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CH6 OPERATIONAL AMPLIFIER
140
Transcript
OPERATIONAL AMPLIFIER
OPERATIONAL AMPLIFIER : OPAM
A NEW LINEAR ACTIVE ELEMENT
- THIS ELEMENT HAS THREE TERMINALS NOT LIKE THE OTHER ELEMENTS.
- TWO DC-POWER SOURCES ARE REQUIRED FOR THIS ELEMENT TO RUN.
- IT IS CONSIDERED AS AN ELEMENT
- BUT THERE IS A CIRCUIT IN IT
- WHICH INCLUDES DEPENDENT SOURCES (TRANSISTORS)
OPAM'S REGIONS: LINEAR, SATURATION
OUTPUT: V0
OPAM'S REGIONS: LINEAR, SATURATION
"A: Open loop gain"
- is in the range of 100000.
- In order to keep the input voltage (Vp-Vn) in small voltage range,
- negative feedback is required.
"If the output voltage (V0)"
- is in the [V-;V+] region then OPAM is in linear region,
- otherwise it is in saturation region.
INPUT: Vp-Vn
LINEAR REGION
SATURATION REGION
IDEAL OPERATIONAL AMPLIFIER
IDEAL OPAM
- Vp, Vn: node voltages
- Vp-Vn=0 virtually short circuit
- ip=0,in=0: almost open circuit, input resistance is in Mega-ohms region
- This OPAM definition relation is mathematically simple, therefore it is ideal
- Alternative equivalent circuit which composed of three elements will be be given later .
EXAMPLE
In order to keep the OPAM in linear region, what should be the Vb voltage?
EXAMPLE SATURATION/LINEAR
OPAM
IN PRACTICE
OPAM USAGE IN PRACTICE
INVERTING AMPLIFIER -Vo/Vs
INVERTING AMPLIFIER
- Output voltage is independent of the load, what does this mean?
- Vs and Rs could be considered as "Thevenin equivalent" of a pre- circuit which is connected as cascade.
- (V0/Vs) is called as "gain" of the amplifier.
- How gain is controlled?
NONINVERTING AMPLIFIER Vo/Vs
NON INVERTING AMPLIFIER
Linearity constrain:
How gain is controlled?
Gain is independent of what?
SUMMATION AMPLIFIER
SUMMATION AMPLIFIER
How to control this summation, Interpretation?
DIFFERENCE AMPLIFIER
DIFFERENCE AMPLIFIER
How the difference is controlled?
Strain gauge is example
BUFFER
BUFFER
- Voltage source resistance is not effective!
- Compare RL element's power when OPAM in and out?
PROBLEM
PROBLEM
- Assume that Vs and Rs represents Thevenin equivalence of a linear circuit and RL is output element.
- Find out RL resistor's power
for the given two circuits: Which circuit transfer most power to the RL load
- Discuss the blue marked OPAM effect on the power transferred to RL load for the given two circuits.
- You could give numerical values to all the parameters.
INDEPENDENT CURRENT SOURCE
- Load current does not depend on RL.
- Definition relation of independent current source
INDEPENDENT CURRENT SOURCE
MORE REALISTIC MODEL OF OPAM
ALTERNATIVE MODEL FOR OPAM
MOE REALISTIC MODEL
(=EQUIVALENT CIRCUIT)
VS
IDEAL OPAM DEFINITION RELATION
INVERTING AMPLIFIER
INVERTING AMPLIFIER
NON INVERTING AMPLIFIER
NON INVERTING AMPLIFIER
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