OPA835 datasheet(39/57 Pages) TI

39 / 57 page

-40

-30

-20

-10

10k

100k

f - Frequency - Hz

Sallen-Key

MFB

V = 5 V,

= 100 mV

OUT

OPA835

330 pF

562 W

6.19 kW

2.2 nF

OPA 835

220 pF

1.82 kW

4.22 kW

1.5 nF

OPA835, OPA2835

www.ti.com

SLOS713H – JANUARY 2011 – REVISED NOVEMBER 2015

9.2.2 Active Filters

The OPA835 and OPA2835 devices can be used to design active filters. Figure 79 and Figure 78 show MFB and

Sallen-Key circuits designed using the WEBENCH® Filter Designer (focus.ti.com) to implement second order low-

pass butterworth filter circuits. Figure 80 shows the frequency response.

MFB and Sallen-Key filter circuits offer similar performance. The main difference is the MFB is an inverting

amplifier in the pass band and the Sallen-Key is noninverting. The primary pro for each is the Sallen-Key in unity

gain has no resistor gain error term, and thus no sensitivity to gain error, while the MFB has inherently better

attenuation properties beyond the bandwidth of the op amp.

Figure 78. MFB 100-kHz Second-Order Low-Pass Butterworth Filter Circuit

Figure 79. Sallen-Key 100-kHz Second-Order Low-Pass Butterworth Filter Circuit

9.2.2.1 Application Curve

Figure 80. MFB and Sallen-Key Second-Order Low-Pass Butterworth Filter Response

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OPA835 Datasheet(PDF) 39 Page - Texas Instruments