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

(1)

where

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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