펄스 기반 피드 포워드 이퀄라이저를 갖춘 고용량 DRAM을 위한 컨트롤러 PHY 설계

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 김수환.A controller PHY for managed DRAM solution, which is a new memory structure to maximize capacity while minimizing refresh power, is presented. Inter-symbol interference is critical in such a high-capacity DRAM interface in which many DRAM chips share a command/address (C/A) channel. A pulse-based feed-forward equalizer (PB-FFE) is introduced to reduce ISI on a C/A channel. The controller PHY supports all the training sequences specified in the DDR4 standard. A glitch-free DCDL is also adopted to perform link training efficiently and to reduce training time. The DQ transmitter adopts quarter-rate architecture to reduce output latency. For the quarter-rate transmitters in DQ, we propose a quadrature error corrector (QEC), in which clock signal phase errors are corrected using two replicas of the 4:1 serializer of the output stage. Pulse shrinking is used to compare and equalize the outputs of these two replica serializers. A controller PHY was fabricated in 55nm CMOS. The PB-FFE increases the timing margin from 0.23UI to 0.29UI at 1067Mbps. At 2133Mbps, the read timing and voltage margins are 0.53UI and 211mV after read training, and the write margins are 0.72UI and 230mV after write training. To validate the QEC effectiveness, a prototype quarter-rate transmitter, including the QEC, was fabricated to another chip in 65nm CMOS. Adopting our QEC, the experimental results show that the output phase errors of the transmitter are reduced to a residual error of 0.8ps, and the output eye width and height are improved by 84% and 61%, respectively, at a data-rate of 12.8Gbps.본 연구에서 용량을 최대화하면서도 리프레시 전력을 최소화할 수 있는 새로운 메모리 구조인 관리형 DRAM 솔루션을 위한 컨트롤러 PHY를 제시하였다. 이와 같은 고용량 DRAM 인터페이스에서는 많은 DRAM 칩이 명령 / 주소 (C/A) 채널을 공유하고 있어서 심볼 간 간섭이 발생한다. 본 연구에서는 이러한 C/A 채널에서의 심볼 간 간섭을 줄이기 위해 펄스 기반 피드 포워드 이퀄라이저 (PB-FFE)를 채택하였다. 또한 본 연구의 컨트롤러 PHY는 DDR4 표준에 지정된 모든 트레이닝 시퀀스를 지원한다. 