Crystal-controlled-reflection-oscillator

Description: This unit is easily tunable and stable, consumes minimal power, and is more cost-effective than other types of oscillators that operate at similar frequencies. This unique combination of features is made possible by a design concept that involves operating the transistor well beyond the 3 dB frequency of its current versus frequency curve. The concept leverages newly available crystals that resonate at frequencies up to approximately 1 GHz. The emitter of transistor Q is connected to a variable capacitor C1 and a series-resonant crystal X. The emitter is also connected to ground through bias resistor R1. The base is connected to the parallel combination of inductor L and capacitor C3 via de-blocking capacitors C4 and is forward biased concerning the emitter by resistors R3 and R4. Impedance Z could be the 220-ohm resistor shown or any small impedance that facilitates the extraction of the output signal through coupling capacitor C2. If Z is a tuned circuit, it is adjusted to the frequency of the crystal.

The described oscillator circuit utilizes a transistor configured to operate in a manner that extends its frequency response beyond typical limits, allowing it to function effectively at high frequencies, specifically near 1 GHz. The design incorporates a variable capacitor (C1) connected to the emitter of the transistor (Q) and a series-resonant crystal (X), which serves as the frequency-determining element of the oscillator. The use of a series-resonant crystal is crucial for achieving stability and precision in frequency generation.

The biasing arrangement for the transistor includes a bias resistor (R1) connected to ground, which helps establish the operating point of the transistor. The base of the transistor is connected to a network consisting of an inductor (L) and a capacitor (C3), which forms a resonant circuit that can influence the oscillation frequency. The de-blocking capacitors (C4) serve to isolate DC biasing from AC signals, ensuring that the transistor operates correctly without interference from unwanted DC components.

Resistors (R3 and R4) provide additional forward biasing to the base of the transistor, enhancing the transistor's conduction and ensuring stable operation. The output signal is extracted through a coupling capacitor (C2), which allows AC signals to pass while blocking DC. The impedance (Z) connected to the output can be a specific resistor value, such as 220 ohms, or a tuned circuit that matches the resonant frequency of the crystal, enabling efficient signal extraction and ensuring that the oscillator operates at the desired frequency.

Overall, this oscillator design is characterized by its simplicity, efficiency, and ability to operate at high frequencies, making it suitable for various applications in communication systems and signal processing where precision frequency generation is essential.This unit is easily tunable and stable, consumes little power, and costs less than other types of oscillators tlmt operate at the same frequencies. This unusual combination of features is made possible by a design concept that includes operation of the transistor well beyond the 3 dB frequency of its currentversus- frequency curve.

The concept takes advantage of newly available crystals that resonate at frequencies up to about 1 GHz. The emitter of transistor Q is connected with variable capacitor Cl and series-resonant crystal X. The emitter is also connected to ground through bias resistor Rl. The base is connected to the parallel combination of inductor L and capacitor C3 through de-blocking capacitor and C4 and is forward biased with respect to the emitter by resistors R3 and R4. Impedance Z could be the 220-0 resistor shown or any small impedance that enables the extraction of the output signal through coupling capacitor C2.

If Z is a tuned circuit, it is tuned to the frequency of the crystal.