User manual

ACTIVE FILTER DEMO BOARD KIT
USER’S GUIDE
© 2006 Microchip Technology Inc. DS51614A-page 19
Chapter 3. Building the Filter Supplied in the Kit
3.1 INTRODUCTION
The accessory bag that comes with this kit makes it quick and easy to evaluate the filter
described below; it was designed in FilterLab V2.0. Items discussed in this chapter
include:
• The Filter Design
• Putting the Filter Together
• Testing the Filter
3.2 THE FILTER DESIGN
See Figure 3-1 for the circuit diagram supported by the accessory bag. This filter is
described as follows:
• Bessel Low-pass
• n = 5, (filter order)
•f
C
= 100 Hz, (cut-off frequency)
• Gain=1V/V
• Sallen-Key sections
• Single Supply
FIGURE 3-1: 5th Order, Bessel, Low-pass Filter Supported by the Active Filter
Demo Board Kit.
This filter was built, and its frequency response was measured; the result is shown in
Figure 3-2. MCP601 op amps were used, instead of MCP6271 op amps, because they
are slower. Notice how close the measured and simulated data are; this happened
because the MCP601 op amp is much faster than the filter, and because 1% resistors
and 5% capacitors were used.
U
1
R11
C11
V
IN
U
2
R21
C21
R22
C22
U
3
R31
C31
V
OUT
R32
C32
10.7k
0.10µ
0.39µ
3.16k 6.81k
0.10µ
0.15µ
0.10µ
5.62k 12.7k
SK-LP1
SK-LP2 SK-LP2
MCP6271 MCP6271
MCP6271