링크 트레이닝을 효율적으로 수행하고 트레이닝 시간을 줄이기 위해 글리치가 발생하지 않는 디지털 제어 지연 라인 (DCDL)을 채택하였다. 컨트롤러 PHY의 DQ 송신기는 출력 대기 시간을 줄이기 위해 쿼터 레이트 구조를 채택하였다. 쿼터 레이트 송신기의 경우에는 직교 클럭 간 위상 오류가 출력 신호의 무결성에 영향을 주게 된다. 이러한 영향을 최소화하기 위해 본 연구에서는 출력 단의 4 : 1 직렬 변환기의 두 복제본을 사용하여 클록 신호 위상 오류를 수정하는 QEC (Quadrature Error Corrector)를 제안하였다. 복제된 2개의 직렬 변환기의 출력을 비교하고 균등화하기 위해 펄스 수축 지연 라인이 사용되었다. 컨트롤러 PHY는 55nm CMOS 공정으로 제조되었다. PB-FFE는 1067Mbps에서 C/A 채널 타이밍 마진을 0.23UI에서 0.29UI로 증가시킨다. 읽기 트레이닝 후 읽기 타이밍 및 전압 마진은 2133Mbps에서 0.53UI 및 211mV이고, 쓰기 트레이닝 후 쓰기 마진은 0.72UI 및 230mV이다. QEC의 효과를 검증하기 위해 QEC를 포함한 프로토 타입 쿼터 레이트 송신기를 65nm CMOS의 다른 칩으로 제작하였다. QEC를 적용한 실험 결과, 송신기의 출력 위상 오류가 0.8ps의 잔류 오류로 감소하고, 출력 데이터 눈의 폭과 높이가 12.8Gbps의 데이터 속도에서 각각 84 %와 61 % 개선되었음을 보여준다.CHAPTER 1 INTRODUCTION 1 1.1 MOTIVATION 1 1.1.1 HEAVY LOAD C/A CHANNEL 5 1.1.2 QUARTER-RATE ARCHITECTURE IN DQ TRANSMITTER 7 1.1.3 SUMMARY 8 1.2 THESIS ORGANIZATION 10 CHAPTER 2 ARCHITECTURE 11 2.1 MDS DIMM STRUCTURE 11 2.2 MDS CONTROLLER 15 2.3 MDS CONTROLLER PHY 17 2.3.1 INITIALIZATION SEQUENCE 20 2.3.2 LINK TRAINING FINITE-STATE MACHINE 23 2.3.3 POWER DOWN MODE 28 CHAPTER 3 PULSE-BASED FEED-FORWARD EQUALIZER 29 3.1 COMMAND/ADDRESS CHANNEL 29 3.2 COMMAND/ADDRESS TRANSMITTER 33 3.3 PULSE-BASED FEED-FORWARD EQUALIZER 35 CHAPTER 4 CIRCUIT IMPLEMENTATION 39 4.1 BUILDING BLOCKS 39 4.1.1 ALL-DIGITAL PHASE-LOCKED LOOP (ADPLL) 39 4.1.2 ALL-DIGITAL DELAY-LOCKED LOOP (ADDLL) 44 4.1.3 GLITCH-FREE DCDL CONTROL 47 4.1.4 DUTY-CYCLE CORRECTOR (DCC) 50 4.1.5 DQ/DQS TRANSMITTER 52 4.1.6 DQ/DQS RECEIVER 54 4.1.7 ZQ CALIBRATION 56 4.2 MODELING AND VERIFICATION OF LINK TRAINING 59 4.3 BUILT-IN SELF-TEST CIRCUITS 66 CHAPTER 5 QUADRATURE ERROR CORRECTOR USING REPLICA SERIALIZERS AND PULSE-SHRINKING DELAY LINES 69 5.1 PHASE CORRECTION USING REPLICA SERIALIZERS AND PULSE-SHRINKING UNITS 69 5.2 OVERALL QEC ARCHITECTURE AND ITS OPERATION 71 5.3 FINE DELAY UNIT IN THE PSDL 76 CHAPTER 6 EXPERIMENTAL RESULTS 78 6.1 CONTROLLER PHY 78 6.2 PROTOTYPE QEC 88 CHAPTER 7 CONCLUSION 94 BIBLIOGRAPHY 96Docto

