• Lecture 16: Crystal oscillator
ECEN 1400 Introduction to Analog and Digital Electronics
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
• Lecture 16: Crystal oscillator
ECEN 1400 Introduction to Analog and Digital Electronics
The Crystal Oscillator
Packages
http://circuit-diagram.net/quartz-crystal-oscillator
Physics
Symbol
Abbreviation
Robert R. McLeod, University of Colorado
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.
166
• Lecture 16: Crystal oscillator
ECEN 1400 Introduction to Analog and Digital Electronics
Internal structure
Quartz crystal oscillator
1
2
3
4
http://www.mtronpti.com/pdf/
contentmgmt/
understanding_quartz_crystals.pdf
1.
2.
3.
4.
http://en.wikipedia.org/wiki/
File:InsideQuartzCrystal.jpg
http://electronic-components.co/
index.php?main_page=index&cPath=4
Very thin slice of a synthetic (grown) quartz rod
Deposited metal (gold, silver, aluminum) electrodes
Physical supports / electrical connections
Bottom of case, hermetically sealed to upper case
Ceramic piezo buzzer/speaker
Robert R. McLeod, University of Colorado
http://
www.jobwerx.com/
news/gep_bizid=948214_604.html
http://lizarum.com/assignments/
physical_computing/2009/piezo.html
167
• Lecture 16: Crystal oscillator
ECEN 1400 Introduction to Analog and Digital Electronics
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)
Gain with feedback (β ≠ 0)
Vo = A( f )Vi
Vo = A( f )[Vi + β ( f )Vo ]
Vo =
A( f )
Vi
1 − β ( f )A( f )
Barkhausen criterion for oscillation: The output will grow from
noise (Vi 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
• Lecture 16: Crystal oscillator
ECEN 1400 Introduction to Analog and Digital Electronics
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
f0 = 11.25 MHz
Narrow bandwidth
Q≡
Robert R. McLeod, University of Colorado
f 0 11.25 MHz
=
= 72,000
Δf
156 Hz
169
• Lecture 16: Crystal oscillator
ECEN 1400 Introduction to Analog and Digital Electronics
Equivalent circuit of a
crystal oscillator
Multisim circuit.
•  Series resistance determined from 50/50 voltage division.
•  f 0 = 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
• Lecture 16: Crystal oscillator
ECEN 1400 Introduction to Analog and Digital Electronics
4060 oscillator + 14 bit
counter chip
Chip structure
Why these two things?,
•  Can have a higher-frequency (more accurate) oscillator, then
•  Divide it down by 214 = 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 << Rt Ct ,
then
Robert R. McLeod, University of Colorado
f osc =
1
2.3Rt Ct
http://pdf1.alldatasheet.com/datasheet-pdf/
view/17721/PHILIPS/HEF4060B.html
171
• Lecture 16: Crystal oscillator
ECEN 1400 Introduction to Analog and Digital Electronics
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
Robert R. McLeod, University of Colorado
http://pdf1.alldatasheet.com/datasheet-pdf/
view/17721/PHILIPS/HEF4060B.html
172