TI LMV1031

LMV1031
LMV1031-20 Amplifier for Internal 3-Wire Analog Microphones and External
Preamplifier
Literature Number: SNOSAP8A
LMV1031-20
Amplifier for Internal 3-Wire Analog Microphones and
External Preamplifier
General Description
Features
The LMV1031 audio amplifier is an ideal replacement for the
JFET preamplifier that is currently used in the electret microphones. The LMV1031 is optimized for applications that
require extended battery life, such as Bluetooth communication links. The supply current for the LMV1031 is only 72 µA.
This is a dramatic reduction from that required for a JFET
equipped microphone. The LMV1031, with its separate output and supply pins, offers a higher PSRR and eliminates the
need for additional external components.
The LMV1031 is guaranteed to operate from 2V to 5V supply
voltage over the full temperature range, has a fixed voltage
gain of 20 dB and enhanced SNR performance. The
LMV1031 is optimized for an output biasing of 1.09V.
The LMV1031 has less than 200Ω of output impedance over
the full audio bandwidth. The gain response of the LMV1031
is flat within the audio band and is stable over the temperature range.
The LMV1031 is available in a large dome 4-bump ultra thin
micro SMD package that can easily fit on the PCB inside the
miniature microphone metal can (package). This package is
designed for microphone PCBs requiring 1 kg adhesion
criteria.
(Typical LMV1031-20, 2V Supply; Unless Otherwise Noted)
n Signal to noise ratio
62 dB
n Output voltage noise (A-weighted)
−86 dBV
n Low supply current
72 µA
n Supply voltage
2V to 5V
> 100 MΩ
n Input impedance
n Max input signal
108 mVPP
n Output voltage
1.09V
n Temperature range
−40˚C to 85˚C
n Large Dome 4-Bump micro SMD package with improved
adhesion technology.
Block Diagram
Electret Microphone
Applications
n
n
n
n
Mobile communications - Bluetooth
Accessory microphone products
Cellular phones
PDAs
20150804
20150801
© 2005 National Semiconductor Corporation
DS201508
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LMV1031-20 Amplifiers for Internal 3-Wire Analog Microphones and External Preamplifier
October 2005
LMV1031-20
Absolute Maximum Ratings (Note 1)
Storage Temperature Range
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Junction Temperature (Note 6)
−65˚C to 150˚C
150˚C max
Mounting Temperature
Infrared or Convection (20 sec.)
235˚C
ESD Tolerance (Note 2)
Human Body Model
2500V
Machine Model
Operating Ratings (Note 1)
250V
Supply Voltage
Supply Voltage
VDD - GND
2V to 5V
Temperature Range
5.5V
−40˚C to +85˚C
2V and 5V Electrical Characteristics
(Note 3)
Unless otherwise specified, all limits are guaranteed for TJ = 25˚C and VDD = 2V and 5V. Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
Min
(Note 4)
Typ
(Note 5)
Max
(Note 4)
90
100
IDD
Supply Current
VIN = GND
72
SNR
Signal to Noise Ratio
f = 1 kHz, VIN = 18 mVPP
62
Units
µA
dB
THD
Total Harmonic Distortion
f = 1 kHz, VIN = 18 mVPP
0.18
%
en
Output Noise
A-Weighted
−86
dBV
AV
Gain
f = 1 kHz, VIN = 18 mVPP
fLOW
Lower −3 dB Roll Off Frequency
RSOURCE = 50Ω, VIN = 18 mVPP
72
Hz
fHIGH
Upper −3 dB Roll Off Frequency
RSOURCE = 50Ω, VIN = 18 mVPP
52
kHz
VIN
Max Input Signal
f = 1 kHz and THD+N < 1%
108
mVPP
> 100
MΩ
ZIN
Input Impedance
CIN
Input Capacitance
VOUT
Output Voltage
VIN = GND
RO
Output Impedance
f = 1 kHz
PSRR
Power Supply Rejection Ratio
2V < VDD < 5V
19.18
19.00
20.1
20.90
21.00
2
890
875
1090
dB
pF
1310
1325
mV
< 200
Ω
56
dB
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.
Note 2: The human body model (HBM) is 1.5 kΩ in series with 100 pF. The machine model is 0Ω in series with 200 pF.
Note 3: Electrical table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of
the device such that TJ = TA. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ > TA.
Note 4: All limits are guaranteed by design or statistical analysis.
Note 5: Typical values represent the most likely parametric norm at the time of characterization.
Note 6: The maximum power dissipation is a function of TJ(MAX) , θJA and TA. The maximum allowable power dissipation at any ambient temperature is PD =
(TJ(MAX) - TA)/θJA. All numbers apply for packages soldered directly onto a PC board.
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2
LMV1031-20
Connection Diagram
4-Bump Ultra Thin micro SMD
20150803
Top View
Note: - Pin numbers are referenced to package marking text orientation.
- The actual physical placement of the package marking will vary slightly from part to part. The package will designate the date code and will vary considerably.
Package marking does not correlate to device type in any way.