Comparison of Individual Retinal Layer Thicknesses between Highly Myopic Eyes and Normal Control Eyes Using Retinal Layer Segmentation Analysis

The incidence of myopia is increasing worldwide, and the investigation on pathophysiology of myopia is becoming more important. This retrospective study aimed to compare the thicknesses of individual retinal layers between high-myopic and control eyes, and to evaluate the effects of age and sex on each retinal layer thickness. We assessed 164 subjects and divided them into two groups based on axial length (AL) (i.e., high-myopic group (AL ≥ 26 mm) and control group (AL < 26 mm)). Individual retinal layer thicknesses of five subfields in the macula were measured using automated retinal segmentation software packaged with the spectral-domain optical coherence tomography and were compared. In high-myopia group, the thicknesses of total retina and all individual retinal layers in central and entire perifoveal subfields were significantly thicker than the corresponding layers in control group after adjustment for ocular magnification (all P < 0.05). There were no significant effects of sex on individual retinal thicknesses, and age had less negative effects on the thicknesses of retina layers in high-myopic eyes than normal eyes. Axially elongated, non-pathologic highly myopic eyes had different structural features than control eyes, with significantly greater individual macular layer thicknesses independent of sex or age.ope

Significant elevation of aqueous endothelin-1 in central retinal vein occlusion

Purpose: To investigate aqueous humor concentrations of endothelin-1 (ET-1) in patients with central retinal vein occlusion (CRVO) compared with patients with branch retinal vein occlusion (BRVO) and a normal control group. Methods: A total 80 subjects were included in this prospective study, including 15 patients with CRVO, 20 patients with BRVO, and 45 patients who underwent cataract surgery and had no concomitant ocular disease. Aqueous humor levels of ET-1 were obtained before intravitreal bevacizumab injection (IVB) and after 1 month. Results: At baseline, the mean aqueous ET-1 level was 12.7±3.6 pg/mL in the CRVO group, 8.0±2.3 pg/mL in the BRVO group, and 2.0±0.9 pg/mL in the control group (P<0.001). After IVB, the mean aqueous level of ET-1 was 3.4±1.9 pg/mL (0.5-6.9 pg/mL) in the CRVO group and 1.8±1.0 pg/mL (0.3-3.2 pg/mL) in the BRVO group (P = 0.008). The mean aqueous ET-1 level was significantly reduced in both the patients with CRVO and those with BRVO (P<0.001). Conclusion: The mean aqueous humor ET-1 level was significant higher in the patients with CRVO than those with BRVO and in the control group. After IVB, the mean level was significantly reduced in both the patients with CRVO and those with BRVO.ope

Changes in peripapillary and subfoveal choroidal thickness in patients with central retinal vein occlusion

Purpose: We sought to evaluate changes of mean peripapillary choroidal thickness (PCT) and subfoveal choroidal thickness (SFCT) over 12 months in patients with unilateral central retinal vein occlusion (CRVO). Methods: Our retrospective, observational study included 19 patients with treatment-naïve, unilateral CRVO who completed at least 12 months of follow-up period. Mean PCT and mean SFCT in CRVO-affected eyes and unaffected contralateral eyes were measured at each follow-up visit, and then compared. Differences between baseline and 12 months (ΔSFCT and ΔPCT) and percentage changes (ΔSFCT or ΔPCT/baseline×100%) were determined. We also investigated the predictive factors for visual outcome in the CRVO-affected eyes. Results: In the CRVO-affected eyes, mean PCT was 146.7±41.9 μm at baseline, and 106.5±24.2 μm at 12 months (P < 0.001). Mean PCT of the contralateral eyes was 129.8±42.6 μm at baseline and 124.6±39.7 μm at 12 months (P = 0.089). Mean SFCT of CRVO-affected eyes was 225.8±77.9 μm at baseline, and 199.4±66.6 μm at 12 months (P = 0.009). Mean SFCT of the contralateral eyes was 218.4±83.0 μm at baseline, and 208.4±78.1 μm at 12 months (P = 0.089). Δ PCT was -41.6±25.3 μm in the CRVO-affected eyes, and -5.2±5.8 μm in the contralateral eyes (P<0.001). % PCT was -24.9±14.0% in the CRVO-affected eyes, and -4.0±0.4% in the contralateral eyes (P = 0.001). Δ SFCT was -26.4±24.6 μm in the CRVO-affected eyes, and -9.5±16.7μm in the contralateral eyes (P = 0.016). % SFCT was -10.4±9.8% in the CRVO-affected eyes, and -3.4±6.4% in the contralateral eyes (P = 0.015). Among the various factors, BCVA at baseline (β = 0.797, P = 0.001) and % SFCT (β = 0.712, P = 0.001) were significantly associated with visual outcome at 12 months in the CRVO-affected eyes. Conclusion: Both peripapillary and subfoveal choroidal thickness reduced significantly over 12 months in the CRVO-affected eyes, but not in the contralateral eyes. In addition, the absolute reduction amount and reduction ratio of PCT and SFCT were significantly greater in the CRVO-affected eyes than the contralateral eyes.ope

Ocular wavefront aberrations in patients with macular diseases

BACKGROUND: There have been reports that by compensating for ocular aberrations using adaptive optical systems it may be possible to improve the resolution of clinical retinal imaging systems beyond what is now possible. To develop such a system to observe eyes with retinal disease, understanding of ocular wavefront aberrations in individuals with retinal disease is required. METHODS: Eighty-two eyes of 66 patients with macular disease (epiretinal membrane, macular edema, macular hole, etc.) and 85 eyes of 51 patients without retinal disease were studied. Using a ray-tracing wavefront device, each eye was scanned at both small and large pupil apertures, and Zernike coefficients up to the sixth order were acquired. RESULTS: In phakic eyes, third-order root mean square errors in the macular disease group were statistically greater than in the control group, an average of 12% for 5-mm and 31% for 3-mm scan diameters (P < 0.021). In pseudophakic eyes, there was also an elevation of third-order root mean square, on average 57% for 5-mm and 51% for 3-mm scan diameters (P < 0.031). CONCLUSION: Higher-order wavefront aberrations in eyes with macular disease were greater than in control eyes without disease. This study suggests that such aberrations may result from irregular or multiple reflecting retinal surfaces. Modifications in wavefront sensor technology will be needed to accurately determine wavefront aberration and allow correction using adaptive optics in eyes with macular irregularities.ope

