參數(shù)資料
型號: LMV1023UR
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): 4/18頁
文件大?。?/td> 623K
代理商: LMV1023UR
20212445
FIGURE 5. Microphone Sensitivity
Microphone with Additional Gain
When gain is added to the electret element, the analog signal
becomes larger and therefore more robust. This can be ac-
complished 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
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.
This is equivalent to 6.33mV
PP.
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.
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 inter-
face 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) in-
stead of dB(V/Pa). To calculate the digital output (Data) in
dBFS the following equation can be written for the LMV1022/
LMV1023:
(1)
Where,
P
REF is the reference power, which is defined as the maximum
allowed input power (Full Scale). P
INPUT is the applied power
www.national.com
12
202124 Version 2 Revision 1
Print Date/Time: 2011/07/08 14:36:52
LMV1022/LMV1023
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