This application note introduces the Pierce oscillator basics and provides some guidelines for a good oscillator design.
This document introduces the basics of the Pierce oscillator topology and explains how to properly design an oscillator circuit to avoid deployment delays caused by non-functional crystals. It details the theoretical principles required for stable operation, including feedback resistor roles, load capacitance calculations, drive level measurements, and startup time considerations.
The guide offers practical advice on selecting suitable external components and provides a list of recommended crystal oscillators and ceramic resonators specifically for STM32F1 and STM8A/S series microcontrollers. Additionally, it includes critical PCB layout hints to minimize stray capacitance and inductance, ensuring reliable oscillator performance.
| Applicable Microcontrollers | STM8S, STM8A, STM32F1 |
|---|---|
| Document ID | 15287 Rev 6 |
In most cases, RF is embedded to make the internal inverter act as an amplifier by biasing it at Vout = Vin and forcing it to operate in the linear region.
RExt is only mandatory if the dissipated power in the crystal exceeds the drive level specified by the crystal manufacturer; otherwise, its value is 0 Ω.
It is highly recommended to apply conformal coatings to protect against moisture, dust, humidity, and temperature extremes that may lead to startup problems.