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Low-pass and high-pass filters

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Inputs

Results

Frequency
159.1549431 Hz
Resistance
1,000 Ω
Capacitance
0.000001 F
Frequency: 1.591549431 – 15,915.49431 Hz (log) · dB

RC and RL use first-order −3 dB models. LC reports ideal resonance; its −3 dB point depends on loading and damping.

Formula and assumptions

fRC = 1/(2πRC); fRL = R/(2πL); fLC = 1/(2π√(LC))

Questions, examples and engineering limits

Calculate RC/RL low-pass and high-pass cutoff, reverse-solve components and plot response. Distinguish LC resonance from loaded −3 dB cutoff.

Content updated:

How is RC and RL Filter Calculator: Cutoff and LC Resonance calculated?

Use fRC = 1/(2πRC); fRL = R/(2πL); fLC = 1/(2π√LC). Calculate RC/RL low-pass and high-pass cutoff, reverse-solve components and plot response. Distinguish LC resonance from loaded −3 dB cutoff.

Sources: wiki.analog.com [1]

How do I calculate this example: R = 1 kΩ, C = 1 µF?

fRC ≈ 159.154943 Hz. This is a calculated example under the model stated above; it is not a measured component specification.

Which units does RC and RL Filter Calculator: Cutoff and LC Resonance use?

Hz, Ω, F, H. Convert prefixes before substituting values; keep the input and output units attached to every number.

Sources: wiki.analog.com [1]

What does −3 dB mean at cutoff?

For the ideal first-order response, amplitude is 1/√2 ≈ 0.707 of the passband value. With equal impedances, this corresponds to half power.

Sources: wiki.analog.com [1]

Is LC resonance always the −3 dB cutoff?

No. Loading, topology and damping determine the transfer function. 1/(2π√LC) alone gives ideal resonance, not a universal −3 dB result.

Sources: wiki.analog.com [1]

Do source and load impedance affect cutoff?

Yes. They alter the effective network and gain. The calculator’s simple RC/RL model is not a substitute for a loaded transfer-function analysis.

Sources: wiki.analog.com [1]

Answers use the stated model and units. Examples are calculated values, not measurements or component ratings.