2nd-Order Pipelined Noise-Shaping SAR ADC Using Error-Feedback Structure
Round 1
Reviewer 1 Report
Good discussion on the SAR based on the 28nm technology. I am fine with the current version. Good work.
Author Response
"Please see the attachment."
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Based on Figure 10 where the digital calibration is employed to improve SNDR distribution when 5% gain variation induced, the authors claim that the proposed structure is robust to the gain variation of the amplifier by PVT variation. Such a conclusion is unacceptable since PVT doesn't only affect the gain, but also effect the THD and stability of amplifier. Furthermore, Table 1 uses simulation results and experiment results to compare, which is unreasonable.
Author Response
Response to Reviewer 2 Comments
Point 1: Based on Figure 10 where the digital calibration is employed to improve SNDR distribution when 5% gain variation induced, the authors claim that the proposed structure is robust to the gain variation of the amplifier by PVT variation. Such a conclusion is unacceptable since PVT doesn't only affect the gain, but also effect the THD and stability of amplifier. Furthermore, Table 1 uses simulation results and experiment results to compare, which is unreasonable.
Response 1: This paper argued that the gain variation of the amplifier by the PVT is robust. It doesn’t mean the overall PVT variation. In order to prevent the occurrence of other interpretations, it is deleted.
To emphasize the advantages of the proposed structure and to show the state-of-the-art performance, Table1 is necessary. We performed sufficient simulation to support the reasonability of the simulation results. Not only noise simulation but also layout was completed, and post-layout simulation was carried out. In addition, we conducted additional corner simulations (simulations for each corner are performed at sampling rates of SS: 160MHz, TT: 175MHz, and FF: 189MHz, and almost the same SNDR is obtained) and added this to the manuscript page 10, line 340. Therefore, the results of the proposed structure in this paper are reliable and a similar result is expected in the experiment (this chip will be fabricated soon).
In case of reference [3] and[4], the circuit designed by us is simulated in the same environment although the process is different. The ADC in this paper is designed to improve the previous design [3], [4]. The performance is better when compared with the simulation results of [3], [4] and the present ADC simulation results. Therefore, it is expected that the performance will be better even in the measurement.
Last, the rest of the references have a larger OSR than this structure, but sampling rate are slow. Considering that this structure is sampling rates of 160MHz in SS corner, if the measurement method is experiment, it can be improved by increasing OSR even if the actual SNDR is lowered. Therefore, it is meaningful to compare the proposed EF PLNS-SAR ADC with the prior works.
Author Response File: Author Response.pdf
Reviewer 3 Report
In this manuscript, a pipelined noise-shaping SAR ADC is presented for high SNDR, wide bandwidth and low power consumption. The results presented are promising. It is novel and interesting. However, there are several issues existed in this manuscript, and the major revision should be made before the possible acceptance for publication.
1. Different variants of the pipelined NS-SAR ADC structure are presented in the paper, but no significant difference between them is highlighted (this concerns section 1). It is necessary to thoroughly explain all of them but rather show what the differences, because it is not clear enough (e.g., how is pipelined NS-SAR ADC as illustrated in [4] different from the Ref. [3] besides the amplifier).
2. What are the CDAC1 and CDAC2 that are illustrated in the Section 2?
3. The origin of Eq. (1) should be explain more in depth. In addition, the going from (1/G)–(1-a–z-1+z-2) to (a±(a2-4)1/2)/2 is not so obvious.
4. Is the zero position optimal after using the zero optimization method? Can the proposed architecture be extended to obtain the higher SNDR based on the zero optimization method?
5. The 28 nm process is used in the simulation, what’s the simulation condition?
6. The authors claim that the proposed PLNS-SAR ADC achieves the high SNDR, wide bandwidth and low power consumption compared to the existed structure, as shown in Table 1. But the measurement of the proposed structure is simulation, while the others are experiment. If the measurement method is also experiment, the performance will be better than others?
7. The English should be improved, and several grammatical mistakes are existed in the manuscript. I suggest that the authors carefully revise the text and correct such mistakes.
Author Response
"Please see the attachment."
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The gain variation is not so important in a negative feedback structure. It is true and not only for the amplifier design, but also for the system design. The THD and stability of amplifier and overall circuit resulted from PVT are more important. As a result, the contribution is not significant if the authors only argued that the gain variation of the amplifier by the PVT is robust.
Regarding the corner simulation, the focus is not on the variation of the sampling frequency, but on the influence of the temperature, especially in the high-gain feedback circuit architecture with 7 times oversampling, the 10% sampling-rate variation is very small.
I still think it is unreasonable to compare the simulation results with the measured results, especially with the work [14]. In addition, please footnote the formula of FoM in Table I to clearly indicate the comparison.
Author Response
"Please see the attachment."
Author Response File: Author Response.pdf
Reviewer 3 Report
All the questions had been addressed. Thanks
Author Response
Thank you
