Pierce Oscillator : Working and Its Applications

We have different types of oscillators available depending on their characteristics and features. But in that, the most widely used oscillators are crystal oscillators, Hartley oscillator, Dynatron oscillator, RC oscillators, etc. The primary aim of these oscillators is to generate stable frequency oscillations continuously & frequently. In among all the different types of oscillator’s crystal oscillators shows the excellent frequency stability. They can generate the oscillations at the resonance frequency without any distortions and even the temperature effect is very low in the crystal oscillator because of the unique feature of the crystal material. The crystal oscillator uses the principle of piezoelectric effect to generate frequency oscillations. By the end of this article, we’ll get knowledge on pierce oscillator definition, diagram, and its applications.

What is a Pierce Oscillator?

This is one type of electronic oscillator particularly used in crystal oscillators to create a stable frequency of oscillations by using the piezoelectric effect principle. Due to the cost, size, complexity, and power compared to the standard oscillators these are widely preferred in most embedded solutions and devices to create stable frequency oscillations. A simple pierce oscillator has the following components like a digital inverter, resistor, two capacitors, and one quartz crystal.

Pierce Oscillator Circuit

The following figure 1 shows the simple pierce oscillator diagram and figure 2 shows the simplified circuit diagram of a piercing oscillator. In the above circuit, X1 indicates the crystal device, R1 resistor as a feedback resistor, U1 is a digital inverter, C1 and C2 are the parallel-connected capacitors. These come under the design part.

Operation

Feedback resistor R1 in figure 1 is to make linear inverter by charging the inverter input capacitance from the output of the inverter and if the inverter is ideal then with infinite input impedance and zero output impedance values. With this, the input and output voltages are to be equal. Therefore the inverter operates in the transition region.

• The inverter U1 provides the 180° phase shift in the loop.
• Capacitors C1 and C2, crystal X1 together provide an additional 180° phase shift to the loop to satisfy the Barkhausen phase shift criteria for oscillations.
• In general C1 and C2 values are chosen to be equal.
• In figure 1 of the Pierce oscillator, crystal X1 is a parallel mode with C1 and C2 to work in the inductive region. This is called parallel crystal.

To generate the oscillations at a resonance frequency the oscillator circuit must satisfy the two conditions which are called Barkhausen criteria. They are:

• The magnitude value of the loop gain must be unity.
• The phase shift around the loop should be 360° or 0°.

If the oscillator satisfies the above two conditions then only they can be a worthy oscillator. Here, this oscillator satisfies the above two Barkhausen conditions by the loop of the circuit and using of an inverter.

Applications

The applications of pierce oscillator include the following.

• These oscillators are applicable in embedded solutions and in phase-locked loop (PLL) devices.
• In microphones, voice-controlled devices and the devices which convert sound energy into electrical energy in those devices these are preferred because of its excellent frequency stability factor.
• Because of its low manufacture cost, it is useful in most consumer electronic applications.

Thus, Pierce oscillator is a widely used oscillator in embedded solutions and some devices because of its simple circuit making, stable resonance frequency. Not any parameter can affect its resonance frequency. So it can generate the constant frequencies of oscillations. But in a few digital inverters, the propagation delay is too small. So we need to consider which don’t have a more propagation delay.