Signal Generators 4
description
Transcript of Signal Generators 4
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It contains an inverting amplifier, and a feedback network which 'shifts' the phase of the amplifier output by 180 degrees at the oscillation frequency.
It consists of:
An Amplifier with gain K
Three section RC network in feedback.
The circuit oscillate at the frequency for which RC Phase shift is 180
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Phase Shift Oscillator
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although two cascaded RC sections eventually provide 180 phase shift, the value of d/d at the oscillator frequency is unacceptably small.
oscillators made with two cascaded RC sections have poor frequency stability. Three equal cascaded RC sections have a much higher d/d and the resulting oscillator has improved frequency stability
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The RC phase shift oscillator
Total loop phase shift=180o-180o=0o
The frequency can be varied by varying R or C values in the phase shift network.
Feedback n/w
phase shift= 60o *3=180o
Gain N/W phase shift= -180o
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The RC phase shift oscillator
( )( )
RR
A
RCf
RC
RC
RCwhere
jVV
f
o
o
o
o
f
===
=
=
=
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1
616
06
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22
2
2
3
32
Total loop phase shift=180o-180o=0o
The frequency can be varied by varying R or C values in the phase shift network.
Feedback n/w
phase shift= 60o *3=180o
Gain N/W phase shift= -180o
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A Phase shift Oscillator with a limiter for amplitude stabilization.
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The op-amp RC oscillators are normally useful for operation in the range of 10 Hz to 100 kHz.
High-frequency oscillations in the range of 100 kHz to hundreds of MHz are obtained using LC or crystal oscillators.
LC Oscillators
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21
31
1
31
1
3120
ZZZZZZRZZAA
ZZZRZZAA
ZZZ
ZZZZwhereZR
ZAVVA
o
v
Lo
Lv
LLo
Lv
f
++++=++
=+=
+=+==
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12
2
1
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312321
21
332211
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)(0)()(
,,
XXA
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v
vv
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=
===+==++
+++====
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21
21
2121
32
21
1
1
2
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32211
&2
1,011
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1,01
1&,:
CCA
CCCCL
fLCC
LXC
XC
XOscilatorColpits
LLA
CLLf
CLL
CXLXLXOscilatorHartley
vo
vo
=+
==+
===
=+==+
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I
FV R
RA =
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CMOS Ring Oscillator.
Cascade connection of identical inverters (Odd Number)
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f = 1/(2.n.p)
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The idea of the quadrature oscillator is to use the fact that the double integral of a sine wave is a negative sine wave of the same frequency and phase, in other words, the original sine wave 180deg phase shifted.
The phase of the second integrator is then inverted and applied as positive feedback to induce oscillation
quadrature oscillator
A quadrature oscillator is a circuit that generates two periodic signals that are in quadrature, i.e., they are 90 degrees out of phase.
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Inverting integrator with a limiter
tV= (1/C) (vo1/2R) dt
0
tvo2 = 2v = (1/C)(vo1/R) dt
0Non inverting integrator
For Rf = 2R