The crystal is a sharp filter that will allow through a single, very narrow band of frequencies - effectively a single frequency. That means you're going to see a sine wave because any other wave would be composed of multiple frequencies, but he crystal only passes one. When you use a capacitor for the positive feedback, it forms an R-C filter with the pair of 100K resistors. That simply charges and discharges through one or the other until the inputs trip the comparator into the opposite state. You can see it's an R-C combination from the shape of the curve. You could raise the frequency by lowering the 100K resistor values.
I know that it can be challenging to create simple RC oscillators of a low frequency, say 60Hz to drive a DC to AC converter, because of the large values required for the two components. In the capacitor arrangement of this circuit, is this a better method to get at low frequencies? I would think not, because we are back to using an RC oscillator.
@@t1d100 I think the main goal of DC to AC converters is to deliver power efficiently, and the point of AC power is that it works well with transformers. The simplest converter is a couple of power transistors cross-coupled by capacitors with a centre-tapped winding as the collector loads, set to run at 50Hz or 60Hz. You don't get a very clean sine wave output, but for a lot of applications, that's no real concern.
The prongs of the crystal oscillate sinusoidally and their deformation generates the piezoelectric voltage. The step discontinuities are due to the stimulus at the collector. You should get a frequency closer to 32,768 Hz if you put the 10 pF capacitor in series with the crystal to reduce the strength of the circuit's pulling the crystal off resonance.
The cameraman is great! I love how genuine the channel is, as well as its message that things don't always go right and we should not let that stop us from learning and having fun.
In the suggested circuit you will notice a series capacitor. I believe it was 10 pF. Rather small. Note that many Crystal oscillator circuits use a single INVERTER and resonate at the PARALLEL resonant frequency. This circuit however uses POSITIVE feedback and resonates at the SERIES resonant frequency. If you build the circuit as shown with the 10 pF cap and then measure the voltage at the point where the cap connects to the Xtal you will see a voltage that is HIGHER than the driving Voltage. Actually, you WOULD see it except that the capacitance of the scope probe dampens it down quit a bit. The equivalent circuit has a very high impedance with a large series inductor and small capacitor.
Crystals are series resonant. The capacitor just charged and discharge. Whenever a voltage level crosses the reference voltage level the polarity swaps and the oscillation begins.
Other than the open collector output, I wonder what the advantage of this circuit is over the standard "cmos inverter with two load caps" approach, if any.
Great video. However there are applications when you need a pure sine wave. In cases like these a comparator will not do. One of the options is going to be a Wien bridge oscillator build on an op amp.
No. that would be very high for those sort of capacitors. The capacitor is being charged and discharged through the 100K resistors used to set the bias point. You can see that from the shape of the curves on the scope, which is a typical R-C charge curve. If you were to change the 100K resistors, you'd get a corresponding change in the frequency.
Harmonics and phase noise are different things. This is a square wave, so by definition it has strong harmonics. Phase noise is the spectrum very near the fundamental frequency. There are several ways to measure it with a spectrum analyzer. I don't think an oscilloscope FFT mode would have enough resolution but I might be wrong.
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Phase noise is probably not much of a concern in a synthesizer. Harmonics could be a concern, or a feature, depending on what you want to do with the signal. Square wave oscillators are common components in synths.
@@stephentrier5569 Of course they are different. The cleanness of oscillator is very important when you want to use them as a local oscillator in frequency conversion or when you use them as a clock in terms of jitter. The dynamic range is defined as the amplitude of highest peak (fundamental frequency) minus the next peak ( i.e. harmonics) in spectrum analyzer in dB. All these harmonics interact with input RF signal and get converted to undesired frequencies. As a clock, it shows up as jitter. As you know the difference between laser and LED is phase noise. I always wanted to make a light (infra red, visible, and ultra violate) spectrum analyzer. Here are some of my ideas how built them: 1. Passing the light through double or multiple parallel slots and putting light sensors on the projected screen,in a line to detect picks or intensity. 2. Mixing light with a known wavelength laser, and then feed the down converted frequencies to RF spectrum analyzer. 3. Passing it through a prism and measure the intensity of the diffracted light on the screen. By the LF311 is discontinued part, that means they do not make it any more. For high speed comparator, the best bet is to use phase detectors of PLL. Of course, you should watch out for delay.
@ Phase noise causes adjustment channels to get converted into the channel, which then determines how close you can put the communication channels, which then means how efficient you can use the spectrum. As you said, in Gilbert cell mixers, or diode ring mixers we prefer to use square wave as local oscillator to get higher gain and lower switching noise , and phase noise here shows up as jitter based on Shannon's Law. Of course, if your Oscillator is under PLL control, the PLL would suppress near frequencies phase noise.
