rc op amps instrumentation lecture
TRANSCRIPT
-
7/27/2019 Rc Op Amps Instrumentation Lecture
1/22
ECE201 Lect-20 1
RC Op-Amp Circuits (5.4)
Dr. Holbert
November 14, 2002
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
2/22
ECE201 Lect-20 2
Digital Meters and Oscilloscopes
Most multimeters and oscilloscopes are now
digital.
A digital multimeter or a digital oscilloscope
has an analog-to-digital (A/D) converter.
Most digital meters and all digital
oscilloscopes have one or more processors.
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
3/22
ECE201 Lect-20 3
Data Acquisition Systems
In many applications, digital meters and
scopes are being replaced by data
acquisition cards that fit into a computer.
The data acquisition cards have A/D
converters.
The computer provides processing andstorage for the data.
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
4/22
ECE201 Lect-20 4
A Generic Digital Meter
Input Switching
and Ranging
Amplifier
A/D Converter
ProcessorDisplay
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
5/22
ECE201 Lect-20 5
Voltage Measurements
Hi Com
10V
1V
100V
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
6/22
ECE201 Lect-20 6
Model for Meter
The ideal metermeasures the voltage acrossits inputs. No current flows into it; it hasinfinite input resistance.
10M Ideal Meter
Hi
Com
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
7/22
ECE201 Lect-20 7
10M Ideal Meter
Hi
ComR
Meter Loading
The 10M meter resistance in parallel withRmay change the voltage that you measure.
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
8/22
ECE201 Lect-20 8
Loading
When measuring the voltage acrossR, we
need to make sure thatR is much less than
10M. IfR is close to 10M, significant current
flows through the meter, changing the
voltage acrossR.
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
9/22
ECE201 Lect-20 9
Loading Example
Without Meter: voltage is 100V
With Meter: measured voltage is 83.3V
10M Ideal Meter
Hi
Com2M50A
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
10/22
ECE201 Lect-20 10
Current Measurements
AmpCom
10V
1V
100V
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
11/22
ECE201 Lect-20 11
Measuring Large Currents
(> 100mA)
The current to be measured is passed
through a small resistor (called ashuntresistor) and the resulting voltage across the
shunt resistor is measured.
From the voltage, the current can be
computed.
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
12/22
ECE201 Lect-20 12
Rs Ideal Meter
Amp
ComR
Meter Loading
TheRs shunt resistance in series withR maychange the current that you measure.
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
13/22
ECE201 Lect-20 13
The Voltage Follower
vin
+
vout
+
+
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
14/22
ECE201 Lect-20 14
Without a Voltage Follower
vA/D
is not equal to vs
vs
Rs
RA/D
+
vA/DSensor A/D
Converter+
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
15/22
ECE201 Lect-20 15
Op-Amp Review
The idealop-amp model leads to the
following conditions:
i+ = i- = 0
v+ = v-
The op amp will set the output voltage to
whatever value results in the same voltages
at the inputs.
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
16/22
ECE201 Lect-20 16
Op-Amp Review
To solve an op-amp circuit, we usually
apply KCL (nodal analysis) at one or both
of the inputs.
We then invoke the consequences of the
ideal model.
We solve for the op-amp output voltage.
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
17/22
ECE201 Lect-20 17
With a Voltage Follower
vA/D
is equal to vs
vsR
s
Sensor
RA/D
+
vA/D
A/DConverter
+
+
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
18/22
ECE201 Lect-20 18
An Integrator
+Vin
+
Vout
R
C
+
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
19/22
ECE201 Lect-20 19
KCL at the Inverting Input
+vin
(t)+
R
C
vout
(t)
iR
(t)
iC(t)
i-
+
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
20/22
ECE201 Lect-20 20
KCL0=i
R
tv
R
vtv
ti ininR)()(
)( =
=
( )
dt
tdvC
dt
vtvdCti
outout
C
)()()( =
=
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
21/22
ECE201 Lect-20 21
Solve forvout(t)
0)()(=+
dt
tdvC
R
tvoutin
RC
tv
dt
tdvinout
)()(=
dxRC
xv
tv
t
in
out
=)(
)(
PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/ -
7/27/2019 Rc Op Amps Instrumentation Lecture
22/22
ECE201 Lect-20 22
Class Example
Learning Extension E5.9
PDF created with pdfFactory trial version www pdffactory com
http://www.pdffactory.com/http://www.pdffactory.com/http://www.pdffactory.com/