Occupying only 0.89 by 1.26 mm of PCB space, the EMIF02-SPK02F2 filter from STMicroelectronics provides filtering for built-in handset speakers or for a stereo headset output. A single EMIF02-SPK02F2 can also be connected to the microphone input to isolate the handset from external sources of noise, such as other cell phones.

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With high attenuation and low series resistance, the filters achieve greater noise reduction while preserving audio signal strength better than other approaches, according to STM. For example, filters built using discrete components are difficult to design for tri-band handsets and typically occupy around 72% more board space than the EMIF02-SPK02F2. Alternatively, single-chip passive filters can be as much as 11% larger and also permit several times more noise at the frequencies used in standards such as GSM.

Furthermore, the EMIF02-SPK02F2 provides better ESD protection than other solutions, the company said. This is important because the level of ESD protection built into chips such as audio ICs is being reduced as ESD-safe manufacturing environments have improved.

The implication for product designers is that devices used specifically to meet product-level ESD standards such as IEC EN 61000-4-2 must provide greater protection. To achieve this, the EMIF02-SPK02F2 has a double-clamping structure that can clamp an ESD spike to just 12 V compared to the 300 V permitted by some ESD protection devices.

The EMIF02-SPK02F2, now in full production, costs $0.16 each for orders over 10,000 pieces.

• STMicroelectronics

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