Design of anti-ESD and EMI interference for audio system in mobile phone

The causes and results of ESD and EMI in mobile phone audio systems. Then we discussed the use of ESD interference suppressors and EMI filters to avoid these threats. Finally, the current three solutions are compared.

Mobile phone circuit designers must ensure that the necessary measures are taken to eliminate ESD damage.

If there is electromagnetic interference (EMI) in the audio circuit, there will be hissing, crackling, buzzing and other sounds, and the sound quality is very poor. Mobile phone users cannot tolerate such interference. Therefore, we must try to filter the electromagnetic interference of the audio circuit.

We can see lightning striking buildings and trees, it is destructive. If the ESD protection of the electronic circuit is not optimal, even a small discharge will destroy the sensitive electronic circuit, which has been detected by people. The mobile phone has certain ESD protection. The external connection of audio circuits is the most common source of ESD. Simply plug in the headphones and amplifier, which may mean that the phone will be affected by ESD.

As shown in Figure 1, what happens when an electronic component is affected by ESD? A tiny hole is created, and the oxide will invade the component.

Figure 1 Affected by ESD, oxide rushes into a small hole


As with all products, mobile phones must be certified for ESD according to the IEC61000-4-2 regulations. The regulations stipulate that the mobile phone can resist 15 kV air discharge (through 330Ω / 150 pF), that is, it should pass through 45 A current not less than 1 nanosecond. In this case, the phone should continue to work without being damaged. The above is a comparison between a high-energy pulse and an ESD human body model experiment. To protect the main chip, additional ESD protection must be added at each potential ESD entry point. In general, devices that suppress ESD generate a controllable output called the clamping voltage.

Figure 2 shows the output (clamp voltage) of an ESD protection device during an ESD event.

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