LMV1022,LMV1023 LMV1022/LMV1023 PDM Output Pre-Amplifier for Electret Microphones Literature Number: SNAS383A July 8, 2011 LMV1022/LMV1023 PDM Output Pre-Amplifier for Electret Microphones General Description Key Specifications The LMV1022 and LMV1023 integrate a pre-amplifier and ADC that can be mounted inside an electret condenser microphone (ECM). The digital output signal is a pulse density modulation (PDM) bitstream that alows the microphone to connect directly to the DSP or baseband processor. Part of National Semiconductor’s Powerwise™ family of products, the LMV1022/LMV1023 consume 900µW of power during operation, offering significant power savings over an analog microphone with an external ADC. The LMV1022 outputs its data on the rising clock edge. The LMV1023 outputs its data on the falling clock edge. Both devices can share the same clock and data lines to create a 4-wire stereo solution. The external clock frequency sets the audio pass band frequency. An 800kHz clock sets the pass band to 7kHz. A 2.4MHz clock sets the pass band to 20kHz. The LMV1022 and LMV1023 are available in 6-bump micro SMD packages with 1kg adhesion properties. (Typical VDD = 1.8V, CLOCK = 1.2MHz, fINPUT = 1kHz, VINPUT = 18mVPP, unless otherwise specified) 61dB ■ SNR A-weighted 5 µVRMS ■ Analog A-weighted noise floor 0.5mA ■ Supply current 0.05% ■ Total harmonic distortion 87dB ■ Power supply rejection ratio Features ■ Integrated 21 dB Pre-Amp and ADC for significant power and space savings ■ Integrated high-pass Filter to reduce 'Plop Noise' ■ Excellent RF immunity (e.g. buzz noise) ■ LMV1022 and LMV1023 combine to create 4-wire Stereo Solution ■ Very thin 0.35mm micro SMD packaging ■ Adhesion technology >1kg Applications ■ ■ ■ ■ ■ ■ Digital audio subsystems and stereo arrays Electret condenser microphones with all digital output Portable communications and small form factor devices Digital audio computing or voice security Automotive or array systems Headphone and headset accessories Typical Application 20212475 For a stereo application, see STEREO OPERATION in the Application Section. © 2011 National Semiconductor Corporation 202124 202124 Version 2 Revision 1 www.national.com Print Date/Time: 2011/07/08 14:36:52 LMV1022/LMV1023 PDM Output Preamp for Electret Microphones OBSOLETE LMV1022/LMV1023 Connection Diagram 6-Bump Ultra Thin micro SMD 20212427 Top View Pin Descriptions Power Supply Pin Name A2 VDD Positive supply voltage Description C1 GND Ground Input C2 Input The microphone is connected to this input pin. Reference B1 VREF A capacitor of 100nF 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 800kHz to 2.4MHz. Data Output B2 Data Over sampled bitstream output. Data is valid if clock is LOW (LMV1022). The data of the LMV1023 is valid when clock is HIGH. When the data is not valid the data output is high impedance. For exact specifications see application section. Ordering Information Package Part Number Package Marking LMV1022UR 6-Bump Ultra Thin micro SMD lead free only Z LMV1022URX LMV1023UR 1 LMV1023URX www.national.com Transport Media 3k Units Tape and Reel 250 Units Tape and Reel 3k Units Tape and Reel 2 202124 Version 2 Revision 1 NSC Drawing 250 Units Tape and Reel Print Date/Time: 2011/07/08 14:36:52 URA06GGA If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage ESD Rating (Note 4) ESD Rating (Note 5) Storage Temperature Range Junction Temperature TJMAX(Note 3) Operating Ratings 235°C (Note 2) Supply Voltage(Note 2) Input Clock Frequency Duty Cycle Operating Temperature Range 3.8V 2000V 200V −65°C to 150°C 150°C max 1.6V to 3.6V 800kHz to 2.4MHz 40% to 60% −40°C to 85°C 1.8V Electrical Characteristics (Note 2) Unless otherwise specified, all limits are guaranteed for TJ = 25°C, VDD = 1.8V, VIN = 18mVPP, fCLK = 1.2MHz, Duty Cycle = 50% and 100nF capacitor between VREF and GND. LMV1022/ LMV1023 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) 56 Units (Limits) SNR Signal to Noise Ratio fIN = 1kHz, A-Weighted, output = -23.5dBFS 61 eND Digital Noise floor of the ADC (Integrated ) Bandwidth = 10 kHz Non Weighted (Note 9) -96 dBFS 5 µVRMS eNA Noise Floor (Input Referred) DR Dynamic range Electrical A-Weighted Acoustic A-Weigthed (Note 10) dB (min) -32 85 dBSPL 80 dB (min) fIN = 1kHz, VIN = 18mVPP 0.05 THD+N Total Harmonic Distortion and Noise fIN = 1kHz, VIN = 18mVPP A-Weighted 0.1 PSRR Power Supply Rejection Ratio VIN = GND, Test Signal on VDD, 217Hz, 400mVPP Input referred. 