LMV1031UR-20 - Texas Instruments High-Performance Analog

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

The LMV1031 audio amplifier is an ideal replacement for the

JFET preamplifier that is currently used in the electret micro-

phones. The LMV1031 is optimized for applications that

require extended battery life, such as Bluetooth communica-

tion 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 out-

put 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 200Ωof output impedance over

the full audio bandwidth. The gain response of the LMV1031

is flat within the audio band and is stable over the tempera-

ture 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.

Features

(Typical LMV1031-20, 2V Supply; Unless Otherwise Noted)

nSignal to noise ratio 62 dB

nOutput voltage noise (A-weighted) −86 dBV

nLow supply current 72 µA

nSupply voltage 2V to 5V

nInput impedance >100 MΩ

nMax input signal 108 mV

nOutput voltage 1.09V

nTemperature range −40˚C to 85˚C

nLarge Dome 4-Bump micro SMD package with improved

adhesion technology.

Applications

nMobile communications - Bluetooth

nAccessory microphone products

nCellular phones

nPDAs

Block Diagram

20150801

Electret Microphone

20150804

October 2005

LMV1031-20 Amplifiers for Internal 3-Wire Analog Microphones and External Preamplifier

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

ESD Tolerance (Note 2)

Human Body Model 2500V

Machine Model 250V

Supply Voltage

- GND 5.5V

Storage Temperature Range −65˚C to 150˚C

Junction Temperature (Note 6) 150˚C max

Mounting Temperature

Infrared or Convection (20 sec.) 235˚C

Operating Ratings (Note 1)

Supply Voltage 2V to 5V

Temperature Range −40˚C to +85˚C

2V and 5V Electrical Characteristics (Note 3)

Unless otherwise specified, all limits are guaranteed for T

= 25˚C and V

= 2V and 5V. Boldface limits apply at the tempera-

ture extremes.

Symbol Parameter Conditions

Min

(Note 4)

Typ

(Note 5)

Max

(Note 4) Units

Supply Current V

= GND 72 90

100 µA

SNR Signal to Noise Ratio f = 1 kHz, V

=18mV

62 dB

THD Total Harmonic Distortion f = 1 kHz, V

=18mV

0.18 %

Output Noise A-Weighted −86 dBV

Gain f = 1 kHz, V

=18mV

19.18

19.00

20.1 20.90

21.00 dB

LOW

Lower −3 dB Roll Off Frequency R

SOURCE

=50Ω,V

=18mV

72 Hz

HIGH

Upper −3 dB Roll Off Frequency R

SOURCE

=50Ω,V

=18mV

52 kHz

Max Input Signal f = 1 kHz and THD+N <1% 108 mV

Input Impedance >100 MΩ

Input Capacitance 2pF

OUT

Output Voltage V

= GND 890

875

1090 1310

1325 mV

Output Impedance f=1kHz <200 Ω

PSRR Power Supply Rejection Ratio 2V <V

<5V 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 kΩin series with 100 pF. The machine model is 0Ωin 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=T

A. 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) -T

A)/θJA. All numbers apply for packages soldered directly onto a PC board.

LMV1031-20

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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 Package Marking Transport Media NSC Drawing

4-Bump Ultra Thin

micro SMD lead free

LMV1031UR-20 Date Code 250 Units Tape and Reel URA04JJA

LMV1031URX-20 3k Units Tape and Reel

LMV1031-20

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Typical Performance Characteristics Unless otherwise specified, V

= 2V, single supply, T

= 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

20150824 20150816

Power Supply Rejection Ratio vs. Frequency Total Harmonic Distortion vs. Frequency

20150817 20150818

LMV1031-20

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Typical Performance Characteristics Unless otherwise specified, V

= 2V, single supply, T

25˚C (Continued)

Total Harmonic Distortion vs. Input Voltage Output Voltage Noise vs. Frequency

20150819 20150820

LMV1031-20

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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

LMV1031-20

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Application Section (Continued)

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.

The signal-to-noise ratio (SNR) is measured witha1kHz

input signal of 18 mV

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 P

Where,

is the measured sound pressure

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).

The conversion is given by:

dBPa = dB SPL + 20*log 20 µPa

dBPa=dBSPL-94dB

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

OUT

= 70 −94 −44 = −68 dBV

This is equivalent to 1.13 mV

Since the LMV1031-20 has a gain of 10 times (20 dB) over

the JFET, the output voltage of the microphone is 11.3 mV

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 dis-

tortion of the signal.

20150822

FIGURE 4. Performance vs. Output Current

20150812

FIGURE 5. Noise Measurement Setup

20150813

FIGURE 6. dB SPL to dBV Conversion

LMV1031-20

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Application Section (Continued) The LMV1031 is optimized to be used in audio band appli-

cations. 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 sup-

ply pins. Using separate pins greatly reduces the output

impedance.

20150821

FIGURE 7. Gain vs. Frequency

LMV1031-20

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Physical Dimensions inches (millimeters)

unless otherwise noted

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.

For the most current product information visit us at www.national.com.

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LMV1031-20 Amplifiers for Internal 3-Wire Analog Microphones and External Preamplifier

Tel: 81-3-5639-7560www.national.com

LMV1031-20 Amplifiers for Internal 3-Wire Analog Microphones and External Preamplifier

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