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 www.national.com 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. www.national.com 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 www.national.com 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 www.national.com 20150818 4 Total Harmonic Distortion vs. Input Voltage Output Voltage Noise vs. Frequency 20150819 20150820 5 www.national.com 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. www.national.com 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 www.national.com 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 www.national.com 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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