Calculadora de Capacitancia de Carga de Cristal
Calcula la capacitancia de carga real del cristal y el error de frecuencia en ppm para osciladores de cristal.
Fórmula
Referencia: IEC 60444 / Crystal manufacturer application notes
Cómo Funciona
Crystal load capacitance is a critical parameter in oscillator circuit design that determines the precise frequency of crystal oscillators. The actual load capacitance (CL_actual) represents the total capacitive load seen by an oscillator crystal, which includes both parallel capacitors and any stray capacitance. Accurate capacitance matching is essential to maintain the crystal's specified operating frequency and minimize frequency drift.
Ejemplo Resuelto
Problem: Design an oscillator with a 32.768 kHz crystal, specified load capacitance of 12.5 pF, and 2 pF of stray capacitance. Calculate the actual load capacitance and potential frequency error. Solution: 1. Set C1 = C2 = 2 * (CL_spec - Cstray) = 2 * (12.5 - 2) = 21 pF 2. Calculate CL_actual = (C1 * C2) / (C1 + C2) + Cstray = (21 * 21) / (21 + 21) + 2 = 11.5 pF 3. Calculate frequency error = (11.5 - 12.5) / (2 * 12.5) * 1,000,000 = -40 ppm
Consejos Prácticos
- ✓Use capacitors with tight tolerance (±5% or better)
- ✓Minimize PCB trace lengths near crystal
- ✓Consider temperature coefficients of capacitors
- ✓Use symmetrical layout for parallel capacitors
Errores Comunes
- ✗Ignoring stray capacitance in load calculations
- ✗Unbalanced parallel capacitor selection
- ✗Failing to match specified load capacitance
- ✗Not considering PCB layout parasitic capacitance
Preguntas Frecuentes
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