• Proposal 551 Readhead Ultra-wideband Analog-to-Digital Converters for ALMA

  • Reviewer 1

Grade: 5

Executive Summary: This project aims to study ultra-fast ADCs and determine their level of suitability and readiness for use in a future ALMA upgrade.

ALMA Development Review

1. Alignment with NA ALMA Partnership strategic goals; The proposal is well aligned with Strategic Goal (1.x), covering the application of new hardware which would increase scientific output. Involving an institution not already widely engaged in ALMA development seems to satisfy (4.x). It does not address operating efficiency (2.x) or cost (3.x), except insofar as a broadband upgrade would improve some classes of observations. No mention is made of young trainees (5.2), nor external institutions (5.1).

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the †̃ALMA 2030â€TM development documents. Broadening the ALMA observing band has myriad impacts across the ALMA science portfolio. This development covers a critical item in the chain toward that broader band.

3. Quality of the upgrade conceptual design;

The conceptual design of the study seems strong; evaluating the suitability of new ultra-fast digitizers is of interest in the case of an eventual broad-band ALMA upgrade. Unfortunately, no mention is made of how these ADCs would integrate with ALMA, what is required beyond this initial study.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development); This study seeks to do preliminary evaluation of new technology for use on an eventual upgrade; it is very much an early-stage development, and would not be ready for use in the field without significant R&D beyond the current project.

5. Strength of the consortium organization (if applicable); The proposing organization is CalTech and the PI has a strong track record of delivering hardware used on other projects.


6. Qualifications of the key personnel of the Study; The key personnel have many years of experience in astronomical instrumentation, are well respected in the community, and well placed to undertake this study.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study; No concerns here, the team has experience with high-speed readout in a variety of contexts, and the facilities are sufficient to perform all needed tests.

8. Assessment of the level of risk inherent in the design; As a nearly part-for-part replacement of the existing correlator, by the people who know the system best, there is very little risk involved in this proposal. The requirement for broader-band digitizers (and broader-band frontends) could limit the immediate usefulness of the proposed system. The project seems largely dependent on a handful of key personnel: only 4 devoting the majority of their time to it, of which only 2 are currently know, one of which (the PI) is anticipated to retire during the project. I have serious reservations about the long-term viability of this staffing. 
 9. Strength of the Scientific Team supporting the Study; Only one member of the Key personnel is listed as part of the scientific team (Scientific Lead), and while this person is well equipped to understand and frame the science, no further statement is made in the proposal. 
 10. Level of support guaranteed by the Institutes; No statement of matching or support from CalTech is included. 
 11. Budgeted cost of the Study; The cost seems plausible given the study parameters. I find the report preparation budget high, but for a comprehensive reference it is well justified.

  • *Reviewer*12

Grade: 2.0

Title: 551 Ultra-wideband Analog-to-Digital Converters for ALMA

1. Alignment with NA ALMA Partnership strategic goals

No stated collaboration with Partners (ESO, NAOJ, or JAO). Strategic goals are aligned.

2. Strength of the scientific case for the proposed ALMA upgrade concept Comment on the relevance to the ‘ALMA 2030’ development documents.

Directly relevant to ALMA 2030 and also has broad application outside of ALMA.

3. Quality of the upgrade conceptual design

Proposal is well defined in scope and measures of success match well with stated study plan. Significant budget is devoted to the purchase of hardware (approx. %50).

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development)

The plan tests existing technology and will evaluate its technical readiness.

5. Strength of the consortium organization (if applicable)

none

6. Qualifications of the key personnel of the Study

Highly qualified.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study

Very strong relevant experience.

8. Assessment of the level of risk inherent in the design

The study is specific and poses little risk.

9. Strength of the Scientific Team supporting the Study

See 6&7.

10. Level of support guaranteed by the Institutes

Not stated.

11. Budgeted cost of the Study

The study has a very high hardware/labor budget.

  • *Reviewer*13

Grade: 5.5

Title: Ultra-wideband Analog-to-Digital Converters for ALMA

1. Alignment with NA ALMA Partnership strategic goals;

Comment: It is very clear that widebanding of ALMA is a very high priority with enormous potential scientific and strategic returns. The extent to which this particular approach to wideband analog-to-digital conversion feeds those goals is questionable

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents.

Comment: In addition to the comment already made on point 1, the ALMA 2030 documents speak extensively of the benefits of wider bandwidths to ALMA’s sensitivity and spectral line coverage with many science cases cited. Though in this proposal, the science case is really very cursory as presented, tough I am not sure wide banding really needs to be justified.

3. Quality of the upgrade conceptual design; Comment: I think rather poor. While I am very supportive of investigations into wideband analog-to-digital conversion, based on my knowledge the Vadatech AMC590 through my own investigation, it is limited to an output data rate of 120 Gbps, and, further, requires that the Fujitsu chip installed on the board be capable of streaming operation. Even if capable of streaming, the output data width at full sampling rate would be limited to 2 bits based on data rate alone. In truth I had a very tough time getting comprehensive information from Vadatech technical sales, and from Fujitsu.

But my knowledge of the Fujitsu CHAIS product, which is primarily sold as ASIC intellection property (IP) and in which I have at times taken a great interest, leads me to think it the siliconis the ROBIN product, which is only capable of a snapshot mode of operation. In the end I happened to make contact with the original designer of the CHAIS chip, but even then the exact capabilities of silicon on the market remains a little uncertain.

The proposers may have better knowledge than me, so it may make sense to ask them to respond to this point.

In addition to the question of streaming vs snapshot mode of operation, the CHAIS ADC achieves 56 GS/s by interleaving 320 SAR (Successive Approximation Register) ADCs each running at the relatively slow rate of 175 MS/s. Interleaving of slow ADCs to achieve a fast ADC rate is a compromise solution. Even relatively few (e.g. 4) interleaved ADCs are prone to interleave artifacts due to imperfections in the offset, gain, phase of the interleaving, as well as core non-linearities. This results in spurious tones, intermodulation products, reduced figures of merit such as spurious free dynamic range (SFDR), signal to noise and distortion ratio (SINAD) related to effective number of bits (ENOB) and noise power ratio (NPR).

I find the interleaving of 320 ADCs to be a scary prospect.

While one should not rule out interleaving as a way to achieved fast sample rates, I would have expected significant discussion from the proposers as to how they plan to handle this issue. Such discussion is essentially absent from the proposal.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

Comment: I think the above comment in 3 about covers it. I don’t think the prospects for production are very good.

5. Strength of the consortium organization (if applicable);

Comment: I think for the work the consortium of pure Caltech personnel is appropriate.

6. Qualifications of the key personnel of the Study;

Comment: Drs Readhead and Kocz are well qualified to do this work. I fully support the need of research into this general area, I just think the particular hardware chosen is not well suited to the work.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

Comment: As far as I know should be fine.

8. Assessment of the level of risk inherent in the design;

Comment: Very high risk given apparent technical limitations of the hardware.

9. Strength of the Scientific Team supporting the Study;

Comment: not applicable.

10. Level of support guaranteed by the Institutes;

Comment: not applicable.

11. Budgeted cost of the Study;

Comment: Appropriate to good value, assuming the concept is technically sound.

-- AlWootten - 2017-07-19
Topic revision: r1 - 2017-07-19, AlWootten
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