LMV1032URX-15/NOPB National Semiconductor, LMV1032URX-15/NOPB Datasheet - Page 9

• Manufacturer Part Number: LMV1032URX-15/NOPB
• Description: IC AMP AUDIO MONO AB MIC 4USMD
• Manufacturer: National Semiconductor
• Type: Class ABr

Specifications of LMV1032URX-15/NOPB

• Output Type: 1-Channel (Mono)
• Voltage - Supply: 1.7 V ~ 5 V
• Features: Microphone
• Mounting Type: Surface Mount
• Package / Case: 4-MicroSMD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Max Output Power X Channels @ Load: -
• Other names: LMV1032URX-15

Application Section
The conversion is given by:
Translation from absolute sound pressure level to a voltage
is specified by the sensitivity of the microphone. A conven-
tional microphone has a sensitivity of −44 dBV/Pa.
Example: Busy traffic is 70 dB SPL
Since the LMV1032-15 has a gain of 5.6 (15 dB) over the
JFET, the output voltage of the microphone is 6.35 mV
replacing the JFET with the LMV1032-15, the sensitivity of
the microphone is −29 dBV/Pa (−44 + 15).
LOW FREQUENCY CUT OFF FILTER
To reduce noise on the output of the microphone a low cut
filter has been implemented in the LMV1032. This filter
reduces the effect of wind and handling noise.
It’s also helpful to reduce the proximity effect in directional
microphones. This effect occurs when the sound source is
very close to the microphone. The lower frequencies are
amplified which gives a bass sound. This amplification can
cause an overload, which results in a distortion of the signal.
dBPa = dB SPL - 94 dB
V
This is equivalent to 1.13 mV
dBPa = dB SPL + 20*log 20 µPa
OUT
= 70 −94 −44 = −68 dBV
FIGURE 4. dB SPL to dBV Conversion
FIGURE 5. Gain vs. Frequency
PP
(Continued)
20084211
20084215
PP
. By
9
The LMV1032 is optimized to be used in audio band appli-
cations. The LMV1032 provides a flat gain response within
the audio band and offers linearity and excellent temperature
stability.
ADVANTAGE OF THREE PINS
The LMV1032 ECM solution has three pins instead of the
two pins provided in the case of a JFET solution. The third
pin provides the advantage of a low supply current, high
PSRR and eliminates the need for additional components.
Noise pick-up by a microphone in a cell phone is a well-
known problem. A conventional JFET circuit is sensitive for
noise pick-up because of its high output impedance. The
output impedance is usually around 2.2 kΩ. By providing
separate output and supply pins a much lower output imped-
ance is achieved and therefore is less sensitive to noise
pick-up.
RF noise is among other caused by non-linear behavior. The
non-linear behavior of the amplifier at high frequencies, well
above the usable bandwidth of the device, causes AM de-
modulation of high frequency signals. The AM modulation
contained in such signals folds back into the audio band,
thereby disturbing the intended microphone signal. The
GSM signal of a cell phone is such an AM-modulated signal.
The modulation frequency of 216 Hz and its harmonics can
be observed in the audio band. This type of noise is called
bumblebee noise.
EXTERNAL PRE-AMPLIFIER APPLICATION
The LMV1032 can also be used outside of an ECM as a
space saving external pre-amplifier. In this application, the
LMV1032 follows a phantom biased JFET microphone in the
circuit. This is shown in Figure 6. The input of the LMV1032
is connected to the microphone via the 2.2 µF capacitor. The
advantage of this circuit over one with only a JFET micro-
phone are the additional gain and the high pass filter sup-
plied by the LMV1032. The high pass filter makes the output
signal more robust and less sensitive to low frequency dis-
turbances. In this configuration the LMV1032 should be
placed as close as possible to the microphone.
FIGURE 6. LMV1032 as External Pre-Amplifier
www.national.com
20084226