Application Section

LOW CURRENT

The LMV1031 has a low supply current which allows for a

longer battery life. The low supply current of 72 µA makes

this amplifier optimal for microphone applications which

need to be always on.

BUILT-IN GAIN

The LMV1031 is offered in the space saving small micro

SMD package which fits perfectly into the metal can of a

microphone. This allows the LMV1031 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.

EXTERNAL PREAMPLIFIER APPLICATION

The LMV1031 can also be used outside of an ECM as a

space saving external preamplifier. In this application, the

LMV1031 follows a phantom biased JFET microphone in the

circuit. This is shown in Figure 2. The input of the LMV1031

is connected to the microphone via a 2.2 µF capacitor. The

advantages of this circuit over one with only a JFET micro-

phone are the additional gain and the high pass filter sup-

plied by the LMV1031. The high pass filter makes the output

signal more robust and less sensitive to low frequency dis-

turbances. In this configuration the LMV1031 should be

placed as close as possible to the microphone.

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 commonly 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.

OUTPUT CURRENT

The LMV1031 is designed for driving high ohmic loads with

several milli amperes of output current. Figure 4 shows the

gain performance of the LMV1031 versus the sinking and

sourcing current. The gain remains constant within the

shown output current range. This sets the operating range of

the LMV1031 with respect to the output current.

20150804

FIGURE 1. Built-in Gain

20150802

FIGURE 2. LMV1031 as external preamplifier

20150811

FIGURE 3. A-Weighted Filter

www.national.com

6