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参数资料
| 型号： | LMV1012XP-15 |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | Pre-Amplified IC’s for High Gain 2-Wire Microphones |
| 中文描述： | 1 CHANNEL, AUDIO PREAMPLIFIER, PBGA4 |
| 封装： | 0.30 MM HEIGHT, LEAD FREE, MO-211CA, MICRO, SMD-4 |
| 文件页数： | 11/15页 |
| 文件大小： | 497K |
| 代理商： | LMV1012XP-15 |
Application Section
(Continued)
SPL needs to be converted to the absolute sound pressure
in dBPa. This is the sound pressure level in decibels referred
to 1 Pascal (Pa).
The conversion is given by:
dBPa = dB SPL + 20*log 20 μPa
dBPa = dB SPL - 94 dB
Translation from absolute sound pressure level to a voltage
is specified by the sensitivity of the microphone. A conven-
tional microphone has a sensitivity of -44 dBV/Pa.
Example: Busy traffic is 70 dB SPL
V
OUT
= 70 94 44 = 68 dBV
This is equivalent to 1.13 mV
PP
Since the LMV1012-15 has a gain of 6 (15.6 dB) over the
JFET, the output voltage of the microphone is 6.78 mV
. By
implementing the LMV1012-15, the sensitivity of the micro-
phone is -28.4 dBV/Pa (44 + 15.6).
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 lower frequencies are
amplified which gives a bass sound. This amplification can
cause an overload, which results in a distortion of the signal.
The LMV1012 is optimized to be used in audio band appli-
cations. By using the LMV1012, the gain response is flat
within the audio band and has linearity and temperature
stability
Figure 5
.
NOISE
Noise pick-up by a microphone in cell phones is a well-
known problem. A conventional JFET circuit is sensitive for
noise pick-up because of its high output impedance, which is
usually around 2.2 k
.
RF noise is amongst other caused by non-linear behavior.
The non-linear behavior of the amplifier at high frequencies,
well above the usable bandwidth of the device, causes AM-
demodulation of high frequency signals. The AM modulation
contained in such signals folds back into the audio band,
thereby disturbing the intended microphone signal. The
GSM signal of a cell phone is such an AM-modulated signal.
The modulation frequency of 216 Hz and its harmonics can
be observed in the audio band. This kind of noise is called
bumblebee noise.
RF noise caused by a GSM signal can be reduced by
connecting two external capacitors to ground, see
Figure 6
.
One capacitor reduces the noise caused by the 900 MHz
carrier and the other reduces the noise caused by 1800/
1900 MHz.
20058711
FIGURE 4. dB SPL to dBV Conversion
20058712
FIGURE 5. LMV1012-15 Gain vs. Frequency Over
Temperature
L
www.national.com
11
相关PDF资料 |
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| LMV1012XP-25 | Pre-Amplified IC’s for High Gain 2-Wire Microphones |
| LMV1012TP-07 | Pre-Amplified IC’s for High Gain 2-Wire Microphones |
| LMV1012TP-15 | Pre-Amplified IC’s for High Gain 2-Wire Microphones |
| LMV1012TP-25 | Pre-Amplified IC’s for High Gain 2-Wire Microphones |
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LMV1012XP-15/NOPB | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LMV1012XP-25 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LMV1012XP-25/NOPB | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LMV1012XPX-15 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Pre-Amplified IC’s for High Gain 2-Wire Microphones |
| LMV1012XPX-15/NOPB | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
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