Versatile Voltage-Mode Biquadratic Filter and Quadrature Oscillator Using Four OTAs and Two Grounded Capacitors
Round 1
Reviewer 1 Report
While the article is clear, the authors could be more clear about the mentioned advantages of the proposed architecture.
For example, at line 285 the authors refer " The proposed filter enjoys the following advantages: (i) four active components and two grounded capacitors are used". Why is this an advantage? Or an advantage relative to what?
The same applies to the abstract (that could be improved): "The proposed biquadratic filter achieves all of the main advantages (...)".
Since there are an handful of ways to achieve the five types of filters mentioned, the authors could also, perhaps, make a broader statement about the state of the art instead of limiting the comparison to previous but similar architectures (three by the same authors).
At line 63, since the number of components is not really a performance parameter, does replacing "parameters" by characteristics makes sense?
Figure 10 contrasts with figure 19. But, aren't the authors supposedly plotting the same?
Both plots refer to vo3 when vi4 = vin and the other inputs are grounded.
At line 118 - the sentence is not clear.
Frequency is not correctly spelled in figure 25.
In figures 19 and 24, the value at the lowest frequency (~10kHz) is similar (if not higher) to the value given by the marker.
Is this real or some artifact?
Regarding the quadrature oscillator the authors mentioned it can be tuned from 38kHz up to 360 kHz can they also comment on the achievable Q quality factor?
Author Response
The authors have revised manuscript and written response letters for each reviewer. Please check the attached manuscript and response file. Please refer to the manuscript and response letter.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Main problem of this manuscript is its low novelty. There were many OTA-C filters and oscillators presented in literature in last 30-40 years. Unfortunately, features of the proposed topology are not revolutionary. Verification with PSpice simulations and with practically obsolete active devices is not sufficient (CMOS designed with significant improvements, such as low-power, high-frequency or other benefit, would be welcomed). Presented results shown in graphs cover only very narrow bandwidth of operation and tuning possibilities are not wide. THD is terrible (very high), automatic gain control is not involved in case of oscillator. Therefore, I suggest to reject this paper.
Author Response
The authors have revised manuscript and written response letters for each reviewer. Please check the attached manuscript and response file. Please refer to the manuscript and response letter.
Author Response File: Author Response.pdf
Reviewer 3 Report
The specific application where the proposed topology could be employed should be specifically addressed. It is not clear along with the paper its scientific relevance. It seems a combining of OTA into a bigger topology.
Please give more details about the importance of the work even compared with the state of the art.
The work is validated using discrete (commercial) components. The presence of such proof-in-concept design using discrete components should be clear since abstract and introduction. Related to this, a photo of the test-bench should be provided in which the different components are highlighted.
A comparison table should specifically mention the ad-hoc IC design or the use of commercial devices. This to properly differentiate the present works with the others. Please specify also the technology node of each commercial component employed. Similarly in the comparison table should include the power consumption and any other characteristics that usually define the Biquadratic Filter.
The matching of theoretical, simulated, and measurement results is remarkable.
The paper lack of comparison with the state of the art. For the topic, the references could be at least doubled. For instance, similar works that appeared in the last years in IEEE TCAS1 and IEEE BioCAS or MDPI, should be also mentioned along with the paper and include in the table of comparison.
Author Response
The authors have revised manuscript and written response letters for each reviewer. Please check the attached manuscript and response file. Please refer to the manuscript and response letter.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Paper was significantly improved after reviews. However, significant drawbacks remain and should be addressed before accepting the paper.
Presented results shown in graphs cover only very narrow bandwidth of operation (only two decades – not sufficient) and tuning possibilities are not wide. THD is terrible (very high), automatic gain control is not involved in case of oscillator. Therefore, paper still have to be improved significantly.
Author Response
Ans: Thanks for your comment. We discussed from lines 301 to 305 in Section 4 of the revised manuscript.
For wideband frequency adjustment and amplitude stabilization, the automatic gain control (AGC) system is required. Therefore, an additional auxiliary AGC circuit technology is necessary. The AGC circuit can improve the unbalance of the voltage amplitude generated and can reduce the THD to achieve better performance. This technique has been presented in the literature [31].
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
Paper could be accepted after minor improvements.
Authors added paragraph about AGC as mentioned in previous review. Unfortunately, they did not try to use it in measurement of their circuit.
Authors ignored previous recommendations about graphs (to show wider band). Before publication, authors should address this issue.
Author Response
Ans: Thanks for your comment. We discussed from lines 299 to 306 of the revised manuscript.
When the tuning transconductance gain gm2 is in the range of 0.5 to 5 mS, to start and maintain the sine wave oscillation under the same oscillation condition, the electronic tuning oscillation frequency range of the oscillator will be between 37.95 and 355.88 kHz.
Regarding for adding the AGC of another paper to the proposed circuit, there may be plagiarism issues. Therefore, we only cite that paper [31] and explain bellows.
For wideband frequency adjustment and amplitude stabilization, the automatic gain control (AGC) system is required. Therefore, an additional auxiliary AGC circuit and technology are necessary. The AGC circuit can improve the unbalance of the voltage amplitude generated and can reduce the THD to achieve better performance. This technique has been presented in the literature [31].
31. Sotner, R.; Jerabek, J.; Langhammer, L.; Dvorak, J. Design and analysis of CCII-based oscillator with amplitude stabilization employing optocouplers for linear voltage control of the output frequency. Electronics 2018, 7, 157.
Author Response File: Author Response.pdf
