Digitally Controlled Fractional-Order Elements Using OTA-C Structures
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper presents active realisations of electronically controlled fractional orders capacitors, and a constant phase element (CPE) and a fractional order inductor, all of them based on OTAs combined with capacitors.
The results are worth of investigation for the implementation of several transfer fuctions with orders not limited to integers, which can be usefull on fine control.
Notheless and despite the advantage of their claim, the authors of this paper must address few remarks.
In the introduction it is not enough clear the importance of farctional orders. It was interesting to include an example stating the advantage of them in realation to a [simple] implementation with integer number of reactive elements.
On line 175, "The transfer function of the circuit in Fig. 4 is defined by (7).", which Vin is considered? (Vin+-Vin,CM), ((Vin-)-Vin,CM) or (Vin+)-(Vin-)? Does the Vout in (7) related to figure 4 is (Vout-Vout,CM)? With Vout,CM and Vin,CM being the DC voltages at the output and input, respectivelly?
Additional details about MOSFETs and Capacitors must be provided: the number of fingers and multipliers of MOSFETs (for example a fictional example to illustrate the piont: cell NMOS_xpto35 and PMOS_xpto35 from the library AMSC35B5), as well as, the number of sub-capacitors with enphasis to the dimensions of the subarrays (a fictional example to illustrate the point required: 3.5pF was implemented using a 7x5 array of unitary capacitors of 0.1pF implemented from the cell CELL_MIM_M11_M12 from the library AMSC35B5).
What was the power consuption?
The authors must explain the procedure followed in the EDA tool to extract the parasitics and how their inclusion were done in the post-layout schematic to allow the ocasional reader to reproduce the simulation procedure.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1. There are no quantitative results in the abstract. This abstract does not help the reader understand the performance of the proposed design. Please include key quantitative findings in the abstract.
2. s in the equations must be well defined, although it is obvious. tau in equation (3) is also not explained till (5).
3. The achievable bandwidth 10 kHz - 100 kHz, is very limited. What is the practical application?
4. The phase increases after 100 kHz, where gain is high at 60 dB, Figure 23, Figure 24. How to mitigate the effect of this frequency range in practical design, eg. filter design.
5. What are the significant to show plots of inputs in figure 18 and etc.? How about the output current?
Comments on the Quality of English LanguageMinor
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsAuthors present an implementation of fractional-order capacitors and inductors using OTA-C's as building block. The FO elements can be tuned by digitally controlling the OTA bias. The writing is excellent, logical and easy to follow. Introduction is well written.
This reviewer's comments are as follows.
1. Figure 9:
In the CPE phase curve, the local peak-to-peak phase difference is less than that of the MMX case. If a small phase can be added (or a small phase offset is removed), then the CPE performance can be better than the MMX. Please add comment on this.
2. Precision in the coefficients of the transfer function:
In Tables 1 to 3, the number of significant digits goes up to 6.
1) Is it possible to realize the coefficients (or the element values) up to 1 ppm precision?
2) Is such a high precision necessary?
In Table 7, the bias current controlling the OTA's has 1 to 3 significant-digit precision.
3) In it not necessary to let the bias current have 1-ppm accuracy?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsMy remarks were addressed.
