[SOLVED] Negative Logic gates, when are they used and why?

[Audioguru]

An Op Amp Configured as an Op amp comparator, my manager calls them differential amps, but they are not differential amps , they are Op am comparators but he calls the differential amps

Are you talking about shorting the output of this opamp to ground? Short it quickly so it does not overheat.

 

[danny davis]

No
They are 741 op amps configured as comparators , either the inverting or non invertering inputs has a voltage dividered that sets up a threshold voltage

My Manager calls them a differential op amp , but they are comparators, how are comparators differential op amps? aren't they two different things

 

[Audioguru]

Why are you talking about opamps configured as comparators?
A comparator has an open collector output so the output can be shorted to ground.
An opamp has a push-pull pair of output transistors so if you short its output to ground when its output is high then it blows up.
The inputs on an LM339 quad comparator are exactly the same as the inputs on an LM324 quad opamp. The inputs are a differential amplifier.

As we discussed before, a comparator output switches quickly. It never has negative feedback so it does not have a frequency compensation capacitor.
An opamp always has negative feedback so it has a frequency compensation capacitor to prevent oscillation and this capacitor slows down its switching speed.

 

[danny davis]

An opamp has a push-pull pair of output transistors so if you short its output to ground when its output is high then it blows up.

LM324 is an Opamp , so you can't short the output pin?

Can you short the output pin to a differential op amp?

 

[Audioguru]

LM324 is an Opamp , so you can't short the output pin?

If its output is low then you can short it to ground and it does not matter.
If the output is high and you short it to ground then it slowly gets hot enough to fail.
Its datasheet tells you all about shorting its output to ground. Read it.

Can you short the output pin to a differential op amp?

Bad English again.
What is a differential opamp? Almost ALL opamps have a differential INPUT.

Do you want to CONNECT the output of an opamp to its (-) input? Of course, then it is a follower.
Do you want to CONNECT the output of an opamp to the input of another opamp? You can if they both use the same supply voltages.

 

[danny davis]

What is a differential opamp? Almost ALL opamps have a differential INPUT.

But is a Op amp comparator considered to be called a differential ?

I thought a differential op amp was using it for common mode rejection not for being a comparator

My Manager calls Op amp comparators , differentials

 

[Audioguru]

But is a Op amp comparator considered to be called a differential ?

No because almost all opamps and all comparators have differential inputs.

I thought a differential op amp was using it for common mode rejection not for being a comparator

A differential input is used because it has a non-inverting input and an inverting input.
Usually an opamp is used as an opamp and a comparator is used as a comparator.

My Manager calls Op amp comparators , differentials

He is WRONG but he can call them anything he wants. He should hear what I call you and him.

 

[danny davis]

No because almost all opamps and all comparators have differential inputs.

Right, so what's the difference between the two, if they both have differential inputs?

The Op amp is a DC differential circuit

What is the difference between an Op amp configured as a comparator different than an Op amp as a DC differential stage?

The Differential op amp , uses both differential inputs, but it compares the DC voltages and will switches it's output

A Comparator does the same thing , so what's the difference? it's a DC differential amp

 

[alexan_e]

If you are interested about the differences then refer to

http://e2e.ti.com/blogs_/archives/b...4/op-amps-used-as-comparators-is-it-okay.aspx

http://encon.fke.utm.my/nikd/latest/sloa067.pdf

 

[FvM]

By referring to OPs and comparators, the discussion has taken one more step off-topic and proceeded from "all about digital logic" to "all about electronics". Time to stop it?

 

[alexan_e]

I agree, I don't think there is a point to keep this thread open any longer