R
Rich
Guest
I'm trying to understand Op Amps first time round. Are the following
statements correct? I've rushed it a bit, so most of it might look like
nonsense.
Please correct or amplify.
1 An Op Amp is basically a DIFFERENTAL amplifier.
2 Unlike a (for want of a better word) a "regular" amplifier, an Op Amp
can have two input voltages.
3 When the Op amp is run as a DIFFERENTIAL amplifier it amplifies the
difference in voltage between the two inputs.
4 Operational amplifiers can be run as "regular" amplifiers (i.e. not
differential).
5 The Op Amp can be run from either a single supply or a split supply
6 The Op Amp run from a split supply power pins will often be
labelled Vcc + and Vcc-
(From hereon I'm a bit shaky):
I'm now trying to say where the reference point is for input and output.
Obviously it takes two points in a circuit to establish a voltage, either an
input or ouput voltage, I mean, just connecting one side of a load or a
generator or battery to one of the input or output points shown on an Op Amp
circuit is no good. I'm going to call the corresponding point the REFERENCE
POINT. I'll probably mess up here, but please correct me.
OP AMPS *NOT* SPECIALLY DESIGNED FOR SINGLE RAIL SUPPLY
SPLIT SUPPLY OPERATION
REFERENCE POINTS
INPUT
7 V+ input: The REFERENCE POINT is VCC- a negative potential with
respect to ground.
8 V- input: The REFERENCE POINT is VCC- a negative potential with respect
to ground.
9 The reverse is true (REFERENCE POINT is VCC+) if transistors are
different type (We have NPN or PNP types).
10 The REFERENCE POINT point is NOT ground.
11 With a split supply, ground (SYSTEM GROUND) is between + and - supply
voltages = 0v+ SUPPLY MIDPOINT.
OUTPUT
12 Vout: The REFERENCE POINT is ground or SUPPLY MIDPOINT = 0v = SYSTEM
GROUND
SINGLE SUPPLY OPERATION
REFERENCE POINTS
INPUT
13 Single-supply operation requires a VIRTUAL GROUND in an OP Amp stage.
14 A VIRTUAL GROUND is at a dc level above SYSTEM GROUND.
15 SYSTEM GROUND is 0v.
16 V+ input: The REFERENCE POINT is ground.
17 V- input: The REFERENCE POINT is ground.
18 Input source and output load will often be referenced to system ground.
19 If the input source of a stage is referenced to ground then the solution
is to ac couple signals to the Op Amp stage. Unless certain conditions
apply.
OUTPUT
20 Vout: The REFERENCE POINT is ground.
OP AMPS SPECIALLY DESIGNED FOR SINGLE RAIL SUPPLY
21 V+ input: The REFERENCE POINT is Ground.
22 V- input: The REFERENCE POINT is Ground.
OUTPUT
23 Vout: The REFERENCE POINT is ground.
statements correct? I've rushed it a bit, so most of it might look like
nonsense.
Please correct or amplify.
1 An Op Amp is basically a DIFFERENTAL amplifier.
2 Unlike a (for want of a better word) a "regular" amplifier, an Op Amp
can have two input voltages.
3 When the Op amp is run as a DIFFERENTIAL amplifier it amplifies the
difference in voltage between the two inputs.
4 Operational amplifiers can be run as "regular" amplifiers (i.e. not
differential).
5 The Op Amp can be run from either a single supply or a split supply
6 The Op Amp run from a split supply power pins will often be
labelled Vcc + and Vcc-
(From hereon I'm a bit shaky):
I'm now trying to say where the reference point is for input and output.
Obviously it takes two points in a circuit to establish a voltage, either an
input or ouput voltage, I mean, just connecting one side of a load or a
generator or battery to one of the input or output points shown on an Op Amp
circuit is no good. I'm going to call the corresponding point the REFERENCE
POINT. I'll probably mess up here, but please correct me.
OP AMPS *NOT* SPECIALLY DESIGNED FOR SINGLE RAIL SUPPLY
SPLIT SUPPLY OPERATION
REFERENCE POINTS
INPUT
7 V+ input: The REFERENCE POINT is VCC- a negative potential with
respect to ground.
8 V- input: The REFERENCE POINT is VCC- a negative potential with respect
to ground.
9 The reverse is true (REFERENCE POINT is VCC+) if transistors are
different type (We have NPN or PNP types).
10 The REFERENCE POINT point is NOT ground.
11 With a split supply, ground (SYSTEM GROUND) is between + and - supply
voltages = 0v+ SUPPLY MIDPOINT.
OUTPUT
12 Vout: The REFERENCE POINT is ground or SUPPLY MIDPOINT = 0v = SYSTEM
GROUND
SINGLE SUPPLY OPERATION
REFERENCE POINTS
INPUT
13 Single-supply operation requires a VIRTUAL GROUND in an OP Amp stage.
14 A VIRTUAL GROUND is at a dc level above SYSTEM GROUND.
15 SYSTEM GROUND is 0v.
16 V+ input: The REFERENCE POINT is ground.
17 V- input: The REFERENCE POINT is ground.
18 Input source and output load will often be referenced to system ground.
19 If the input source of a stage is referenced to ground then the solution
is to ac couple signals to the Op Amp stage. Unless certain conditions
apply.
OUTPUT
20 Vout: The REFERENCE POINT is ground.
OP AMPS SPECIALLY DESIGNED FOR SINGLE RAIL SUPPLY
21 V+ input: The REFERENCE POINT is Ground.
22 V- input: The REFERENCE POINT is Ground.
OUTPUT
23 Vout: The REFERENCE POINT is ground.