Visual acuity and multifocal electroretinographic changes after arteriovenous crossing sheathotomy for macular edema associated with branch retinal vein occlusion

PURPOSE: To evaluate the influence of arteriovenous (AV) sheathotomy on retinal function with central multifocal electroretinography (mfERG) in eyes with macular edema secondary to branch retinal vein occlusion (BRVO). METHODS: Fifteen patients (15 eyes) who underwent AV sheathotomy for macular edema secondary to BRVO were included in the study. Best-corrected visual acuity and mfERG responses from the most central seven hexagons were analyzed before and 6 months after the operation. RESULTS: The mean preoperative Early Treatment Diabetic Retinopathy Study (ETDRS) score +/- SD was 34.1 +/- 12.7 letters (Snellen equivalent, 20/50) and significantly improved up to 40.5 +/- 10.9 letters (Snellen equivalent, 20/40) at 6 months after AV sheathotomy (P = 0.027, Wilcoxon signed rank test). The mean preoperative P1 amplitude +/- SD of the most central 7 hexagons was 39.30 +/- 10.86 nV/deg(2) for the affected eye versus 47.72 +/- 6.67 nV/deg(2) for the normal fellow (control) eye (P = 0.013, Mann-Whitney U test) and significantly increased up to 50.71 +/- 15.58 nV/deg at 6 months after the operation (P = 0.014, Wilcoxon signed rank test). Significant correlations between preoperative and postoperative ETDRS score and preoperative P1 amplitude were present (r = 0.929, P < 0.001; r = 0.768, P = 0.001; respectively [Spearman correlation]). CONCLUSIONS: AV sheathotomy improved macular function and anatomical outcome as measured by ETDRS score and mfERG responses in patients with macular edema due to BRVO.ope

Long-term treatment response after intravitreal bevacizumab injections for patients with central serous chorioretinopathy

Purpose: To investigate long-term treatment response after intravitreal bevacizumab injections (IVBIs) for central serous chorioretinopathy (CSC). Methods: This retrospective, interventional study investigated the medical records of 45 eyes of 44 patients with CSC who underwent IBVIs and completed at least 2-year follow-up period. Complete resolution (CR) was defined as complete resolution of subretinal fluid at least 3 months after the last IVBI. Thick-choroid CSC was defined as mean subfoveal choroidal thickness more than 300.0 μm. The main outcome measure was long-term treatment outcome after IVBIs in patients with CSC. Results: Thirty-five patients (79.5%) were male, and their mean age was 45.5 ± 9.6 years. The mean follow-up period was 35.1 ± 11.5 months. Twenty-two eyes (48.9%) had acute CSC, and 40 eyes (88.9%) achieved CR. Twenty eyes (50.0%) developed recurrence, the mean number of IVBIs to achieve the first CR was not significantly different between eyes with and without recurrences (2.6 ± 1.6 vs. 2.9 ± 1.9; P = 0.658). Thick-choroid CSC was significantly difference between the eyes with and without recurrence (17 eyes, 85.0% vs. eyes, 50.0%; P = 0.020). Among the baseline characteristics, serous pigment epithelial detachment (B = - 2.580, P = 0.032) and thick-choroid (B = 1.980, P = 0.019) were significantly associated with recurrence. Conclusion: Eyes with CSC treated with IVBI and achieving complete resolution of subretinal fluid have 50% chance of recurrence in the long term. Thinner choroid and serous pigment epithelial detachment appear protective for recurrences.ope

