Searching \ for '[EE] OPAMP use' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=opamp+use
Search entire site for: 'OPAMP use'.

Exact match. Not showing close matches.
PICList Thread
'[EE] OPAMP use'
2004\06\11@060924 by Luis Moreira

flavicon
face
Hi Guys
For years I been using the inverting OPAMP circuit when amplifying a signal,
by using two stages to get the signal in the right phase. But Now someone
that works with me just designed a circuit with a non inverting OPAMP
configuration, and apart form the fact the gain can not be lower than 2 I
can not see any problems with using this configuration. in top of it all I
only need one OPAMP not two.
I read a few things about it and it seems that the non inverting
configuration puts more strain on the OPAMP...
Do any of you have any info on this and any other problems that could arise
by using this configuration over the inverting one.
best regards
               Luis

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\06\11@062621 by Richard Graziano

picon face
The input impedance of a non-inverting configuration is significantly
higher.  That is an important consideration when the signal to be amplified
or buffered is relatively small.  The trade-off, however, is that the
non-inverting configuration tends to be less stable around zero than the
inverting configuration.    If you are working with AC signals it may not
add significantly to your error budget but if you are designing DC control
then you may want to account for this, depending on your budget and
application.  The inverting configuration is usually more desireable in
precision applications.  Non-inverting is good for things like video
applications, etc. Non-inverting buffers, such as the old LM310, for
example, have a very high open loop gain to help stabalize the near-zero
operation. The open loop gain is much higher than for a typical op-amp.  If
you are going to work with DC near zero, you may want high open loop gain
devices when designing a non-inverting circuit.


{Original Message removed}

2004\06\11@094952 by Harold Hallikainen

face picon face
Regarding "straining the op amp" in the non-inverting mode, I believe the
writer was refering to the fact that in non-inverting mode, there is a
large common mode voltage on the input in non-inverting mode, while the
common mode voltage in inverting mode is zero.

For some notes on using what I call "the theory of the happy op amp"
(differential input voltage ideally zero), see
http://kauko.hallikainen.org/cuesta/et113/InstrumentationAmpAnalysis.pdf .
This is an analysis of an instrumentation amplifier using this approach.

Harold


{Quote hidden}

> {Original Message removed}

2004\06\11@101504 by Mike Hord

picon face
It always makes me vaguely uneasy when people start asking questions
about the use of op-amps...I worry that I don't know as much as I
thought I did...So as a check on myself, let me propose this as a
solution to the gain < 1 non-inverting op-amp:

Unity gain voltage follower into a high impedence voltage divider, with
another voltage follower lowering the output impedence of said
divider.  If the output impedence of the signal source is low enough,
the first voltage follower can be omitted.

Choose resistor values based on input bias current of op-amp; with a
good FET input op-amp and resistors in the 10's of kOhms, the input
current can be ignored (hundreds of uA of signal current vs. 10's of
pA of input bias current).

Now...does anyone have anything to say about my solution?
Preferably not too abusive, but enlightening me as to any...
shortcomings in my understanding of op-amps?

Mike H.

{Quote hidden}

_________________________________________________________________
Stop worrying about overloading your inbox - get MSN Hotmail Extra Storage!
http://join.msn.click-url.com/go/onm00200362ave/direct/01/

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\06\11@103411 by David VanHorn

flavicon
face
>
>I read a few things about it and it seems that the non inverting
>configuration puts more strain on the OPAMP...

Strain?  In what way?

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\06\11@103413 by Luis Moreira

flavicon
face
Hi Mike
That is what more or less we are doing so you are correct. My question is
way use the inverting amp. configuration when you can use the non-inverting
amp. configuration as it looks simpler.
regards
               luis

{Original Message removed}

2004\06\11@103958 by Luis Moreira

flavicon
face
exactly my question.