Ordering Information
Package
Part Number
4-Bump Ultra Thin
micro SMD lead free
LMV1031UR-20
LMV1031URX-20
Package Marking
Date Code
3
Transport Media
250 Units Tape and Reel
3k Units Tape and Reel
NSC Drawing
URA04JJA
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LMV1031-20
Typical Performance Characteristics
Unless otherwise specified, VS = 2V, single supply, TA = 25˚C
Supply Current vs. Supply Voltage
Output Voltage vs. Supply Voltage
20150815
20150823
Gain vs. Supply Voltage
Closed Loop Gain and Phase vs. Frequency
20150816
20150824
Power Supply Rejection Ratio vs. Frequency
Total Harmonic Distortion vs. Frequency
20150817
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20150818
4
Total Harmonic Distortion vs. Input Voltage
Output Voltage Noise vs. Frequency
20150819
20150820
5
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LMV1031-20
Typical Performance Characteristics Unless otherwise specified, VS = 2V, single supply, TA =
25˚C (Continued)
LMV1031-20
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 available. The input of the amplifier is connected to the microphone via the PCB.
20150802
FIGURE 2. LMV1031 as external preamplifier
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 response weighting filters are introduced. One of those filters
is the A-weighted filter.
20150804
FIGURE 1. Built-in Gain
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 microphone are the additional gain and the high pass filter supplied by the LMV1031. The high pass filter makes the output
signal more robust and less sensitive to low frequency disturbances. In this configuration the LMV1031 should be
placed as close as possible to the microphone.
20150811
FIGURE 3. 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.
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6
The conversion is given by:
dBPa = dB SPL + 20*log 20 µPa
(Continued)
dBPa = dB SPL - 94 dB
Translation from absolute sound pressure level to a voltage
is specified by the sensitivity of the microphone. A conventional microphone has a sensitivity of −44 dBV/Pa.
20150822
FIGURE 4. Performance vs. Output Current
MEASURING NOISE AND SNR
The overall noise of the LMV1031 is measured within the
frequency band from 10 Hz to 22 kHz using an A-weighted
filter. The input of the LMV1031 is connected to ground with
a 5 pF capacitor.
20150813
FIGURE 6. dB SPL to dBV Conversion
Example: Busy traffic is 70 dB
VOUT = 70 −94 −44 = −68 dBV
This is equivalent to 1.13 mVPP
Since the LMV1031-20 has a gain of 10 times (20 dB) over
the JFET, the output voltage of the microphone is 11.3 mVPP.
By replacing the JFET with the LMV1031-20, the sensitivity
of the microphone is −24 dBV/Pa (−44 + 20).
LOW FREQUENCY CUT-OFF FILTER
The LMV1031 has a low cut-off filter on the output of the
microphone, to reduce low frequency noises, such as wind
and vibration. This also helps 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.
20150812
FIGURE 5. Noise Measurement Setup
The signal-to-noise ratio (SNR) is measured with a 1 kHz
input signal of 18 mVPP using an A-weighted filter. This
represents a sound pressure level of 94 dB with a standard
ECM sensitivity. No input capacitor is connected.
SOUND PRESSURE LEVEL
The volume of sound applied to a microphone is commonly
stated as the pressure level with respect to the threshold of
hearing of the human ear. This sound pressure level (SPL) in
decibels is defined by:
Sound pressure level (dB) = 20 log Pm/PO
Where,
Pm is the measured sound pressure
PO is the threshold of hearing (20 µPa)
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 1 Pascal (Pa).
7
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LMV1031-20
Application Section
LMV1031-20
Application Section
(Continued)
The LMV1031 is optimized to be used in audio band applications. As shown in Figure 7, the LMV1031 provides a flat
gain response within the audio band and offers excellent
temperature stability.
ADVANTAGE OF THREE PINS
When implemented in an Electret Condenser Microphone
(ECM) the LMV1031 adds the advantages of a three pin
configuration. The third pin provides a low supply current,
higher PSRR, and eliminates the need for additional external
components.
It is well known that cell phone microphones are sensitive to
noise pick-up. A conventional JFET circuit is sensitive to
noise pick-up because of its high output impedance, which is
usually around 2.2 kΩ. The LMV1031 is less sensitive to
noise pick-up because it provides separate output and supply pins. Using separate pins greatly reduces the output
impedance.
20150821
FIGURE 7. Gain vs. Frequency
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8
inches (millimeters)
NOTE: UNLESS OTHERWISE SPECIFIED.
1. FOR SOLDER BUMP COMPOSITION, SEE "SOLDER INFORMATION" IN THE PACKAGING SECTION OF THE NATIONAL SEMICONDUCTOR WEB
PAGE (www.national.com).
2. RECOMMEND NON-SOLDER MASK DEFINED LANDING PAD.
3. PIN A1 IS ESTABLISHED BY LOWER LEFT CORNER WITH RESPECT TO TEXT ORIENTATION.
4. XXX IN DRAWING NUMBER REPRESENTS PACKAGE SIZE VARIATION WHERE X1 IS PACKAGE WIDTH, X2 IS PACKAGE LENGTH AND X3 IS
PACKAGE HEIGHT.
5. NO JEDEC REGISTRATION AS OF NOVEMBER 2004.
4-Bump Ultra Thin micro SMD with Large Dome Bump Technology
NS Package Number URA04JJA
X1 = 1.179 mm X2 = 1.179 mm X3 = 0.35 mm
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
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LMV1031-20 Amplifiers for Internal 3-Wire Analog Microphones and External Preamplifier
Physical Dimensions
unless otherwise noted
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LMV1031-20 Amplifiers for Internal 3-Wire Analog Microphones and External Preamplifier
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