Stable quartz oscillator operating in a wide range of supply voltages. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes
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By assembling a modified Pierce oscillator and a single-gate FET buffer source follower, a crystal oscillator can be obtained that has increased stability to changes in the supply voltage. Such a crystal oscillator is inexpensive to manufacture, simply matched to a TTL IC, and powered directly from a 5V TTL IC power supply.
High stability of the output frequency with changes in the supply voltage is achieved by using resistors with large resistances in the source circuits of both stages and by using large constant capacitors in the gate and drain circuits of the generator stage. Even when the supply voltage changes from 3 to 9 V, the output frequency deviates by no more than 1 Hz from the nominal value of 1 MHz.
(click to enlarge)
The circuit itself is so stable that the characteristics of the generator as a whole are determined only by the quality of the quartz resonator. High-quality thermostatted quartz resonator provides instability after warm-up 10-8 per day. When the ambient temperature is sufficiently constant, the circuit as a whole provides similar stability.
Good matching with TTL ICs is achieved with a Schmitt trigger, such as the 7413 type. The 2,2 kΩ input resistor biases the Schmitt trigger within hysteresis without excessively loading the oscillator source follower. The Schmitt trigger type 7413 generates a signal level sufficient to trigger a TTL IC, even when the generator supply voltage is reduced to 3 V.
The output of the Schmitt trigger is rich in high frequency harmonics and can therefore be mixed with the standard 10 MHz frequency signal broadcast by the National Bureau of Standards, allowing the oscillator to be tuned to within 0,1 Hz of the nominal frequency. Using this method of measurement, it is possible to determine daily short-term and long-term stability with sufficient accuracy. In this case, the oscillator can be used as a secondary frequency standard tested against the National Bureau of Standards standard.
Capacitor Cd sets the calibration range, which is carried out using a trimmer capacitor. Capacitance Cd may vary depending on the type of quartz resonator.
Posted by King, Oroco Communications Inc. (Middletown, NY); Publication: N. Bolshakov, rf.atnn.ru
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