July 20, 2009 LMV1024/LMV1026 (Stereo) PDM Output with Pre-Amplifier for Electret Microphones General Description Features National’s LMV1024 and LMV1026 stereo amplifiers are solutions for the new generation of voice enrichment capabilities. National has integrated sigma delta modulation and analog cores to improve the voice quality and the performance and to support designer’s choices. Each 20 kHz preamplifier drives a Pulse Density Modulated (PDM) signal at an over sampled 60 bit stream, offering versatility. These solutions provide immediate conversion to high performance audio spectrum, thus completing a high quality audio system. The LMV1024 and LMV1026 operate from 1.6V to 3V. National’s new adjustable clock frequency technology is designed for stereo, performance and ease of use. The stereo function is either a rising or falling edge clock command. The high drive, robust PDM signal directly from an ECM (Electret Condenser Microphone), upgrades existing lower quality, low-level signal constraints. These advanced mixed signal preamplifiers cleanly, accurately and creatively eliminate older, poorer quality systems, which restricted performance and versatility. The 4-wire PDM signaling reduces RF noise and simplifies layout. Using National’s PDM solutions is the choice for higher quality mono or stereo and multi-array applications. National’s 518uA circuits deliver stereo portability with audio quality bandwidth. These solutions enable rapid system evaluation and enhance consumer satisfaction. National provides the LMV1024 and LMV1026 in 6-bump micro SMD packages with 1 kg adhesion properties. (Typical VDD = 1.8V, CLOCK = 1.2 MHz, fINPUT = 1 kHz, VINPUT = 18 mVPP, unless otherwise specified) ■ Enhanced high-performance, full PDM output from the element ■ Stereo chipset and array routing 59 dB ■ SNR A-weighted −89 dBFS ■ Digital A-weighted noise floor 518 µA ■ Supply current 400 kHz to 2.4 MHz ■ Clock frequency 0.03% ■ Total harmonic distortion 100 dB ■ Power supply rejection ratio ■ Adhesion technology >1 kg ■ Highly integrated stereo or mono signaling ■ Maximized system performance ■ Reduced components and layout ■ RF (buzz noise) managed with 4 wire signaling ■ Thinnest 0.35 mm micro SMD packaging Applications ■ ■ ■ ■ ■ ■ Digital output audio subsystems and stereo arrays Electret condenser microphones with all digital output Portable communications and small form factor Digital audio computing or voice security Automotive or array systems Headphone and Headset accessories Typical Application 20133475 For a stereo application, see STEREO OPERATION in the Application Section. © 2009 National Semiconductor Corporation 201334 201334 Version 3 Revision 4 www.national.com Print Date/Time: 2009/07/20 17:12:49 LMV1024/LMV1026 PDM Output with Pre-Amplifier for Electret Microphones OBSOLETE LMV1024/LMV1026 Junction Temperature (Note 6) Mounting Temperature Infrared or Convection (20 sec.) 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 Machine Model Supply Voltage VDD - GND Storage Temperature Range Operating Ratings 150°C max 235°C (Note 1) Supply Voltage Input Clock Frequency Duty Cycle Operating Temperature Range 2500V 250V 3.3V −65°C to 150°C 1.6V to 3.0V 400 kHz to 2.4 MHz 40% to 60% −40°C to 85°C 1.8V Electrical Characteristics (Note 3) Unless otherwise specified, all limits are guaranteed for TJ = 25°C, VDD = 1.8V, VIN = 18 mVPP, fCLK = 1.2 MHz, Duty Cycle = 50% and 100 nF capacitor between VREF and GND. