How to Design Crystal Oscillator Circuit

A crystal oscillator circuit is a type of electronic circuit that produces a particularly accurate and steady electrical signal at a certain frequency by means of a unique part known as a piezoelectric crystal.

For many electronic gadgets, this frequency is essential.

Circuit Working:

Lets understand about this circuit through the above diagram:

Crystal Oscillators: The Electronic Heartbeat

Electronic circuits known as crystal oscillators rely on a special characteristic of the mineral quartz.

The piezoelectric effect may be seen in this substance and occasionally in others like tourmaline and Rochelle salt.

This phenomenon indicates that the crystal physically vibrates at its inherent frequency when an electrical voltage is applied to it.

On the other hand, if the crystal is physically vibrated a little voltage is produced.

Because of this unique quality, quartz crystals are perfect for producing extremely steady oscillations.

This phenomenon is used by a crystal oscillator circuit to provide a continuous electrical signal at a certain frequency.

The crystal itself determines this frequency, which is very resistant to variations in temperature or other environmental conditions.

The ability of crystal oscillators to produce a steady and dependable timing signal accounts for their widespread use.

For this reason, they are essential parts of several electrical gadgets, such as: electronic watches, microcontrollers and microprocessors, clock circuits

A detailed description of crystal oscillator circuit construction and functioning is provided.

As a transducer, the inexpensive naturally occurring quartz crystal transforms electrical energy into vibrations and vice versa.

Usually set up between two metal plates, the circuit uses electrical components to simulate the physical characteristics of the crystal and keep it oscillating.

There are two components to the analogous circuit model that illustrate how the crystal behaves:

A circuit with a series RLC that represents the internal resistance Rs, stiffness Ls-inductor, and intrinsic capacitance Cs of the crystal.

An illustration of the capacitance between the metal plates supporting the crystal is a parallel capacitor Cp.

Crystal oscillators may be designed and used for a variety of electronic applications by knowing these parts and how they work together.

Optimizing the circuit for particular frequencies in crystal oscillators

To get a given output frequency, two primary types of crystal oscillators may be designed: series resonance and parallel resonance.

To obtain the desired frequency in either scenario we must carefully choose the values of external electrical components.

Formulas:

Series Resonance Formulas:

Resonance frequency : f_s = 1 / 2π√L_s * C_s

where,

• The inductance is represented by Ls in henries, H.
• The capacitance is represented by Cs in farads, F.
• The resonance frequency, expressed in hertz Hz is fs.

Specifically, the phrase √LsCs: is referred to as the LC circuits natural or resonant frequency.

It shows the frequency at which the capacitor and inductor, two reactive components, resonate with one another and exchange energy between their magnetic and electric fields.

Resonance State: Maximum current flow and minimal impedance across the circuit occur when the reactive components cancel each other out at a specific frequency, which is known as resonance in an LC circuit.

The angular frequency (ωs) is as follows: The angular frequency equivalent to ω_s = 2πf_s.

It shows how quickly the oscillations phase changes over time.

Derivation of Formula:

The connection between the capacitive reactance (X_C = 1 / _ωC_s) and inductive reactance (X_L = ω_Ls) yields the resonance frequency fs of the electrical circuit.

These reactances are opposite in phase and equal in magnitude at resonance, which results in:

ω_Ls ​= 1​ / ωC_s​

Finding the value of ω and translating it to frequency fs:

f_s​ = 1​ / 2πL_s​C_s​​

Note:​

The relationship between a series LC circuits resonance frequency, fs capacitance, and inductance, Ls is summarized in formula f_s ​= 1​ / 2πL_s​C_s​​

It is essential to comprehending and building circuits where resonance is a key factor in the operation and behavior of the system.

Parallel Resonance Formulas

In the below formula is corresponds to the parallel resonance frequency fp of an Inductor Capacitor LC circuit operating in parallel.

Let us dissect and clarify this formula:

f_p = 1 / [2π√L_s(C_p*C_s / C_p + C_s)]

where,

fp: The frequency of parallel resonance in hertz, Hz.
Ls: The inductors inductance in henries, H.
Cp: One capacitors capacitance measured in farads, F.
Cs: Another capacitors capacitance in farads, F.

