Colpitts Crystal Oscillator Fundamentals

[@Nichetronix]

33-year RF engineer here. I've designed many Colpitts and other crystal oscillators. This is the best description I've seen of the process in a single KZbin video. All my engineering co-op students are going to be watching this video.

[@sbybill3271]

Wow, 33-year is a long time. Could you please tell us what is the best method of reducing that distortion?

[@jitu1973]

Seriously I wish he be my teacher ❤ better explain then anyone in my university 😅

[@fzigunov]

Man, this is by far the best explanation on Colpitts oscillators that I've encountered in the internet in weeks of research. Thank you very much for taking your time to put all of this together! It was really helpful!

[@Analogzoo]

+Fernando Zigunov Thanks, glad it was helpful!

[@acestudioscouk-Ace-G0ACE]

As a semi retiree, I never thought I would learn the maths, but your detail and pace have made fairly easy. Thank-you!

[@4tviewer]

Best circuit analysis of this design I have every seen. Excelent tutorial by someone who clearly really knows what they are talking about.

[@michael.mcshan]

I've been re-designing the oscillator section of a Ramsey QRP transmitter kit to eliminate chirp from the signal, and this video has been very helpful. A big thank you!

[@timothyfidler2088]

I had a look at Ramsey stuff even though I am not in US and I came to conclusion it was hastily cobbled together pieces of crop with no documentation and over priced to boot. To hear it has fundamental design issues.. what .. me surprised ??

[@to-tt7fc]

None of my instructors ever explained this in such details. Many thanks.

[@Neverforget71324]

Agree. The way I was taught in college was: Here's the circuit. It oscillates because the open loop gain is equal to or over 1 and the phase shift is zero. Figure it out... good luck!

[@dowonkim574]

This video clip is what I have been looking for. This explanation shows the presenter fully understand the principle of the oscillator and knows what we want. Fantastic job! Thanks.

[@TheChemicalRobot]

This video has fantastic detail. Nice job!

[@Analogzoo]

+TheChemicalRobot Thanks!

[@chenitimohamed4141]

@@Analogzoo please make videos on colpitt oscillator based on saw surface acoustic wave

[@shomonercy]

Duuude, where have you been when I needed your vids the most.

[@BinAlladin]

Eating hamburger :)

[@1SmokedTurkey1]

3 words; YOU ARE AWESOME!. Thank you so much for this video. Seriously, this cleared some stuff that has been a puzzle to me since graduating from EE school!

[@tumu_3799]

Your work just took my thesis research to level I couldn't imagine getting to now. Super excited I found this versed explanation. Thanks a thousandfold.....

[@dinodubroja7433]

colpits oscillator for a thesis?

[@holgerreichel7396]

Excellent explanation! I haven’t found something like this in books or elsewhere. Thanks a lot! Looking forward to your other schematics tutorials!

[@rjrodrig]

One of the best video explanations I have seen on this topic. Thank so much for it

[@belalmohammed2265]

I regret seeing this video earlier and saying that it's too long This video is perfect many thanks for the free knowledge you just gave

[@kiwiblue1606]

I used this video together with the book "Foundations of Oscillator Circuit Design" and was able to design a 1M Hz oscillator that worked perfectly on its first revision. I tried three different crystals and the worst I got was 999.97K Hz. Thanks!

[@duality4y]

I just love this channel everything is clearly explained and in a understandable way.

[@dogdogdogdogdog2546]

this outta be the most useful video I have ever seen. I was so done with learning crystal oscillators because I was confused about the gain of the circuit and the reason for the capacitors. Thanks from New Zealand

[@wizardofboz76]

These are at the exact level I require. Thank you so much for taking the time.

[@samtzam3774]

Very good video. Combine the theory, the approximated models and the practical world. Pretty nice job

[@Neverforget71324]

I wish I had you as a buddy in college. WELL DONE!!!

[@alalv8617]

Great tutorial. You've just won another subscriber from Spain

[@carmelpule6954]

I like your diagram at 2:47 as it clearly shows what I think/perceive, when I look at this circuit. Just like there is an autotransformer effect with a tapped inductor, which can have a gain of more than 1, well there can be the same effect using the two capacitors (plus the crystal) as you showed them so the " feedback network" has a voltage gain of more than one complete with the phasing required. It is this which makes up for the less than 1 gain of the emitter follower, to full fill the maintenance condition of the oscillator, while the crystal sees to the determination of the frequency. In transfer of knowledge of the working of electronic circuits a slight modification of how to draw the circuit could make a lot of difference is " seeing the explanation" Congratulations for drawing the feedback network in isolation as you did . Normally the Colpitts Oscillator, uses the centre tapped twin capacitor in an earthed/ground mode to phase change the feedback voltage as the feedback network is normally supplied from the collector and so the phasing needs a 180 degree change to meet the condition at the base. Some people seem to think that all oscillators need a phase change of 180 degees but that is not correct as you have shown so well.