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min (Note 4) Typ (Note 5) SNR Signal to Noise Ratio fIN = 1 kHz, A-Weighted 59 eN Digital Noise Floor (Integrated) f = 20 Hz to 10 kHz, A-Weighted, 4.7 pF Capacitor Connected from Input to GND to Simulate ECM, No Signal −89 Max (Note 4) Units dB dBFS(A) THD Total Harmonic Distortion fIN = 1 kHz, VIN = 18 mVPP 0.03 IDD Supply Current VIN = GND, CLK = ON, High Impedance Load (Note 7) 518 VIN = GND, CLK = OFF 503 % µA 600 VIL CLOCK Input Logic Low Level VIH CLOCK Input Logic High Level VOL DATA Output Logic Low Level VOH DATA Output Logic High Level VIN Max Input Signal fIN = 1 kHz, THD < 1% 243 mVPP VOUT Max Output Signal fIN = 1 kHz, THD < 1% −6.8 dBFS PSRR Power Supply Rejection Ratio VIN = GND, Test Signal on VDD = 217 Hz, 100 mVPP 100 dB tA Time from CLOCK Transition to DATA Becoming High Impedance (See also Figure 10, Application Section) LMV1024: On Rising Edge of the CLOCK 65 ns Time from CLOCK Transition to DATA Becoming Valid (See also Figure 10, Application Section) LMV1024: On Falling Edge of the CLOCK 90 ns 2 pF 1000 MΩ tB CIN Input Capacitance RIN Input Impedance 0.3 1.5 V 0.1 1.7 LMV1026: On Falling Edge of the CLOCK LMV1026: On Rising Edge of the CLOCK www.national.com 2 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 V V V (Note 3) Unless otherwise specified, all limits are guaranteed for TJ = 25°C, VDD = 2.7V, VIN = 18 mVPP, fCLK = 1.2 MHz, Duty Cycle = 50% and 100 nF capacitor between VREF and GND. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min (Note 4) Typ (Note 5) Max (Note 4) Units SNR Signal to Noise Ratio fIN = 1 kHz, A-Weighted 59 dB en Digital Noise Floor (Integrated) f = 20 Hz to 10 kHz, A-Weighted, 4.7 pF Capacitor Connected from Input to GND to Simulate ECM, No Signal −89 dBFS(A) THD Total Harmonic Distortion fIN = 1 kHz, VIN = 18 mVPP 0.03 % IDD Supply Current VIN = GND, CLK = ON, High Impedance Load (Note 7) 535 μA VIN = GND, CLK = OFF 519 650 VLOW CLOCK Logic Low Level VHIGH CLOCK Logic High Level VOL DATA Output Logic Low Level VOH DATA Output Logic High Level VIN Max Input Signal fIN = 1 kHz, THD < 1% 249 mVPP VOUT Max Output Signal fIN = 1 kHz, THD < 1% −6.6 dBFS PSRR Power Supply Rejection Ratio VIN = GND, Test Signal on VDD = 217 Hz, 100 mVPP 100 dB tA Time from CLOCK Transition to DATA Becoming High Impedance (See also Figure 10, Application Section) LMV1024: On Rising Edge of the CLOCK 65 ns Time from CLOCK Transition to DATA Becoming Valid (See also Figure 10, Application Section) LMV1024: On Falling Edge of the CLOCK 90 ns 2 pF 1000 MΩ tB CIN Input Capacitance RIN Input Impedance V 0.3 V 2.4 V 0.1 V 2.6 LMV1026: On Falling Edge of the CLOCK LMV1026: On Rising Edge of the CLOCK 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. 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 into a PC board. Note 7: The Supply Current depends on the applied Clock Frequency and the load on the DATA output. 3 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 www.national.com LMV1024/LMV1026 2.7V Electrical Characteristics LMV1024/LMV1026 Connection Diagram Large Dome 6-Bump Ultra Thin micro SMD 20133427 Top View Pin Descriptions Pin Name Description A2 VDD Positive supply voltage C1 GND Ground Input C2 Input The microphone is connected to this input pin. Reference B1 VREF A capacitor of 100 nF is connected between VREF and ground. This capacitor is used to filter the internal converter reference voltage. Clock Input A1 Clock The user adjustable clock frequency ranges from 400 kHz to 2.4 MHz. Data Output B2 Data Over sampled bitstream output. Data is valid if clock is LOW (LMV1024). The data of the LMV1026 data is valid when clock is HIGH. When the data is not valid the data output is Hi-Z. For exact specifications see application section. Power Supply Ordering Information Package Part Number Package Marking LMV1024UR 6-Bump Ultra Thin micro SMD lead free only IE LMV1024URX LMV1026UR IF LMV1026URX Transport Media 3k Units Tape and Reel 250 Units Tape and Reel 3k Units Tape and Reel Block Diagram 20133426 www.national.com 4 201334 Version 3 Revision 4 NSC Drawing 250 Units Tape and Reel Print Date/Time: 2009/07/20 17:12:49 URA06GGA Unless otherwise specified, measurements are performed on an LMV1024 with VDD = 1.8V, Clock Duty Cycle = 50% and a 100 nF capacitor is placed between VREF and GND, TJ = 25°C. Supply Current