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CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Operational Amplifiers (OpAmps) and Comparators
Signal Conditioning, Buffering, Etc.
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Operational Amplifier
+
- Characteristics
Infinte GainDraws No Input Current
Difference Amplifier
V+ > V- then the output is driven in the Positive direction
V- > V+ then the output is driven in the Negative direction
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Operational Amplifier
+
- Characteristics
Infinte GainDraws No Input Current
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
+
-
Vout
Vin
How do we use Op-Amps then?
Negative Feedback
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
The Golden Rules:Apply only when the op-amp is operated:
Within its listed specifications
In Negative Feedback
1) The Inputs Draw no Current
2) The inverting and Non-inverting inputsremain at the same voltage
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
The Golden Rules:Apply only when the op-amp is operated:
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
+
- R1
R2
A
B
Vout Vin
Inverting Amplifier
Vout
R2 R1
-Vin =
Vout
Vin
R2
R1 = -
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
+
- R1
R2
A
B
Vout Vin
Inverting Amplifier
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
+
- R1
R2
A
B
Vout
Vin
Non-Inverting Amplifier
= Vin R1
Vout R1 + R2
= Vin R1
Vout R2 1 +
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
+
- R1
R2
A
B
Vout
Vin
Non-Inverting Amplifier
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
+
-
Vout
Vin
=
Non-Inverting Buffer
Vin Vout
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Vin
Source Resistance
True
PerceivedVin
+
- R1
R2
A
B
Vout
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
What Happens to the output if we tie the two inputs together?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Input Offset Voltage
V
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Input Offset Voltage Specifications
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Effects of Input Offset Voltage
+ V
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Input Bias Current
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Input Bias Current Specifications
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Can We Correct for Input Bias Current?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Does that fix the bias current problem?
Not Quite
The two bias currents are not exactly equal
This is the Input Offset Current
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Does that fix the bias current problem?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Output Voltage Limitations
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Output Voltage Specifications
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
The Importance of Test Conditions“RL = 2k”
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Specifications that you shouldn’t use:
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Specifications that you shouldn’t use:
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
+
- R1
R2
A
B
Vout
Vin
What is the minimum values for R1 & R2 if Vout is driving a 10k load and we want to achieve a 3.3V output?
LM324
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Frequency Effects
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Large Signal Frequency Response
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
0 .00 0u 20 .0 0u 40 .0 0u 60 .0 0u 80 .0 0u 10 0 .0uTim e (s )
(V
)
10.00
9.000
8.000
7.000
6.000
5.000
4.000
3.000
2.000
1.000
0 .000
ou tp u t
in pu t*10
Slew Rate Effects
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
0 .00 0u 2 .00 0u 4 .00 0u 6 .00 0u 8 .00 0u 10 .0 0uTim e (s )
(V
)
10.00
9.000
8.000
7.000
6.000
5.000
4.000
3.000
2.000
1.000
0 .000
ou tp u t
in pu t*10
Extreme Slew Rate Effects
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
P a r a m e ter L M 3 2 4 L M 6 1 4 4 L M C 6 4 8 4 L M C 6 4 9 4In p u t O ffse t Vo ltag e 7 m V 3 .3 m V 3 .7 m V 6 .8 m VIn p u t B ia s C u rren t 2 5 0 n A 5 2 6 n A 4 p A 2 0 0 p AIn p u t O ffse t C u rre n t 5 0 n A 8 0 n A 2 p A 1 0 0 p AO u tp u t Vo lta g e H i @ 1 0 K 3 .5 V 4 .8 7 VO u tp u t Vo lta g e L o @ 1 0 K 0 .0 2 V 0 .0 5 VO u tp u t Vo lta g e H i @ 2 K 3 V 4 .8 V 4 .7 V 4 .7 VO u tp u t Vo lta g e L o @ 2 K 0 .1 3 0 .2 4 V 0 .2 4 VO u tp u t Vo lta g e H i @ 6 0 0 4 .2 4 V 4 .2 4 VO u tp u t Vo lta g e L o @ 6 0 0 0 .6 5 V 0 .6 5 VU n ity G a in B a n d w id th 1 M H z 6 M H z 1 .5 M H z 1 .5 M H zS lew R a te 0 .4 2 V /S 11 V /S 0 .6 3 V /S 0 .5 V /SIn p u t C o m m o n M o d e R a n g e 0 -3 .5 V 0 -5 V 0 -5 V 0 -5 VC o st @ 1 k $ 0 .0 8 8 $ 2 .8 0 $ 1 .3 9 $ 1 .5 9Te m p e ra tu re R a n g e 0 ° – 7 0 ° C -4 0 ° – 8 5 ° C -4 0 ° – 8 5 ° C -4 0 ° – 1 2 5 ° C
A Comparison of Some Op-Amps
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Questions?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
What is This?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
How might you use it?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Without With
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
How do you achieve it?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Eliminating the separate VREF
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
What’s going on?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Inverting Comparator Design ProcedureTrip point at 1.5V, 0.25V Hysterisis
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
The Non-Inverting configuration:
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
How does this circuit Behave?
R1=3k, R2=R3=1KVin sweeps from 0-5V
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
How about this one?
Vin = 5 to -5V Sin
What are the thresholds?