Still don't understand where the sign wave came from with the crystal. Since there's no inductive element how did the crystal change that? And if it did why do we not see this in a regular computer clock crystal. Mmmm I might have a beer. De ZL1NAY
A crystal is a _mechanical_ resonator that generates a voltage depending on the amount of deformation of the crystal. The mechanical resonance is very precise, and is fixed at a single frequency, so no matter what signal is applied to it, only one frequency can pass. A single frequency has to be a sine wave, because all other wave shapes are composed of multiple frequencies.
Crystals are electromechanical, but from an electrical viewpoint they function like an inductor in series with a capacitor, in parallel with another capacitor. That's where the inductance is coming from. Electrically it's a very narrow LC tuned circuit. If you are thinking of the little metal cans with four pins, those aren't crystals -- they are crystal oscillators. They have the whole oscillator circuit, including the crystal, in a convenient container. You can get them with either sine or square wave output, but the square wave ones are much more common.
@@IMSAIGuy Crystals will deform with a dc voltage across them (not by much, of course), and that can lead to inaccuracies in the frequency (should be 32,768Hz but you're close). It's not a big deal, but just best practice to block dc from appearing across a crystal.
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The crystal is a sharp filter that will allow through a single, very narrow band of frequencies - effectively a single frequency. That means you're going to see a sine wave because any other wave would be composed of multiple frequencies, but he crystal only passes one.
When you use a capacitor for the positive feedback, it forms an R-C filter with the pair of 100K resistors. That simply charges and discharges through one or the other until the inputs trip the comparator into the opposite state. You can see it's an R-C combination from the shape of the curve. You could raise the frequency by lowering the 100K resistor values.
I know that it can be challenging to create simple RC oscillators of a low frequency, say 60Hz to drive a DC to AC converter, because of the large values required for the two components. In the capacitor arrangement of this circuit, is this a better method to get at low frequencies? I would think not, because we are back to using an RC oscillator.
@@t1d100 I think the main goal of DC to AC converters is to deliver power efficiently, and the point of AC power is that it works well with transformers. The simplest converter is a couple of power transistors cross-coupled by capacitors with a centre-tapped winding as the collector loads, set to run at 50Hz or 60Hz. You don't get a very clean sine wave output, but for a lot of applications, that's no real concern.
The prongs of the crystal oscillate sinusoidally and their deformation generates the piezoelectric voltage. The step discontinuities are due to the stimulus at the collector. You should get a frequency closer to 32,768 Hz if you put the 10 pF capacitor in series with the crystal to reduce the strength of the circuit's pulling the crystal off resonance.
I just wanted to ask about the 10pF capacitor!
You need to fire that cameraman! :-)
he cannot fire himself..
I can try, I'll have a talk with him 😎
The cameraman is great! I love how genuine the channel is, as well as its message that things don't always go right and we should not let that stop us from learning and having fun.
In the suggested circuit you will notice a series capacitor. I believe it was 10 pF. Rather small. Note that many Crystal oscillator circuits use a single INVERTER and resonate at the PARALLEL resonant frequency. This circuit however uses POSITIVE feedback and resonates at the SERIES resonant frequency. If you build the circuit as shown with the 10 pF cap and then measure the voltage at the point where the cap connects to the Xtal you will see a voltage that is HIGHER than the driving Voltage. Actually, you WOULD see it except that the capacitance of the scope probe dampens it down quit a bit. The equivalent circuit has a very high impedance with a large series inductor and small capacitor.
Crystals are series resonant.
The capacitor just charged and discharge.
Whenever a voltage level crosses the reference voltage level the polarity swaps and the oscillation begins.
That is very cool and intriguing. You explain it well and have great equipment too.👍🍻🤓
Very nice, digestible vignettes, thanks! :)
thanks for the circuit, it help me lot.
Perfect filming...
Makes total sense...cheers
He was drawing the circuit and I had to imagine how it was going.
Isn't it a sin wave because the crystal sharply attenuates the harmonics from the square wave being fed back?
Thanks!
Other than the open collector output, I wonder what the advantage of this circuit is over the standard "cmos inverter with two load caps" approach, if any.
that is fine, this gives +/- large voltage output
Interesting how on a 40+ old part that's been around, the manufacturers update the applications list in the datasheet to suit to modern technologies.
Great video. However there are applications when you need a pure sine wave. In cases like these a comparator will not do. One of the options is going to be a Wien bridge oscillator build on an op amp.
