B =

= 1.9 kHz

S

x 6.2 k: x 27 nF

1

B =

= 1.6 kHz

S

x 6.2 k: x 33 nF

1

B =

1

= 11.2 kHz

S

x 27 nF

1

2 k: x 6.2 k: x 45:

2 k: + 6.2 k:

= 9.2 kHz

S

x 33 nF

1

2 k: x 6.2 k: x 45:

2 k: + 6.2 k:

1

2SC

R1

R2

C

C

R3

R1

R2

C

C

R3

+

-

+

-

LMV841, LMV842, LMV844

www.ti.com

SNOSAT1G – OCTOBER 2006 – REVISED FEBRUARY 2013

ACTIVE FILTER

The rail-to-rail input and output of the LMV841/LMV842/LMV844 and the wide supply voltage range make these

amplifiers ideal to use in numerous applications. One of the typical applications is an active filter as shown in

Figure 40. 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 center frequencies.

Figure 40. Active Filter

The center frequency of the separate band-pass filters can be calculated by:

(13)

In this example a filter was designed with its pass band at 10kHz. The two separate band-pass filters are

designed to have a center frequency of approximately 10% from the frequency of the total filter:

C = 33nF R1 = 2K

Ω R2 = 6.2KΩ R3 = 45Ω

(14)

This will give for filter A:

(15)

and for filter B with C = 27nF:

(16)

Bandwidth can be calculated by:

(17)

For filter A this will give:

(18)

and for filter B:

(19)

The response of the two filters and the combined filter is shown in Figure 41.

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