EMRFD Message Archive 8283

Message Date From Subject
8283 2013-02-22 16:13:28 Glen Leinweber A no-bias LC oscillator
Have been looking at the ubiquitous Pierce crystal oscillators used to
clock so
very many digital circuits. Perhaps the 74HCU04 logic gate can be used in
an LC-type VFO, with reasonable performance? Yes!
Turns out that an LC version, optimized to match the amplifier Z to the
resonator Z looks very much like a Vackar oscillator. Changing the input's
capacitive voltage divider to a tap on the resonator's inductor results in
an oscillator with only reactive components (one coil, two capacitors).
Have documented measurements and design here:
8287 2013-02-23 03:44:13 Ashhar Farhan Re: A no-bias LC oscillator
There is also the franklin variation where a parallel tuned circuit is
lightly coupled to the input and output of a cascade of two inverting gates
(each biased to linear region with a feedback resistor). I have tried it
recently and it works quite well too. I am not sure of the phase noise
though. I only have a bitx to hear the phase noise with. the stability was
amazingly good with 2.2pf coupling capacitors (using 0805 smd capacitors).

i would also make sense to evaluate a 'tickler' circuit where a secondary
drives the feedback, back into the tank. i haven't evaluated this
configuration yet.

i seem to get much lesser temperature drift with smd components than the
leaded components. any explanations?

- farhan

8289 2013-02-23 13:58:26 Dana Myers Re: A no-bias LC oscillator