Cool.
Interesting.
Hello, Did your circuit have the 10pf cap in series with the crystal? thanks
no, read below
check the Buchla 259 circuit.
Could that be the self-resonance point of the capacitors?
No. that would be very high for those sort of capacitors. The capacitor is being charged and discharged through the 100K resistors used to set the bias point. You can see that from the shape of the curves on the scope, which is a typical R-C charge curve. If you were to change the 100K resistors, you'd get a corresponding change in the frequency.
“White Goods” is a high-fallutin way to say appliances….
I haven't heard high fallutin in a long time. I'll have to work that in.
What if you toss an inductor in there instead?
It would have been interesting to see an inductor in series with a capacitor in the feedback loop. It should behave in a similar way to the crystal.
Of course, if you make your oscillators this way ,you would have very bad phase noise. Do a FFT on your oscilloscope and see all the harmonics.
Harmonics and phase noise are different things. This is a square wave, so by definition it has strong harmonics. Phase noise is the spectrum very near the fundamental frequency. There are several ways to measure it with a spectrum analyzer. I don't think an oscilloscope FFT mode would have enough resolution but I might be wrong.
Phase noise is probably not much of a concern in a synthesizer. Harmonics could be a concern, or a feature, depending on what you want to do with the signal. Square wave oscillators are common components in synths.
@@stephentrier5569 Of course they are different. The cleanness of oscillator is very important when you want to use them as a local oscillator in frequency conversion or when you use them as a clock in terms of jitter.
The dynamic range is defined as the amplitude of highest peak (fundamental frequency) minus the next peak ( i.e. harmonics) in spectrum analyzer in dB.
All these harmonics interact with input RF signal and get converted to undesired frequencies.
As a clock, it shows up as jitter.
As you know the difference between laser and LED is phase noise.
I always wanted to make a light (infra red, visible, and ultra violate) spectrum analyzer.
Here are some of my ideas how built them:
1. Passing the light through double or multiple parallel slots and putting light sensors on the projected screen,in a line to detect picks or intensity.
2. Mixing light with a known wavelength laser, and then feed the down converted frequencies to RF spectrum analyzer.
3. Passing it through a prism and measure the intensity of the diffracted light on the screen.
By the LF311 is discontinued part, that means they do not make it any more. For high speed comparator, the best bet is to use phase detectors of PLL. Of course, you should watch out for delay.
@ Phase noise causes adjustment channels to get converted into the channel, which then determines how close you can put the communication channels, which then means how efficient you can use the spectrum.
As you said, in Gilbert cell mixers, or diode ring mixers we prefer to use square wave as local oscillator to get higher gain and lower switching noise , and phase noise here shows up as jitter based on Shannon's Law.
Of course, if your Oscillator is under PLL control, the PLL would suppress near frequencies phase noise.
Wow, thank you. Redrawing the circuit was nice. Can I model this in LTSpice?
Why don’t you try, Tony.
Not only is the answer yes, many of my viewers will tell you, you MUST before designing anything 😐
I wasn’t trying to be snarky, but realistic. Put some effort into your journey peeps. Thank you IMASI for the post. 🎈
Still don't understand where the sign wave came from with the crystal. Since there's no inductive element how did the crystal change that? And if it did why do we not see this in a regular computer clock crystal.
Mmmm I might have a beer.
De ZL1NAY
A crystal is a _mechanical_ resonator that generates a voltage depending on the amount of deformation of the crystal. The mechanical resonance is very precise, and is fixed at a single frequency, so no matter what signal is applied to it, only one frequency can pass. A single frequency has to be a sine wave, because all other wave shapes are composed of multiple frequencies.
Crystals are electromechanical, but from an electrical viewpoint they function like an inductor in series with a capacitor, in parallel with another capacitor. That's where the inductance is coming from. Electrically it's a very narrow LC tuned circuit.
If you are thinking of the little metal cans with four pins, those aren't crystals -- they are crystal oscillators. They have the whole oscillator circuit, including the crystal, in a convenient container. You can get them with either sine or square wave output, but the square wave ones are much more common.
You almost have a capacitor meter.
Capacitor missing in your drawn circuit.
that is to block DC, didn't seem to be needed for my xtal
@@IMSAIGuy Crystals will deform with a dc voltage across them (not by much, of course), and that can lead to inaccuracies in the frequency (should be 32,768Hz but you're close). It's not a big deal, but just best practice to block dc from appearing across a crystal.
@@RexxSchneider ok, good to know