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Old 17th January 2013, 06:53 PM   #31
Mooly is offline Mooly  United Kingdom
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OK thanks

I guess we're just going to have to see what you come up with. Extending the LF response by reconfiguring the circuit is easy of course... and does what you ask... but I guess that's not what your getting at.

The first simulation here wouldn't work in practice using real parts (although it does work in spice)

The second would work of course but its totally standard and can't be what you are getting at. It does have the added bonus though of decoupling the opamp rails though, which is is a "huge" benefit.

So I guess its over to you to show what you have come up with

(we are all intrigued)
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Old 18th January 2013, 08:08 PM   #32
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Mooly:

The approach has been quite good, so that you can verify that this is not yet the configuration I'm using, I'll upload a comparison with the diagram on the right you have kindly uploaded. With respect to the other scheme that you have uploaded, it will not be considered by what you said.

Give me time to compare the schemes in terms of other parameters of interest, since both magnitude and phase are only a small part of the story.

The blue curve corresponds to what you have kindly uploaded.

regards

Click the image to open in full size.
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Last edited by diegomj1973; 18th January 2013 at 08:12 PM.
 
Old 19th January 2013, 06:54 AM   #33
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The choice of opamp (its input impedance) makes a small difference here to the graphs. I'm just using standard models from the spice library. The 741 has quite a low input impedance (by todays standards).
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Old 19th January 2013, 02:34 PM   #34
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Originally Posted by Mooly View Post
The choice of opamp (its input impedance) makes a small difference here to the graphs. I'm just using standard models from the spice library. The 741 has quite a low input impedance (by todays standards).
However, given the relatively low external resistor values​​, the parameters of the operational amplifier does not substantially affect the low frequency response. The final response at low frequencies is governed mainly by the external components.

The high frequency response is more influenced by the parameters of the operational amplifier, apart from any component in the feedback loop (eg, an external capacitor).

Also, from what I could check on your latest proposal, the offset can be a problem (if the gain grows), unlike the scheme that I use (which lacks this drawback).

Anyway, give me a little more time to expose some additional advantages of my scheme (compared to those proposed).

regards
 
Old 19th January 2013, 05:01 PM   #35
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Originally Posted by diegomj1973 View Post
However, given the relatively low external resistor values​​, the parameters of the operational amplifier does not substantially affect the low frequency response. The final response at low frequencies is governed mainly by the external components.
That is what you would expect (its what I would have expected too... give or take) but the reality seems somewhat different. This is the circuit I posted above (#post 31, first picture) but with the 0.1uf shorted. Two different opamps used as shown on the pic.
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Old 19th January 2013, 05:13 PM   #36
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Quote:
Originally Posted by Mooly View Post
That is what you would expect (its what I would have expected too... give or take) but the reality seems somewhat different. This is the circuit I posted above (#post 31, first picture) but with the 0.1uf shorted. Two different opamps used as shown on the pic.
... but the LF response seems identical to me?

jan
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Old 19th January 2013, 05:17 PM   #37
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... but the LF response seems identical to me?

jan
Its me going cross eyed looking at it... your right
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Old 19th January 2013, 05:49 PM   #38
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Mooly:

You can superimpose the two curves and add a grid?. I think I see that both curves do not differ at low frequencies (this indicates no dependence of the operational amplifier used). Clearly both curves differ beyond 20 KHz (this indicates that there is dependence of the operational amplifier used).

It seems to be just as I had anticipated you.

Precisely, it was the fact that we can not have big government on the parameters in the high frequency area, which made ​​me look for improvements in the low frequency area, where what defines performance in the low frequencies are mostly external components and no necessarily the op amp.

regards
 
Old 19th January 2013, 06:04 PM   #39
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Yes, my mistake on that
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Old 19th January 2013, 06:56 PM   #40
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Looking at this from an entirely different perspective.......
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