Oscillators are electronics circuits that generates continuous signal wave and are used in signal generators, function generators, as clock source, in communication electronics as local oscillators and have other applications. There are many ways to design oscillators such as using operational amplifier, transistors(BJT or FET or MOSFET) and are also available in integrated circuit. Oscillators are also often classified as high frequency oscillator and low frequency oscillators. High frequency oscillators are designed with inductors and capacitors with transistor as amplifying element. Colpitts oscillator, Hartley oscillator, crystal oscillator are high frequency frequency oscillator that are used in communication electronics system such as FM or AM signal modulation and demodulation. The Pierce oscillator is a type of electronic oscillator that is commonly used in radio frequency (RF) and audio frequency (AF) circuits. It was invented by George W. Pierce in 1921 and has been widely used ever since. In this blog post, we will explore the working principle of the Pierce oscillator, its advantages, and its applications.
Working Principle
The Pierce crystal oscillator is a type of feedback oscillator that uses a quartz crystal as its frequency-determining element. The oscillator circuit consists of an amplifier, a feedback network which consist of capacitor(s) and a quartz crystal resonator. The feedback network provides the necessary phase shift for oscillation and the amplifier provides the necessary gain to the signal which loses energy while going through the feedback loop. The crystal resonator acts as a frequency-selective element that determines the frequency of oscillation. Basically, Pierce oscillator is modified Colpitts oscillator replacing the inductor with a quartz crystal. The crystal behaves as an inductor.
The following shows the basic Pierce crystal oscillator build on a breadboard.
When the oscillator is turned on, a small amount of current flows through the crystal, causing it to vibrate at its resonant frequency. The crystal resonator acts as a filter, passing only the frequency at which it is resonant and rejecting all other frequencies. The feedback network provides the necessary phase shift to sustain the oscillation.
Another way of constructing Pierce crystal oscillator is using the internal capacitance of transistor instead of C1 and C2. That is the separate capacitors C1 and C2 are not required. This is illustrated in the blog post Bipolar Transistor Based Pierce Crystal Oscillator.
Advantages
The Pierce oscillator has several advantages over other types of oscillators. Firstly, it is highly stable and precise due to the use of a quartz crystal resonator. Secondly, it has a low output impedance, which makes it suitable for driving RF and AF circuits. Thirdly, it has a wide frequency range, which can be easily adjusted by changing the values of the feedback network components.
Applications
The Pierce oscillator is widely used in various electronic applications, including:
- RF transmitters and receivers
- Frequency synthesizers
- Microcontrollers
- Audio tone generators
- Clock generators
Conclusion
The Pierce oscillator is a simple yet effective oscillator that is widely used in electronic circuits. It is highly stable, precise, and has a wide frequency range, making it suitable for a variety of applications. Its use of a quartz crystal resonator ensures a high degree of frequency stability, making it ideal for RF and AF circuits. With its numerous advantages, the Pierce oscillator continues to be a popular choice in the field of electronics.
References:
[1] 2N2222 Phase Shift Oscillator
