Re: crystal series resonant circuit

On Nov 25, 1:33 am, Tom Bruhns <k7...@xxxxxxx> wrote:
On Nov 24, 8:48 pm, Johnny Chang <johnny...@xxxxxxxxx> wrote:



i'm trying to create a standalone crystal circuit to create a square
wave but all I can find are parallel resonance circuits. the series
resonant circuits don't seem to have a resistor and it is my
understanding that you change the frequency of the crystal by having
different series resistances, listed here:

http://rocky.digikey.com/WebLib/Epson/Web%20Data/C-2-TYPE,C-TYPE.pdf

does anyone have an example circuit I can use with this crystal? i
dont think i can use a parallel resonance circuit with it because of
the 6pF to infinity statement.

this is the only place i've seen with series resonance:http://www.geocities.com/SiliconValley/Peaks/3938/uexosc.htm

but i don't understand how to select my frequency of oscillation or
the purpose of the op amps at the end.

So why, with those crystals, do you think you want to use series
resonance? They are specified for a particular load capacitance,
which to me implies parallel resonance. It's usual to order a crystal
for a particular load capacitance, and if you want to adjust the
frequency, provide a variable capacitor in the load circuit.
Actually, it's not too different for a circuit that uses series
resonance, since a capacitor in series with the crystal will also
adjust the frequency of oscillation, as the net resonant circuit
equivalent capacitance is the series combination of the motional
capacitance and the external capacitance...though you must also
account for the holder capacitance. And be aware that the frequency
of oscillation will depend to some extent on all the external parts as
well as on the crystal itself.

In your second link, I don't see any "op amps at the end." I see only
logic gates. Their purpose is to buffer the crystal oscillator output
so that the oscillator is isolated from changes in load impedance.

Cheers,
Tom

i'm confused, the link i gave provides series resistance for frequency
ranges while load capacitance is 6pF to infinity, which doesnt give
any information for getting the right frequency between 20 - 165 KHz.
am i supposed to buy a bunch and experiment? i did not know there were
variable capacitors? for series, they list series resistance, so i
assumed i need some kind of resistor to vary the frequency. but i
suppose it could just be the amount of resistance it looks like.

well, if i can use that crystal in parallel mode, then i will. i was
just confused by the lack of data on the *** as i was only familiar
with parallel resistance and specific #'s.

as for the circuits, im referring to the other 74LS04 inverters.

are there specific specs i should be looking for inverters based on
frequency? output current?
.

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