Op.Amp. vs. Diff.Amp.

[autir]

What are the differences between an operational and a differential amplifier?

 

[audioguru2]

Hi Autir,
An opamp is a building block with extremely high voltage gain and differential inputs.

A differential amplifier is a circuit using a single opamp or 3 of them, with the inputs properly biased and with negative feedback for a certain defined voltage gain.

Some differential amplifier circuits are already made as an IC and are called Intrumentation Amplifiers. Some even have differential outputs.
;D

 

[autir]

So, as a rule, I buy Op.Amp ICs? And I decide whether I will use these ICs as Op.Amps or create with them a diff.amp. circuit?

 

[audioguru2]

There are only a few applications for differential amplifiers. A balanced input for a dynamic microphone's preamp would use a differential amp if you didn't want to use a transformer.
Ordinary opamp circuits usually have only one input.

 

[prateeksikka]

hi audioguru!
we generally call opamps as linear ICs .
Do u know why is it so?

 

[audioguru2]

Opamps usually operate with a linear input and output. They aren't used in switching circuits very much.
Because opamps have such a lot of voltage gain, with negative feedback their non-linearity is extremely low. Therefore they are linear amplifiers.

 

[prateeksikka]

Are the simple FETs and BJTs which we use non linear amplifiers?
By linear do you mean Y=m*X kind of relation?
or in otherwords gain independent of input?
i think u are right gain of a single transistor amplifier depends on i/p level.

 

[audioguru2]

Individual FETs and BJTs have non-linearity. An opamp is much better.

 

[Alun]

And op-amp isn't always that much better it's just negitive feedback makes it better.

 

[audioguru2]

Well, a single transistor amplifer needs a lot of negative feedback to make it linear, then it doesn't have any voltage gain. An opamp amplifier has both.
A two and three transistors amplifier is much better but approaches becoming an opamp.
http://www.dself.dsl.pipex.com/ampins/discrete/cfp.htm
http://www.dself.dsl.pipex.com/ampins/discrete/singleq.htm
http://www.dself.dsl.pipex.com/ampins/discrete/twoq.htm
http://www.dself.dsl.pipex.com/ampins/discrete/discrop.htm

 

[prateeksikka]

Any other ICs which are called linear Ics along with op amps?

 

[audioguru2]

Any other ICs which are called linear Ics along with op amps?

Lots of ICs like linear voltage regulators and radio ICs. The timing section of a 555 timer IC operates linearly.
Many circuits use Cmos digital inverters DC-biased so that they are linear amplifiers.

 

[prateeksikka]

I had a misconception that it is their manufacturing process which makes tham called so i.e linear ICs. It is because that they operate linearly.
thanx buddies!

 

[Alun]

It's the design that makes it linear of analogue, you can use an op-amp as a digital comparator, and you can just as easily use a 4011 as an analogue amplifier. IC's are called analogue or digital because it's how they are normally used. You can also use a BJT as a digital switch or an analogue amplifier.

 

[prateeksikka]

hi alun!
i guess digital - analog and linear -non linear are two different clasifications.
as far as i know opamps are always linear.

 

[Alun]

They aren't if you're using them as comparators.

 

[prateeksikka]

Then why do you think we call them as linear ICs. I mean any vendor would say 741 linear IC unlike any other IC.

 

[Alun]

That's because it's designed to be used as a linear IC.

 

[prateeksikka]

by using the word linear here,do you mean a linear operation like
i/o slope is constant?
like constant increase in o/p leads to constant increase in o/p?