Lecture 16 Crystal oscillators Internal structure Analysis of a harmonic oscillator Frequency response of the crystal oscillator The 4060 oscillator driver / counter http://www.mineralminers.com/html/phantom_quartz_crystal.htm Robert R. McLeod, University of Colorado http://hilaroad.com/camp/projects/magnet.html 165
The Crystal Oscillator Packages http://circuit-diagram.net/quartz-crystal-oscillator Physics Symbol Abbreviation Greek χ pronounced ch and is used as an abbreviation for crystal, thus a crystal oscillator is XO. This is the origin of Xmas for Christmas. Robert R. McLeod, University of Colorado 166
1 2 Internal structure Quartz crystal oscillator 4 3 http://www.mtronpti.com/pdf/ contentmgmt/ understanding_quartz_crystals.pdf http://en.wikipedia.org/wiki/ File:InsideQuartzCrystal.jpg http://electronic-components.co/ index.php?main_page=index&cpath=4 1. Very thin slice of a synthetic (grown) quartz rod 2. Deposited metal (gold, silver, aluminum) electrodes 3. Physical supports / electrical connections 4. Bottom of case, hermetically sealed to upper case Ceramic piezo buzzer/speaker http:// www.jobwerx.com/ news/gep_bizid=948214_604.html http://lizarum.com/assignments/ Robert R. McLeod, University of Colorado physical_computing/2009/piezo.html 167
Basic harmonic oscillator structure Positive feedback system (β>0) Input voltage Sum Amplifier with gain A Output voltage A( f ) Feedback β ( f ) http://www.ligo.caltech.edu/~vsanni/ph5/pdf/ph5.chapter.basicsonoscillators.pdf Gain without feedback (β= 0) V = o A ( f ) V i Gain with feedback (β 0) Vo = A( f )[ Vi + β ( f ) Vo ] A( f ) V = V o 1 β ( f ) A( f ) i Barkhausen criterion for oscillation: The output will grow from noise (V i almost 0) when (βa)=1+j0. This will occur first for a specific frequency f. Robert R. McLeod, University of Colorado http://www.electronics-tutorials.ws/oscillator/oscillators.html 168
Frequency response of a crystal oscillator Multisim circuit. The series resistor has been adjusted to give 50/50 voltage division at the resonant frequency. AC analysis showing voltage across the crystal. Δf = 156 Hz f 0 = 11.25 MHz Narrow bandwidth Q f Δ f 11.25 MHz 156 Hz 0 = = 72,000 Robert R. McLeod, University of Colorado 169
Equivalent circuit of a crystal oscillator Multisim circuit. Series resistance determined from 50/50 voltage division. f0 = 1 ( 2π LC ) Other values typical of XOs C1 is due to electrodes C2 & L1 are resonating xtal R1 is mechanical loss AC analysis showing voltage across the model crystal. Response is not perfectly identical, so my model values are not quite right. Robert R. McLeod, University of Colorado 170
4060 oscillator + 14 bit Chip structure counter chip Why these two things?, Can have a higher-frequency (more accurate) oscillator, then Divide it down by 2 14 = 16384 Very common crystal oscillator is 32,768 Hz, resulting in 2 Hz output. Note only highest 10 bits of counter available Generally only last (pin 3) is used RC Relaxation oscillator, similar to 555 timer if Rt << R2, R2C2 then f osc << 1 = 2.3R C t t R C t t, http://pdf1.alldatasheet.com/datasheet-pdf/ Robert R. McLeod, University of Colorado view/17721/philips/hef4060b.html 171
4060 and crystal oscillator Details The multisim 4060 model seems to be broken, so we can t simulate Crystal oscillators are touchy they work or they don t You need to build this very tight stray capacitance and inductance of wires can influence the results. Don t attach scope probes to the analog portion of the circuit, instead probe the buffered output, pin 9 Thus, I recommend you build your clock with a 555 relaxation oscillator, then build a separate circuit with the XO and 4060 that you can wire in if/when it works. This solves the multisim/ultiboard problem as well http://pdf1.alldatasheet.com/datasheet-pdf/ Robert R. McLeod, University of Colorado view/17721/philips/hef4060b.html 172