astable multivibrators ©paul godin created february 2007 modified march 2015 oscillator basics...
TRANSCRIPT
![Page 1: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/1.jpg)
Astable Multivibrators
©Paul GodinCreated February 2007Modified March 2015
Oscillator Basics
Technician Series
![Page 2: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/2.jpg)
Definitions
◊ Astable◊ No stable state◊ Produces alternate high/low states
◊ Astable Multivibrators are also known as:◊ Clocks◊ Oscillators
astable 1.2
![Page 3: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/3.jpg)
Uses of Astables
◊ Provide edges for edge-triggered devices◊ flip-flops◊ counters◊ shift registers◊ Digital to Analog / Analog to Digital converters◊ microprocessors◊ communications, etc…
◊ Can provide sound for certain applications◊ practical audible sound in the 100Hz to 5kHz range◊ exercise caution when applying square waves
to speakers
astable 1.3
![Page 4: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/4.jpg)
Period and Duty Cycle
◊ Duty cycle describes the ratio of the time in the high state versus the overall period of the pulse.
%100tt
tD.C.
LH
H
T
tH tL
Review
astable 1.4
![Page 5: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/5.jpg)
Does Duty Cycle Matter?
◊ To an edge-triggered device, does the duty cycle affect its operation?
◊ If a 10% D.C. clock is applied to the following circuit, what is the output D.C.?
Review
astable 1.5
![Page 6: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/6.jpg)
Square waves and speakers
◊ Cautions:◊ The average power for a square wave is higher than
for a sine wave with the same peak voltage. Speaker coil damage may result.
◊ A speaker is an electro-mechanical device. It is physically unable to produce the instantaneous motion of a square wave. Damage to the cone and physical structure may result.
◊ Speakers have a low impedance and likely represents a greater load than the driving circuit is capable of handling. Damage to the driving circuit may result.
!
astable 1.6
![Page 7: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/7.jpg)
Speaker Interfaces
◊ Use cheap speakers!◊ Keep the output voltages low.◊ Use an output device that can handle the load.◊ Filter the output square waves
◊ Use an RC circuit in series.◊ Use an audio transformer.
Discussion in class
astable 1.7
![Page 8: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/8.jpg)
Schmitt-Triggered Oscillators
astable 1.8
![Page 9: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/9.jpg)
Oscillator Circuits
◊ Describe the output for the following device:
astable 1.9
![Page 10: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/10.jpg)
Oscillator Parameters
◊ In the previous oscillator circuit:◊ What determines the output frequency?◊ What is the waveform of the output?◊ What determines the duty cycle?
◊ How can we slow the process down?
In-Class Discussion
astable 1.10
![Page 11: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/11.jpg)
Controlling the Simple Oscillator
◊ The output frequency of the oscillator can be adjusted by adding an RC to the circuit:
astable 1.11
![Page 12: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/12.jpg)
Schmitt Oscillator
◊ The separation between Vt+ and Vt- can be used to create an oscillating circuit.
◊ An RC network is used to control the oscillation rate by controlling the charge and discharge time of the capacitor voltage.
◊ Easy oscillator to build. Used where precise or accurate frequency isn’t necessary.◊ displays◊ visual effects
astable 1.12
![Page 13: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/13.jpg)
Simple Oscillator Output
Vc: Charge/Discharge Cycle
Discharge Time
Charge Time
Oscillator Animationastable 1.13
![Page 14: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/14.jpg)
Schmitt Trigger Oscillator Control
Schmitt Triggered Oscillators may be controlled by the use of RC circuits.
To achieve a specific frequency, the values of R and C may be calculated.
astable 1.14
![Page 15: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/15.jpg)
The Simple Schmitt Oscillator
◊ Advantages:◊ Easy to build◊ Fair range of frequency◊ Small footprint
◊ Disadvantages:◊ Unstable, as the frequency will vary with temperature
variations.◊ Difficult to predict values due to the range of Vt+ and
Vt- between different gates, even within the same IC package.
astable 1.15
![Page 16: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/16.jpg)
Crystal Oscillators
astable 1.16
![Page 17: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/17.jpg)
Crystal Oscillators
◊ Crystal Oscillators are commonly used in conjunction with microprocessors, communications circuits and other frequency-sensitive devices because of their:◊ reliability◊ stability◊ accuracy◊ ease of use
Symbol
astable 1.17
![Page 18: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/18.jpg)
Crystal Oscillators
◊ A crystal oscillator is constructed from a piece of quartz crystal that is cut and shaped to the appropriate size.
◊ A property called piezoelectricity happens with quartz crystals.◊ If pressure is applied, it creates voltage◊ If voltage is applied, it physically vibrates
◊ When a voltage is applied to the crystal, it vibrates at a very specific frequency.
◊ Crystal oscillators commonly require small capacitors to aid with the back-and-forth voltage, and require a source of current.
astable 1.18
![Page 19: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/19.jpg)
Crystal Oscillator Circuits
There are many different configurations for crystal oscillators. Following are some examples of basic circuits:
astable 1.19
![Page 20: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/20.jpg)
Crystal Oscillator Circuits
There are many other ways to create a stable oscillation with crystals.
astable 1.20
![Page 21: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/21.jpg)
Crystal Oscillator Circuits
astable 1.21
![Page 22: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/22.jpg)
Crystal Oscillators
◊ Crystal Oscillators are often packaged in an oval-shaped metallic “can”.
◊ Those with 2 leads require external circuitry; those with 4 leads typically already possess the internal circuitry required to produce the oscillation (voltage and ground needs to be applied).
astable 1.22
![Page 23: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/23.jpg)
Operation of the Simple Oscillator
0
1- Logic 0 read by input of inverter.
1
2-Output becomes logic 1.
5- The capacitor discharges to
VT-.
4-Output becomes logic 0.
0
3- Capacitor voltage increases to VT+. The gate senses a
logic 1 input.
1
Animated
astable 1.23
![Page 24: Astable Multivibrators ©Paul Godin Created February 2007 Modified March 2015 Oscillator Basics Technician Series](https://reader033.vdocument.in/reader033/viewer/2022052702/56649f0d5503460f94c21e27/html5/thumbnails/24.jpg)
©Paul R. Godinprgodin°@ gmail.com
END
astable 1.24