[@Analogzoo]

Correct! The important phase shift relationship is that the total phase shift through the feedback loop, which must be 360 degrees. I'm glad you liked my depiction of the feedback network, I think that it makes the operation of the feedback network much clearer.

[@dinodubroja7433]

Thank you very much for this video, just got a clean 16 MHz sinewave from my first colpitts oscillator :)

[@louco2]

This is very good! Thank you for taking the time to do this video you are a very good teacher!

[@jasoncater5737]

I'm currently going through an class on RF equipment. I'm in the oscillator section of the class right now. I've had a bit of frustration getting my oscillators to...well oscillate. I watched this vid, built this circuit and lo' I've got oscillation at 12Mhz! This a great confirmation for me and I can now take the training wheels off! Thanks for the great vid!

[@pnjunction5689]

Thank you very much for this video and the time and effort you put into it! I finally understood how the circuit works! Great explanation!

[@Analogzoo]

+Pn Junction Glad to do it, happy it helped! Great user name BTW. :)

[@VikasVJois]

Very detailed, practical and intuitive explanation. Thanks

[@Nick-pr5gw]

awesome video! Always struggled to understand this circuit in detail. Quick note reference the crystal ESR: This crystal is an old style HC49 @12MHz so 40ohms max is a good assumption, a modern equivalent 12MHz crystal could be a 2.5 x 2.0mm package where the ESR would be spec up to 300ohms max. so some of the assumptions that this is low should be checked. Quick comment regarding tuning the Cload to make an accurate frequency: perhaps use a trimmer capacitor to find the correct value, but don't leave it on the circuit they change value a lot due to atmospheric conditions (humidity, temperature etc) so the frequency would not be stable if this is left in the circuit.

[@codijack9577]

Best ever explanation, very easy to understand. Thank you

[@saicharanmarrivada5077]

Excellent video on Colpitts oscillator

[@zopilotesky3014]

A fantastic explanation of this circuit. Thanks for sharing!

[@kkeygogogo]

Hello. How did you get a 0.6 ohm equivalent resistance at 29:04

[@gyrgrls]

It is instructive to note that since Impedance is a complex value, "j" denotes the square root of -1. "i" is not used here because it is already reserved for AC current value...

[@StewartClarkGadgetman]

Perfect - just what I have been looking for.

[@timothyetherige8556]

Excellent video! One comment: The way you have drawn your schematic implies that there is always DC applied across the crystal, which keeps the crystal constantly stressed, which may not be ideal. You probably want a DC blocking capacitor (short at RF) to prevent this or a Pierce oscillator.

[@deuce-way1440]

I’m relatively new to building frequency based circuits, what type of board are you using? How is it connected to your scope ? Is this something that can be done using rg58 coax? Your help is greatly appreciated 🙏🏾

[@stefano.a]

Barkhausen criterion specify that A x Beta has to be strictly equal to 1. So, there is to be an intrinsic behavior of the system, that lower the loop gain to one to avoid saturation

[@joaquimsilva7671]

Nice job. Thanks for the time and knowledge.

[@timothyfidler2088]

xtal is dissipating 2mW and you start talking 100 to 500 mW .. I think you mean 500 micro watts being normal drive level...

[@acmefixer1]

Thank you for the informative video. After 10:03 you use the terms impedances as you pointed at X1, X2, etc. X is the term used for reactance, whereas Z is used for impedance. This was a bit confusing -- they're not the same thing. Thanks.

[@ohmslaw6856]

In the case he was referring too.. jts kinda the same thing

[@jeremiahgeorge3548]

You nailed it sir, the concepts were well explained. Just a little mistake though; the parallel combination of the base resistances should be less than or equal to 0.1*Bmin*Re

[@kiyphysicas1541]

Question about 7:10 to 7:25. On the oscilloscope we can see there that output signal e2 (Green) changes. It is what we expect. Why input e1 (Yellow) changes so much too? I understood that the signal generator has 50 ohms impedance. Therefore the amplitude of the input e1 suppose to change, depending on the load's impedance. However, why it changes so much? Is the load impedance approaches to zero? I've never seen crystal's impedance even at series resonance is less than 30 Ohms, which means it cannot reduce the input signal from 50 ohms generator down to almost zero volts. Video is the best explanation of the Colpitts Oscillator on internet, though. Thanks.

