LMV1012UP-20 National Semiconductor, LMV1012UP-20 Datasheet - Page 10

• Manufacturer Part Number: LMV1012UP-20
• Description: AMP, MICROPHONE, 20DB GAIN, SMD, 1032
• Manufacturer: National Semiconductor

Specifications of LMV1012UP-20

• No. Of Channels: 1
• Supply Voltage Range: 2V To 5V
• Thd + N: 0.18% @ VDD=5V
• Load Impedance: 2.2kohm
• Operating Temperature Range: -40°C To +85°C
• Amplifier Case Style: BGA
• No. Of Pins: 4
• Svhc: No
• Rohs Compliant: Yes

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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.
FIGURE 1. Built in Gain
DD
through a resistor. This
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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 with a 1 kHz
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
m
O
is the threshold of hearing (20 µPa)
is the measured sound pressure
FIGURE 3. Noise Measurement Setup
FIGURE 2. A-Weighted Filter
PP
using an A-weighted filter. This
m
/P
O
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