vs. Supply Voltage @ CLOCK = 1.2 MHz Supply Current vs. Supply Voltage @ CLOCK = 2.4 MHz 20133446 20133430 Supply Current vs. Supply Voltage CLOCK = OFF SNR, SINAD and -THD vs. Input Amplitude @ CLOCK = 408 kHz, 3.4 kHz Audio BW 20133431 20133447 SNR, SINAD and -THD vs. Input Amplitude @ CLOCK = 960 kHz, 8 kHz Audio BW SNR, SINAD and -THD vs. Input Amplitude @ CLOCK = 1.2 MHz, 10 kHz Audio BW 20133448 20133449 5 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 www.national.com LMV1024/LMV1026 Typical Performance Characteristics LMV1024/LMV1026 SNR, SINAD and -THD vs. Input Amplitude @ CLOCK = 1.92 MHz, 16 kHz Audio BW SNR, SINAD and -THD vs. Input Amplitude @ CLOCK = 2.4 MHz, 20 kHz Audio BW 20133450 20133432 SNR, SINAD and -THD vs. Output @ CLOCK = 408 kHz, 3.4 kHz Audio BW SNR, SINAD and -THD vs. Output @ CLOCK = 960 kHz, 8 kHz Audio BW 20133451 20133452 SNR, SINAD and -THD vs. Output @ CLOCK = 1.2 MHz, 10 kHz Audio BW SNR, SINAD and -THD vs. Output @ CLOCK = 1.92 MHz, 16 kHz Audio BW 20133453 www.national.com 20133454 6 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 SINAD vs. Frequency @ CLOCK = 408 kHz, 3.4 kHz Audio BW 20133433 20133455 SINAD vs. Frequency @ CLOCK = 960 kHz, 8 kHz Audio BW SINAD vs. Frequency @ CLOCK = 1.2 MHz, 10 kHz Audio BW 20133456 20133457 SINAD vs. Frequency @ CLOCK = 1.92 MHz, 16 kHz Audio BW SINAD vs. Frequency @ CLOCK = 2.4 MHz, 20 kHz Audio BW 20133458 20133434 7 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 www.national.com LMV1024/LMV1026 SNR, SINAD and -THD vs. Output @ CLOCK = 2.4 MHz, 20 kHz Audio BW LMV1024/LMV1026 Noise vs. Frequency @ CLOCK = 408 kHz, 3.4 kHz Audio BW Noise vs. Frequency @ CLOCK = 960 kHz, 8 kHz Audio BW 20133459 20133460 Noise vs. Frequency @ CLOCK = 1.2 MHz, 10 kHz Audio BW Noise vs. Frequency @ CLOCK = 1.92 MHz, 16 kHz Audio BW 20133461 20133462 Noise vs. Frequency @ CLOCK = 2.4 MHz, 20 kHz Audio BW PSRR vs. Frequency @ CLOCK = 1.2 MHz 20133444 www.national.com 20133463 8 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 Output vs. Input Amplitude @ CLOCK = 408 kHz, 3.4 kHz Audio BW 20133436 20133464 Output vs. Input Amplitude @ CLOCK = 960 kHz, 8 kHz Audio BW Output vs. Input Amplitude @ CLOCK = 1.2 MHz, 10 kHz Audio BW 20133465 20133466 Output vs. Input Amplitude @ CLOCK = 1.92 MHz, 16 kHz Audio BW Output vs. Input Amplitude @ CLOCK = 2.4 MHz, 20 kHz Audio BW 20133467 20133437 9 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 www.national.com LMV1024/LMV1026 PSRR vs. Frequency @ CLOCK = 2.4 MHz LMV1024/LMV1026 Output vs. Frequency @ CLOCK = 408 kHz, 3.4 kHz Audio BW Output vs. Frequency @ CLOCK = 960 kHz, 8 kHz Audio BW 20133468 20133469 Output vs. Frequency @ CLOCK = 1.2 MHz, 10 kHz Audio BW Output vs. Frequency @ CLOCK = 1.92 MHz, 16 kHz Audio BW 20133470 20133471 Output vs. Frequency @ CLOCK = 2.4 MHz, 20 kHz Audio BW 20133438 www.national.com 10 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 The LMV1024/LMV1026 consist of a pre-amplifier and sigma delta converter for placement inside an electret condenser microphone (ECM). The output of the LMV1024/LMV1026 is a robust digital serial bit stream eliminating the sensitive lowlevel analog signals of conventional JFET microphones. This application section describes, among others, a typical application, a sensitivity comparison between different ECM types, stereo operation and layout recommendations on the ECM PCBs. 20133424 FIGURE 1. Typical Application BUILT-IN PRE-AMPLIFIER / ADC The LMV1024/LMV1026 are offered in a space saving small 6-bump micro SMD package in order to fit inside small ECM canisters. The LMV1024 or LMV1026 IC is placed on the PCB. This PCB forms the bottom of the microphone, which is placed in the cell phone. 20133474 20133443 FIGURE 3. Cross section of a Microphone FIGURE 2. Built-in Pre-Amplifier / ADC Figure 3 depicts a cross section of a microphone with the IC inside the ECM canister. The PCB of the microphone has 4 pads that connects VDD, Ground, DATA and the CLOCK. 