"911, what’s your emergency?” – look inside the eCall audio subsystem

The emergency call (eCall) system is a European-driven initiative to develop technological solutions with the purpose to bring rapid assistance to motorists involved in a collision. After an accident, the eCall system will automatically connect to an emergency center and transmit the car’s location, time and direction of travel, regardless of the driver’s ability to communicate.

Earlier this summer, the European Parliament passed legislation to equip all new cars with eCall starting in April 2018, with United Nations and Russian ERA-GLONASS proposals also in the works. The European eCall standard specifies that the system needs to sustain 8-10 minutes of voice conversation and remain on the network for at least 60 minutes afterwards for emergency services to call back to the driver.

Because the conditions of an accident are unpredictable, an eCall system has several important considerations affecting both the power and signal paths; see Figure 1.

Figure 1: eCall System Block Diagram

The audio subsystem is affected by two surrounding modules in the signal path. First, the microcontroller (MCU) will activate an emergency call if an accident occurs, which will cause the connectivity module to make the actual call. Second, the connectivity module then outputs digital audio signals to interface with the audio subsystem. The audio subsystem afterwards converts the signal to analog and drives the speaker and microphone input for the call itself.

When looking deeper into the audio subsystem, TI offers two devices that can help meet one of eCall’s system-level needs: the ability to sustain a 10-minute telephone call. Additionally, given variations in the design of eCall systems, these devices offer the flexibility of fitting into different solutions to meet eCall standard requirements.

The TLV320AIC3104-Q1 plus TAS5411-Q1 combo optimizes power consumption and enables hands-free calling with clear audio quality. The TLV320AIC3104-Q1 is an audio codec with low power consumption that helps the power path conserve more energy for longer call times. The device’s functionality also allows for subsystem flexibility and connection with all kinds of connectivity modules, as the codec can handle most digital input types, and its integrated microphone enables clearer conversation.

The TAS5411-Q1 is a Class-D 8W audio amplifier with integrated diagnostic and protection capabilities. One important diagnostic capability is that the amplifier can detect an open load in case the accident causes the speaker to disconnect. As a Class-D amplifier, the TAS5411-Q1 is also highly efficient, which helps with battery conservation on the power path.

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