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The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> Can anyone give me more information on this amplifier structure? https://designers-guide.org/forum/YaBB.pl?num=1457680699 Message started by Littlepotato on Mar 10th, 2016, 11:18pm |
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Title: Can anyone give me more information on this amplifier structure? Post by Littlepotato on Mar 10th, 2016, 11:18pm I remember I saw this architecture once, but I forgot where it was.. Can anyone tell me what's this architecture for or where can I find more information on this architecture. Thanks a lot |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by raja.cedt on Mar 11th, 2016, 3:03am Common Architecture for Ring oscillator--where you interpolate delay (from min to max) by varying the fast and slow path strengths. refer razavi book, he explained clearly::) |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by Littlepotato on Mar 11th, 2016, 8:57am This actually is not an oscillator, it's an amplifier |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by Littlepotato on Mar 11th, 2016, 8:57am This actually is not an oscillator, it's an amplifier....... raja.cedt wrote on Mar 11th, 2016, 3:03am:
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Title: Re: Can anyone give me more information on this amplifier structure? Post by ULPAnalog on Mar 11th, 2016, 10:03am Perhaps you are looking for a feedforward compensated opamp(?) You may find some details about the same here http://www.ee.iitm.ac.in/~nagendra/papers/tcas2-wlanfilter-pap.pdf |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by Littlepotato on Mar 11th, 2016, 10:11am what if I add another stage of amplifier at the output of the circuit? |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by Littlepotato on Mar 11th, 2016, 10:11am what if I add another stage of amplifier at the output of the circuit? ULPAnalog wrote on Mar 11th, 2016, 10:03am:
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Title: Re: Can anyone give me more information on this amplifier structure? Post by Littlepotato on Mar 11th, 2016, 10:12am what if I add another stage of amplifier at the output of the circuit? raja.cedt wrote on Mar 11th, 2016, 3:03am:
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Title: Re: Can anyone give me more information on this amplifier structure? Post by ULPAnalog on Mar 11th, 2016, 1:55pm It totally depends on what you intend to do. In general adding additional gain stages to an amplifier intended to be operated in feedback requires careful considerations about stability. |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by loose-electron on Mar 11th, 2016, 11:30pm that is a feedforward system |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by Littlepotato on Mar 23rd, 2016, 11:22pm can this system be stable? |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by Littlepotato on Mar 23rd, 2016, 11:22pm loose-electron wrote on Mar 11th, 2016, 11:30pm:
Can this system be stable? |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by buddypoor on Mar 24th, 2016, 3:00am Littlepotato wrote on Mar 23rd, 2016, 11:22pm:
Why not? If there is no feedback, there will be no reason for instability. |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by ULPAnalog on Mar 24th, 2016, 6:23pm buddypoor wrote on Mar 24th, 2016, 3:00am:
Isn't this opamp going to be eventually used in some sort of feedback? If so why does the stability not matter? |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by RobG on Mar 27th, 2016, 3:14pm As people have said, this looks like feedforward. Regarding stability, that is the purposes of the feedforward stage. You have two OTAs in parallel. One uses multiple stages to provide high DC gain. Unfortunately the multiple stages will need to have limited bandwidth to achieve stability. Therefore they put a high bandwidth single stage in parallel with it. Basically the multistage OTA acts like an open circuit at high frequency and all you have is the single stage. I found another article from Thandri and Silva, JSSC, Feb 2003 http://amsc.tamu.edu/SIS/Publications/pub/jounal/2003_6.pdf Feedforward is old but suffers from "doublets" which cause slow settling time. Achieving feedforward with parallel OTAs is relatively new and I don't know a lot about the drawbacks. Have any of you used this technique? |
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Title: Re: Can anyone give me more information on this amplifier structure? Post by raja.cedt on Mar 27th, 2016, 3:57pm Hi- Basically Feed forward compensation is to get higher gain without compromising on bandwidth (on the contrary to Miller). Or another way to think about it is feed forward (aka fast path) is a kind of low phase which decides stability and low frequency path (main path with 2 or 3 stages) is for high dc gain. Since there two path there will be an low frequency pole zero doublet relative to UGB, which may cause some under-estimation to settling related to UGB. This is the reason why people use this amp for the smooth signals like narrowband signals in filters rather step like i/p. Another problem is FF compensation is conditionally stable, hence we cant use this for any feed back network as this is the case for miller, this could be a problem for general purpose opamp. Best regards, Raj. |
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