The growing complexity of portable and wireless devices is making such equipment increasingly vulnerable to electrostatic discharges (ESD) and electromagnetic interference (EMI). In particular, it is necessary to reduce EMI in order to achieve high audio quality in electronic devices such as stereo headsets, mobile phones, portable multimedia players, PDAs or notebook computers.
| | PRODUCT PROFILE: COMBINED DUAL AUDIO FILTER |
 | | The package of the CA04F2FT5AUD010G ESD/EMI audio filter features a footprint of 1.37 x 1.0 mm². | Key data | | | Max. DC operating voltage | 5.5 V | | Contact discharge ESD capability | 8 kV | | Typical insertion loss | -20 to -60 dB | | Max. clamping voltage (1 A, 8/20 µs) | 30 V |
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EMI can be generated by RF transmissions and affect the audio lines. At the same time the audio inputs or outputs can cause distortion on the RF lines. EPCOS developed a new combined dual ESD/EMI audio filter (CA04F2FT5AUD010G) that effectively reduces parasitic noise and increases audio quality. The filter features low series resistance and combines EMI filtering and ESD protection in a 0405, 2-fold array, package.
| | FIGURE 1: PROTECTION OF AUDIO APPLICATIONS |
Application example for integrated ESD/EMI protection of audio lines. |
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The design of the new ESD/EMI audio filter integrates ten discrete component functions in one chip (Fig. 1). Its cut-off frequency of 20 MHz and low serial resistance of 0.2 Ω make it a very good solution for applications requiring low bandpass attenuation. At frequencies from 200 MHz to 4 GHz, the attenuation is higher than -20 dB for all quad-band GSM (850/900/1800/1900 MHz) and UMTS standards (2.1 GHz) as well as for GPRS/WLAN and Bluetooth (2.4 GHz). At 900 MHz it offers very high attenuation of more than -60 dB (Fig. 2).
| | FIGURE 2: INSERTION LOSS |
The CA04F2FT5AUD010G ESD/EMI audio filter offers high attenuation over a wide frequency range. |
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Filters that employ TVS and Zener diodes in the audio signal path possess highly nonlinear characteristics. They therefore can seriously increase total harmonic distortion (THD). By contrast, EPCOS’ dual ESD/EMI audio filter features a low THD and noise value less than -100 dB at 1 kHz and thus offers excellent audio capabilities for ultra-clear sound.
| | FIGURE 3: DUAL PROTECTION AGAINST OVERVOLTAGE |
A double-clamping function provides improved protection from ESD pulses. The first varistor clamps the ESD signal from 8 kV to around 200 V (red), and the second varistor further reduces the signal to 70 V (blue). |
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The design of the ESD/EMI audio filter also enables excellent ESD protection for sensitive ICs (IEC 61000-4-2, level 4 standard). Its internal structure provides a double-clamping function and is thus able to reduce the ESD pulses from 8 kV to 70 V (Fig. 3). Moreover, the ESD/EMI audio filter features a highly stable ceramic structure. Even after ±1000 ESD pulses, the dual ESD/EMI audio filter continues to deliver the same high filtering performance.
Authors: Antoine D’Arbonneau, Product Marketing Manager Multilayer Ceramic Components; Thomas Feichtinger, Product Development Manager Multilayer Ceramic Components
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