11 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 www.national.com LMV1024/LMV1026 TYPICAL APPLICATION Figure 1 depicts a typical application, where the LMV1024 or LMV1026 is built inside the ECM canister. This ECM can be directly connected to a DSP in a digital audio system, like a baseband chip in a cell phone. Connecting is easy because of the digital LMV1024/LMV1026 interface. A digital filter in the DSP or Baseband decimates the audio signal. Application Section LMV1024/LMV1026 to conventional microphones. This section compares the various microphone types and their sensitivity. Examples are given to calculate the resulting output for a given sound pressure. A-WEIGHTED FILTER The human ear has a frequency range from about 20 Hz to 20 kHz. Within this range the sensitivity of the human ear is not equal for each frequency. In order to approach a natural hearing response, weighting filters are introduced. One of these 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. The filter improves the correlation of the measured data to the signal-to-noise ratio perceived by the human ear. Sound Pressure Level The volume of sound applied to a microphone is usually stated as a sound pressure in dB SPL. This unity of dB SPL refers to the threshold of hearing of the human ear. The sound pressure in decibels is defined by: SPL = 20 log (PM/PO) Where,SPL is the Sound Pressure in dB SPLPM is the measured absolute sound pressure in PaPO is the threshold of hearing (20 µPa) In order to calculate the resulting output voltage of the electret element for a given sound pressure in dB SPL, the absolute sound pressure PM must be known. This is the absolute sound pressure in decibels referred to 1 Pa instead of 20 µPa. The absolute sound pressure PM in dBPa is given by:PM = SPL (dB SPL) + PO (dBPa)PM = SPL + 20*log 20 µPaPM = SPL - 94 dB JFET Microphone Translation from the absolute sound pressure level to a voltage can be done when the electrets sensitivity is known. A typical electret element has a sensitivity of −44 dB(V/Pa). This is also the typical sensitivity number for the JFET microphone, since a JFET usually has a gain of about 1x (0 dB). A block diagram of a microphone with a JFET is given in Figure 5. Example: Busy traffic has a Sound Pressure of 70 dB SPL. Microphone Output = SPL + C + S Where,SPL is the Sound Pressure in dB SPLC is the dB SPL to dBPa conversion (−94 dB)S is the Sensitivity in dB(V/Pa) Microphone Output = 70 – 94 – 44 = −68 dBVThis is equivalent to 1.13 mVPP. The analog output signal is so low that it can easily be distorted by interference from outside the microphone. Additional gain is desirable to make the signal less sensitive to interference. 20133440 FIGURE 4. A-weighted Filter SENSITIVITY Sensitivity is a measure for the transfer from the applied acoustic signal to the output of the microphone. Conventional JFET microphones and microphones with built-in gain have a sensitivity that is expressed in dB(V/Pa), where 0dB = 1V/ Pa. A certain pressure on the electret of the microphone gives a certain voltage at the output of the microphone. Since the LMV1024 microphone has a digital output, the sensitivity will be stated in dB(Full Scale/Pascal) or dB(FS/Pa) as opposed www.national.com 12 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 LMV1024/LMV1026 20133445 FIGURE 5. Microphone Sensitivity band chip significantly. To minimize interference ultimately, an Analog-to-Digital converter is integrated in both the LMV1024/LMV1026, realizing a digital interface between the microphone and the baseband. Microphone with Additional Gain When gain is added to the electret element, the analog signal becomes larger and therefore more robust. This can be accomplished by using a pre-amplifier with a higher gain then the JFET. The sensitivity of the microphone consists of the sensitivity