driver information into one module; they offer AM/FM and satellite radio, music and video CD/DVD playback, navigation systems, data and multimedia ports (USB, Bluetooth, lines) Input, line output, video input), and general vehicle status information.
The host is indeed the brain and core of the car audio system. Modern mainframes are very complex automotive systems that integrate high-speed processors and interface lines, very sensitive signal chain modules, and high-output audio and power components are densely integrated in the center of the dashboard.
In view of the limitations of such a small space, the cost of printed circuit board (PCB) area and component count in a car audio host system is high. What auto OEMs need to do is enhance functionality, reduce subsystem size, and increase differentiation.
Audio in the host
Figure 1 is a simplified block diagram of a typical host system.
Figure 1: Typical Host Simplified Block Diagram (SBD)
From the figure, you can notice:
The input front end and output of the audio signal are often combined into a single codec consisting of one or more analog-to-digital converters (ADCs) and digital-to-analog converters (DACs).
If the audio processor or system-on-chip (SoC) has integrated DACs, no codecs are needed because the DAC portion of the audio signal chain is already integrated into the mixed-signal SoC.
Audio line level inputs from external sources are converted to digital samples by the ADC and transmitted to the system's audio processor or SoC.
At the output, a DAC (integrated into the SoC or codec) converts the digital audio signal from the processor into an analog signal.
Because the voltage and current of the signal from the DAC is low, an audio amplifier is needed to provide the high voltage and high current signals needed to drive the driver of the speaker system.
Audio Amplifier: Class AB and Class D
Automotive system designers have two choices when choosing the best audio amplifier for a car audio host system: Class AB or Class D.
Class AB audio amplifiers are standard accessories for today's car audio systems. Class AB audio amplifiers are linear amplifiers that do not generate electromagnetic interference (EMI) and do not require many external electronic components. However, Class AB audio amplifiers are very inefficient and require a large number of passive or even active thermal management methods such as heat sinks and fans.
Class D audio amplifiers, on the other hand, are highly efficient switching amplifiers that require very little thermal management; however, Class D audio amplifiers require the use of an output inductor for EMI problems.
Compared with the AB class, the advantages are more and more obvious, the total system cost is close to that of the AB system, and the class D audio amplifier is becoming more and more popular.
Efficiency: speaker channel.
As infotainment systems become more complex, car manufacturers have increased the number of speaker channels to increase system differentiation and market appeal. The power of the host audio amplifier increases as the number of speaker channels required increases, but space and heat dissipation limit the power consumption of the host to within a few watts.
For Class AB-based amplifiers, this can be solved by adding an external audio amplifier box or trunk amplifier, but it adds complexity and cost to the system.
The high efficiency of the D-class based amplifier allows it to meet the power requirements of high channel count systems without the need for an external audio amplifier. Its low power consumption enables multiple integrated circuits to be used directly in the host, providing a more cost-effective and simple solution.
Figure 2: A host based on a Class D amplifier greatly simplifies thermal management of the host.
TI's high-efficiency automotive Class D amplifiers reduce heat dissipation and total system cost by removing fans and expensive aluminum heat sinks; Class D amplifiers such as the TI TAS5404-Q1 achieve higher channel counts than Class AB amplifiers. The subwoofer's 2Ω load does not require an external amplifier for the host output power.
By utilizing small, low cost, automotive grade metal alloy inductors, these Class D amplifiers achieve a very small size solution of only 10 cm2, enabling six or more channels in a space-constrained host system.
The second article in this blog series will discuss EMI. At the same time, log in to post a comment below, telling me about your problems with host audio design and space limitations.
other information
View TI Designs 100W High Efficiency Compact Automotive Amplifier Reference Design with Boost Converter
Download the TAS5404-Q1EVM User Manual.
Watch the video: TAS5404-Q1 low-cost, full-featured Class D audio amplifier for car audio consoles.
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