87 Max Input Signal fIN = 1kHz, THD < 1% 150 mVPP Acoustic Overload Point fIN = 1kHz, THD < 10% (Note 10) 115 dBSPL Max Digital Output level fIN = 1kHz, THD < 1% -5 Acoustic Overload Point fIN = 1kHz, THD < 10% (Note 10) -3 FCLK = 1.2MHz 17 Hz FCLK = 2.4MHz 33 Hz THD VIN VDOUT Total Harmonic Distortion fLOW Lower -3dB Corner Frequency CIN Input Capacitance RIN Input Impedance IDD Supply Current VIN = 0VDC % dB dBFS 2 pF >1000 MΩ VIN = GND, CLK = ON, High Impedance Load 0.5 0.75 mA (max) VIN = GND, CLK = OFF, High Impedance Load 0.45 0.6 mA (max) 3 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 www.national.com LMV1022/LMV1023 Mounting Temperature Infrared or Convection (20 sec.) Absolute Maximum Ratings (Note 1) LMV1022/LMV1023 3.3V Electrical Characteristics (Note 2) Unless otherwise specified, all limits are guaranteed for TJ = 25°C, VDD = 3.3V, VIN = 18mVPP, fCLK = 2.4MHz, Duty Cycle = 50% and 100nF capacitor between VREF and GND. LMV1022/ LMV1023 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) 56 Units (Limits) SNR Signal to Noise Ratio fIN = 1kHz, A-Weighted, output = -23.5dBFS 61 eND Digital Noise floor of the ADC (Integrated ) Bandwidth = 20 kHz Non Weighted (Note 9) -96 dBFS 5 µVRMS eNA Noise Floor (Input Referred) DR Dynamic range Electrical A-Weighted Acoustic A-Weigthed (Note 10) -32 85 dB (min) dBSPL 80 dB (max) fIN = 1kHz, VIN = 18mVPP 0.05 THD+N Total Harmonic Distortion and Noise fIN = 1kHz, VIN = 18mVPP A-Weighted 0.1 PSRR Power Supply Rejection Ratio VIN = GND, Test Signal on VDD, 217Hz, 400mVPP Input referred. 87 Max Input Signal fIN = 1kHz, THD < 1% 150 mVPP Acoustic Overload Point fIN = 1kHz, THD < 10% (Note 10) 115 dBSPL Max Digital Output level fIN = 1kHz, THD < 1% -5 Acoustic Overload Point fIN = 1kHz, THD < 10% (Note 10) -3 FCLK = 1.2MHz 17 Hz FCLK = 2.4MHz 33 Hz THD VIN VDOUT Total Harmonic Distortion fLOW Lower -3dB Corner Frequency CIN Input Capacitance RIN Input Impedance IDD Supply Current VIN = 0VDC % dB dBFS 2 pF >1000 MΩ VIN = GND, CLK = ON, High Impedance Load 0.6 0.9 mA (max) VIN = GND, CLK = OFF, High Impedance Load 0.5 0.65 mA (max) www.national.com 4 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 Unless otherwise specified, all limits are guaranteed for TJ = 25°C, 1.6V < VDD < 3.6V, VIN = 18 mVPP, 800kHz < fCLK < 2.4 MHz, Duty Cycle = 50% and 100nF capacitor between VREF and GND. Symbol Parameter Conditions Typical (Note 6) Limits (Note 7) Units (min/ max) VLOW CLOCK Logic Low Level 0.1*VDD V (max) VHIGH CLOCK Logic High Level 0.9*VDD V (min 0.1 V (min) VDD-0.1V V (max VOL DATA Output Logic Low Level ISINK = 0.5mA VOH DATA Output Logic High Level ISOURCE = 0.5mA tHZ Time from CLOCK Transition to DATA LMV1022: On Rising Edge of the CLOCK Becoming High Impedance (See also LMV1023: On Falling Edge of the CLOCK Figure 10, Application Section) 65 ns tDV Time from CLOCK Transition to DATA LMV1022: On Falling Edge of the CLOCK Becoming Valid (See also Figure 10, LMV1023: On Rising Edge of the CLOCK Application Section) 90 ns Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and the device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed. Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature, TA. The maximum allowable power dissipation is PDMAX = (TJMAX - TA) / θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LMV1022, LM1023 see power derating curves for additional information. Note 4: Human body model, applicable std. JESD22-A114C. Note 5: Machine model, applicable std. JESD22-A115-A. Note 6: Typical values represent most likely parametric norms at TA = +25°C, and at the Recommended Operation Conditions at the time of product characterization and are not guaranteed. Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis. Note 8: The Supply Current depends on the applied Clock Frequency and the load on the DATA output. Note 9: Quantization Noise level of the modulator (verified by simulation) Note 10: Calculated for Typical microphone as described in the Application section Digital Microphone 5 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 www.national.com LMV1022/LMV1023 Digital Interface Electrical Characteristics LMV1022/LMV1023 Typical Performance Characteristics Unless otherwise specified, measurements are performed on an LMV1022/ LMV1023 with VDD = 1.8V, Clock Duty Cycle = 50% and a 100nF capacitor is placed between VREF and GND, TJ = 25° C, Vin =18 mVpp Output Spectrum at 16kBit/s, CLOCK Frequency = 0.8MHz Output Spectrum at 48kbit/s, CLOCK Frequency = 2.4MHz 20212430 20212446 Output Spectrum, Stereo Operation at 48kbit/s, CLOCK Frequency = 2.4MHz Output Noise Spectrum at16kbit/s and 48kbit/s 20212448 20212431 THD and Output Level vs. Frequency at 16bBit/s, CLOCK Frequency = 0.8MHz Vin = 50mVpp THD and Output Level vs. Frequency at 24kbit/s, CLOCK Frequency = 1.2MHz Vin = 50mVpp 20212450 20212449 www.national.com 6 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 THD and Output Level vs. Frequency at 48kbit/s, CLOCK Frequency = 2.4MHz , Vin = 50mVpp 20212452 20212432 THD vs. Input Level at 16kbit/s, CLOCK Frequency = 0.8MHz THD vs. Input Level at 24kbit/s, CLOCK Frequency = 1.6MHz 20212454 20212453 THD vs. Input Level at 32kbit/s, CLOCK Frequency = 1.6MHz THD vs. Input Level at 48kbit/s, CLOCK Frequency = 2.4MHz 20212456 20212433 7 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 www.national.com LMV1022/LMV1023 THD and Output Level vs. Frequency at 32kbit/s, CLOCK Frequency = 1.6MHz Vin = 50mVpp LMV1022/LMV1023 PSRR vs. Frequency for VDD = 1.8V and 3.3V at 16kbit/s, CLOCK Frequency = 0.8MHz PSRR vs. Frequency for VDD = 1.8V and 3.3V at 48kbit/s, CLOCK Frequency = 2.4MHz 20212457 20212458 IDD vs. VDD CLOCK Frequency = 0.8MHz and 2.4MHz 20212434 www.national.com 8 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 The LMV1022 and LMV1023 consist of a pre-amplifier and sigma-delta converter for placement inside an electret condenser microphone (ECM). The output of the LMV1022/ LMV1023 is a robust digital serial bit stream eliminating the sensitive low-level 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. 20212424 FIGURE 1. Typical Application LOW FREQUENCY CUT OFF FILTER To reduce noise on the output of the microphone a low frequency cut off filter has been implemented. 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 air pressure wave results in very low frequency, large amplitude signals that when amplified gives a 'plop' sound. This large signal can cause a temporary overload in the amplifier, which results in distortion of the signal The corner frequency of the integrated high pass filter is linear proportional to the input clock frequency of the part. 20212443 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. BUILT-IN PRE-AMPLIFIER / ADC The LMV1022/ LMV1023 are offered in a space saving small 6-bump micro SMD package in order to fit inside small ECM canisters. The LMV1022 or LMV1023 IC is placed on the PCB. This PCB forms the bottom of the microphone, which is placed in the device. 