[@robthorn3910]

At the point where you discuss loaded Q, you showed a series resistance of 0.6 ohms. When I did this calculation and included the 4.7k ohm emitter resistor across one of the caps, I got a series resistance contribution from that resistor of 1.65 ohms (1.65-j176) which then added to the 0.6 which comes from the 48k bias divider, for a total series resistance of 2.3 ohms. That seems significant if I'm right (but its late and I'm not sure of anything, lol).

[@robthorn3910]

OR maybe the 4.7k ohm emitter resistor is reduced by a factor of beta+1 so it is much less. Now I're really confusing myself. I read one article that says the amplifier presents a negative resistance to the tank.

[@davidevacca619]

Very helpful video... either for my English listening pratice and for make my own oscillator too !!! Thanks for it !!!

[@timothyfidler2088]

There seem to be a few flaws here. Capacitors C1 (top feedback cap.) and C2 (Bottom capacitor) are solely for feedback purposes. The point of the topology of the C1/ C2 is that it is an impedance match between the low Z of the voltage follower and the required high load Z of the crystal circuit (or it will fail to oscillate ) . This circuit is covered in some detail in analog.intgckts.com/impedance-matching/tapped-capacitor-matching/ and the final formula is Rin/RL = (1+C2/C1)^2 where Rin is the impedance seen looking towards the Emitter resistor by the crystal circuit. If C2 = C1 (which is arrived at with two 150 pF capacitors) then the as seen Z will be four times 4.7k ohms using the as built emitter resistor or a nominal 20K ohms as seen by the crystal circuit. This business of C1 and C2 participating in the tuned circuit of the crystal. No, I don't buy it. If so, those capacitors would move the operating frequency with temperature far more than is the case - the crystal is self contained and includes EFFECTIVELY L and C components, which can operate in series mode or parallel mode. In the case of a free running true L C oscillator then C1 and C2 do participate in the tuned circuit . See en.wikipedia.org/wiki/Crystal_oscillator note that adding capacitance across the crystal will DROP the operating frequency slightly but does not set the frequency, which nearly one hundred percent controlled by the quartz crystal. Derivation of transconductance for a BJT. You have used a generic formula which applies only at audio frequencies. I looked up what is available on the 2n3903 and because Y21 = h21/h 11 (Y21 being the transconductance) you can get a value of 0,025 (mhos) amps (collector) per volt (on the base using Hfe= 100 and Hie = 4 E3 ohms. NB these values too came from audio frequency data - www.onsemi.com/pub/Collateral/2N3903-D.PDF . Finally you make a very interesting point that this oscillator works without a 360 degree phase shift (or 180 degrees plus an input to an inverting amplifier). This would be very unusual for an audio oscillator but is not uncommon with RF oscillators, particularly quartz based ones. Here's a question which I open to any competent person - . your formula for loop gain versus ESR ( Re) would not be applicable if the osc. was in parallel mode, where the Re cannot be seen and the impedance of the crystal appears infinite - does this mean that the Colpitts crystal necessarily runs with the crystal in series mode ONLY when this circuit is used ? My suspicion is that this not always the case.

[@lingua9926]

Thank you sir, but how do you calculate the small resistance of 0.6 ohms?

[@gilbertjuly]

Nice video! I wonder how it is possible for Colpitts oscillator to achieve automatic loop gain control? Considering the gain needs to be greater than 1 during starting period, and to be 1 during stable period.

[@deweywsu]

Fantastic video. Your knowledge is impressive! Could you please pass on a couple things? Do you have any recommendations for books that delve into the Colpitts? Also, you mentioned that the Colpitts oscillator commonly doesnt produce a good sine wave, which is my experience as well. Yours was the first explanation why over heard: because the transistor isn't operating mainly in the linear region. You mentioned a way to filter the feedback to fix that, but it doesnt look like you had time to go into that. Can you point to somewhere that might have this extra info? Thank you for an awesome video.

[@Aligreta]

Great video. Would be great to watch one about overtone crystal oscillator. Most i can found for radio application are of this kind :)

[@davistroy]

@devttys0 … I stumbled across your channel and your videos are outstanding. I see you haven’t posted in a while, hope to see more from you at some point!

