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r/AskElectronics • … • u/coderemover

What is the modern and power-efficient way to drive a crystal oscillator?

I've been experimenting with a few ways of creating crystal/ceramic oscillators and I'm disappointed that the oldschool method with a bulky, big THT CD4049 (6 unbuffered inverters designed in 80s?) works the best. We're talking about relatively low frequencies here, like 1 MHz.

CD4049 approach: \- nice output waveform after passing through one more inverter (one inverter to generate, second one to shape the output), no overshoots, but quite fast ramps. \- relatively low power consumption at 5V (< 2 mA)

Then I tried to "improve it". Replaced CD4049 with 74HCU04 (made sure I got the genuine, unbuffered one from TI), it should be more modern, lower voltage, so should draw less power, correct? Nope, the power draw went up to about 10 mA. The output square wave edges got sharper though.

Let's try some modern chips then. 74LVC1GX04 is said to be designed especially for the purpose of driving a crystal oscillator and the data sheet says it is low-power. I did the reference design from the data sheet. At 5V and 1 MHz it draws 15 mA. Wat?! Ok, I must say the after reducing the supply to 3.3V the draw decreases dramatically to about 4-5 mA. But that's still IMHO not good for such a simple thing... and anyway, everything I have in that part of the circuit is designed for 5V so won't change now to 3.3. The chip I got from TME, so I trust it is genuine.

So my question is, what is the desired modern and cost-efficient way of creating moderately low frequency oscillators (hundreds kHz up to tens MHz) with low power draw, like < 1 mA? Can be with SMT parts, but please don't recommend some super fancy Analog Devices / Maxim chips that draw microamps but cost $10 / piece.

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