crystal series resonant circuit

resonance:

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

Regardless of what your links may say, you do not change the frequency of a crystal oscillator by changing the resistance. You change it by varying the capacitor. You can only change the frequency of a crystal about +/-.01% or so. Also, no crystal oscillator inherently has square wave output. You get a square wave by having enough gain in the system so that the sine wave gets squared up.

Tam

resonance:

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 sheet 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?

thanks for the information, i actually want a sine wave output and was considering running it through a low pass filter afterwards, but with what you're saying I just need to find a low gain inverter?

thanks for the information, i actually want a sine wave output and was considering running it through a low pass filter afterwards, but with what you're saying I just need to make the circuit low gain ?

thanks for the information, i actually want a sine wave output and was considering running it through a low pass filter afterwards, but with what you're saying I just need to make the circuit low gain ?

resonance:

If you are wanting a frequency range of between 20 - 165 KHz then you don't want to use crystals at all unless like you say you'll need a bunch of $them$.

What would be so wrong with using a $34 Elenco function generator?

What IS your time worth?

"op amps at the end." hold the secret to the desired square wave output. Their gain is so high that on and off ramps become more or less vertical. But those aren't op amps, they are gates - they are just drawn like op amps some times are drawn. I'm not bad, I'm just drawn that way...

--
No, that\'s the maximum series resistance _of the crystal_ when it\'s
oscillating in parallel resonance mode in the various frequency
ranges indicated.


>does anyone have an example circuit I can use with this crystal?

resonance:

There is a Phillips chip I ran into when I needed to pull a crystal without a varactor. The Philips design involved changing the transconductance of a long tail pair by varying the tail current.

Since you're building a discrete design, look around for the varactor based designs.

You may not need it. The signal at the output side of the crystal will be a sine wave. Capacitively couple that to an emitter follower. Bias the base of the EF at half of VCC.

Tam

I have seen TV 3.58 MHz PLLs that work something like that. Changing the current causes a change in the phase shift of the oscillator.

Tam

John Fields wrote: > On Sat, 24 Nov 2007 20:48:24 -0800 (PST), Johnny Chang > wrote: >

Actually it is the xystal ESR at resonance and is a minimum. 50K is pretty much the standard for that 32KHz thing. Off resonance ESR goes to infinity and is the main cause of start-up failure. That ESR value only holds for a small band of frequencies about Fresonant, and the same goes for the ESC and ESL.

resonance:

You need to separate the crystal parameters from the circuit parameters. The "load capacitance" is a circuit parameter, and is the capacitance which the crystal "sees" from your circuit. You can adjust it (the capacitance) to adjust the frequency of oscillation. You (or the crystal manufacturer) specify the desired capacitance, and the manufacturer guarantees oscillation within the stated tolerance when the crystal is operated in a circuit in which it "sees" that load capacitance. The parameters in the data sheet you linked to immediately below that, from "series resistance" to "shock resistance," are all parameters of the crystal and its holder. Series resistance is the electrical equivalent circuit resistance for the crystal. You should be able to find info through a Google search on the generally-accepted equivalent circuit of a quartz crystal; a first- order equivalent is a series R-L-C, shunted by the C of the holder. In actuality, there are other series RLC's resonant at other frequencies that correspond to minor resonances, but you probably don't have to worry about those in your application.

I'm QUITE sure you can find a LOT more info on crystal oscillators on the web, through a Google search. You can also find a lot of info in various ham radio publications like the Radio Amateur's Handbook. From a combination of thinking about the circuit, looking at the available info, and experimenting with some circuits, you should be able to learn a lot and become much more comfortable with how crystals and crystal oscillators behave, and what the important parameters are.

Bingo. A very clever design.

Most people go with the varactor if you can use one of the cheap types used in radios.

I don't know why I didn't reference VXCO in the first place when the topic came up.

The M E Ferking reference is quite a book. You need an IEEE membership to read it.

Guess I should add that the ESR specification is at resonance and at a given power level, like uWatts. The highly nonlinear ESR is also a function of power level, recall seeing a graph showing that 32KHz 50K going asymptotic to 500K at small powers like nanowatts, even at the resonant frequency. That is the start-up failure mechanism.