Crystal Oscillator Circuit and Working

A crystal oscillator is an electronic oscillator circuit that is used for the mechanical resonance of a vibrating crystal of piezoelectric material. It will create an electrical signal with a given frequency. This frequency is commonly used to keep track of time for example wristwatches are used in digital integrated circuits to provide a stable clock signal and also used to stabilize frequencies for radio transmitters and receivers. Quartz crystal is mainly used in radio-frequency (RF) oscillators. Quartz crystal is the most common type of piezoelectric resonator, in oscillator circuits, we are using them so it became known as crystal oscillators. Crystal oscillators must be designed to provide a load capacitance.

There are different types of oscillator electronic circuits that are in use they are namely: Linear oscillators – Hartley oscillator, Phase-shift oscillator, Armstrong oscillator, Clapp oscillator, Colpitts oscillator. Relaxation oscillators – Royer oscillator, Ring oscillator, Multivibrator and Voltage Controlled Oscillator (VCO). Soon we are going to discuss in detail crystal oscillators like working and applications of a crystal oscillator.

What is a Quartz Crystal?

A quartz crystal exhibits a very important property known as the piezoelectric effect. When mechanical pressure is applied across the faces of the crystal, a voltage which is proportional to mechanical pressure appears across the crystal. That voltage causes distortion in the crystal. The distorted amount will be proportional to the applied voltage and also an alternate voltage applied to a crystal it causes to vibrate at its natural frequency.

The below figure represents the electronic symbol of a piezoelectric crystal resonator and also quartz crystal in an electronic oscillator that consists of resistor, inductor, and capacitors.

Crystal Oscillator Circuit Diagram

The above figure is a 20psc New 16MHz Quartz Crystal Oscillator and it is one kind of crystal oscillators, that works with 16MHz frequency.

Generally, bipolar transistors or FETs are used in the construction of Crystal oscillator circuits. This is because operational amplifiers can be used in different low-frequency oscillator circuits which are below 100KHz but operational amplifiers do not have the bandwidth to operate. It will be a problem at the higher frequencies that are matched to crystals which are above 1MHz.

To overcome this problem Colpitts crystal oscillator is designed. It will work at higher Frequencies. In this Oscillator, the LC tank circuit that provides the feedback oscillations has been replaced by a quartz crystal.

Crystal Oscillator Working

The crystal oscillator circuit usually works on the principle of the inverse piezoelectric effect. The applied electric field will produce a mechanical deformation across some materials. Thus, it utilizes the vibrating crystal’s mechanical resonance, which is made with a piezoelectric material for generating an electrical signal of a particular frequency.

Usually, quartz crystal oscillators are highly stable, consist of good quality factor(Q), they are small in size, and are economically related. Hence, quartz crystal oscillator circuits are more superior compared to other resonators like LC circuits, tuning forks. Generally in Microprocessors and Micro controllers we are using an 8MHz crystal oscillator.

The equivalent electrical circuit also describes the crystal action of the crystal. Just look at the equivalent electrical circuit diagram shown in the above. The basic components used in the circuit, inductance L represents crystal mass, capacitance C2 represents compliance, and C1 is used to represent the capacitance that is formed because of crystal’s mechanical moulding, resistance R represents the crystal’s internal structure friction, The quartz crystal oscillator circuit diagram consists of two resonances such as series and parallel resonance, i.e., two resonant frequencies.

The series resonance occurs when the reactance produced by capacitance C1is equal and opposite to the reactance produced by inductance L. The fr and fp represents series and parallel resonant frequencies respectively, and the values of ‘fr’ and ‘fp’ can be determined by using the following equations shown in the figure below.

The above diagram describes an equivalent circuit, plot graph for Resonant frequency, Formulae for Resonant frequencies.

Uses of Crystal Oscillator

In general, we know that, in the design of microprocessors and microcontrollers, crystal oscillators are used for the sake of providing the clock signals. For instance, let us consider 8051 microcontrollers, in this particular controller an external crystal oscillator circuit will work with 12MHz that is essential, even though this 8051 microcontroller (based on model) is capable to work at 40 MHz (max) have to provide 12MHz in most of the cases because for a machine cycle 8051 requires 12 clock cycles, so that to give effective cycle rate at 1MHz (taking 12MHz clock) to 3.33MHz (taking the maximum 40MHz clock). This particular crystal oscillator which is having cycle rate at 1MHz to 3.33MHz is used to generate clock pulses that are required for the synchronization of all the internal operations.

Application of Crystal Oscillator

There are various applications for crystal oscillator in various fields and some of the crystal oscillator applications are given below

Colpitts Crystal Oscillator Application

Colpitts Oscillator is used to generate a sinusoidal output signal at very high frequencies. This oscillator can be used as the different types of sensors such as temperature sensors Because of the SAW device which we are using in Colpitts circuit it senses directly from its surface.

The applications of the Colpitts oscillators mainly involve where the wide range of frequencies is used. Also used in undamped and continuous oscillation condition. Using some devices in the Colpitts circuit, we can achieve greater temperature stability and high frequency.

Colpitts used for the development of mobile communications and radio communications.

Applications of Armstrong Crystal Oscillator

This circuit was popular until the 1940s. These are widely used in the regenerative radio receivers. In that input, the radio frequency signal from the antenna is coupled magnetically into the tank circuit through an additional winding, and feedback is reduced to gain control in the feedback loop. Finally, it produces a narrow-band radio-frequency filter and amplifier. In this Crystal oscillator, the LC resonant circuit is replaced with feedback loops.

In Military and Aerospace

For the efficient communication system, Crystal Oscillators are used in military and aerospace. The communication system is to establish and for the navigation purpose and electronic warfare in the guidance systems

In Research and Measurement

The crystal oscillators are used in research and measurement for the celestial navigation and the space tracking purpose, in medical devices and in the measuring instruments.

Industrial Applications of Crystal Oscillator

There are many industrial applications of the crystal oscillator. They are widely used in computers, instrumentation, digital systems, in phase-locked loop systems, modems, marine, telecommunications, in sensors and also in disk drives.

Crystal Oscillator is also used in engine controlling, clock and to trip computer, stereo, and in GPS systems. This is an Automotive application.

Crystal oscillators are used in many consumer goods. For example, cable television systems, video cameras, personal computers, toys and video games, cellular phones, radio systems. This is the Consumer Application of Crystal Oscillator.

This is all about what is a Crystal Oscillator, it’s working, and Applications. We believe that the information given in this article is helpful for you for a better understanding of this concept. Furthermore, any queries regarding this article or any help in implementing electrical and electronics projects, you can approach us by commenting in the comment section below. Here is a question for you, What is the main function of crystal oscillator?

Photo Credits:

• Quartz Crystal Circuit capacitors
• Crystal Oscillator dhresource
• Crystal Oscillator Circuit circuitstoday
• Crystal Oscillator Working indiastudychannel
• Colpitts Crystal Oscillator hqew
• Armstrong Crystal Oscillator wikimedia