2N3904 Crystal Oscillator Circuit

 In electronic circuits, there are several ways to generate precise and stable oscillations. One of the most popular methods is the crystal oscillator. A crystal oscillator is an electronic circuit that uses the mechanical resonance of a piezoelectric crystal to generate a stable frequency signal. Here basics of constructing 2N3904 crystal oscillator circuit is explained with its working principle.

The 2N3904 is a common NPN bipolar junction transistor used in various electronic circuits. In the crystal oscillator circuit, the transistor is used as an amplifier. The circuit consists of a feedback loop containing a crystal, a capacitor, and the transistor.

Below is circuit diagram of 2N3904 crystal oscillator circuit diagram.

2N3904 Crystal Oscillator Circuit


When an AC voltage is applied across the crystal, it vibrates at its natural frequency, which is determined by its physical dimensions. The crystal generates a voltage across its terminals in response to its mechanical vibration. This voltage is then applied to the base of the transistor, which amplifies it and sends it back to the crystal through the capacitor. The capacitor in the feedback loop provides a phase shift to the signal, which helps to sustain the oscillations.

The crystal oscillator circuit operates in the parallel resonance mode, where the crystal XTAL and capacitors C1 and C2 form a resonant circuit. In the above 2N3904 bipolar transistor crystal oscillator, the capacitors C1 and C2 provides the necessary feedback with 180 degree of phase shift for sustained oscillation as in colpitts oscillator design. The 2N3904 crystal oscillator frequency is determined by the resonant frequency of this circuit, which is equal to the natural frequency of the crystal. The rest of the circuit is 2n3904 amplifier circuit to recover amount of signal lost during feedback propagation. The crystal provides the necessary stability to the circuit by ensuring that the frequency of oscillation remains constant over a wide range of temperature and voltage variations. The above crystal oscillator circuit generates a stable sine wave signal. The above circuit works upto 20MHz. For further stability when this oscillator is to be connected to the rest of the circuit a buffer amplifier can be connected at the output.

Such simple crystal oscillator circuit can be used as a clock source in digital circuits, as a reference oscillator in communication systems, and in various other applications that require precise and stable frequency signals. The frequency of oscillation of the circuit can be adjusted by changing the values of the capacitor or the crystal.

In conclusion, the 2N3904 crystal oscillator circuit is a simple and reliable way to generate stable oscillations at a precise frequency. A crystal oscillator like the one shown here generates sinusoidal signal which more stable like for example a op amp oscillator, Hartley oscillator circuit etc and provides higher frequency signal than like Wien bridge oscillator or RC phase shift oscillator. The circuit is widely used in various electronic applications and provides superior frequency stability compared to other oscillators. By understanding the basic principles of the crystal oscillator circuit example above, one can design and build complex electronic systems that require precise timing and frequency control.

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