Load Capacitor Assistant

A tool that assists board design engineers in selecting appropriate load capacitors for MHz or kHz pierce oscillator circuits.

About

This tool helps ensure that the gain margin (safety factor) and frequency tolerance of a crystal are within project constraints. It performs the necessary calculations based on crystal parameters from the datasheet and the measured frequency from the board.

Requirements

• Python with Jupyter Notebook
• NumPy
• Matplotlib

Installation

# Install dependencies from requirements.txt
pip install -r requirements.txt

Usage

Run the notebook:

jupyter notebook cl-vs-freq.ipynb

Enter your crystal parameters in the notebook:

• fs: Series resonant frequency
• cm: Motional capacitance
• c0: Shunt capacitance
• cl_nominal: Nominal load capacitance from datasheet
• c1c2: Current capacitors on customer schematic
• f_customer_board: Measured frequency on-board

The notebook will output:

• Recommended C1=C2 capacitor values
• Board stray capacitance estimate
• Trim sensitivity, anti-resonant frequency, and motional parameters
• Visual plots showing CL vs frequency relationships
• Text file (output.txt) with all calculated parameters

License

GPL License - See LICENSE for details

Contact

Ryan Thompson - @rthomp10

Project Link: https://github.com/rthomp10/load-capacitor-assistant