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"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

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Fundamentals of Low-Pass Filters<br />

16-4<br />

|A| — Ga<strong>in</strong> — dB<br />

φ — Phase — degrees<br />

0<br />

–<strong>10</strong><br />

–20<br />

–30<br />

–40<br />

–50<br />

–60<br />

–70<br />

1st Order Lowpass<br />

4th Order Lowpass<br />

Ideal 4th Order Lowpass<br />

–80<br />

0.01 0.1 1<br />

Frequency — Ω<br />

<strong>10</strong><br />

0<br />

–90<br />

–180<br />

–270<br />

Ideal 4th<br />

Order Lowpass<br />

4th Order Lowpass<br />

1st Order Lowpass<br />

–360<br />

0.01 0.1 1<br />

Frequency — Ω<br />

<strong>10</strong><br />

Note: Curve 1: 1st-order partial low-pass filter, Curve 2: 4th-order overall low-pass filter, Curve 3: Ideal 4th-order low-pass filter<br />

Figure 16–4. Frequency and Phase Responses of a Fourth-Order Passive RC Low-Pass Filter<br />

<strong>The</strong> corner frequency of <strong>the</strong> overall filter is reduced by a factor of α ≈ 2.3 times versus <strong>the</strong><br />

–3 dB frequency of partial filter stages.<br />

<strong>10</strong>0<br />

<strong>10</strong>0

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