Are you an engineer or manufacturer who wants to understand the frequency of tracking time or stabilizing radio transmitters and receivers? If yes, you need to have a broad understanding of a crystal oscillator circuit with load capacitance. That way, you can build a project, like a watch that keeps track of time or provides clock signals. Also, you’ll mostly find the crystal oscillator circuits in RF oscillators.
So, in this article, we’ll be talking extensively about crystal oscillators.
What Is a Crystal Oscillator Circuit?
Crystal Oscillator Diagram
Source: Wikimedia Commons
In simpler terms, a crystal oscillator circuit is the electronic circuit board that houses the device that produces a specific frequency. It’s also an electronic oscillator circuit that works with a vibrating crystal’s mechanical resonance—to generate a consistent frequency.
Furthermore, you can use the frequency produced from a crystal oscillator to the following:
- Track time in quartz watches
- Generate steady signal for Digital ICs
- Stabilize and Maintain a wide range of Radio Receiver and Transmitter Frequencies
Also, a crystal oscillator depends heavily on transposed piezoelectricity or electrostriction to function effectively. And the process happens when you’ve alterations in a quartz crystal’s shape within an electric field.
How Does the Crystal Oscillator Work?
The crystal oscillator uses the inverse piezoelectric effect principle. And the resonant circuit comprises resistance (crystal’s internal structure friction), inductance (crystal mass), Capacitance C1 (capacitance from the crystal’s mechanical molding), and Capacitance C2 (compliance).
So, when you apply an electrical model field to the circuit, it will generate mechanical deformation across some materials. The course also produces a potential difference across the crystal’s opposite faces.
Equally, if you have a potential difference that applies across one of the faces, mechanical stress will result. And this mechanical stress is the Piezoelectric effect.
Typically, the best crystal to use for this circuit is Quartz. Besides that, it’s more superior to most resonators; Quartz is portable. Also, they are highly stable, economically related, readily available, and have a good quality factor.
That said, your piezoelectric crystal can have a mechanical vibration when you subject it to a suitable alternating potential. Further, when your alternating voltage’s frequency range equals your crystal’s natural frequency, you’ll get a maximum of your mechanical vibrations’ amplitude.
In addition, the equivalent electrical circuit explains the crystal’s mode of operation. Also, the quartz crystal oscillator has two fundamental resonances, like parallel and series resonances.
How to Build Crystal Oscillator Circuits?
Here are some examples of crystal oscillator circuits:
1. Crystal Oscillator Circuits Using 74LS04
Crystal Oscillator using 74LS04
Source: Researchgate ℅ Xiao Chen
It’s pretty common to find this type of circuit in digital applications. And that’s because it produces different waveforms. Also, they help to create a range of frequencies to be a base time.
Some of the parts the circuit uses include:
- Crystal to joint with a resistor
- A capacitor and resistor in the RC oscillator circuit
- The LC-oscillator circuit with capacitors and wires
This circuit matches two resistors of the same resistance (1K to 4.7K) with a crystal oscillator design (1MHz to 10MHz). And it works with two inverter gates that are within IC1 parallel resonance.
Based on the crystal your circuit uses, it can generate an output overtone frequency tolerance of 1MHz to 10MHz. No doubt, you may experience some minor defects in the output frequency stability.
And this happens because of temperature changes when the circuit operates. Consequently, it affects the crystal’s capacity and creates frequency tolerances. But if you compare this circuit to the common oscillators that use LC or RC networks, it has a lesser value.
Further, this circuit uses low current consumption. Hence, you can opt for a constant power supply of 5V. In addition, you can maintain output to a steady voltage by using a DCV supply of 9 to 12 volts to a DC regulator IC2-78L05.
When the capacitors (C1, C2) filter current, C2 draws a high frequency and protects the circuit from interference.
That said, here are the components you need for this circuit:
- XTAL1 – crystals between 1MHz to 10MHz
- R1, R2 – 1K to 4.7K (1/4W + 5%)
- C3 – 2.2µF (16V) electrolytic
- IC1 – 74LS04, Inverter gate IV
- C1 – 10µF (16V) electrolytic
- IC2 – 78L05 (5V)
- Universal PCB board
- D1 – 1N4001 (1A 50V) diode
- C2 – 0.1µF (50V) polyester
Testing the Circuit with TTL 74LS04
Since this circuit is cheap and straightforward, you need a crystal, a TTL SN7404, and four resistors. The resistors (R1 to R4) will bias the tree inverter gates into the linear regions while the crystal gives feedback.
