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A8E_EE-Times-Eur_2-375x10-875_A8.qxd 8/26/15 4: shown in figure 3. This produces a differential (compared to singleended) MEMS technologies & environmental sensors Surface Mount (and Plug In) Transformers and Inductors See Pico’s full Catalog immediately w ww. p i co ele ctro n ics.c o m Low Profile from 4,5mm ht. Audio Transformers Impedance Levels 10 ohms to 250k ohms, Power Levels to 3 Watts, Frequency Response ±3db 20Hz to 250Hz. All units manufactured and tested to MIL-PRF-27. QPL Units available. Power & EMI Inductors Ideal for Noise, Spike and Power Filtering Applications in Power Supplies, DC-DC Converters and Switching Regulators Pulse Transformers 10 Nanoseconds to 100 Microseconds. ET Rating to 150 Volt Microsecond, Manufactured and tested to MIL-PRF-21038. Multiplex Data Bus Pulse Transformers Plug-In units meet the requirements of QPL-MIL-PRF 21038/27. Surface units are electrical equivalents of QPL-MIL-PRF 21038/27. DC-DC Converter Transformers Input voltages of 5V, 12V, 24V And 48V. Standard Output Voltages to 300V (Special voltages can be supplied). Can be used as self saturating or linear switching applications. All units manufactured and tested to MIL-PRF-27. 400Hz/800Hz Power Transformers 0.4 Watts to 150 Watts. Secondary Voltages 5V to 300V. Units manufactured to MIL-PRF-27 Grade 5, Class S (Class V, 1550C available). Delivery-Stock to one week for sample quantities PICO Electronics, Inc. 143 Sparks Ave. Pelham, N.Y. 10803 E Mail: info@picoelectronics.com www.picoelectronics.com Pico Representatives Germany ELBV/Electronische Bauelemente Vertrieb E mail: info@elbv.de Phone: 0049 (0)89 4602852 Fax: 0049 (0)89 46205442 England Ginsbury Electronics Ltd. E-mail: rbennett@ginsbury.co.uk Phone: 0044 1634 298900 Fax: 0044 1634 290904 output, which has several advantages. A dual back-plate MEMS microphone minimizes distortion due to its symmetrical construction. The same principle is used for high end studio condenser microphones. A differential element is more readily managed through the audio processing chain (pre-amp, ADC, etc.), which potentially reduces power requirements for the ASIC. It also reduces RF Fig. 3: Infineon’s dual back-plate MEMS design for high AOP microphones. interference, resulting in fewer signal processing steps. A dual back-plate device is more robust against wind noise due to the fact that higher AOP Manufacturers of single back-plate devices typically use a filter to eliminate low frequency wind noise, with subsequent impact on audio quality. This filter removes bass, which is particularly important in recording music. After all, it really is all about the bass. A result of the above is that a dual back-plate device shows a much more linear behavior until it reaches the AOP. Compared to conventional single ended microphones the SPL where audible distortion begins (2 percent) is pushed out by approximately 10 dB. This has significant impact on the quality of the audio signal as shown on the graph of figure 4. Infineon-based high SPL microphones use a dual back-plate design. This achieves a very high AOP while matching or exceeding the SNR of alternatives in the market today. Audio testing has shown that with excellent audio playback and listening conditions, THD greater than 2 percent is noticeable. Thus, achieving an AOP greater than the current minimum industry level of 130 dB SPL with less than 2 percent THD is significant. Infineon commissioned a study by an independent institute to assess microphone performance according to the latest ITU-T recommendation utilizing POLQA (Perceptual Objective Listening Quality Analysis). The results confirm the findings with the subjective listening test box and demonstrate the outstanding performance of microphones based on Infineon’s dual back-plate MEMS Technology. There are many elements that affect the final performance of the silicon microphones in a smartphone, including the design of the audio processing chain and the overall microphone array. Multiple variables also affect the overall power consumption of the microphone array, though the reduction of signal-processing complexity made possible with a dual-plate design can be an advantage. In the end, the best starting point for design of the microphone path is a listening test. Available test boxes pictured in figure 5 can be used to compare low and high AOP microphone elements and provide a baseline for development. Fig. 4: Measured THD on microphones from a major smartphone tear-down. Fig. 5: Portable live demonstrator of high and low AOP microphones. www.electronics-eetimes.com Electronic Engineering Times Europe February 2016 41


EETE FEB 2016
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