9 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 www.national.com LMV1022/LMV1023 TYPICAL APPLICATION Figure 1 depicts a typical application, where the LMV1022 or LMV1023 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 LMV1022/ LMV1023 interface. A digital filter in the DSP or Baseband decimates the audio signal. Application Section LMV1022/LMV1023 20212474 FIGURE 3. Cross section of a Microphone www.national.com 10 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 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 SPL PM is the measured absolute sound pressure in Pa PO is the threshold of hearing (20µPa) 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 1Pa instead of 20µPa. The absolute sound pressure PM in dBPa is given by: PM = SPL (dB SPL) + PO (dBPa) PM = SPL + 20*log 20µPa PM = SPL - 94dB 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 −44dB(V/Pa). This is also the typical sensitivity number for the JFET microphone, since a JFET usually has a gain of about 1x (0dB). A block diagram of a microphone with a JFET is given in Figure 5. Example: Busy traffic has a sound pressure of 70dB SPL. Microphone Output = SPL + C + S Where, SPL is the Sound Pressure in dB SPL C is the dB SPL to dBPa conversion (−94dB) S is the Sensitivity in dB(V/Pa) Microphone Output = 70 – 94 – 44 = −68dBV This is equivalent to 1.13mVPP. 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. 20212440 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. Because a microphone using the LMV1022/ LMV1023 has a digital output, the sensitivity will be stated in dB(Full Scale/Pascal) or dB(FS/Pa) as opposed 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. 11 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 www.national.com LMV1022/LMV1023 A-WEIGHTED FILTER The human ear has a frequency range from about 20Hz to 20kHz. 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. LMV1022/LMV1023 20212445 FIGURE 5. Microphone Sensitivity This is equivalent to 6.33mVPP. The pre-amplifier with additional gain reduces the impact of noise on the wiring and traces from the microphone to the baseband chip significantly. To reduce interference further, an Analog-to-Digital converter is integrated in both the LMV1022and LMV1023, 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 than 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 15dB is added by the pre-amplifier. This results in a sensitivity of −29dB(V/Pa) with a typical electret element of −44dB(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 (70dB SPL), the output voltage of the microphone with the LMV1015 is: Microphone Output = SP + C + S Where, SP is the Sound Pressure in dB SPL C is the dB SPL to dBPa conversion (−94dB) S is the Sensitivity in dB(V/Pa) Microphone output = 70 - 94 - 29 = −53dBV. www.national.com Digital Microphone By integrating the Analog-to-Digital converter (ADC) in the LMV1022/ LMV1023 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 LMV1022/ LMV1023: (1) Where, PREF is the reference power, which is defined as the maximum allowed input power (Full Scale). PINPUT is the applied power 12 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 (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 LMV1022/ LMV1023 the reference voltage VREF is 1.5VP (1.06 VRMS) and the Gain A is 21dB. These parameters are fixed inside the device. Knowing this, Equation 2 can be simplified: Digital Output (dBFS) = VINPUT (dBV) - 0.5 + 21 Digital Output (dBFS) = VINPUT (dBV) + 20.5 The sensitivity of the digital microphone is the sensitivity of a conventional microphone plus the input to output transfer of the LMV1022/ LMV1023. The sensitivity of a typical digital microphone is therefore: −44 + 20.5 = −23.5dB(FS/Pa). ANALOG-TO-DIGITAL CONVERTER The ADC used in the LMV1022/ LMV1023 is an one bit sigmadelta 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 LMV1022/ LMV1023 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. 