Application Section

HIGH GAIN

The LMV1012 series provides outstanding gain versus the

JFET and still maintains the same ease of implementation,

with improved gain, linearity and temperature stability. A high

gain eliminates the need for extra external components.

BUILT IN GAIN

The LMV1012 is offered in 0.3 mm height space saving

small 4-pin micro SMD packages in order to fit inside the

different size ECM canisters of a microphone. The LMV1012

is placed on the PCB inside the microphone.

The bottom side of the PCB usually shows a bull’s eye

pattern where the outer ring, which is shorted to the metal

can, should be connected to the ground. The center dot on

the PCB is connected to the V

phantom biasing allows both supply voltage and output sig-

nal on one connection.

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.

This filter 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 LMV1012 is measured within the

frequency band from 10 Hz to 22 kHz using an A-weighted

filter. The input of the LMV1012 is connected to ground with

a 5 pF capacitor, as in Figure 3. Special precautions in the

internal structure of the LMV1012 have been taken to reduce

the noise on the output.

The signal to noise ratio (SNR) is measured witha1kHz

input signal of 18 mV

represents a sound pressure level of 94 dB SPL. No input

capacitor is connected for the measurement.

SOUND PRESSURE LEVEL

The volume of sound applied to a microphone is usually

stated as a pressure level referred to the threshold of hear-

ing of the human ear. The sound pressure level (SPL) in

decibels is defined by:

Sound pressure level (dB) = 20 log P

Where,

P

P

In order to be able to calculate the resulting output voltage of

the microphone for a given SPL, the sound pressure in dB

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FIGURE 1. Built in Gain

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FIGURE 2. A-Weighted Filter

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FIGURE 3. Noise Measurement Setup

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