Also, oscillation occurs only at the crystal’s primary frequency. Then, at 5V p-p, your output signal should form a Square Wave Oscillator.
2. Overtone Oscillator
Source: Researchgate ℅ Peter Pfeifer
An overtone oscillator is useful when you can’t make standard-cut crystals, and your quartz wafer is pretty thin. For instance, your oscillator will have a tuned load of a 144 transmitter with a frequency source.
And the load usually has an odd multiple of the crystal’s primary frequency. Hence, an overtone oscillator is best suited for this application. The overtone crystals in this oscillator are 11.6MHz, and it tunes to the third harmonic of 34.8MHz.
The primary turns of this circuit are 15 with an output transformer (Amidon T-50_6). As for the secondary turns, it depends on what you connect to the setup. So, if your output follows a more triple circuit, the device will be the source for a transceiver of 104 MHz crystal.
3. CD4060 Crystal Oscillator Circuit
Crystal Oscillator with CD4060
That said, the course comprises IC4013 and IC4060. This circuit has a frequency size of about 1Hz or 2Hz. And you can use it for a standard digital clock or a regular clock circuit. Also, the IC4060 is a single-acting Oscillator and Counter. And you can determine the frequency with the external capacitor and resistor.
Further, the IC4060 has quartz crystal, and it’s the circuit’s standard frequency generator. The capacitor isn’t left out as it helps in period adjustment. And the IC4060 has counter courses within—with a frequency of 2Hz that divides out the pin 3. Also, if you want to divide two of the clock signal frequencies, use the IC4015.
4. Radio Frequency Oscillators
RF Oscillator circuit design
Source: Researchgate ℅ CCBY
If you look closely at the circuit diagram, you’ll notice the main crystal oscillator in the lower-left corner. Also, you’ll see a small 1W power amplifier.
The component helps to drive a low pass filter and matching circuit.
Then, the oscillator uses a key shaping circuit to switch the oscillator on and off.
Consequently, the circuit will start and stop gently. Further, it helps to avoid the transmission of clicks.
The device offers more power and a cleaner waveform, and it’s all thanks to its FET oscillator’s drain circuit. Interestingly, the course has power coming from a 40m amateur band QRP Morse code or continuous wave (microswitch) transmitter.
5. Inverting Gate Oscillators
Inverting Gate Oscillators
The inverting gate oscillators are one of the simplest oscillators you can make. The best part is that you can opt for almost any inverting gate CMOS, which will work. So, you can use inverting gate CMOS like 74HC14, 4069, 74HC04, etc.
Further, all-digital gates usually have again. But if you want them to work like amplifiers, bias them with a resistor of about 1M5 and above. Also, your circuit may offer a phase shift of 1800. And the only way you can make positive feedback of 3600 and initiate oscillation is to use capacitors. The capacitors will help you to provide the remaining phase shift.
That said, none of the components in this circuit are critical. So, the capacitors (C1 and C2) can range from 10p to 100p. On the other hand, your resistor (R1) can be between 10K to 10M. In short, your values should depend on your crystal’s cut and frequency.
What if you want precise values? You can get this by ensuring that your C1 is a variable capacitor. But if you don’t need that precision, opt for a second 39p capacitor.
Applications of The Crystal Oscillator
You can use the crystal oscillator for the following critical applications:
- Video games
- Personal computers
- Automotive application
- Engine control
- Digital systems
- GPS systems
- Temperature sensors
- Cable television systems
The Bottom Line
No doubt, having in-depth information above the crystal oscillator circuit gives you a considerable edge when creating specific electronic devices—primarily DIY.
That’s why we wrote this article—to help you on your journey to learning about crystal oscillator circuits.
Hence, we’ll be happy to answer any of your questions regarding this article. So, feel free to reach us, and we’ll get back to you as soon as we can.