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參數(shù)資料
型號: LT1115CSW#PBF
廠商: Linear Technology
文件頁數(shù): 15/16頁
文件大?。?/td> 0K
描述: IC OPAMP AUDIO MONO AB 16SOIC
標(biāo)準(zhǔn)包裝: 47
放大器類型: 音頻
電路數(shù): 1
轉(zhuǎn)換速率: 15 V/µs
增益帶寬積: 70MHz
電流 - 輸入偏壓: 50nA
電壓 - 輸入偏移: 50µV
電流 - 電源: 8.5mA
電壓 - 電源,單路/雙路(±): ±4 V ~ 20 V
工作溫度: 0°C ~ 70°C
安裝類型: 表面貼裝
封裝/外殼: 16-SOIC(0.295",7.50mm 寬)
供應(yīng)商設(shè)備封裝: 16-SO
包裝: 管件
LT1115
8
1115fa
Therefore, to realize truly low noise performance it is
important to understand the interaction between voltage
noise (en), current noise (in) and resistor noise (rn).
Total Noise vs Source Resistance
The total input referred noise of an op amp is given by
et = [en2 + rn2 + (inReq)2]1/2
where Req is the total equivalent source resistance at
the two inputs
and rn = √4kTReq = 0.13√Req in nV/√Hz at 25°C
As a numerical example, consider the total noise at 1kHz
of the gain of 1000 amplifier shown below.
Req = 100 + 100||100k ≈ 200
rn = 0.13√200 = 1.84nV/√Hz
en = 0.85nV/√Hz
in = 1.0pA/√Hz
et = [0.852 + 1.842 + (1.0 x 2.0)2]1/2 = 2.04nV/√Hz
output noise = 1000 et = 2.04V/√Hz
At very low source resistance (Req < 40) voltage noise
dominates. As Req is increased resistor noise becomes the
largest term—as in the example above—and the LT1115’s
voltage noise becomes negligible. As Req is further
increased, current noise becomes important. At 1kHz,
when Req is in excess of 20k, the current noise
component is larger than the resistor noise. The Total
Noise vs Matched Source Resistance plot in the Typical
Performance Characteristics section, illustrates the above
calculations.
+
100
100k
100
LT1115
LT1115 AI01
The plot also shows that current noise is more dominant
at low frequencies, such as 10Hz. This is because resistor
noise is flat with frequency, while the 1/f corner of current
noise is typically at 250Hz. At 10Hz when Req > 1k, the
current noise term will exceed the resistor noise.
When the source resistance is unmatched, the Total Noise
vs Unmatched Source Resistance plot should be con-
sulted. Note that total noise is lower at source resistances
below 1k because the resistor noise contribution is less.
When Rs > 1k total noise is not improved, however. This
is because bias current cancellation is used to reduce
input bias current. The cancellation circuitry injects two
correlated current noise components into the two inputs.
With matched source resistors the injected current noise
creates a common-mode voltage noise and gets rejected
by the amplifier. With source resistance in one input only,
the cancellation noise is added to the amplifier’s inherent
noise.
In summary, the LT1115 is the optimum amplifier for
noise performance—provided that the source resistance
is kept low. The following table depicts which op amp
manufactured by Linear Technology should be used to
minimize noise—as the source resistance is increased
beyond the LT1115’s level of usefulness.
Best Op Amp for Lowest Total Noise vs Source Resistance
Note 1: Source resistance is defined as matched or unmatched, e.g.,
RS = 1k means: 1k at each input, or 1k at one input and zero at the
other.
SOURCE RESISTANCE
BEST OP AMP
(NOTE 1)
AT LOW FREQ (10Hz)
WIDEBAND (1kHz)
0 to 400
LT1028/1115
400 to 4k
LT1007/1037
LT1028/1115
4k to 40k
LT1001*
LT1007/1037
40k to 500k
LT1012*
LT1001*
500k to 5M
LT1012* or LT1055
LT1012*
> 5M
LT1055
*These op amps are best utilized in applications requiring less bandwidth
than audio.
APPLICATIO S I FOR ATIO
WU
UU
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