Datasheet

LMV821-N, LMV822-N, LMV822-N-Q1
LMV824-N, LMV824-N-Q1
SNOS032G –AUGUST 1999–REVISED NOVEMBER 2013 www.ti.com
Butterworth Response as Measured by the HP3577A Network Analyzer
Figure 43. 300 kHz, Low-Pass Filter
In addition to performance, DAAFs are relatively easy to design and implement. The design equations for the
low-pass and high-pass DAAFs are shown below. The first two equation calculate the Fc and the circuit Quality
Factor (Q) for the LPF (Figure 41). The second two equations calculate the Fc and Q for the HPF (Figure 42).
(2)
To simplify the design process, certain components are set equal to each other. Refer to Figure 41 and
Figure 42. These equal component values help to simplify the design equations as follows:
(3)
To illustrate the design process/implementation, a 3 kHz, Butterworth response, low-pass filter DAAF (Figure 41)
is designed as follows:
1. Choose C
1
= C
3
= C = 1 nF
2. Choose R
4
= R
5
= 1 kΩ
3. Calculate R
a
and R
2
for the desired Fc as follows:
(4)
4. Calculate R
3
for the desired Q. The desired Q for a Butterworth (Maximally Flat) response is 0.707 (45
degrees into the s-plane). R
3
calculates as follows:
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