of the electret plus the gain of the pre-amplifier. When choosing National Semiconductor's LMV1015-15 for instance, a gain of 15 dB is added by the pre-amplifier. This results in a sensitivity of −29 dB(V/Pa) with a typical electret element of −44 dB(V/Pa). National Semiconductor has a wide range of pre-amplifiers with different gain factors, which can be used to replace the JFET inside the microphone canister. Please visit www.national.com for more information on the LMV1015 and LMV1032 pre-amplifier series. A block diagram with the LMV1015 pre-amplifier inside an ECM is given in Figure 5. When taking the same example of busy traffic (70 dB SPL), the output voltage of the microphone with the LMV1015 is: Microphone Output = SP + C + S Where,SP is the Sound Pressure in dB SPLC is the dB SPL to dBPa conversion (−94 dB)S is the Sensitivity in dB(V/Pa) Microphone output = 70 - 94 - 29 = −53 dBV. This is equivalent to 6.33 mVPP. The pre-amplifier with additional gain reduces the impact of noise on the wiring / traces from the microphone to the base- Digital Microphone By integrating the Analog-to-Digital converter (ADC) in the LMV1024/LMV1026 all analog signals are kept within the “shielded” microphone canister. The output is a digital interface that is robust and insensitive to interference and noise from outside the canister. The output is expressed in dBFS and therefore the sensitivity is also stated in dB(FS/Pa) instead of dB(V/Pa). To calculate the digital output (Data) in dBFS the following equation can be written for the LMV1024/ LMV1026: (1) Where, PREF is the reference power, which is defined as the maximum allowed input power (Full Scale). PINPUT is the applied power on the input pin and “A” is the gain of the pre-amplifier in decibels. Written into voltages, the equation is: 13 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 www.national.com LMV1024/LMV1026 Where,SP is the Sound Pressure in dB SPLC is the dB SPL to dBPa conversion (−94 dB)S is the Sensitivity in dB(V/Pa) Taking the example of busy traffic (70 dB SPL) again results in the following digital output (dBFS): Digital Output (dBFS) = SP - C + SDigital Output (dBFS) = 70 - 94 - 28.8 = −52.8 dBFS (2) Or in decibels:Digital Output (dBFS) = Input (dBV) - Reference (dB) + A Where,Input = 20 Log VINPUT (VRMS)Ref = 20 Log VREF (VRMS)A is the Gain (dB) For the LMV1024/LMV1026 the reference voltage VREF is 1.5VP (1.06 VRMS) and the Gain A is 15.7 dB. These parameters are fixed inside the device. Knowing this, Equation 2 can be simplified: Digital Output (dBFS) = VINPUT (dBV) - 0.5 + 15.7Digital Output (dBFS) = VINPUT (dBV) + 15.2 The sensitivity of the digital microphone is the sensitivity of a conventional microphone plus the input to output transfer of the LMV1024. The sensitivity of a typical digital microphone is therefore: −44 + 15.2 = −28.8 dB(FS/Pa). Digital Output = SP + C + S ANALOG-TO-DIGITAL CONVERTER The ADC used in the LMV1024/LMV1026 is an one bit sigma delta converter with a Pulse Density Modulated output signal (PDM). The output of this ADC can be either High (one) or Low (zero). Assume that the LMV1024/LMV1026 input is at the minimum level. In that case the DATA output will produce almost only “zeros”. When the input increases, the amount of “ones” increases too. At mid-point, where the input is 0V, the number of “zeros” will equal the number of “ones”. At the time that the input approaches the maximum level, the DATA output produces a majority of “ones”. Figure 6 shows the resulting DATA output as function of the input. 