20212472 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 Over Sampling Ratio (OSR). The factor of two comes from the Nyquist theorem. The 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 10kHz is desired, the clock frequency needs to be 1.2MHz 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 of interest 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 Clock Frequency (MHz) Sample Rate after Audio Bandwidth Decimation (kHz) (kbit)/s 0.8 16 7 1.2 24 10 1.6 32 14 2.4 48 20 13 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 www.national.com LMV1022/LMV1023 Digital Output = SP + C + S Where, SP is the Sound Pressure in dB SPL C is the dB SPL to dBPa conversion (−94dB) 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 + S Digital Output (dBFS) = 70 - 94 - 23.5= −47.5dBFS on the input pin and “A” is the gain of the pre-amplifier in decibels. Written into voltages, the equation is: LMV1022/LMV1023 phone will have a LMV1022 built-in and the other will have a LMV1023 built-in. These two microphones share the same interface lines to minimize wiring (Figure 9). 20212425 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 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 edge of this clock is the proper moment for latching the data to the attached application. The LMV1022 is positive edge triggered while the LMV1023 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. 20212461 FIGURE 7. Frequency Spectrum A low-pass decimation filter implemented in the baseband chip or DSP eliminates the noise above the band of interest. The resulting frequency spectrum contains only the frequency components left within the band of interest. Figure 8 depicts the frequency spectrum after filtering. 20212429 20212473 FIGURE 10. Timing stereo application FIGURE 8. Frequency Spectrum after Filtering STEREO OPERATION The LMV1022 and the LMV1023 are designed to operate together in a stereo solution with two microphones. One micro- www.national.com 14 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 20212476 FIGURE 11. Application schematic for PCB Layout 20212428 FIGURE 12. PCB Layout provides the means by using a DIP socket to evaluate parts on DIP conversion boards and offers a four pin interface to connect other digital PDM sources like microphones containing LMV1022 alike parts. The user guide for this demoboard can be found as application note AN-1784 DEMOBOARD The LMV1022/LMV1023 demo board provides a means for easy evaluation of digital PDM microphone amplifiers like the LMV1022, LMV1023, LMV1024 and LMV1026. The demo board has the LMV1022 and the LMV1023 in the 6 pin μSMD package mounted ready for evaluation. This demo board also 15 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 www.national.com LMV1022/LMV1023 crophone PCB has two capacitors. One capacitor (100nF) is connected to the reference pin of the LMV1022/ LMV1023. The other capacitor (100nF) is used as decoupling for high frequencies on the supply. No capacitors should be placed on the data output of the LMV1022/ LMV1023 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. LAYOUT CONSIDERATIONS To obtain the best possible performance from the microphone, special care needs to be taken for the design of the PCB. 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 12. The mi- LMV1022/LMV1023 Revision History Rev 1.0 Date 04/04/08 Description Initial release. www.national.com 16 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 LMV1022/LMV1023 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 = 1.128mm, X2 = 1.628mm, X3 = 0.35mm 17 202124 Version 2 Revision 1 Print Date/Time: 2011/07/08 14:36:52 www.national.com LMV1022/LMV1023 PDM Output Preamp for Electret Microphones Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com 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 References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets 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 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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