Switchable Crystal Oscillator Circuit Diagram – Build Your Own!

Description

This oscillating circuit enables the electronic switching of crystals utilizing logic commands. The circuit is most readily comprehended when initially disregarding all crystals. It is also assumed that all diodes are effectively short circuits and their corresponding 1kO resistors are open. The two 1kO resistors situated at the non-inverting input of IC1 (LT1016) are configured to establish an output signal equal to half the power supply, specifically +2.5V. The RC network connecting the output to pin 3 creates phase-shifted feedback, presenting the circuit as a wide-band unity gain follower in the DC domain. When crystal X1 is integrated (with D1 temporarily bypassed), positive feedback arises and oscillation initiates at the crystal’s natural resonant frequency.

Circuit diagram:

Following the consideration of D1 and its 1kO resistor as integral components of the circuit, sustained oscillation can solely be maintained if logic input A is supplied with a high bias. Likewise, the circuit’s operation at crystal X2’s frequency is contingent upon logic input B being activated. Supplemental crystal/diode/1kO resistor arrangements facilitate the logic-based selection of the crystal frequency.

For AT-cut crystals, approximately a millisecond is required for the circuit output to stabilize, due to the exceptionally high Q factors involved. Crystal frequencies can reach up to 16MHz before propagation delays within the comparator impede dependable operation.

More about components

IC1, identified as an LT1016, is a versatile operational amplifier widely used in various electronic circuits. This integrated circuit possesses multiple operational amplifier functionalities within a single package, offering features such as high gain, low input bias current, and excellent slew rate. The LT1016 is frequently employed as a comparator, buffer, or general-purpose amplifier, making it a common component in oscillator circuits and other analog applications. Its precision and performance characteristics contribute to the stability and reliability of the overall circuit design.