-----Original Message-----
From: David VanHorn [spam_OUTdvanhornTakeThisOuTspamCEDAR.NET]
Sent: 11 June 2004 15:34
To: .....PICLISTKILLspamspam@spam@mitvma.mit.edu
Subject: Re: [EE] OPAMP use


>
>I read a few things about it and it seems that the non inverting
>configuration puts more strain on the OPAMP...

Strain?  In what way?

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\06\11@111115 by Spehro Pefhany

picon face
At 06:50 AM 6/11/2004 -0700, you wrote:
>Regarding "straining the op amp" in the non-inverting mode, I believe the
>writer was refering to the fact that in non-inverting mode, there is a
>large common mode voltage on the input in non-inverting mode, while the
>common mode voltage in inverting mode is zero.

Not necessarily zero (depending on the configuration), but a fixed value
that does not vary with the input voltage. Of course you can run into
problems with the classic non-inverting follower (gain = 1) with common
mode *input* range, even if the *output* is rail-to-rail.

One subtle issue that is easy to miss is that the offset voltage of
rail-to-rail I/O op-amps can undergo a shift as the input stage changes
from one type to the other (with common mode voltage range). This can
result in nonlinearity in the transfer function if the common mode
voltage moves through that region (which also could be expected to
vary somewhat from unit to unit). The effect is rather large (hundreds
of microvolts) in some op-amps.

I use non-inverting in many very precise measuring instruments, but
you do have to be aware of all the gotchas with the parts you are using.
For example, if the input voltage is only 100mV full scale, it's "almost"
constant common mode input voltage.

Another issue is that the characteristics change substantially as you
approach saturation in some kinds of op-amps, so you may see some ill
effects at 100mV output voltage when full saturation is more like 40mV.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\06\11@111323 by Spehro Pefhany

picon face
At 09:33 AM 6/11/2004 -0500, you wrote:
> >
> >I read a few things about it and it seems that the non inverting
> >configuration puts more strain on the OPAMP...
>
>Strain?  In what way?

Maybe he's thinking of using op-amps as comparators- an adventure
fraught with peril.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\06\11@135806 by Shawn Wilton

flavicon
face
The only thing that should concern you regarding strain would be that if
you drop your gain too low then the amp will no longer be stable as it's
receiving positive feeback instead of negative feedback and as a result
the amp will receive too much positive feedback (goes to infinity) and
you will eventually have a situation where it is being pushed too hard
and will fail.

This can be ovserved in the bode plots for the gain of the amp.  It has
to do with the gain and the phase at which it occurs.  You would be wise
to construct a simple bode of the magnitude and phase and look at
whether or not the gain comes back to less than one before it hits 180*.
 If not, then you will at least know what minimum gain is required for
stable operation.

-Shawn



Luis Moreira wrote:

> exactly my question.
>
> {Original Message removed}

2004\06\11@154304 by Mike Hord

picon face
The non-inverting amplifier can only produce a gain >1.  By
using a voltage divider and follower combination, you can
produce a gain <1, for example, to bring a +/- 10V signal
to a +/-5V circuit.

Mike H.

>Hi Mike
>That is what more or less we are doing so you are correct. My question is
>way use the inverting amp. configuration when you can use the non-inverting
>amp. configuration as it looks simpler.
>regards
>                 luis

_________________________________________________________________
Check out the coupons and bargains on MSN Offers! http://youroffers.msn.com

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\06\11@190238 by David VanHorn

flavicon
face
At 11:23 AM 6/11/2004 -0400, Spehro Pefhany wrote:

>At 09:33 AM 6/11/2004 -0500, you wrote:
>>>
>>>I read a few things about it and it seems that the non inverting
>>>configuration puts more strain on the OPAMP...
>>
>>Strain?  In what way?
>
>Maybe he's thinking of using op-amps as comparators- an adventure
>fraught with peril.

VBG. That's why they make comparators.

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\06\12@025006 by Richard Graziano

picon face
One of the considerations of a FET op-amp is the stability.  The offset
drift due the temperature is much greater in FETs than in bipolar devices.
So if stability is an issue, then the choice of fet-input needs to be
weighted in the trade-offs.  Application usually dictates all.