[@pramitchaudhury1821]

A fan of your channel wonderful explaination ❤️

[@koenvandemoortel2206]

Nice explanation, but it doesn't seem to work... I tried with a 32.768kHz crystal, adusted the bias on the base of a BC548C with a potentiometer to get a 4.5V average on the emitter, but only some noise comes out! Most weirdly: I see a very nice and stable sine wave of 24.55MHz, 230mVpp at the BASE of the transistor! I tried also with a 2N2222: 23.97MHz, 478mVpp. What on earth am I doing wrong??? Why is the emitter not following the base??? I have no clue what is happening! Anyone here having a suggestion?

[@abdullahsy7072]

oh thanks so much for the effort you've put in this video cus it's a fantastic one

[@kapchedefoangejonathan8660]

I don't really understand how the concept of ensuring that the series equivalent resistance being smaller than the internal resistance of the crystal degrades the high Q of the crystal? Why does that condition need to be met??

[@VeryMuchBlessed]

Excellent video. Very good information. Thanks much.

[@seanhunt138]

Best video on oscillators!

[@PapasDino]

Very nice balance between theory and practicality Craig. Before I start digging thru my texts, when you approximated the transconductance you had a divisor of "26" and I don't recall you mentioning where that number came from.

[@Analogzoo]

+Dino Papas I didn't; I already felt there was enough math for one video! :) Transconductance (gm) is just the ratio of output current to input voltage. The output current (Ic) for a BJT varies with temperature, and gm can be expressed as Ic/Vt, where Vt is the thermal voltage, which is a characteristic voltage for semiconductors. Thermal voltage for a PN junction is equal to kT/q, which is ~26mV at room temperature.

[@PapasDino]

+devttys0 See, I told you I didn't have to dig out an old text! Thanks Craig.

[@falconhawker]

Suppose I want to reduce the amplitudeof the oscillation in the hope of reducing the distortion and aging f the crystal. How is this accomplished ?

[@ThePaulbilek]

I liked your thorough design explanation of collpitts oscillator I'm interested in resonance of a load as in hho dry cell. What oscillator would you use and how would you figure out the frequency? Furthermore the resonance needs to be locked in in other words stay resonating with changes in temperature and the voltage/ current without use of crystal as it will vary.

[@ThePaulbilek]

I found fit first time a schematic for such an self resonating circuit although I need help in figuring out what values to use for l1 and l2. Can you shed some light? Thanks.

[@ThePaulbilek]

That's the basic idea I had when trying except I was going to use a mosfet as the pulses need to be sharp and short, about 300ns and have an adjustable dead zone (no pulses). Also the pulses per cell need to peak to about 7 volts. I have 3 neutral plates

[@ThePaulbilek]

The current and voltage will be regulated to certain values like 16 volts and 8 amps. Oh here's ther basic circuit I found kzbin.info/www/bejne/qHu0eI2Zr6-me68 Pic iamconnect.com/storage/a/posts/1667218578Screenshot_20221031-072900_KZbin.jpg iamconnect.com/storage/a/posts/1667219223signal-2022-10-31-082440_002.jpeg My measured cell inductance at room temperature is 2.1 micro Henry and 462 micro farads I tried using a joule thief circuit driving a mosfet. The resonant frequency should be around 2 -5khz using bifilar coil

[@pakistan010203]

I like your videos, they are very informative and useful. For crystal Oscillator , there is one simple solution which i have used is my project. I brought a 30 MHz 4 pin Crystal oscillator , it gives a square wave output (Normally used with micro-controllers, sine wave is also available), from a square wave(Bi-polar) we can get a sine wave by simply connecting a LC narrow band pass filter in series with the crystal oscillator to filter out it 1st harmonic frequency. You must try this , very simple and less component oscillator. Very useful of High frequency applications.

[@Or5mr]

Thank you very much for this video, very well explained

[@avonfonds2567]

Doesn't the frequency get multiplayed at the output?

[@coffeecuppepsi]

10:34 . i'm still confused about the relationship between e1 and e2... in the previous equation we saw 1v at e1 and 2v at e2 - that's fine on it's own, but in the transistor circuit, why isn't e1 just e2 - the the diode drop of the transistor.... which is actually the voltage relationship in an emitter follower....

[@marceloalvarocoronelcastro3463]

At that point, he's analyzing the signal not the DC.

