[Introduction]Nowadays, wireless in-ear headphones and headphones are rapidly gaining popularity around the world, and it is the completely wireless earphones with independent wireless left and right earpieces that lead the market to gradually expand. TDK is supporting the development of wireless in-ear headphones and headphones with its notch filters with built-in ESD protection.
The market for wireless in-ear headphones and headphones is expanding rapidly around the world. According to the 2021 Worldwide Electronics Market released by Fuji Chimera Research Institute, the number of wireless earphones in the market is estimated to have reached 210 million in 2019, and it is predicted to grow to 776 million in 2026 (about 3.6 times as many as in 2019). One driving factor is the emergence of fully wireless in-ear headphones (TWS: True Wireless Stereo*1) with independent wireless connections on the left side and each part.
The main advantage of the TWS is that it doesn’t have the hassle of a headphone cable. You can enjoy music while commuting to get off work or school, exercising, doing chores or shopping in a more comfortable way than traditional wired headphones. In the future, TWS will not only be used for listening to music or as an accessory for smartphones, it is also expected to become a hearable device*2 that will change our lives and society. The so-called hearable device is a computer worn on the ear: a wearable device that focuses on voice input and output. It is also expected to enable applications such as hands-free calling, biometric monitoring and simultaneous interpretation.
In order for TWS to continue to grow in the future, improving sound quality and reducing size are critical. While TWS and other wireless audio-equipped devices bring us convenience, they have a structural problem of their own: the wireless signal permeates the audio signal as noise, manifesting as an audible hum. Suppressing this noise as much as possible is a prerequisite for achieving high-fidelity sound quality.
Adding to the challenge, the TWS, unlike its wired counterparts, requires the antenna and battery to be housed within the earpiece, limiting the space for amplifiers and driver vibrations. This results in larger enclosures and inferior sound quality, thus requiring smaller circuits and fewer components.
Against this background, TDK developed the AVRF series of notch filters with built-in ESD protection. A notch filter is an element that removes noise by blocking signals at specific frequencies, such as those used for wireless communications.
Due to its unique material and structural design, the AVRF series has excellent attenuation characteristics*3 at specific frequencies. It suppresses noise and improves the reception sensitivity of TWS and other wireless communications, contributing to excellent sound quality.
The difference between with and without TDK filter (based on TDK research)
Another advantage is its built-in ESD (Electrostatic Discharge)*4 and surge protection. ESD is the electrostatic discharge generated when charged objects such as the human body come into contact with Electronic equipment. Since wireless audio equipment and other electronic equipment are usually operated by human hands, ESD protection is required.
A component called a TVS diode*5 is commonly used to protect electronic equipment from ESD. While providing ESD protection, TVS diodes are ineffective as noise countermeasures, so another component, such as an MLCC, is required. The AVRF series integrates filter (noise suppression) and ESD protection functions using TDK’s proprietary build-up process and material technology. In this way, both noise and ESD countermeasures can be implemented with a single chip, eliminating the need to use TVS diodes larger than notch filters, resulting in a significant reduction in circuit size.
Noise and ESD Countermeasures on a Single Chip
Katsuyuki Takei, Manager of the Piezoelectric and Protection Devices Division of TDK, talked about the future prospects of the AVRF series. “The AVRF series notch filters are ideal EMC (Electromagnetic Compatibility)*6 measures, not only for TWS, but also for audio circuits of devices such as smartphones and smart speakers. Implementing EMC measures means that devices can create a noise-resistant Environment. Wireless and communication equipment is expected to connect all devices in the future, so noise countermeasures will become more and more important. Currently, the AVRF series is mainly aimed at audio equipment for wireless communication, but we hope to expand its scope to automobiles, industrial equipment, energy and healthcare.”
Through notch filters, TDK will continue to provide optimized solutions for high-fidelity audio equipment, laying the foundation for future communication networks.
Noise and ESD Protection for Wireless Communication Audio Equipment
AVRF series notch filter with built-in ESD protection
The family includes products covering the 2.4, 5GHz bands for Bluetooth and Wi-Fi, cellular bands (700MHz to 2.7GHz), and noise suppression in Class D amplifiers. For product details, please long press the QR code below to view.
1. Wireless in-ear headphones/headphones: There are two types, the fully wireless type (true wireless stereo) where the left and right sides are completely independent, and the integrated type (semi-wireless) where the two sides are connected by cables.
2. Hearable devices: Computers and terminals that can be worn on the ears, as well as wireless in-ear headphones with built-in voice assistant functions, are collectively referred to as hearable devices.
3. Attenuation characteristic: A numerical value indicating the effectiveness of reduction across the entire spectrum in the filter circuit.
4. ESD: Abbreviation for Electrostatic Discharge. A classic example of ESD is the static electricity generated by the human body while walking on a carpet, which is released when it comes into contact with metal or other objects. The voltage of ESD is generally several thousand volts, which can cause serious damage to the circuit.
5. TVS Diodes: Transient Voltage Suppression (TVS) diodes protect voltage sensitive components from electrostatic discharge (ESD).
6. EMC: Abbreviation for Electromagnetic Compatibility. It is a combination of electromagnetic interference (EMI) and electromagnetic susceptibility (EMS) concepts.