Datasheet

Table Of Contents
MCP6271/1R/2/3/4/5
DS21810F-page 18 © 2008 Microchip Technology Inc.
4.9.3.5 Second Order MFB with an Extra
Pole-Zero Pair
Figure 4-14 is a second order multiple feedback low-
pass filter with Chip Select. Use the FilterLab
®
software
from Microchip Technology Inc. to determine the R and
C values for op amp A’s second order filter. Op amp B
can be used to add a pole-zero pair using C
3
, R
6
and
R
7
.
FIGURE 4-14: Second Order Multiple
Feedback Low-Pass Filter with an Extra Pole-
Zero Pair.
4.9.3.6 Second Order Sallen-Key with an
Extra Pole-Zero Pair
Figure 4-15 is a second order Sallen-Key low-pass
filter with Chip Select. Use the Filterlab
®
software from
Microchip to determine the R and C values for
op amp As second order filter. Op amp B can be used
to add a pole-zero pair using C
3
, R
5
and R
6
.
FIGURE 4-15: Second Order Sallen-Key
Low-Pass Filter with an Extra Pole-Zero Pair and
Chip Select.
4.9.3.7 Capacitorless Second Order
Low-Pass filter with Chip Select
The low-pass filter shown in Figure 4-16 does not
require external capacitors and uses only three
external resistors; the op amp’s GBWP sets the corner
frequency. R
1
and R
2
are used to set the circuit gain. R
3
is used to set the Q. To avoid gain peaking in the
frequency response, Q needs to be low (lower values
need to be selected for R
3
). Note that the amplifier
bandwidth varies greatly over temperature and
process. This configuration, however, provides a low
cost solution for applications with high bandwidth
requirements.
FIGURE 4-16: Capacitorless Second Order
Low-Pass Filter with Chip Select.
A
CS
R
1
R
6
C
3
V
OUT
MCP6275
B
R
5
R
4
V
DD
R
7
C
1
R
3
R
2
V
IN
A
CS
R
5
C
3
V
OUT
MCP6275
B
R
6
R
4
R
3
V
IN
R
2
R
1
C
1
C
2
A
CS
R
3
R
2
V
OUT
MCP6275
B
V
REF
R
1
V
IN