20133472 FIGURE 6. DATA Output versus Input Amplitude The high corner of the band of interest (knee) is determined by the clock frequency divided by 2 times the OSR. The factor of two comes from the Nyquist theorem. The over sampling ratio (OSR) of this particular ADC is chosen at 60. This sets the high corner of the band at the clock frequency divided by 120. For instance when a bandwidth of 10 kHz is desired, the clock frequency needs to be 1.2 MHz or higher. Figure 7 depicts the noise shaping effect in a frequency spectrum plot, where a 1 kHz signal is applied. An important characteristic of the sigma delta converter is that the noise is shifted out of the band to frequencies above the band of interest. The band that can be used (Audio Bandwidth) relates directly the applied clock frequency. Table 1 shows the relation between the Clock Frequency and a couple of common Audio Bandwidths. TABLE 1. Audio Bandwidth vs. Clock Frequency cy Audio Bandwidth 3.4 kHz 8 kHz 10 kHz 16 kHz 20 kHz 20133461 FIGURE 7. Frequency Spectrum www.national.com 14 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 20133473 20133429 FIGURE 8. Frequency Spectrum after Filtering FIGURE 10. Timing STEREO OPERATION The LMV1024 and the LMV1026 are designed to operate together in a stereo solution with two microphones. One microphone will have a LMV1024 built-in and the other will have a LMV1026 built-in. These two microphones share the same interface lines to minimize wiring (Figure 9). LAYOUT CONSIDERATIONS To obtain the best possible performance from the microphone, special care needs to be taken for the design of the PCB. Especially the VIN trace is very sensitive as it is connected to the high impedance electret element. It is essential to isolate and shield the VIN trace as much as possible from the digital signal traces (DATA and CLOCK). This needs to be done to avoid any switching noise coupling directly into the input of the IC. An example of a PCB layout is given in Figure 11. The microphone PCB has two capacitors. One capacitor (100 nF) is connected to the reference pin of the LMV1024/ LMV1026. The other capacitor (10 nF) is used as decoupling for high frequencies on the supply. No capacitors should be placed on the data output of the LMV1024/LMV1026 since it will only load the output driver and would degrade the performance. This is opposite to the regular analog phantom biased microphones, where capacitors are needed to improve RFI. 20133425 FIGURE 9. Stereo Application Both microphones produce valid data in only one half of a clock cycle to allow the two microphones to operate on the 20133428 FIGURE 11. PCB Layout 15 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 www.national.com LMV1024/LMV1026 same I/O lines (Data and Clock). To avoid overlap between the drivers of the microphones, one microphone always goes into a high impedance state before the second microphone starts driving the data-line. The LMV1024 is positive edge triggered while the LMV1026 is negative edge triggered. The timing between the two microphones is shown in Figure 10. For exact timing values, please see the Electrical Characteristics table. To eliminate the noise above the band of interest a low pass decimation filter is implemented in the baseband chip or DSP. The resulting frequency spectrum contains only the frequency components left within the band of interest. Figure 8 depicts the frequency spectrum after filtering. LMV1024/LMV1026 www.national.com 16 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 LMV1024/LMV1026 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 MARCH 2003 6-Bump Ultra Thin micro SMD NS Package Number URA06GGA X1 = 1.128 mm, X2 = 1.628 mm, X3 = 0.35 mm 17 201334 Version 3 Revision 4 Print Date/Time: 2009/07/20 17:12:49 www.national.com LMV1024/LMV1026 PDM Output with Pre-Amplifier for Electret Microphones Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage Reference www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Solutions www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise® Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic Wireless (PLL/VCO) www.national.com/wireless www.national.com/training PowerWise® Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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