[@user-xj5id6xr1j]

brill, great explanation

[@wrqnine7675]

In the power dissipation segment you seemed to say your power dissipation was 2mW while the allowance was for 100 to 500 mW typically. I don't see how that could present a problem. Nice job though and I feel much better about trying this on my own.

[@coffeecuppepsi]

The gain equation for voltage using capacitors make sense, but another part of me cant get over the fact that the emitter is 0.6 V below the base...

[@stevee4444]

fantastic explanation, thanks!

[@Rev22-21]

Excellent job and info.

[@dannyperry8070]

I have watched your video many times. Very nicely presented. One question. I have experimented with this type of circuit. If I want to use this as a small transmitter can different bias settings increase the output power. I have tried that on a simulator and noticed no change with different bias settings. So if I wanted to increase the output power as a transmitter, what kind of additional stages would you suggest. Thanks

[@sanderverhage5148]

How could this design be modified if you want a lot of power into the crystal? For example driving a piezoelectric mist generator.

[@warrendyckman6317]

The benefit of your presentation was clearly breaking down the design of the Colpitts Quartz Crystal circuit design into the required components for setup. I was very disappointed that you didn't treat the Crystal with the adequate specifications needed to particularly design a oscillator that requires a crystal anyway. You need to consider Crystal current for ageing and phase noise for starters. Your measurement across the crystal is very inaccurate since the shunt probe capacitance will dampen the actual packaged crystal. The best way is to insert a series capacitor of about 20 to 30 pf in series and measure the drop across the capacitor. That skirts the problem and acquires the accurate Ix data. 1 microwatt is a good operating level for AT and AT strip designs and gives good starting time results. If one doesn't consider these terms the crystal requirements one reaps the results! Other cuts of quartz require more careful considerations as appropriate. Warren Dyckman, K2WD

[@bigfoottoo2841]

Excellent video, thanks

[@nukiduki2]

Oh my god, I've been trying for weeks to understand oscillators, been reading through Grob's Basic Electronics and The Art of Electronics and they completely fail to EXPLAIN how this oscillator works. Most places they just toss around some circuit diagrams with placeholders "C1" "L1" and handwaving explanations like "the network provides feedback" or "the capacitive voltage divider" YEAH YOU FUCK A DIVIDER CAN BE ANYWHERE FROM 1:1 to 1:10'000 SO WHAT DO YOU DO?! Thanks man, really appreciated. I'd like to donate, where I can I donate?

[@valentingomez4546]

May I ask why you're not using a collector resistor?

[@hecanet]

@35:32 Is it really possible to get two voltage levels at the same point (the Crystal is parallel to the 120k resistor as well as the series of C1 and C2 of which C1 is connected to the base of the transistor)? Now since the base is set to 5.2 V by the voltage divider, how did you get 3.6 V at Crystal unless you are saying that the base voltage would drop to this same level?

[@mohamedrushdy5336]

Thanks Really you are very good ,In my opinion you are THE BEST...Thanks again

[@omar_nagib]

Fantastic video, thanks!

[@jsebtarot5006]

Yes! Very Great! Thank you

[@pablomarco5118]

very good, thanks

[@ajingolk7716]

What about capacitors type resistors types

[@sabaku7732]

this circuit wouldnt work for a 32.678 khz crystal right? i have followed all the constraints of the design and i created a circuit in multisim unfortunately it refuses to oscillate

[@anmingren8747]

he said it works only when the xtal is a high frequency one, you should retry it with a Mhz xtal.

[@hectorbarrera9496]

Nice job excellent explanation,congratulations, I would like to know what happen if I replace de crystal for an inductor? how the configuration change?

[@slaquers]

Thank you so very much!!

[@kevinkang4308]

Nice video with a lot of details. One comment at 28:13, it should be pF instead of ohms?

[@ebubekircosgun2794]

Hi Dev My question about how did you find transistor biasing voltage(5.2 and 4.5)minute 20:29 and while you are calculating gm(transconductance) where did you get 26 mV is it common for bjt or what else ? thanks for your answer by the way that'S good video for learning about crystal osc.

[@CSFitness1]

Isn't a common-collector amplifier a buffer? Not a common-emitter?

[@rockndancenroll]

yes common collector (common drain in mos) or emitter follower (source follower) is a buffer. He probably meant emmiter follower

[@MarkMcDaniel]

It's so weird how the positive voltage levels are oddly distorted while the negative range is a perfect looking sinusoid.

