Crystal Oscillator Calculator

A crystal oscillator is a timing component used in electronics to generate a precise clock frequency — this Crystal Oscillator Calculator analyzes your crystal's electrical model to find its resonant frequencies and the capacitor values needed to drive it correctly. Enter your crystal frequency, motional inductance (Lm), motional capacitance (Cm), shunt capacitance (Co), load capacitance (CL), and stray capacitance (Cs) to get the Parallel Resonance Frequency (Fp). Secondary outputs include the Series Resonance Frequency (Fs) and the two external load capacitor values (C1 and C2) required by your circuit.

MHz

Fundamental frequency of the crystal

mH

Series inductance of the crystal

pF

Series capacitance of the crystal

pF

Parallel capacitance of the crystal

pF

Required load capacitance for the circuit

pF

Parasitic capacitance from PCB traces and components

Results

Parallel Resonance Frequency (Fp)

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Series Resonance Frequency (Fs)

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Required Capacitor C1

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Required Capacitor C2

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Frequently Asked Questions

What is load capacitance in crystal oscillators?

Load capacitance (CL) is the total capacitance seen by the crystal in the oscillator circuit. It determines the operating frequency and must match the crystal's specified load capacitance for optimal performance and frequency stability.

How do I calculate the required external capacitors C1 and C2?

The external capacitors are calculated using the formula: C1 = C2 = 2 × (CL - Cs), where CL is the load capacitance and Cs is the stray capacitance. Both capacitors are typically equal in value for symmetric circuits.

What happens if the load capacitance is incorrect?

Incorrect load capacitance can cause frequency drift, poor frequency stability, difficulty starting oscillation, or complete failure to oscillate. The crystal will not operate at its specified frequency, affecting circuit timing accuracy.

What is the difference between series and parallel resonance frequencies?

Series resonance frequency (Fs) is the crystal's natural frequency without external capacitance. Parallel resonance frequency (Fp) is slightly higher and occurs when the crystal operates with its specified load capacitance in the circuit.

How does stray capacitance affect crystal oscillator design?

Stray capacitance from PCB traces, component leads, and IC pins adds to the total load capacitance. It must be accounted for when calculating external capacitor values, typically ranging from 2-5 pF in most circuits.

What are typical load capacitance values for crystals?

Common load capacitance values are 12.5 pF, 18 pF, and 20 pF for most crystals. Watch crystals (32.768 kHz) typically use 12.5 pF, while higher frequency crystals may use 18-20 pF loads.

Why is crystal oscillator frequency stability important?

Frequency stability ensures accurate timing in digital systems, proper communication protocols, and reliable clock generation. Poor stability can cause data errors, timing violations, and system malfunctions in sensitive applications.