Technology Independent Synthesis of CMOS Operational Amplifiers

Analog circuit design does not enjoy as much automation as its digital counterpart. Analog sizing is inherently knowledge intensive and requires accurate modeling of the different parametric effects of the devices. Besides, the set of constraints in a typical analog design problem is large, involving complex tradeoffs. For these reasons, the task of modeling an analog design problem in a form viable for automation is much more tedious than the digital design. Consequently, analog blocks are still handcrafted intuitively and often become a bottleneck in the integrated circuit design, thereby increasing the time to market. In this work, we address the problem of automatically solving an analog circuit design problem. Specifically, we propose methods to automate the transistor-level sizing of OpAmps. Given the specifications and the netlist of the OpAmp, our methodology produces a design that has the accuracy of the BSIM models used for simulation and the advantage of a quick design time. The approach is based on generating an initial first-order design and then refining it. In principle, the refining approach is a simulated-annealing scheme that uses (i) localized simulations and (ii) convex optimization scheme (COS). The optimal set of input variables for localized simulations has been selected by using techniques from Design of Experiments (DOE). To formulate the design problem as a COS problem, we have used monomial circuit models that are fitted from simulation data. These models accurately predict the performance of the circuit in the proximity of the initial guess. The models can also be used to gain valuable insight into the behavior of the circuit and understand the interrelations between the different performance constraints. A software framework that implements this methodology has been coded in SKILL language of Cadence. The methodology can be applied to design different OpAmp topologies across different technologies. In other words, the framework is both technology independent and topology independent. In addition, we develop a scheme to empirically model the small signal parameters like \u27gm\u27 and \u27gds\u27 of CMOS transistors. The monomial device models are reusable for a given technology and can be used to formulate the OpAmp design problem as a COS problem. The efficacy of the framework has been demonstrated by automatically designing different OpAmp topologies across different technologies. We designed a two-stage OpAmp and a telescopic OpAmp in TSMC025 and AMI016 technologies. Our results show significant (10–15%) improvement in the performance of both the OpAmps in both the technologies. While the methodology has shown encouraging results in the sub-micrometer regime, the effectiveness of the tool has to be investigated in the deep-sub-micron technologies

Enhanced photoelectrochemical activity of Co-doped β-In2S3 nanoflakes as photoanodes for water splitting

This work is primarily focused on indium sulfide (β-In2S3) and cobalt (Co)-doped β-In2S3 nanoflakes as photoanodes for water oxidation. The incorporation of cobalt introduces new dopant energy levels increasing visible light absorption and leading to improved photo-activity. In addition, cobalt ion centers in β-In2S3 act as potential catalytic sites to promote electro-activity. 5 mol% Co-doped β-In2S3 nanoflakes when tested for photoelectrochemical water splitting exhibited a photocurrent density of 0.69 mA cm−2 at 1.23 V, much higher than that of pure β-In2S3

Effect of carbon materials on In2S3 for PEC water splitting

Energy consumption is one of the primary global challenges in the present scenario. Photo electrochemical (PEC) water splitting is one of the attractive solutions to solve the energy crisis. The primary focus of this thesis work is to look at different carbon materials like reduced graphene oxide (RGO), carbon nanotubes (CNT), graphene for their role as photosensitizers of semiconductor materials in PEC water splitting. In this work, we have used β-In2S3 as a photoactive semiconductor which intrinsically has low electrical conductivity and high recombination rate. We have studied the property enhancement of β-In2S3 using various carbons. Pure In2S3 sample showed a photocurrent density of 0.25 μA/cm2. However, addition of carbons to β-In2S3 led to much improved photocurrents. Photocurrent densities of 0.007, 0.8 and 0.9 mA/cm2 are observed for In2S3 - Graphene (5 mg), In2S3 - CNT (2 mg), In2S¬3 - RGO (10 mg) composites respectively at 1.23 V vs RHE. The massive improvement in current densities in the case of RGO and CNT is due to the polar functional groups on their surface which helps in growth of In2S3 on the surface of these carbons. If we compare CNT vs RGO, we required much lower loading of CNT (2mg) to achieve the same current density as for RGO loading which required much higher loading (10mg). However, these studies showed that the use of carbons can significantly improve the performance of semiconducting materials for water splitting

Tin disulfide based ternary composites for visible light driven photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting could potentially solve the global energy crisis and environmental pollution. In the present work, ternary composites consisting of 2D nanomaterials of SnS2, reduced graphene oxide (RGO), and mesoporous graphitic carbon nitride (mpg-C3N4) are synthesized with layered architecture. The photocurrent density of the ternary composite is 1.45 mA/cm 2 at 1.23 V vs RHE, which is over 23 times higher than that of pure SnS2. The superior photocatalytic activity of mpg-C3N4/SnS2/RGO composite is attributed to synchronous effects of all the materials leading to enhanced electron-hole pair separation, as well as increased visible-light absorption