Fully Differential Current-Mode Configuration for the Realization of First-Order Filters with Ease of Cascadability

Round 1

Reviewer 1 Report

The paper presents a cascadable, fully differential circuit implemented using a current conveyor capable of realizing low-pass, high-pass, and all-pass filter topologies.

The language used needs to be improved to understand the article better. It would be best for the paper to be proofread by someone more familiar with the English language.

There is a possible typo on line 179. Table 1 reference is the one in the template that needs to be changed.

Some references are more than ten years old. Most of them are mentioned in the introduction section. Given that they seem to be part of the "state of the art," how relevant are they?

Figure 6 shows the AP filter phase response to different bias currents. The gain response should also be plotted because an AP filter needs a flat response, like in Figure 3.

On line 159, it is stated that the filter can work at 73MHz using a 2pF capacitor. What is the bias current value for this frequency? 

Figure 6 shows the transient response of the AP filter at 73MHz. The gain and phase characteristics are a better way to show the frequency capabilities of the proposed topology; also, they must be present for every filter type (AP, LP, HP). Is there any reason why only the transient response for the AP filter is presented?

Is the consumed power value from line 174 measured or calculated? For example, is the maxim consumed power, or is it for a specific frequency value and filter type (AP, LP, HP)?  

In table two, the power consumption value is present only for the current work. There is no other value for comparison. Why? Usually, when comparing current work with previous works, only the parameters that appear at each are shown in the table.

Are the experimental results obtained from a practical realization of the circuit in Figure 10? If yes, a picture of it would have increased the quality of the presentation.

On line 227, R2 appears twice.

How relevant is the experimental part where the supply voltage values, the capacitor value, and the input signal frequencies are very different from the ones used in the simulations, which are key features that illustrate the advantages of the proposed first-order FD circuit stated on lines 175-177.

The cascading ability is presented only for the low-pass filter. There are no mentions of any limitations regarding this capability. Is the presented circuit suitable for obtaining high-order high-pass and all-pass filters? 

When cascading the first-order blocks, does one need any other circuits like current mirrors? In Figure 13, there is a direct connection between the blocks. No additional circuity is present.

Figure 14 presents the gain and phase characteristics of the third-order filter obtained by cascading three blocks. Can you also include the transient response?

On line 262 there is mentioned the dissipated power. I think you mean the consumed power presented earlier.

In conclusion, the introduction and the presentation of the proposed circuit are adequate, but the rest of the work needs improvement. The presentation of the simulation results starts with the frequency characteristics of the LP, HP, and AP filters. Then, no more frequency characteristics are presented, only the transient responses and only for one type of filter (mostly for the all-pass one). The simulation results should validate the theoretical results obtained in the previous chapter, where most of the conclusions refer to the frequency response of the circuit. It is quite difficult to observe the effects of the parameters for which the analyzes were performed on the transient responses. Presenting the frequency characteristics and the transient responses would greatly improve the quality of the presentation.

Author Response

"Please see the attachment." 

Author Response File: Author Response.pdf

Reviewer 2 Report

In my view there are two main problems with this paper. 

The first one is the inclusion of experimental result on a discrete component prototype that does not have anything to do with the design in Fig. 2. In the circuit in Fig. 10, bipolar based components are used, the system is clearly non fully differential and therefore I cannot understand why the authors believe that it has any relevance whatsoever. Assuming that their work has any significance, the experimental results on a completely different system with respect to the main subject of the design is really meaningless and only create confusion.

The second problem has to do with the very limited detail in which parameter variations, which are expected to be a crucial aspect in a design like the one being proposed, are discussed. I do not see the point in going through Eq. 7 to 16 without discussing what the actual range of values for the alphas ad the gammas are expected to be and what is the effect of the spread in crucial parameters (see below). 

Montecarlo simulation cannot be reported as a few simulated time traces as in Fig. 8a and 9a. Moreover, it appears that the only investigated parameter is the pole frequency, while a number of other parameters would be relevant , especially for the claim that more filters can be cascaded (equivalent input or output offsets, for instance).

Figures and circuit diagrams are, in general, not easy to interpret and only bare minimum comments are present. As an example, there is more than one plot in Fig. 8a, but the different curves are not labeled in any way, with marked differences among them that cannot be understood form the data provided by the authors.  As another example, there is no comment on the quite strange distribution obtained in Fig. 8.

As for the schematic diagram, the voltages and current names in Eq.1 have no correspondence in the  names in Fig.1. One may guess that IP in Fig. 1 is either Iin1 or -In1 in Fig. 1 and so on, but not having a clear definition of all symbols is not acceptable in a scientific paper. 

In my view, before even addressing the issue of the evaluation of the merit of the work that has been done, the authors need to make the effort of rethinking the entire organization of to manuscript and correcting the shortcomings I have listed above. 

The English does not appear to be a major concern to me (but I am not a native English speaker), however in a few instances it needs to be improved. For instance, in the introduction, the sentence "The  main reasons for being a popular on analog....." does not seem to make much sense to me.  Finally, I believe that the term "high power" is sometimes used improperly to mean "high voltage supply" that is a quite different thing.

Author Response

"Please see the attachment." 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thanks for the changes made to the article. All suggestions were treated with the utmost seriousness, thus increasing the quality of the presentation.

Reviewer 2 Report

The authors have made an effort to improve the manuscript. I still believe that one of my main objections has not been addressed, that is the fact that the experimental circuit  and the experimental results have nothing to do with the subject of the paper. When developing a new circuit, the interesting part is not how it should work in ideal conditions but, rather, within which limits the actual operation can be assumed as sufficiently consistent with the desired one. The fact that a different circuit with different components can provide the same function is non interesting and it is distracting. I would also note that the fact that, again, in ideal conditions a circuit behaves "as if" it was differential, does not mean that its structure is "fully differential". In short, the paper has merit and although I still that the experimental section does only subtract to the merit of the paper, I have no strong objection to the publication of the paper in the present form.