Elevated aqueous endothelin-1 concentrations in advanced diabetic retinopathy

Purpose: Endothelin-1 (ET-1) is a potent vasoconstrictor which seems to be involved in the pathogenesis of diabetic retinopathy (DR). However, studies on intraocular ET-1 in DR have been limited. Thus, we investigated aqueous ET-1 levels in patients with DR. Methods: A total 85 subjects were included in this prospective study. Those were classified into three groups: advanced DR group included those with severe nonproliferative DR or proliferative DR, whereas early DR group included those with mild nonproliferative DR or moderative nonproliferative DR. Those who underwent cataract surgery and had no concomitant ocular disease were included in the control group. Aqueous humor levels of ET-1 were obtained before intravitreal bevacizumab injection (IVB) and after 1 month for the DR patients, and at the time of cataract surgery for the control group. Results: Advanced DR group included 40 eyes (47.1%), whereas early DR group did 19 eyes (22.4%), and control group (26 eyes, 30.5%). Mean aqueous ET-1 level was 10.1±4.1 pg/mL (6.0-21.0 pg/mL) in advanced DR group, 1.9±0.7 pg/mL (0.6-2.8 pg/mL) in early DR group, and 2.1±1.0 pg/mL (0.7-3.9 pg/mL) in control group (P < 0.001). Advanced DR group was further subdivided into severe nonproliferative DR (15 eyes, 12.8%) and proliferative DR (25 eyes, 34.3%). Mean aqueous ET-1 level was 10.1±4.3 pg/mL (6.0-20.1 pg/mL) in patients with severe nonproliferative DR, and 10.0±4.0 pg/mL (6.0-21.0 pg/mL) in those with proliferative DR (P = 0.928) at baseline. Mean ET-1 level at 1 month after intravitreal injection was 2.5±1.0 pg/mL (0.3-4.8 pg/mL) in patients with severe proliferative DR and 2.9±1.7 pg/mL (1.0-7.0 pg/mL) in those with proliferative DR (P = 0.443). Mean aqueous ET-1 level was significantly reduced in both groups (P < 0.001, respectively). Conclusion: The mean aqueous ET-1 level was significantly higher in the eyes with advanced DR than those with early DR and the control group. The mean aqueous ET-1 level was significantly reduced after intravitreal injections in the advanced DR group. Based on our results, future studies on the exact role of ET-1 in the pathogenesis of DR and future implication for intervention would be helpful for managing DR.ope

Prevalence of focal lamina cribrosa defects in eyes with pachychoroid disease spectrum

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Focal lamina cribrosa defects and significant peripapillary choroidal thinning in patients with unilateral branch retinal vein occlusion

Purpose: To investigate the prevalence of focal lamina cribrosa (LC) defects in patients with unilateral branch retinal vein occlusion (BRVO) and to compare ocular characteristics between eyes with and without focal LC defect and those eyes with normal-tension glaucoma (NTG). Methods: This retrospective, cross-sectional study included 121 patients. Thirty-nine patients had unilateral BRVO (BRVO group), 36 patients had NTG (NTG group), and 36 patients had vitreous floaters, but no other ocular diseases (control group). In addition to baseline characteristics such as age, sex, refractive errors, the ocular characteristics such as peripapillary choroidal thickness (PCT), retinal nerve fiber layer thickness, and subfoveal choroidal thickness were retrospectively analyzed. Results: Focal LC defects were detected in 20 eyes of 14 patients (38.9%) in the BRVO group, 24 eyes of 15 patients (41.7%) in the NTG group, and none in the control group (P<0.001). In the BRVO-affected eyes, the mean PCT was 102.7±31.1 μm in the eyes with focal LC defects, and 163.1±70.1 μm in the eyes without LC defects (P = 0.009). In the BRVO-affected eyes, the mean PCT was 102.7±31.1 μm in the eyes with focal LC defects, and 163.1±70.1 μm in the eyes without LC defects (P = 0.009). In the NTG group, the mean PCT was 133.1±48.9 μm in the eyes with focal LC defects and 170.8±81.9 μm in those without (P = 0.042). The other baseline and ocular characteristics were not significantly different between the eyes with and without focal LC defects in both the BRVO group and the NTG group. Conclusions: About 40% of the patients with unilateral BRVO had focal LC defect in the BRVO-affected eyes and unaffected fellow eyes, similar prevalence to the patients with NTG. The mean PCT was significantly thinner in the eyes with focal LC defect than those without in the patients with BRVO and those with NTG, suggesting possible pathophysiologic correlation between these two diseases.ope