Clapp Oscillator Frequency
f = 1/(2π√(L·Cs)), 1/Cs = 1/C1+1/C2+1/C3
Quick answer
This calculator solves f = 1/(2π√(L·Cs)), 1/Cs = 1/C1 + 1/C2 + 1/C3 for Frequency. With Inductance 100 µH, Capacitor C1 100 nF, Capacitor C2 0.22 µF, Capacitor C3 0.47 µF, the result is 64.99 kHz. It solves in 3 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
The Clapp oscillator is a Colpitts variant with an extra capacitor C3 placed in series with the tank inductor. Because the three capacitors are in series, the small C3 dominates the resonant capacitance and largely decouples the frequency from the transistor’s drifting junction capacitances (which set C1 and C2). This gives the Clapp markedly better frequency stability than a plain Colpitts.
Variables
- f — Oscillation frequency (Hz)
- L — Tank inductance (H)
- C1 — Feedback divider capacitor (F)
- C2 — Feedback divider capacitor (F)
- C3 — Series tuning capacitor (F)
Practical Notes
Make C3 much smaller than C1 and C2 so it sets the frequency and swamps transistor capacitance variation. Tuning C3 sweeps frequency with minimal effect on the feedback ratio.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| f | Frequency | MHz | Hz, kHz, MHz, GHz |
| L | Inductance | µH | nH, µH, mH, H |
| C1 | Capacitor C1 | nF | pF, nF, µF, mF, F |
| C2 | Capacitor C2 | nF | pF, nF, µF, mF, F |
| C3 | Capacitor C3 | nF | pF, nF, µF, mF, F |
Step by step
- 1. What you know: Inductance 100 µH, Capacitor C1 100 nF, Capacitor C2 0.22 µF, Capacitor C3 0.47 µF
- 2. The relation: f = 1/(2π√(L·Cs)), 1/Cs = 1/C1 + 1/C2 + 1/C3
- 3. Substitute: L = 100 µH, C1 = 100 nF, C2 = 0.22 µF, C3 = 0.47 µF
- 4. Result: Frequency = 64.99 kHz
Worked examples
Minimum range
Given: Inductance 100 nH, Capacitor C1 100 pF, Capacitor C2 0.22 nF, Capacitor C3 0.47 nF
Result: Frequency = 64.99 MHz
Low range
Given: Inductance 1 µH, Capacitor C1 1 nF, Capacitor C2 2.2 nF, Capacitor C3 4.7 nF
Result: Frequency = 6.499 MHz
Typical
Given: Inductance 100 µH, Capacitor C1 100 nF, Capacitor C2 0.22 µF, Capacitor C3 0.47 µF
Result: Frequency = 64.99 kHz
High range
Given: Inductance 0.47 mH, Capacitor C1 1 µF, Capacitor C2 2.2 µF, Capacitor C3 4.7 µF
Result: Frequency = 9.479 kHz
Maximum range
Given: Inductance 4.7 mH, Capacitor C1 10 µF, Capacitor C2 22 µF, Capacitor C3 47 µF
Result: Frequency = 0.9479 kHz
Solving for each variable
Solve for Frequency
Inductance 100 nH, Capacitor C1 100 pF, Capacitor C2 0.22 nF, Capacitor C3 0.47 nF → 64.99 MHz
Solve for Inductance
Frequency 100 kHz, Capacitor C1 100 pF, Capacitor C2 0.22 nF, Capacitor C3 0.47 nF → 42.23 mH
Solve for Capacitor C3
Frequency 100 MHz, Inductance 100 µH, Capacitor C1 100 nF, Capacitor C2 0.22 µF → 0.02533 pF
How Frequency changes with Inductance
| Inductance (input) | Frequency (result) |
|---|---|
| 10 µH | 0.2055 MHz |
| 25 µH | 130 kHz |
| 50 µH | 91.91 kHz |
| 75 µH | 75.04 kHz |
| 100 µH | 64.99 kHz |
| 150 µH | 53.06 kHz |
| 0.2 mH | 45.95 kHz |
| 0.4 mH | 32.49 kHz |
| 0.7 mH | 24.56 kHz |
| 1 mH | 20.55 kHz |
The same result in other units
| Unit | Value |
|---|---|
| Hz | 64990 |
| kHz | 64.99 |
| MHz | 0.06499 |
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<p><a href="https://vbatpower.com/formulas/clapp-oscillator/">Clapp Oscillator Frequency</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Clapp Oscillator Frequency?
Use f = 1/(2π√(L·Cs)), 1/Cs = 1/C1 + 1/C2 + 1/C3. With Inductance 100 µH, Capacitor C1 100 nF, Capacitor C2 0.22 µF, Capacitor C3 0.47 µF, Frequency works out to 64.99 kHz.
What is the formula for Clapp Oscillator Frequency?
The formula is f = 1/(2π√(L·Cs)), 1/Cs = 1/C1 + 1/C2 + 1/C3. The Clapp oscillator is a Colpitts variant with an extra capacitor C3 placed in series with the tank inductor.
How do you find Inductance when you know the other values?
Rearrange for Inductance: with Frequency 100 kHz, Capacitor C1 100 pF, Capacitor C2 0.22 nF, Capacitor C3 0.47 nF, Inductance is 42.23 mH.
How do you find Capacitor C3 when you know the other values?
Rearrange for Capacitor C3: with Frequency 100 MHz, Inductance 100 µH, Capacitor C1 100 nF, Capacitor C2 0.22 µF, Capacitor C3 is 0.02533 pF.
What units does Clapp Oscillator Frequency use?
Frequency is shown in Hz, kHz, MHz. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
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