A basic crystal oscillator circuit. - Page 1
Forum section: electronics / projects

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 19, 2016, 12:52:09 am
content: Hi everyone,Let me introduce as a newcomer at this forum, doesn't matter how old I am.I want to talk about a basic crystal oscillator ( from online) which I want to apply just having interesting and meaning full waveform on scope,.,My plan is to apply this circuit somewhere I need.If you can see, from the left side an crystal has feed to Q1 transistor with reasonable bias, C1 and C2 capacitors might used for suppressing DC component of disturbance from crystal and indeed parallel.After this point Q1 emitter is connected to second transistors base, it means signal amplification is taking part, isnt it?If you can look deeply, C4 is making a bridge with both stage, that making in/out RC filter.Whole circuit output filter is taken across C5.lets consider1. Input/out put impedance2. Transistor amplification factors.3. Maximum energy transfer capabilities.4. Wide BW gain factors.What is the purpose of this circuit you think?

author: danadak
author_rank: Super Contributor
timestamp: December 19, 2016, 12:02:35 pm
content: This is a colpitts oscillator -https://en.wikipedia.org/wiki/Colpitts_oscillatorThe second stage looks largely to be a buffer to eliminate load effectson oscillator.Regards, Dana.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 20, 2016, 01:23:08 am
content: Thank you very much Sir danadak.Yes, I studied colpitts oscillator 10 years back may be.Lets talk about it more, because its an application circuits.QuoteCould you kindly explain it how?From the past, people use Tank circuit instead of crystal.The Colpitts oscillator uses a single stage bipolar transistor amplifier usually as the gain element which produces a sinusoidal output.Are you talking about the issues in attachment?I have seen this effect in Howland constant current source.

author: danadak
author_rank: Super Contributor
timestamp: December 20, 2016, 01:56:57 am
content: An amplifier, such as a simple CE BJT, has an input Z. This amp hasdegenerative feedback from R6 and R4. Without circuit values I cannottell how much, in order to predict G and Zin.Here is a straightforward way of calcing it -http://www.electronics-tutorials.ws/amplifier/input-impedance-of-an-amplifier.htmlThe idea of a buffer is to isolate load changes to its preceding circuit. You can calculate thisby examining sensitivity ( d Zin/ d Load ) and normalizing it.http://www.embedded.com/design/real-time-and-performance/4007541/Analyzing-circuit-sensitivity-for-analog-circuit-designRegards, Dana.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 20, 2016, 02:11:45 am
content: Thank you sir dana.For the calculation, kindly see the attachment.Things might be very basic, lets study carefully your references.I want to share a book that is very interesting may be, kindly find it here,https://bgaudioclub.org/uploads/docs/Crystal_Oscillator_Circuits_Krieger_Matthys.pdfDont you believe this book could give me how efficiently I can apply crystal in a circuit?Now, from your huge expertise, suggest me examples of CMOS or any ICs who can do the same operation.

author: danadak
author_rank: Super Contributor
timestamp: December 20, 2016, 01:25:09 pm
content: Here is your forward G and Zin sims, attached.Note operating point, I think bias could improve Ic, hence gm, therefore moreG.Regards, Dana.

author: danadak
author_rank: Super Contributor
timestamp: December 20, 2016, 01:27:46 pm
content: Questions -1) What is clock for ?2) Load environment for clock, 50 ohms, hi z ...?3) Clock frequency ?4) Clock tolerance, jitter ?5) What is clock for ?Regards, Dana.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 21, 2016, 01:38:41 am
content: Dear Sir Dana,Mind-blowing simulation and analysis you did!My LT spice was telling it cant simulate large number of point or several sub circuit, I gave up after 2 months, now using Muiltisim.Anyway, lets concentrate on calculation,Can we take Beta ( ? ) of the transistor as 100?In theory, the quiescent current with no input signal flows through the Collector and Emitter of the transistor, then we can say that, IC = IE = IQHow do you improve Ic? You mean by changing the values of biasing resistors ?The voltage across R5 here is 7.62v.(voltage divider rule)Similarly we can calculate voltage across R4.Looking at your simulation, its interesting to see at this operating point gain drops below 1Kz and goes up until 10Mhz. Does it mean a good range of BW to having gain by 2N3904?Could you kindly explain why?Need to think whats going on in second graph.How you will explain G and Zin sims?If the input capacitor is 1n and your input AC signal has particular source frequency, we can find capacitor impedance.As we have a crystal in first stage which is making oscillation, it could have frequency range 1.5 MHz to 8 MHz.Function can be modified to change the frequency of RC components (R1, C1, and C2).QuoteAre not you talking about clock of crystal?QuoteThis question seems like you are talking about output impedance ?QuoteIn my explanation.QuoteI have made this circuit on pcb , but didn't sit under a scope.Yes you picked-up a reasonable factor here to compare signals.If anything come in your mind to consider, let me know.Next step to count the oscillation number.