05 signal conditioning - amplifiers + filterselektro.umk.ac.id/1qbal/si/materi/04 signal...
Transcript of 05 signal conditioning - amplifiers + filterselektro.umk.ac.id/1qbal/si/materi/04 signal...
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Signal Conditioningmohammad iqbal� [email protected]
Teknik Elektro
Universitas Muria Kudus
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Signal Conditioning
1. Introduction to signal conditioning
2. Bridge circuits
3. Amplifiers
4. Filters
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Amplifiers
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Op amp characteristic
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Summing amplifier
+−= 2
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1
2 VR
RV
R
RVout
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Noninverting amplifier
inout
outinin
VR
RV
R
VV
R
V
II
+=
=−+
=+
1
2
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21
1
0
0
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Exercise 7
Design a high impedance
amplifier with a voltage
gain of 42 if R1 = 1 kΩ is
chosen.
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Differential amplifier
( )CMRRCMRA
ACMRR
VVV
cm
bacm
10log20
2
=
=
+=
( )baout VVAV −=• The transfer function;
• Common mode rejection;
( )121
2 VVR
RVout −=
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Voltage-to-Current converter
( )
( )
543
354
42531
31
2
RRR
RI
VRR
R
RRRRR
VRR
RI
m
sat
ml
in
++
−+
=
=+
−=
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Current-to-Voltage converter
IRVout −=
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Integrator
tRC
KV
dtVRC
V
dt
dVC
R
V
out
inout
outin
−=
−=
=+
∫1
0
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Exercise 8
Use an integrator to
produce a linear ramp
voltage rising at 10 V per
ms. Determine the R and C.
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Differentiator
dt
dVRCV
R
V
dt
dVC
inout
outin
−=
=+ 0
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Linearization
( )
=
=+
R
VGV
VIR
V
inout
outin 0
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Linearization
( ) ( )
( ) ( )RIVV
VIVI
eincout
outout
0
0
log1
log1
exp
αα
α
−=
=
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Filters
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Filters
• Filter : a circuit that is designed to pass signals with desired frequencies and reject or attenuate others
• 4 types of filters:
1. Low-pass filter: passes low frequencies and stops high frequencies
2. High-pass filter: passes high frequencies and rejects low frequencies
3. Band-pass filter: passes frequencies within a frequency band and blocks or attenuates frequencies outside the band
4. Band-reject filter: passes frequencies outside a frequency band and blocks or attenuates frequencies within the band
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Low-pass RC filter
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Low-pass RC filter
• Critical frequency:
• Output-to-input voltage ratio:
RCfc π2
1=
( )2/11
cin
out
ffV
V
+=
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Exercise 9
A measurement signal has a frequency less than
1 kHz, but there is unwanted noise at about 1
MHz. Design a lowpass filter that attenuates the
noise to 1% if a capacitor 0.01 µF has been
used. What is the effect on the measurement
signal at its maximum of 1 kHz?
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High-pass RC filter
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High-pass RC filter
• Critical frequency:
• Output-to-input voltage ratio:
RCfc π2
1=
( )( )2/1/
c
c
in
out
ff
ff
V
V
+=
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Exercise 10
Pulses for a stepping motor are
being transmitted at 2000 Hz.
Design a highpass filter to reduce
60 Hz noise and reduce the pulses
by no more than 3 dB.
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Design Methods
1. Determine critical frequency, fc
2. Select standard capacitor (µF – pF)
3. Calculate required resistance (1 kΩ - 1 MΩ)
4. Use nearest resistance standard value to
calculated value
5. Consider tolerance in resistors and capacitors
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Practical considerations
1. Very small resistance -> lead to large currents and
loading effects -> avoid large capacitance
(R= kΩ -MΩ, C= µF – pF)
2. The exact fc is not important, choose R and C of
approximately to the fc
3. Isolation filter input/output with voltage follower
4. Cascade RC filters to improved fc sharpness ->
consider loading
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Band-pass RC filter
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Band-pass RC filter
• Critical frequency:
• Output-to-input voltage ratio:
HHL CR
fπ2
1=
( ) ( )[ ]
L
H
HLLH
H
in
out
R
Rr
ffrffff
ff
V
V
=
+++−=
2222 1
LLH CR
fπ2
1=
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Exercise 11
A signal conditioning system uses a frequency
variation from 6 kHz to 60 kHz to carry
measurement information. There is considerable
noise at 120 Hz and at 1 MHz. Design a
bandpass filter to reduce the noise by 90%.
What is the effect on the desired passband
frequencies if r = 0.01? Determine all the
resistors and capacitors.
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Band-pass RC filter
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Band-reject RC filter
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Twin-T notch filter
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Twin-T notch filter
• Critical frequency:
• Grounding resistor and capacitor:
cn ff 785.0= RCfC π2
1=
cH ff 57.4=cL ff 187.0=
101R
Rπ=
πC
C10
1 =