{Original Message removed}

2004\06\12@025628 by Richard Graziano

picon face
fraught with peril may even be an understatement!

----- Original Message -----
From: "Spehro Pefhany" <EraseMEspeffspam_OUTspamTakeThisOuTINTERLOG.COM>
To: <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Sent: Friday, June 11, 2004 11:23 AM
Subject: Re: [EE] OPAMP use


{Quote hidden}

reward"
> @spam@speffKILLspamspaminterlog.com             Info for manufacturers:
http://www.trexon.com
> Embedded software/hardware/analog  Info for designers:
http://www.speff.com
>
> --
> http://www.piclist.com hint: The list server can filter out subtopics
> (like ads or off topics) for you. See http://www.piclist.com/#topics
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

2004\06\12@040213 by Richard Graziano

picon face
An inverter-scaler can be configured by using a larger input resistance as
compared to the feedback resistance.  Although it is not exactly a voltage
divider  it appears that way because of the differential amplifier
configurations internally.  The bipolar devices are actually current devices
and setting the currents determines the gain.  There is a very good book
(that will date me) by Tobey, et al (Burr Brown) on Op amps.  It may still
be available in libraries.  I am sure many on this list must have read it if
they are in my age group.


{Original Message removed}

2004\06\12@040627 by Richard Graziano

picon face
Excellent point, although I must admit that "STRAIN" is a terminology I have
not been exposed to.  The non-inverting configuration for many video op-amps
require a gain of at least 10.

----- Original Message -----
From: "Shawn Wilton" <KILLspamshawnKILLspamspamBLACK9.NET>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Friday, June 11, 2004 1:58 PM
Subject: Re: [EE] OPAMP use


{Quote hidden}

> > {Original Message removed}

2004\06\12@042743 by Luis Moreira

flavicon
face
Hi Richard
Why do they need at least gain if 10 ?
regards
               Luis

-----Original Message-----
From: Richard Graziano [spamBeGonergrazia1spamBeGonespamROCHESTER.RR.COM]
Sent: 12 June 2004 09:06
To: TakeThisOuTPICLISTEraseMEspamspam_OUTmitvma.mit.edu
Subject: Re: [EE] OPAMP use


Excellent point, although I must admit that "STRAIN" is a terminology I have
not been exposed to.  The non-inverting configuration for many video op-amps
require a gain of at least 10.

----- Original Message -----
From: "Shawn Wilton" <RemoveMEshawnspamTakeThisOuTBLACK9.NET>
To: <PICLISTEraseMEspam.....MITVMA.MIT.EDU>
Sent: Friday, June 11, 2004 1:58 PM
Subject: Re: [EE] OPAMP use


{Quote hidden}

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

2004\06\12@115413 by Dave Dilatush

picon face
Luis wrote...

>For years I been using the inverting OPAMP circuit when amplifying a signal,
>by using two stages to get the signal in the right phase. But Now someone
>that works with me just designed a circuit with a non inverting OPAMP
>configuration, and apart form the fact the gain can not be lower than 2 I
>can not see any problems with using this configuration. in top of it all I
>only need one OPAMP not two.
>I read a few things about it and it seems that the non inverting
>configuration puts more strain on the OPAMP...
>Do any of you have any info on this and any other problems that could arise
>by using this configuration over the inverting one.

I'm unsure what you mean when you say the non-inverting amplifier
configuration "puts more strain" on the opamp; perhaps you're
referring to input common-mode voltage effects?

If that is so, keep in mind that these effects are usually VERY
small; and unless your application is very demanding and requires
a truly EXTREME level of precision, you are unlikely to notice
them.

My advice is to use whatever amplifier configuration (inverting,
non-inverting, or differential) is most convenient in a given
application.

Dave D.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

More... (looser matching)
- Last day of these posts
- In 2004 , 2005 only
- Today
- New search...