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LMV1032UP-25 Datasheet(PDF) 8 Page - National Semiconductor (TI) |
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LMV1032UP-25 Datasheet(HTML) 8 Page - National Semiconductor (TI) |
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8 / 12 page  Application Section LOW CURRENT The LMV1032 has a low supply current which allows for a longer battery life. The low supply current of 60µA makes this amplifier optimal for microphone applications which need to be always on. BUILT-IN GAIN The LMV1032 is offered in the space saving small micro SMD package which fits perfectly into the metal can of a microphone. This allows the LMV1032 to be placed on the PCB inside the microphone. The bottom side of the PCB has the pins that connect the supply voltage to the amplifier and make the output avail- able. The input of the amplifier is connected to the micro- phone via the PCB. A-WEIGHTED FILTER The human ear has a frequency range from 20 Hz to about 20 kHz. Within this range the sensitivity of the human ear is not equal for each frequency. To approach the hearing re- sponse weighting filters are introduced. One of those filters is the A-weighted filter. The A-weighted filter is usually used in signal-to-noise ratio measurements, where sound is compared to device noise. It improves the correlation of the measured data to the signal- to-noise ratio perceived by the human ear. MEASURING NOISE AND SNR The overall noise of the LMV1032 is measured within the frequency band from 10 Hz to 22 kHz using an A-weighted filter. The input of the LMV1032 is connected to ground with a 5 pF capacitor. The signal-to-noise ratio (SNR) is measured witha1kHz input signal of 18 mV PP using an A-weighted filter. This represents a sound pressure level of 94 dB SPL. No input capacitor is connected. SOUND PRESSURE LEVEL The volume of sound applied to a microphone is usually stated as the pressure level with respect to the threshold of hearing of the human ear. The sound pressure level (SPL) in decibels is defined by: Sound pressure level (dB) = 20 log P m/PO Where, P m is the measured sound pressure P O is the threshold of hearing (20µPa) In order to be able to calculate the resulting output voltage of the microphone for a given SPL, the sound pressure in dB SPL needs to be converted to the absolute sound pressure in dBPa. This is the sound pressure level in decibels which is referred to as 1 Pascal (Pa). 20084202 FIGURE 1. Built-in Gain 20084209 FIGURE 2. A-Weighted Filter 20084210 FIGURE 3. Noise Measurement Setup www.national.com 8 |
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