I have an old 30KHz crystal in a big can that measures about 1.5 inchby 5/8 and hooked it up with a couple logic gates as an oscillator andthe frequency is just about right at 30Khz. Then I tried to make anoscillator using a couple transistors as inverters with a little biasto get it going on a 1.5 volt battery, but the frequency is lower at29.9982 Khz.The second inverter has a 5.6K load resistor in the collector thatdrives the crystal. Other side of the crystal is connected through a20k resistor to the input of the first inverter. No caps used.Why is frequency slow and how to increase it?-Bill

The difference is about 60ppm. Might be accounted for by differences in parasitic and device capacitances of the two circuits.

Why does crystal oscillator run slow?

Apr 05, 2011 21 Replies

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Vladimir 15 years ago

and

Hi Bill,

Looks so that these crystals were used for filtration, instead of for generation.

For generation such crystals is better to use in schemes which contain crystals instead of the feedback capacitor. The LC-contour is thus used for adjustment of reactance of crystal. In ? Hartley oscillator the crystal should be connected on between LC-contour and transistor's gate. Don't forget the gate to earth through the 1M - 2M resistor.

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Vladimir.

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Bill Bowden 15 years ago

tal

Yes, the crystals could have been used for filters, not sure what they were used for. I think the Hartley oscillator is a sine wave type, I was trying to generate a square wave clock signal using a couple transistors at low voltage. I added a third transistor with a tuned LC in the collector and 10K series resistor to filter out the harmonics and generate a nice sine wave. It doesn't have much use, just produces a pretty picture on a scope.

-Bill

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