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参数资料
| 型号： | LM1894MTBD |
| 厂商： | National Semiconductor |
| 文件页数： | 17/19页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION LM1894 |
| 标准包装： | 1 |
| 主要目的： | 音频，音频处理 |
| 已用 IC / 零件： | LM1894 |
| 已供物品： | 板 |
| 相关产品： | LM1894MX-ND - IC NOISE REDUCT SYS DYNAM 14SOIC LM1894M-ND - IC DYNAM NOISE REDUCT SYS 14SOIC |
SNAS551C – DECEMBER 1994 – REVISED APRIL 2013
External Component Guide
(Figure 1)
Component
Value
Purpose
C1
0.1
μF–100 μF
May be part of power supply, or may be added to suppress power supply
oscillation.
C2, C13
1
μF
Blocks DC, pin 2 and pin 13 are at DC potential of VS/2. C2, C13 form a low
frequency pole with 20k RIN.
C14
25
μF–100 μF
Improves power supply rejection.
C3, C12
0.0033
μF
Forms integrator with internal gm block and op amp. Sets bandwidth
conversion gain of 33 Hz/
μA of gm current.
C4, C11
1
μF
Output coupling capacitor. Output is at DC potential of VS/2.
C5
0.1
μF
Works with R1 and R2 to attenuate low frequency transients which could
disturb control path operation.
C6
0.001
μF
Works with input resistance of pin 6 to form part of control path frequency
weighting.
C8
0.1
μF
Combined with L8 and CL forms 19 kHz filter for FM pilot. This is only
required in FM applications(1).
L8, CL
4.7 mH, 0.015
μF
Forms 19 kHz filter for FM pilot. L8 is Toko coil CAN-1A185HM(1)(2).
C9
0.047
μF
Works with input resistance of pin 9 to form part of control path frequency
weighting.
C10
1
μF
Set attack and decay time of peak detector.
R1, R2
1 k
Ω
Sensitivity resistors set the noise threshold. Reducing attenuation causes
larger signals to be peak detected and larger bandwidth in main signal path.
Total value of R1 + R2 should equal 1 k
Ω.
R8
100
Ω
Forms RC roll-off with C8. This is only required in FM applications.
(1)
When FM applications are not required, pin 8 and pin 9 hook-up as follows:
(2)
Toko America Inc., 1250 Feehanville Drive, Mt. Prospect IL 60056
Circuit Operation
The LM1894 has two signal paths, a main signal path and a bandwidth control path. The main path is an audio
low pass filter comprised of a gm block with a variable current, and an op amp configured as an integrator. As
seen in Figure 11, DC feedback constrains the low frequency gain to AV = 1. Above the cutoff frequency of the
filter, the output decreases at
6 dB/oct due to the action of the 0.0033 μF capacitor.
The purpose of the control paths is to generate a bandwidth control signal which replicates the ear's sensitivity to
noise in the presence of a tone. A single control path is used for both channels to keep the stereo image from
wandering. This is done by adding the right and left channels together in the summing amplifier of Figure 11. The
R1, R2 resistor divider adjusts the incoming noise level to open slightly the bandwidth of the low pass filter.
Control path gain is about 60 dB and is set by the gain amplifier and peak detector gain. This large gain is
needed to ensure the low pass filter bandwidth can be opened by very low noise floors. The capacitors between
Copyright 1994–2013, Texas Instruments Incorporated
7
Product Folder Links: LM1894
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM1894MX | 功能描述:特殊用途放大器 RoHS:否 制造商:Texas Instruments 通道数量:Single 共模抑制比（最小值）: 输入补偿电压: 工作电源电压:3 V to 5.5 V 电源电流:5 mA 最大功率耗散: 最大工作温度:+ 70 C 最小工作温度:- 40 C 安装风格:SMD/SMT 封装 / 箱体:QFN-20 封装:Reel |
| LM1894MX/NOPB | 功能描述:特殊用途放大器 RoHS:否 制造商:Texas Instruments 通道数量:Single 共模抑制比（最小值）: 输入补偿电压: 工作电源电压:3 V to 5.5 V 电源电流:5 mA 最大功率耗散: 最大工作温度:+ 70 C 最小工作温度:- 40 C 安装风格:SMD/SMT 封装 / 箱体:QFN-20 封装:Reel |
| LM1894N | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:OC White Company 功能描述:Dynamic Noise Reduction System 14-Pin PDIP Rail |
| LM1895 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:AUDIO POWE RAMPLIFIER |
| LM1895N | 制造商:NSC 制造商全称:National Semiconductor 功能描述:AUDIO POWE RAMPLIFIER |
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