LMV321M7SLASHNOPB datasheet(24/52 Pages) TI1

24 / 52 page

LMV321-N, LMV321-N-Q1, LMV358-N

LMV358-N-Q1, LMV324-N, LMV324-N-Q1

SNOS012J – AUGUST 2000 – REVISED DECEMBER 2014

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Typical Applications (continued)

9.2.4.1 Detailed Design Procedure

The following paragraphs explain how to select values for R1, R2, R3, R4, C1, and C 2 for given filter requirements,

such as ALP, Q, and fc.

The standard form for a 2nd-order low pass filter is

(4)

where

Q: Pole Quality Factor

ωC: Corner Frequency

A comparison between Equation 3 and Equation 4 yields

(5)

(6)

To reduce the required calculations in filter design, it is convenient to introduce normalization into the

components and design parameters. To normalize, let

ωC = ωn = 1 rad/s, and C1 = C2 = Cn = 1F, and substitute

these values into Equation 5 and Equation 6. From Equation 5, we obtain

(7)

From Equation 6, we obtain

(8)

For minimum DC offset, V+ = V−, the resistor values at both inverting and non-inverting inputs should be equal,

which means

(9)

From Equation 2 and Equation 9, we obtain

(10)

(11)

The values of C1 and C2 are normally close to or equal to

(12)

As a design example:

Require: ALP = 2, Q = 1, fc = 1 kHz

Start by selecting C1 and C2. Choose a standard value that is close to

(13)

(14)

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Product Folder Links: LMV321-N LMV321-N-Q1 LMV358-N LMV358-N-Q1 LMV324-N LMV324-N-Q1

LMV321M7/NOPB Datasheet(PDF) 24 Page - Texas Instruments