[@taojiang719]

thank you sir

[@brunoomare]

Thanks for such an explicative video! I was wondering... what if i want to use an overtone? I want to design a 100MHz oscillator so I would have to use the third o fifth harmonic of a crystal to aproximately get that 100MHz. How do I do that? Hope you can answer! Thanks!

[@the_moo000oon]

hi dev, i notice when you go over the gain in the feedback network you model the crystal as being inductive in reactance. are you suggesting the crystal is operating in its inductive region? i ask because i am trying to develop a humidifier driver and those crystals must operate in the inductive to nebulize (not sure why)

[@rocknation316]

wow, this is so nice! thanks a lot

[@yaningcui2277]

I don't understand well on how to choose a crystal? Can I use a lower frequency crystal (5MHz) to take place of it?

[@SopanKotbagi]

What changes would need to be made to drive this crystal at one of its overtones?

[@andrewel5383]

How do you make an amplifier for a this crystal oscillator circuit? I'm trying to increase the voltage to about 6volts and have an oscillation of 32mhz

[@hadireg]

great video! Thanks 👍👍

[@enricoincognito8595]

I looked for the datasheet of the transistor and tey said the basis emitter voltage is 5volts as "testconditions" so is this the working voltage for amplification or the saturation voltage. When i loking at the cirquit in this video it must be the voltage for amplifikatoon in positiv and negativ direktion?

[@user-xr4kb6ub4i]

Hello, Indeed it is the best explanation in the net! I would like please to ask two questions: 1.You said that one of the conditions for oscillation is AB>=1 but according to your explanation AB=(e1/e2)(e2/e1), which is always equal to 1 and can't be greater than 1? 2.At minute 3:30 you present the feedback network as a serial circuit with current I, but the current I (from the emitter) split into two branch: Xc2 and Xc1+Xe? Best Regards, Marco

[@Analogzoo]

1. Your assertion that AB will always be equal to 1 assumes that the gain of A and/or B doesn’t affect the original input voltage (e2), but since we have positive feedback, that’s not necessarily the case. To make the numbers simple, let’s say that the gain of A is 0.9, the gain of B is 2, and the initial voltage at the amplifier input (e2) is 1 volt. The loop gain will then be AB = (0.9*2)*1v = 1.8v. That’s a voltage gain, and seems to violate the math..but remember that *this 1.8v is being fed back to the amplifier’s input, e2, so the input e2 voltage is no longer the original value of 1v*. This amplification and feedback process continues until practical circuit limitations prevent further amplification (this is referred to as “limiting”). Since further amplification is not possible due to limiting, at this point the circuit stabilizes to a total loop gain of 1, just as you predicted. 2. Yes, as I mentioned in the video, some current will go down the Xc2 branch as well. But as described, due to the reactances at the resonant frequency, a voltage gain is realized through the Xc1+Xe branch. The current through Xc2 is not terribly important to focus on, but rather Xc2’s affect on the resonant circuit, which is essential to realize a voltage gain through the Xc1+Xe branch of the circuit. Some current also goes through the emitter resistor too!

[@mdesm2005]

Impressive presentation. Will you cover RF construction techniques in a future video? BTW, at the very end, you seem to say that a higher amplitude would help S/N even when the noise was phase noise. Isn't phase noise another word for jitter? How would a higher amplitude improve the jitter (wander in phase).?

[@Analogzoo]

+mdesm2005 Yes, jitter is basically phase noise, but viewed in the time domain, rather than frequency domain. Saying that a higher amplitude equals better phase noise is perhaps confusing as it only pertains to this context (i.e., oscillators). For example, adding a subsequent amplifier stage after the oscillator will worsen phase noise, as the amplifier will amplify the existing signal and noise equally, as well as adding its own noise to the signal. This would worsen the signal to noise ratio, and give you worse phase noise / jitter. What needs to be done is to amplify the desired signal by a greater amount than the undesired noise. This is exactly what an oscillator does: it filters out only the desired signal and re-amplifies it again and again until it can’t amplify it any longer, usually due to limitations on the amplification circuitry. Raising these limitations allows the oscillator to amplify the signal farther above the noise level, providing a better signal to noise ratio. Since a “jittery” signal is the result of random variations in the period of a waveform, and period is the inverse of frequency, that means that more variation in frequency means more jitter. So if you can amplify one frequency while suppressing other undesired frequencies, you get less jitter.

[@armandoleantesanabria8355]

Could this oscillator be FM modulated by adding varicap in series with xtal to ground?

[@tryhard2451]

Hey can you do this without using a crystal and only a inductor tank circuit