This article briefly explores the causes and consequences of ESD and EMI in mobile audio systems. The use of ESD interference suppressors and EMI filters was then discussed to avoid these threats. Finally, the current three solutions are compared.
Modern materials and technologies cause electrostatic discharge (ESD) and electromagnetic interference (EMI) and are a constant risk. Our wearing and our contact items can cause electrostatic discharge. Digital technology has electromagnetic interference. Electrostatic discharge can damage electronic components in your phone. The phone is easy to replace, but it hurts the user a lot. Cell phone circuit designers must ensure that the necessary steps are taken to eliminate ESD damage.
If there is electromagnetic interference (EMI) in the audio circuit, sounds such as 嘶嘶, 噼啪, 嗡嗡, etc. may occur, and the sound quality is poor. Mobile phone users cannot tolerate such interference. Therefore, it is necessary to try to filter the electromagnetic interference of the audio circuit.
Electrostatic discharge - causes, results and inhibition
cause
Almost everyone has experienced the effects of static currents. When we were a caveman in the prehistoric Stone Age, we have seen it in lightning. Of course, it is still a major threat today, everywhere. Using a plastic comb to comb the head, you can see the generation of static charge. Put your arm close to the screen of the TV and you will see the hair on your arm stand up. This is also an electrostatic effect.
When you open the door and walk out of your car, you may feel a shock, which comes from electrostatic discharge. With more and more electrical equipment at home and at work, static electricity is a constant danger. People who manufacture or repair electrical equipment protect themselves and the equipment they use, and they connect themselves to the equipment to avoid damage from electrostatic discharge from electrical equipment.
in conclusion
We can see lightning striking buildings and trees, which are destructive. If the ESD protection of electronic circuits is not optimal, even a small amount of discharge will destroy sensitive electronic circuits, which has been detected. The phone has a certain ESD protection. The external connection of the audio circuit 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 electronic components are affected by ESD? Will create a tiny hole and the oxide will invade the part.
Figure 1. Oxide is affected by ESD and the oxide is punched into a small hole.
inhibition
As with all merchandise, mobile phones must be certified for ESD according to IEC61000-4-2 regulations. The regulations stipulate that the mobile phone can withstand 15 kV air discharge (through 330 Ω / 150 pF), that is, about 45 mA through the current of about 45 mA. In this case, the phone should be able to continue working without being destroyed. The above is a comparison of high energy pulses with ESD mannequin experiments. In order to protect the main chip, additional ESD protection must be added at every potential ESD entry point. In general, devices that suppress ESD generate a controllable output called a clamp voltage.
Figure 2 shows the output of the ESD protection device (clamp voltage) during an ESD event.
Electromagnetic Interference EMI - Causes, Results and Filters
cause
Current flows, creating a magnetic field around the conductor. As the current changes, the magnetic field changes. Therefore, simply switching the current will produce a change in the magnetic field. A change in the magnetic field can cause signals from other nearby conductors. The above is the basic electrical principle.
Both household and industrial power use 50 Hz or 60 Hz AC. This is an audible frequency range. The current continues to change, and conductors of the same frequency nearby will produce a signal. If you've used Hi-Fi, use separate players and amplifiers, and at the same time they're not connected together, you'll hear a click.
Thinking about today's electronic world, the signal is constantly changing everywhere:
• Audio input/output can generate radiation and conduct EMI, and then emit higher frequency RF lines, resulting in signal distortion.
• The cell phone antenna (TDMA pulse) emits an RF signal that can be received by a long-line headset, resulting in EMI noise in the audio signal path.
The GSM (Global Access) handset standard uses frequency division multiplexing and time division multiplexing to simultaneously transmit a large number of phones, as shown in Figure 3.
A particular mobile phone only transmits when it belongs to it. The fundamental frequency of the envelope signal is 1/4.615 ms = 217 Hz. The harmonic frequencies are 434 Hz, 651 Hz, and the like. This frequency is audible. As shown in Figure 4, it is the envelope signal of the mobile phone.
result
When the mobile phone communicates with the base station, or when the two mobile phones are close to each other, the transmitting pulse passes through the loudspeaker, the speaker, or the headset line to transmit the audio path. See Figure 5. The result is a dramatic reduction in audio quality.
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