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參數資料
| 型號： | LM1972NNOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 消費家電 |
| 英文描述： | SPECIALTY CONSUMER CIRCUIT, PDIP20 |
| 封裝： | PLASTIC, DIP-20 |
| 文件頁數： | 12/12頁 |
| 文件大小： | 406K |
| 代理商： | LM1972NNOPB |
the signal level being measured is of the same frequency such
that a true indication of crosstalk may be obtained. Also, to
ensure an accurate measurement, the measured channel's
input should be AC grounded through a 1
μF capacitor.
CLICKS AND POPS
So, why is that output buffer needed anyway? There are three
answers to this question, all of which are important from a
system point of view.
The first reason to utilize a buffer/amplifier at the output of a
μPot is to ensure that there are no audible clicks or pops due
to attenuation step changes in the device. If an on-board
bipolar op amp had been used for the output stage, its re-
quirement of a finite amount of DC bias current for operation
would cause a DC voltage “pop” when the output impedance
of the
μPot changes. Again, this phenomenon is due to the
fact that the output impedance of the
μPot is changing with
step changes and a bipolar amplifier requires a finite amount
of DC bias current for its operation. As the impedance
changes, so does the DC bias current and thus there is a DC
voltage “pop”.
Secondly, the
μPot has no drive capability, so any desired
gain needs to be accomplished through a buffer/non-inverting
amplifer.
Third, the output of a
μPot needs to see a high impedance to
prevent loading and subsequent linearity errors from ocurring.
A JFET input buffer provides a high input impedance to the
output of the
μPot so that this does not occur.
Clicks and pops can be avoided by using a JFET input buffer/
amplifier such as an LF412ACN. The LF412 has a high input
impedance and exhibits both a low noise floor and low THD
+N throughout the audio spectrum which maintains signal in-
tegrity and linearity for the system. The performance of the
system solution is entirely dependent upon the quality and
performance of the JFET input buffer/amplifier.
LOGARITHMIC GAIN AMPUFIER
The
μPot is capable of being used in the feedback loop of an
amplifier, however, as stated previously, the output of the
μPot needs to see a high impedance in order to maintain its
high performance and linearity. Again, loading the output will
change the values of attenuation for the device. As shown in
μPot used in the feedback loop creates a loga-
rithmic gain amplifier. In this configuration the attenuation
levels from Table 1, now become gain levels with the largest
possible gain value being 78dB. For most applications 78dB
of gain will cause signal clipping to occur, however, because
of the
μPot's versatility the gain can be controlled through
programming such that the clipping level of the system is
never obtained. An important point to remember is that when
in mute mode the input is disconnected from the output. In
this configuration this will place the amplifier in its open loop
gain state, thus resulting in severe comparator action. Care
should be taken with the programming and design of this type
of circuit. To provide the best performance, a JFET input am-
plifier should be used.
1197814
FIGURE 10. Digitally-Controlled Logarithmic Gain Amplifier Circuit
1197813
FIGURE 11. n-
μPot Daisy-Chained Circuit
9
www.national.com
LM1972
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM1973 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:レPot⑩3-Channel 76dB Audio Attenuator with Mute |
| LM1973M | 功能描述:衰減器 -IC RoHS:否 制造商:Skyworks Solutions, Inc. 最大衰減:18 dB 容差: 阻抗: 功率額定值:30 dBm 安裝風格:SMD/SMT 工作溫度范圍:- 40 C to + 85 C |
| LM1973M/NOPB | 功能描述:有源衰減器 RoHS:否 制造商:TriQuint Semiconductor 通道數量: 最大頻率: 阻抗: 最大 VSWR: 位數: 最大工作溫度: 最小工作溫度: |
| LM1973MX | 功能描述:衰減器 -IC RoHS:否 制造商:Skyworks Solutions, Inc. 最大衰減:18 dB 容差: 阻抗: 功率額定值:30 dBm 安裝風格:SMD/SMT 工作溫度范圍:- 40 C to + 85 C |
| LM1973MX/NOPB | 功能描述:衰減器 -IC RoHS:否 制造商:Skyworks Solutions, Inc. 最大衰減:18 dB 容差: 阻抗: 功率額定值:30 dBm 安裝風格:SMD/SMT 工作溫度范圍:- 40 C to + 85 C |
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