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Fundamentals of Low-Pass Filters
0
–10
|A| — Gain — dB
–20
–30
–40
–50
–60
–70
1st Order Lowpass
4th Order Lowpass
Ideal 4th Order Lowpass
–80
0.01 0.1 1 10
Frequency — Ω
100
0
φ — Phase — degrees
–90
–180
–270
Ideal 4th
Order Lowpass
4th Order Lowpass
1st Order Lowpass
–360
0.01 0.1 1 10
Frequency — Ω
100
Note:
Curve 1: 1 st -order partial low-pass filter, Curve 2: 4 th -order overall low-pass filter, Curve 3: Ideal 4 th -order low-pass filter
Figure 16–4. Frequency and Phase Responses of a Fourth-Order Passive RC Low-Pass Filter
The corner frequency of the overall filter is reduced by a factor of α ≈ 2.3 times versus the
–3 dB frequency of partial filter stages.
16-4