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Application Information
(Continued)
Total Input Noise vs. Source Resistance
The noise model for the non-inverting amplifier configuration
showing all noise sources is described in Figure 5 In addi-
tion to the intrinsic input voltage noise (e
) and current noise
(i
n
= i
n+
= i
n
) sources, there also exits thermal voltage noise
associated with each of the external resistors.
Equation 1 provides the general form for total equivalent
input voltage noise density (e
ni
). Equation 2 is a simplifica-
tion of Equation 1 that assumes
(1)
R
f
||R
g
=R
seq
for bias current cancellation. Figure 6 illustrates
the equivalent noise model using this assumption. The total
equivalent output voltage noise (e
no
) is e
ni
*
A
V
.
(2)
If bias current cancellation is not a requirement, then R
||R
g
does not need to equal R
. In this case, according to
Equation 1, R
R
should be as low as possible in order to
minimize noise. Results similar to Equation 1 are obtained
for the inverting configuration on Figure 2 if R
is replaced
by R
and R
is replaced by R
g
+ R
. With these substitu-
tions, Equation 1 will yield an e
referred to the non-inverting
input. Referring to e
to the inverting input is easily accom-
plished by multiplying e
ni
by the ration of non-inverting to
inverting gains.
Noise Figure
Noise Figure (NF) is a measure of the noise degradation
caused by an amplifier.
(3)
The noise figure formula is shown is Equation 3. The addi-
tion of a terminating resistor R
, reduces the external ther-
mal noise but increases the resulting NF.
20016542
FIGURE 3. Non-Inverting Amplifier Configuration
20016543
FIGURE 4. Inverting Amplifier Configuration
20016544
FIGURE 5. Non-Inverting Amplifier Noise Model
20016545
FIGURE 6. Noise Model with R
f
||R
g
= R
seq
L
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| LMH6655MMX/NOPB | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMH6657 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:270MHz Single Supply, Single & Dual Amplifiers |
| LMH6657MF | 制造商:Texas Instruments 功能描述:OP Amp Single Volt Fdbk ±6V/12V 5-Pin SOT-23 T/R 制造商:Texas Instruments 功能描述:AMP, 3V 270MHZ, POWERWISE, SOT23-5 制造商:Texas Instruments 功能描述:AMP, 3V 270MHZ, POWERWISE, SOT23-5; Op Amp Type:High Speed; No. of Amplifiers:1; Slew Rate:700V/s; Supply Voltage Range:3V to 12V; Amplifier Case Style:SOT-23; No. of Pins:5; Bandwidth:270MHz; Operating Temperature Min:-40C; ;RoHS Compliant: Yes |
| LMH6657MF/NOPB | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMH6657MFX | 功能描述:運(yùn)算放大器 - 運(yùn)放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補(bǔ)償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-16 轉(zhuǎn)換速度:0.89 V/us 關(guān)閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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