LMV321-N, LMV321-N-Q1, LMV358-N, LMV358-N-Q1
LMV324-N, LMV324-N-Q1
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SNOS012I –AUGUST 2000–REVISED FEBRUARY 2013
Figure 59. Simple Low-Pass Active Filter
Figure 60. Frequency Response of Simple Low-Pass Active Filter in Figure 11
Note that the single-op-amp active filters are used in the applications that require low quality factor, Q( ≤ 10), low
frequency (≤ 5 kHz), and low gain (≤ 10), or a small value for the product of gain times Q (≤ 100). The op amp
should have an open loop voltage gain at the highest frequency of interest at least 50 times larger than the gain
of the filter at this frequency. In addition, the selected op amp should have a slew rate that meets the following
requirement:
Slew Rate ≥ 0.5 × (ω HVOPP) × 10−6 V/µsec
(1)
where ωH is the highest frequency of interest, and VOPP is the output peak-to-peak voltage.
Sallen-Key 2nd-Order Active Low-Pass Filter
The Sallen-Key 2nd-order active low-pass filter is illustrated in Figure 61. The DC gain of the filter is expressed
as
(2)
Its transfer function is
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