Download Chapter 21 - La Sierra University

electronics fundamentals
circuits, devices, and applications
THOMAS L. FLOYD
DAVID M. BUCHLA
Chapter 20 (IA)
and Flash ADC
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter
IA
and Flash
1 ADC
Instrumentation amplifiers
An instrumentation amplifier (IA) is a special integrated
circuit designed for applications where small signals are in
noisy environments. They have high input impedance and a
high CMRR for excellent noise rejection.
R3 to R6 are equal
Vin1 + Vcm
values. If R1 = R2,
then the closed-loop
gain is set by a single
R
external resistor, RG, G
supplied by the user.
The gain is:
2 R Vin2 + Vcm
Acl  1 
RG
Electronics Fundamentals 8th edition
Floyd/Buchla
R3
+
- R
1
-
R2
+
R5
R4
Vout =
Acl (Vin2-Vin1)
+
R6
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter
IA
and Flash
1 ADC
Instrumentation amplifiers
For R1 = R2 = 10 kW, what value of RG will set
the gain to 40?
2R
Acl  1 
RG
Solving for RG,
2R
RG 
Acl - 1
2 10 kW 
RG 
 513 W
40 - 1
Vin1
R3
+
- R
1
RG
-
R2
Vin2
+
R5
R4
Vout
+
R6
(510 W is the nearest standard value).
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter
IA
and Flash
1 ADC
Instrumentation amplifiers
The bandwidth of instrumentation amplifiers decreases
when higher gain is selected. The frequency response is
published by the manufacturer. For example the
frequency response of an INA333 is shown.
If the required frequency response is
less than about 300 Hz, a gain of 1000
can be selected. The INA333 can
operate on as little as 1.8 V, so is used
in portable medical, handheld
instrumentation, weigh scales and data
acquisition applications.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter
IA
and Flash
1 ADC
Flash Analog-To-Digital Converter
Comparators can be used to
convert analog-to-digital (AD)
signals.
The Flash AD Converter or
Direct Conversion ADC, are
simple and extremely fast AD
converters.
More comparators are needed as
the required bit-precision
increases: 2n-1 comparators for nbits of precision.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter
IA
and Flash
1 ADC
Binary-weighted input D/A Converter
A weighted inverting summing
Operational Amplifier can be
used to convert digital-to-analog
signals.
Setting the 3 input resistor values
at multiple powers of two, the
output of the operational
amplifier represents the analog
value of the 3-bit binary data.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.