Upload
john-shuman
View
233
Download
0
Embed Size (px)
Citation preview
8/13/2019 Ch23 Oscillator Circuits1
1/31
112/16/2013
Chapter 23 Oscillator Circuits
Applications of Electronic Devices
225
Andrew E. Milks PE
8/13/2019 Ch23 Oscillator Circuits1
2/31
212/16/2013
Chapter 23 Oscillator Circuits
Positive Feedback and Oscillators
Phase Shift Oscillator
Wien Bridge Oscillator
Tuned Oscillator
Crystal Oscillator
555 Timer
Voltage Controlled Oscillator
8/13/2019 Ch23 Oscillator Circuits1
3/31
312/16/2013
Chapter 23 Oscillator Circuits
Positive Feedback
8/13/2019 Ch23 Oscillator Circuits1
4/31
412/16/2013
Chapter 23 Oscillator Circuits
Positive Feedback
Causes the system to become unstable (oscillate)
and increase the size of the output
8/13/2019 Ch23 Oscillator Circuits1
5/31
512/16/2013
Chapter 23 Oscillator Circuits
Phase Shift Oscillator
Gain must be high enough to cause oscillation
8/13/2019 Ch23 Oscillator Circuits1
6/31
612/16/2013
Chapter 23 Oscillator Circuits
Phase Shift Oscillator
Gain must be high enough to cause oscillation
The RC components cause a total shift of 180 degrees
62
1
RCf
8/13/2019 Ch23 Oscillator Circuits1
7/31
712/16/2013
Chapter 23 Oscillator Circuits
Phase Shift Oscillator
Practical FET and BJT phase shift oscillators
62
1
RCf
8/13/2019 Ch23 Oscillator Circuits1
8/31
812/16/2013
Chapter 23 Oscillator Circuits
Phase Shift Oscillator
Practical FET and BJT phase shift oscillators
62
1
RCf
8/13/2019 Ch23 Oscillator Circuits1
9/31
912/16/2013
Chapter 23 Oscillator Circuits
Wien Bridge Oscillator
If and
22112
1
CRCR
fo
2121 , CCRR 24
3
R
R
RCfo
2
1
8/13/2019 Ch23 Oscillator Circuits1
10/31
1012/16/2013
Chapter 23 Oscillator Circuits
Wien Bridge Oscillator
8/13/2019 Ch23 Oscillator Circuits1
11/31
1112/16/2013
Chapter 23 Oscillator Circuits
OP AMP Wien Bridge Oscillator
8/13/2019 Ch23 Oscillator Circuits1
12/31
1212/16/2013
Chapter 23 Oscillator Circuits
Tuned Oscillator
Based on the resonant frequency
eqeq
oCL
f2
1
8/13/2019 Ch23 Oscillator Circuits1
13/31
1312/16/2013
Chapter 23 Oscillator Circuits
Colpitts FET Tuned Oscillator
Based on the resonant frequency
C1 and C2 can be considered to be in series since no currentflows in to the gate
21
212
1
CC
CCL
fo
8/13/2019 Ch23 Oscillator Circuits1
14/31
1412/16/2013
Chapter 23 Oscillator Circuits
Colpitts BJT Tuned Oscillator
Based on the resonant frequency
C1 and C2 are in series
21
212
1
CC
CCL
fo
8/13/2019 Ch23 Oscillator Circuits1
15/31
1512/16/2013
Chapter 23 Oscillator Circuits
Colpitts Op Amp Tuned Oscillator
Based on the resonant frequency
C1 and C2 are in series
21
212
1
CC
CCL
fo
8/13/2019 Ch23 Oscillator Circuits1
16/31
1612/16/2013
Chapter 23 Oscillator Circuits
Hartley Tuned Oscillator
Based on the resonant frequency
Similar to Colpitts exceptL1 and L2 are in series
The combination is parallel with C
M is the mutual inductance
CMLLCLf
eq
o)2(2
1
2
1
21
8/13/2019 Ch23 Oscillator Circuits1
17/31
1712/16/2013
Chapter 23 Oscillator Circuits
Crystal Oscillator
Applying voltage to a crystal causes oscillations
Each crystal oscillates at 2 frequencies f1 when connected inseries f2 when connected in parallel which can be amplified in an
oscillator
8/13/2019 Ch23 Oscillator Circuits1
18/31
8/13/2019 Ch23 Oscillator Circuits1
19/31
1912/16/2013
Chapter 23 Oscillator Circuits
Crystal Oscillator
Series square wave oscillator circuit (f1)
8/13/2019 Ch23 Oscillator Circuits1
20/31
2012/16/2013
Chapter 23 Oscillator Circuits
Crystal Oscillator
Parallel oscillator circuit (f2)
8/13/2019 Ch23 Oscillator Circuits1
21/31
2112/16/2013
Chapter 23 Oscillator Circuits
Crystal Oscillator
Miller parallel oscillator circuit (f2)
8/13/2019 Ch23 Oscillator Circuits1
22/31
2212/16/2013
Chapter 23 Oscillator Circuits
IC Timers 555
Modes of operation
Astable
square wave oscillator Monostable one shot pulse generator
Both modes are based on capacitor charging and
discharging
8/13/2019 Ch23 Oscillator Circuits1
23/31
2312/16/2013
Chapter 23 Oscillator Circuits
IC Timers 555
Function blocks
2 comparators RS flip flop
Capacitor
discharging BJT
switch
8/13/2019 Ch23 Oscillator Circuits1
24/31
2412/16/2013
Chapter 23 Oscillator Circuits
IC Timers 555
Astable Oscillator
Output is on (high) whencapacitor is charging through 2
resistors
Output is off (low) when
capacitor is discharging
through 1 resistor
Note the duty cycle cannot be
50%
8/13/2019 Ch23 Oscillator Circuits1
25/31
2512/16/2013
Chapter 23 Oscillator Circuits
IC Timers 555
Astable Oscillator
CRTT
CRRTT
BlowOFF
BAhighON
)(7.0
)(7.0
8/13/2019 Ch23 Oscillator Circuits1
26/31
2612/16/2013
Chapter 23 Oscillator Circuits
IC Timers 555
Mono stable One Shot
One output pulse for each timethe circuit is triggered
CRTTT PhighON )(1.1
8/13/2019 Ch23 Oscillator Circuits1
27/31
2712/16/2013
Chapter 23 Oscillator Circuits
Voltage Controlled Oscillator
VCO 556
The oscillator output frequency
depends on the input
modulation voltage
Square and triangular wave outputs
available
V
VV
CRf Co
11
2
CV
8/13/2019 Ch23 Oscillator Circuits1
28/31
2812/16/2013
Chapter 23 Oscillator Circuits
Voltage Controlled
Oscillator VCO 556
V
VV
CRf Co
11
2C
V
8/13/2019 Ch23 Oscillator Circuits1
29/31
2912/16/2013
Chapter 23 Oscillator Circuits
Voltage Controlled
Oscillator VCO 556
HzV
VV
CRf Co 8.31
2
11
CV
8/13/2019 Ch23 Oscillator Circuits1
30/31
3012/16/2013
Chapter 23 Oscillator Circuits
Phase Locked Loop PLL 565
Used in communication
circuits
Square wave output
Closed loop operation
The output signal is
compared to a reference and
adjusted to get the same zero
crossing
8/13/2019 Ch23 Oscillator Circuits1
31/31
3112/16/2013
Chapter 23 Oscillator Circuits
Phase Locked Loop PLL 565
Used in communication
circuits
Frequency Demodulation
FM
Frequency Synthesis
multiples of the fundamentalinput locked in phase