2

C =

1

C

K - 1

=

1

C

Q

0

1

Z

R

(K-1)Q

OUT

LMP8278

+

-

Preamplifier

+IN

-IN

Output Buffer

Gain = 2

A1

A2

Gain = 7

100 k:

8

1

3

4

5

Internal

=

2

R

1

R

2

Q

2

R =

1

R

(

1 Q

K -

LMP8278

www.ti.com

SNAS575A – FEBRUARY 2012 – REVISED MARCH 2013

equation:

(7)

For the gain of 2 for the LMP8278 this results in:

(8)

Figure 21. Second Order Low Pass Filter

For instance, the value of Q can be set to 0.5

√2 to create a Butterworth response, to 1/√3 to create a Bessel

last step of the design procedure is to calculate the required value of C to give the desired low-pass cut-off

frequency using:

(9)

Which for the gain=2 will give:

(10)

(11)

Or, for a gain=2, C2=C1

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