參數(shù)資料
型號(hào): LMV841
廠(chǎng)商: National Semiconductor Corporation
英文描述: CMOS Input, RRIO, Wide Supply Range Operational Amplifier
中文描述: CMOS輸入,RRIO,寬電源電壓范圍運(yùn)算放大器
文件頁(yè)數(shù): 12/16頁(yè)
文件大?。?/td> 899K
代理商: LMV841
To determine if the noise is acceptable for the application, use
the following formula for resistor noise :
where:
e
th
= Thermal noise voltage (Vrms)
k = Boltzmann constant (1.38 x 10–23 J/K)
T = Absolute temperature (K)
R = Resistance (
Ω)
B = Noise bandwidth (Hz), fmax - fmin
Given in an example with a resistor of 1MOhm at 25°C (298
K) over a frequency range of 100 kHz:
To keep the noise of the application low it might be necessary
to decrease the resistors to 100k, which will decrease the
noise to –97.8 dBV (12.8 uV).
The op amp's input-referred noise of 20 nV/
equivalent to the noise of a 24 k
Ω
resistor.
at 1 kHz is
ACTIVE FILTER
The rail-to-rail input and output of the LMV841, and its wide
supply voltage range makes this amplifier ideal to use in nu-
merous applications. One of the typical applications is an
active filter as shown in
Figure 3
. This example is a band-pass
filter, for which the pass band is widened. This is achieved by
cascading two band-pass filters, with slightly different centre
frequencies.
20168358
FIGURE 3. Active Filter
The centre frequency of the separate band-pass filters can be
calculated by:
In this example a filter was designed with its pass band at 10
kHz. The two separate band-pass filters are designed to have
a centre frequency of approximately 10% from the frequency
of the total filter:
C = 33 nF
R1 = 2 k
Ω
R2 = 6.2 k
Ω
R3 = 45
Ω
This will give for Filter A
And for filter B with C = 27 nF:
Bandwidth can be calculated by:
For filter A this will give
and for filter B:
The response of the two filters and the combined filter is
shown in
Figure 4
.
20168359
FIGURE 4. Active Filter Curve
www.national.com
12
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