Comparator equal to Op-Amp

Thread Starter

menewbie

Joined Jan 31, 2006
34
I know the Op-Amp can be used as a comparator, signifies the difference of the input voltages. I am wondering can a comparator be used as an operational amplifier? If so, how? I I think in order for a comparator to be used as an Op-Amp, the comparator itself would need to have a very high gain. But not so sure if that is right...
 

Papabravo

Joined Feb 24, 2006
14,378
Originally posted by menewbie@Mar 9 2006, 12:55 AM
I know the Op-Amp can be used as a comparator, signifies the difference of the input voltages. I am wondering can a comparator be used as an operational amplifier? If so, how? I I think in order for a comparator to be used as an Op-Amp, the comparator itself would need to have a very high gain. But not so sure if that is right...
[post=14800]Quoted post[/post]​
An opamp and a comparator both have high open loop gain and may differ in details like frequency response, common mode range, input bias currents and so forth.

The really important distinction is that a comparator usually has an open collector digital (not analog) output. The output is usually pulled up to a logic supply which is different from the analog supply. This output is generally very uncomfortable in any state between the lower supply rail and the logic supply. An opamp can both source and sink current. An open collector output can only sink current.
 

Thread Starter

menewbie

Joined Jan 31, 2006
34
Originally posted by Papabravo@Mar 9 2006, 07:17 PM
An opamp and a comparator both have high open loop gain and may differ in details like frequency response, common mode range, input bias currents and so forth.

The really important distinction is that a comparator usually has an open collector digital (not analog) output.  The output is usually pulled up to a logic supply which is different from the analog supply.  This output is generally very uncomfortable in any state between the lower supply rail and the logic supply.  An opamp can both source and sink current. An open collector output can only sink current.
[post=14803]Quoted post[/post]​
Thank you for the reply...I can see why comparator cannot be used as an opamp. But can a comparator function as an inverting-amplifier circuit if the comparator is designed to produce analog output??
 

Papabravo

Joined Feb 24, 2006
14,378
Originally posted by menewbie@Mar 9 2006, 04:20 AM
Thank you for the reply...I can see why comparator cannot be used as an opamp. But can a comparator function as an inverting-amplifier circuit if the comparator is designed to produce analog output??
[post=14804]Quoted post[/post]​
The answer is a qualified maybe. It is sometimes hard to answer hypothetical questions like this without direct experience. In my opinion the investment of time in researching this question has a most dubious payoff. This is something I would not even contemplate doing in an actual design.

Let me know your answer if you decide to look into this.
 

mozikluv

Joined Jan 22, 2004
1,437
hello,

its been quite a long time that i've visited the forum.

if i might add, try to compare the internal circuit design of a comparator and an op-amp. i believe it will provide you the answer to your query. :D

moz
 

pebe

Joined Oct 11, 2004
626
Originally posted by mozikluv@Mar 13 2006, 11:35 AM
hello,

its been quite a long time that i've visited the forum.

if i might add, try to compare the internal circuit design of a comparator and an op-amp. i believe it will provide you the answer to your query. :D

moz
[post=14930]Quoted post[/post]​
Hi Moz.
Welcome back!
 

Thread Starter

menewbie

Joined Jan 31, 2006
34
Originally posted by Papabravo@Mar 10 2006, 02:46 AM
The answer is a qualified maybe. It is sometimes hard to answer hypothetical questions like this without direct experience. In my opinion the investment of time in researching this question has a most dubious payoff. This is something I would not even contemplate doing in an actual design.

Let me know your answer if you decide to look into this.
[post=14815]Quoted post[/post]​
I will spend some more time to investigate this problem...and I will keep your updated.
 

Thread Starter

menewbie

Joined Jan 31, 2006
34
Originally posted by mozikluv@Mar 13 2006, 11:35 PM
hello,

its been quite a long time that i've visited the forum.

if i might add, try to compare the internal circuit design of a comparator and an op-amp. i believe it will provide you the answer to your query. :D

moz
[post=14930]Quoted post[/post]​
Thank you for the reply. I will look into the internal circuit design.
 
Top