Pierceoscillatorer

Pierceoscillatorer, more commonly referred to as a Pierce oscillator, is a crystal-based oscillator circuit in which a quartz crystal provides the frequency-determining element in the feedback path of a high-gain, inverting amplifier. The arrangement typically uses a transistor, operational amplifier, or a logic inverter as the active element, with the crystal connected between the input and output and two capacitors to ground forming the load network.

In operation, the crystal, together with the load capacitors, creates a feedback phase shift near the crystal’s resonance. When the loop gain and phase meet the Barkhausen criterion, oscillations begin and are sustained at the crystal’s fundamental frequency (or an overtone, if the circuit is designed accordingly). The frequency is primarily set by the crystal, while the surrounding components determine startup conditions, stability, and loading.

Design considerations include selecting the crystal with the desired frequency and minimum series resistance (Rs), choosing the appropriate load capacitance (CL) through the two capacitors and stray capacitances, and ensuring the inverting amplifier provides sufficient gain without introducing excessive distortion. Temperature stability, drive level, and supply regulation all influence frequency accuracy and long-term stability. Overtone operation requires attention to the driving conditions to favor the desired mode and suppress unwanted modes.

Common applications for Pierce oscillators include microcontroller clock sources, RF front-ends, and other compact, low-cost timing references where a stable, readily available crystal-based oscillator is advantageous. The topology is valued for its simplicity, small size, and compatibility with standard quartz crystals and logic/inverter technologies.