User manual

Active Filter Demo Board Kit User’s Guide
DS51614A-page 22 © 2006 Microchip Technology Inc.
FIGURE 3-5: Gain Error (Monte Carlo simulation) vs. Frequency.
FIGURE 3-6: Pass-Band Frequency (Monte Carlo simulation) Histogram.
Using components with tighter tolerances (e.g., 2% capacitors) will improve the
variability of the filter response. This is especially important for filters with a sharp cutoff
characteristic (i.e., Chebyshev).
3.4.3 Checking Output Headroom
It is also possible to check op amp overdrive issues by testing the output of all of the
op amps (every Active Filter Section). The worst-case signal(s) needs to be applied at
the first input. Figure 3-7 shows the frequency response of the filter in Figure 3-1. None
of the traces goes above 0 dB, so this filter should not have output voltage range issues
when the input is a sinewave.
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
10 100 1,000
Frequency (Hz)
Gain Spread (dB)
+3.3 sigma
-3.3 sigma
100 MC Sims
1% R's
5% C's
0%
2%
4%
6%
8%
10%
12%
14%
16%
18%
20%
22%
24%
26%
90 92 94 96 98
100 102 104 106 108 110
Pass-Band Frequency at -3.01 dB (Hz)
Percentage of Occurrences
100 MC Sims
1% R's
5% C's