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參數(shù)資料
| 型號： | LMV1022URX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | AUDIO PREAMPLIFIER, PBGA6 |
| 封裝： | MICRO, SMD-6 |
| 文件頁數(shù)： | 3/18頁 |
| 文件大?。?/td> | 623K |
| 代理商： | LMV1022URX |
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.
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 out-
put, 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 out-
put for a given sound pressure.
Sound Pressure Level
The volume of sound applied to a microphone is usually stat-
ed as a sound pressure in dB SPL. This unity of dB SPL refers
to the threshold of hearing of the human ear. The sound pres-
sure in decibels is defined by:
SPL = 20 log (P
M/PO)
Where,
SPL is the Sound Pressure in dB SPL
P
M is the measured absolute sound pressure in Pa
P
O is the threshold of hearing (20Pa)
In order to calculate the resulting output voltage of the electret
element for a given sound pressure in dB SPL, the absolute
sound pressure P
M must be known. This is the absolute sound
pressure in decibels referred to 1Pa instead of 20Pa.
The absolute sound pressure P
M in dBPa is given by:
P
M = SPL (dB SPL) + PO (dBPa)
P
M = SPL + 20*log 20Pa
P
M = SPL - 94dB
JFET Microphone
Translation from the absolute sound pressure level to a volt-
age 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 1.13mV
PP.
The analog output signal is so low that it can easily be dis-
torted by interference from outside the microphone. Addition-
al gain is desirable to make the signal less sensitive to
interference.
11
www.national.com
202124 Version 2 Revision 1
Print Date/Time: 2011/07/08 14:36:52
LMV1022/LMV1023
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| LMV1024 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:PDM Output with Pre-Amplifier for Electret Microphones |
| LMV1024_09 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:PDM Output with Pre-Amplifier for Electret Microphones |
| LMV1024UR | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:PDM Output with Pre-Amplifier for Electret Microphones |
| LMV1024UR/NOPB | 功能描述:IC PRE AMP MIC MONO AB ADC 6USMD RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LMV1024URX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:PDM Output with Pre-Amplifier for Electret Microphones |
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