A Low-Voltage, Ultra-Low-Power, High-Gain Operational Amplifier Design for Portable Wearable Devices
Round 1
Reviewer 1 Report
Thanks to the authors for this updated document. However, despite of their improvements the main question about their approach still open. I have appointed in my previous review that the authors must demonstrate the usefulness of their approach in comparison with literature.
Also, I said that GBW could be a nice comparison parameter. Look at this, I am only using and comparing the authors data.
GBW[18]/GBW[paper] = 420/4.75 = 88.42 times better in terms of GBW.
Let see the G:
G[paper] @10^3 =74.1 dB (I use this frequency based on figure 19).
G[18] @ 10^3=112,46 dB
@10^3Hz -> G[paper]-G[18] = -38,36 dB
On the other hand, if you look to the power consumption P.
10 log P[18]/P[paper] = 10 log (0.114/0.0112) = 10 dB
Conclusion: It means that you only need to consume 10 dB more and you will obtain 38,3 dB extra in your gain. The reference 18 is best than your approach.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The revised version did not resolve the main criticism of the previous review, meaning that the article looks more like an assignment rather than a scientific article.
A stand-alone design of a fully-differential opamp is not particularly interesting if not tailored to an application, showing the advantages with respect to current solutions. The title mentions that is for portable wearable devices, but this kind of application is not eviscerated in the Introduction, nor translated into electronic specifications this design could solve.
Among the various applications mentioned in the Introduction, consider adding sensorics (e.g., 10.1109/JSEN.2021.3119766). This type of mixed signal processes are common for the electronic front-ends in that context.
Although some additional info on the layout has been added, the process itself is not a very recent one, and experimental results are still missing.
The comparison with other articles has slightly been widened.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thanks to the authors for their clarification to me as reviewer.
In my opinion, when you include a table in a paper. You must explain it in detail what you see in the data as author of the paper. Because a reader can not see all that you see in the table. This is the case of the advantages and disadvantages of your approach.
Finally, just in order to clarify the added sentences (lines 352-356), i recommend to include some values or computations like your response to my comments. It will increase the size of the current short discussion section and enforce the use of the table.
Good job dear researchers.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 2 Report
I appreciate the efforts by the authors: the revised manuscript is much improved in the form.
Regarding the question on applications: I was referring to the final use of this type of opamps and signal conditioning; one major example could be in sensors. That is why I was suggesting to add that reference; you might do so in the final version.
Nevertheless, the main criticism reimains, namely the fact that there is not enough novelty and that experimental results are typically needed for this type of work.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
In general the authors try to explain a CMOS Op-amp developed in 0.13um technology. Their proposal is based in to reduce the power supply.
Obviously, if you reduce the supply voltage, you reduce also the power consumption. However, despite of the authors obtain a similar Gain to literature approaches, they forget that the power reduction will also reduce the GBW.
The comparison done is not valid. Their reference 2 is most recent (2019). References 13 and 14 are from 2015. It is quite simple to do a google or IEEE search about CMOS Op-amp and there hundred of approaches. In addition, the authors do not include crucial information about their references in the comparison. For example, see table 7 in their reference 13 (https://arxiv.org/pdf/1411.3506.pdf). The proposed Op-amp must be compared with similar nowadays works.
The obvious information must be removed from the document. The whole manuscript must be reedited deeply because most of your sentences are too long and lies to the reader. Please remember, that in technical documents, one idea -> one sentence. The authors provide obvious information along that you try to expose your proposal. For more details check the comments after this paragraphs.
Formula enumeration is very confusing: (2-2)
Line 78 start with comma.
Line 78-79: English: “The ability to suppress common mode noise is stronger, and the power consumption is lower”
I don’t understand this sentence. Stronger ? Lower?
The authors uses intricate sentences including obvious information that lies the reader. An example is the Abstract: for example lines 8-10
“Based on the SMIC 0.13um CMOS process model, in order to reduce power consumption, this paper uses a 0.8V power supply voltage to design a low-voltage, ultra-low-power, high-gain two-stage fully differential operational amplifier.”
Those lines said that the proposal is to reduce the voltage. Are you sure? Or your proposal is a methodology or method to optimize a OPAMP reducing its power supply.
Or for example: Lines 41-43:
“This article is based on 41 the 0.13um CMOS process environment, abandoning the commonly used 1.2V power supply voltage, and adopting with a lower 0.8V power supply voltage.”
Environment ? -> What is it? The process?
Abandoning? Adopting? -> Those lines to said that your proposal is to use 0.8V instead of 1.2V ?
Line 79 & Figure 2: “The overall framework is shown in Figure 2.”
Framework? I never have been this block diagram referred as “Framework”. Please, check the literature and define correctly its name. This word is always used as synonym of tool or developer environment.
Line 83: “four modules” however, the Figure 2 has 5 modules.
Line 99: “is not large”. What is the limit to be or not “large”? Large is not an objective measurement. You must be specific. In similar way there are a lot of sentences in the paper… Line 118: “very jammy”. Cool language, but it is not technical.
Line120: “output resistance Rout”, I haven’t see Rout in your paper… where is it?
Figures 4 and 5. What is it the purpose of to present two common used circuits in literature. The Figure 4 is presented and not used, and Figure 5 is also used in literature.
Figure 6 also introduces a common flow used by designers. This flowchart is shown but nothing new is introduced. So, why do you need to include it in your document?
Reviewer 2 Report
As far I understand the paper presents a proposal of design for an operational amplifier. I do not understand the concept of "experimental simulation analysis". I would reserve the word experimental for the measurements of the fabricated circuit. In my opinion it could be valid in some congresses but not for an engineering journal. I would suggest to wait for the fabricated prototype measurements to publish it.
-You claim that the main novelty is a topological design of a new common mode feedback (fig. 5). Do you consider this novelty enough to justify the publication of the design without measurements?
-Technology: You use SMIC models of 0.13um CMOS. You mention MOS tubes. I understand you refer to symmetric MOS devices. Is that correct or you refer to both, NMOS and PMOS? In the first case, are they included in the SMIC library of models?
-Table 1. I understand that you emphasize in this table the low power consumption, within other CMOS technology implementations, but maybe to provide some global perspective you could give some BJT classic OPAmps figures, like 741 with typical SR 0.5V/us or high speed OPAMPs around 100 v/us, to understand the trade-off consumption-response.
-Line 162-164: Root. zero, pole should not be plural?
-Line 121: biggger
-Noise models of the MOS tubes were the standard provided in the library of the technology?
Reviewer 3 Report
In my opinion, this article has two main drawbacks. The first relates to the topic itself, meaning the stand-alone design of a fully-differential opamp would not be very interesting if not tailored to an application.
Among the applications mentioned in the Introduction, please add sensorics (e.g., 10.1109/JSEN.2021.3119766). This type of mixed signal processes are common for the electronic front-ends in that context.
The second concerns the fact that experimental results are missing, and that the process itself is not a very recent one. Please include any layout considerations.
The literature study is not sufficient and does not provide a proper view of the state-of-the-art. A much more extensive one should be undertaken.
Overall, the article looks more like an assignment rather than a scientific article.
Reviewer 4 Report
- Please correct the connections for Voutp-n, and Vip-n, for all figures. This is a very fundamental setup, to allow the subsequent review.
- The design is very conventional and lack of innovation.
- There is also not measured results to support the design.
- The article is a good tutorial based paper.