The effective capacitance (Cp​*Cs / Cp​+Cs​​​) in the parallel configuration is taken into consideration by this formula, which influences the resonance frequency of the LC circuit.

Parallel Frequency of Resonance:

The frequency at which the parallel LC circuit demonstrates maximum impedance, or resonance, is denoted as fp.

A high impedance across the circuit results from the equal and opposing reactances of the capacitors (X_CpCs​ ) and the inductor (X_L​=_ωL_s​) at resonance.

Finding the Formulas Origin:

Depending on how the circuit is configured, the situation where the total impedance (resistive component) is minimized or maximized yields the parallel resonance frequency fp.

The total capacitance C total for a parallel LC circuit is determined by:

1 / C_total = 1 / C_p + 1 / C_s

where,

• Using the formula, the parallel resonant frequency Fp is determined.

Note:

A parallel LC circuits parallel resonance frequency Fp, is described by the aforementioned formula.

It is essential to comprehend and design circuits when optimal circuit performance necessitates resonance at particular frequencies.

Optimizing the Circuit in Crystal Oscillators for Specific Frequencies

There are two main types of crystal oscillators that may be built to achieve a certain output frequency: series resonance and parallel resonance.

In both cases, we have to carefully select the values of external electrical components in order to get the correct frequency.

Parallel Oscillator for Resonance:

In this case, the reactance of the parallel capacitor Cp is cancelled out by the combined reactance of the series capacitance Cs and series inductance Ls.

Moreover, this cancellation takes place at the intended frequency Fp.

This causes the impedance of the crystal to reach its maximum, which reduces the feedback in the circuit in comparison to the series resonance oscillator.

Selecting the Appropriate Resonance Mode

The intended oscillator characteristics determine which of the two resonance modes series or parallel to use.

Stronger feedback is provided by series resonance which is advantageous for establishing and sustaining oscillations.

Parallel resonance, however can be the better option when reducing power consumption is a top concern.

Crystal Oscillator circuit diagram:

Constructing Crystal Oscillators: Complementary vs Series Resonance

A crystal oscillator circuit can be set up in one of two primary methods each of which produces a distinct kind of resonance:

Resonance Oscillator in Series:

In this configuration, a transistor set up in common emitter mode has a crystal and a coupling capacitor put between its base and collector terminals.

Accordingly, the base of the transistor regulates the current that flows between the collector and emitter functioning as an amplifier.

This collector terminal provides the output signal of the oscillator.

Clock with Parallel Resonance:

Here, the collector and emitter terminals of the common emitter transistor are exactly across from the crystal element.

As before, the collector terminal provides the output signal.

Despite the identical transistor design common emitter in both scenarios the kind of resonance attained series or parallel depends on where the crystal and capacitors are placed in relation to the transistor.

Building Blocks and Device Integration for Crystal Oscillators

A bipolar junction transistor BJT a field effect transistor FET or a metal oxide semiconductor field effect transistor MOSFET might be the “switching component” in the center of a crystal oscillator circuit.

By serving as amplifiers, these transistors aid in preserving the oscillations in the circuit.

Integration of Microcontroller and Microprocessor

A crystal oscillator element can be connected to built in terminals on a large number of contemporary microcontrollers and microprocessors.

This simplifies the design overall by doing away with the requirement for a different external oscillator circuit.

Usually, these integrated terminals are set up to function within a particular crystal frequency range in order to guarantee the correct functioning of the digital integrated circuit IC.

Conclusion:

The quartz crystals special qualities are used by crystal oscillators the electronic equivalent of metronomes, to produce accurate and reliable electrical signals.

We can acquire certain desired frequencies by integrating these crystals into circuits with different geology.

These oscillators are essential for accurate timing and dependable performance in a wide range of electronic equipment, from little wristwatches to robust computers.

They are an essential component of contemporary electronics due to their adaptability and features like integrated functions seen in microcontrollers.

References:

Crystal oscillator