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| 型号： | MAX9814EVKIT+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 12/14页 |
| 文件大小： | 0K |
| 描述： | EVALUATION KIT FOR MAX9814 |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 1 |
| 放大器类型： | AB 类 |
| 输出类型： | 1-通道（单声道） |
| 电源电压： | 2.7V ~ 5.5V |
| 工作温度： | -40°C ~ 85°C |
| 板类型： | 完全填充 |
| 已用 IC / 零件： | MAX9814 |
| 已供物品： | 板 |
Microphone Amplifier with AGC and
Low-Noise Microphone Bias
MAX9814 AGC DISABLED
400
μs/div
VMICIN
100mV/div
VMICOUT
(AC-COUPLED)
1V/div
MAX9814 fig01a
MAX9814 AGC ENABLED
400
μs/div
VMICIN
100mV/div
VMICOUT
(AC-COUPLED)
1V/div
MAX9814 fig01b
0V
Detailed Description
The MAX9814 is a low-cost, high-quality microphone
amplifier with automatic gain control (AGC) and a low-
noise microphone bias. The MAX9814 consists of sever-
al distinct circuits: a low-noise preamplifier, a variable
gain amplifier (VGA), an output amplifier, a microphone-
bias-voltage generator, and AGC control circuitry.
An internal microphone bias voltage generator pro-
vides a 2V bias that is suitable for most electret con-
denser microphones. The MAX9814 amplifies the input
in three distinct stages. In the first stage, the input is
buffered and amplified through the low-noise preampli-
fier with a gain of 12dB. The second stage consists of
the VGA controlled by the AGC. The VGA/AGC combi-
nation is capable of varying the gain from 20dB to 0dB.
The output amplifier is the final stage in which a fixed
gain of 8dB, 18dB, 20dB is programmed through a sin-
gle tri-level logic input. With no compression from the
AGC, the MAX9814 is capable of providing 40dB,
50dB, or 60dB gain.
Automatic Gain Control (AGC)
A device without AGC experiences clipping at the output
when too much gain is applied to the input. AGC pre-
vents clipping at the output when too much gain is
applied to the input, eliminating output clipping. Figure 1
shows a comparison of an over-gained microphone
input with and without AGC.
The MAX9814’s AGC controls the gain by first detect-
ing that the output voltage has exceeded a preset limit.
The microphone amplifier gain is then reduced with a
selectable time constant to correct for the excessive
output-voltage amplitude. This process is known as the
attack time. When the output signal subsequently low-
ers in amplitude, the gain is held at the reduced state
for a short period before slowly increasing to the nor-
mal value. This process is known as the hold and
release time. The speed at which the amplifiers adjust
to changing input signals is set by the external timing
capacitor CCT and the voltage applied to A/R. The
AGC threshold can be set by adjusting VTH. Gain
reduction is a function of input signal amplitude with a
maximum AGC attenuation of 20dB. Figure 2 shows the
effect of an input burst exceeding the preset limit, out-
put attack, hold and release times.
If the attack and release times are configured to
respond too fast, audible artifacts often described as
“pumping” or “breathing” can occur as the gain is
rapidly adjusted to follow the dynamics of the signal.
For best results, adjust the time constant of the AGC to
accommodate the source material. For applications in
which music CDs are the main audio source, a 160s
attack time with an 80ms release time is recommend-
ed. Music applications typically require a shorter
release time than voice or movie content.
Figure 1. Microphone Input with and Without AGC
MAX9814
Maxim Integrated
7
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| MAX9814EVKIT+ | 功能描述:音频 IC 开发工具 MAX9814 Eval Kit RoHS:否 制造商:Texas Instruments 产品:Evaluation Kits 类型:Audio Amplifiers 工具用于评估:TAS5614L 工作电源电压:12 V to 38 V |
| MAX981CPA | 功能描述:校验器 IC Single Comparator / Reference RoHS:否 制造商:STMicroelectronics 产品: 比较器类型: 通道数量: 输出类型:Push-Pull 电源电压-最大:5.5 V 电源电压-最小:1.1 V 补偿电压（最大值）:6 mV 电源电流（最大值）:1350 nA 响应时间: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SC-70-5 封装:Reel |
| MAX981CPA+ | 功能描述:校验器 IC Single Comparator / Reference RoHS:否 制造商:STMicroelectronics 产品: 比较器类型: 通道数量: 输出类型:Push-Pull 电源电压-最大:5.5 V 电源电压-最小:1.1 V 补偿电压（最大值）:6 mV 电源电流（最大值）:1350 nA 响应时间: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SC-70-5 封装:Reel |
| MAX981CSA | 功能描述:校验器 IC RoHS:否 制造商:STMicroelectronics 产品: 比较器类型: 通道数量: 输出类型:Push-Pull 电源电压-最大:5.5 V 电源电压-最小:1.1 V 补偿电压（最大值）:6 mV 电源电流（最大值）:1350 nA 响应时间: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SC-70-5 封装:Reel |
| MAX981CSA+ | 功能描述:校验器 IC Single Comparator / Reference RoHS:否 制造商:STMicroelectronics 产品: 比较器类型: 通道数量: 输出类型:Push-Pull 电源电压-最大:5.5 V 电源电压-最小:1.1 V 补偿电压（最大值）:6 mV 电源电流（最大值）:1350 nA 响应时间: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SC-70-5 封装:Reel |
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