Nikhil M. Kriplani’s research while affiliated with North Carolina State University and other places

SUMMARY Power amplifier asymmetry is captured by a behavioural model that contains multiple slices representing the amplifier's nonlinearity and long-term, that is low frequency, memory. The simulation is performed entirely in the time domain, and the expense associated with performing a purely transient radio frequency (RF) simulation is circumvented by scaling down the carrier frequency by two orders of magnitude. This leads to a manageable transient simulation with results scaling back to the original carrier frequency. The model is empirical and can be easily implemented in any general purpose circuit simulation environment. The baseband portion of the model parameters was extracted and the simulation result was compared with measurement, thereby demonstrating that a nonlinear and accurate transient analysis routine can be effectively employed to capture memory-related RF power amplifier phenomena. Copyright © 2012 John Wiley & Sons, Ltd.

A parallel transient simulation technique for multiphysics circuits is presented. The technique develops partitions utilizing the inherent delay present within a circuit and between physical domains. A state-variable-based circuit delay element is presented, which implements the coupling between two spatially or temporally isolated circuit partitions. A parallel delay-based iterative approach for interfacing delay-partitioned subcircuits is applied, which achieves the reasonable accuracy of nonparallel circuit simulation if both incorporate the same interblock delay. The partitioned subcircuits are distributed to different cores of a shared-memory multicore processor and solved in parallel. A multithreaded implementation of the methodology using OpenMP is presented. Examples showing superlinear speedup compared to unpartitioned single-core simulation using the direct method are presented. This paper also discusses the impact of load balancing and absolute delay on simulation speedup.

The essence of radar, radio and wireless sensor engineering is extracting small information-bearing signals. This is notoriously difficult and engineers compensate by transmitting high power signals, reducing range, and spacing wireless systems in frequency and time. New understandings of passive intermodulation distortion, thermal effects, time-frequency effects, and noise are presented. It is seen that the familiar frequency-domain-based abstractions have missed important underlying physics. Through greater understanding, RF engineers can develop microwave systems with far lower levels of distortion and noise.

A transient electrothermal simulation of a 3-D integrated circuit (3DIC) is reported that uses dynamic modeling of the thermal network and hierarchical electrothermal simulation. This is a practical alternative to full transistor electrothermal simulations that are computationally prohibitive. Simulations are compared to measurements for a token-generating asynchronous 3DIC clocking at a maximum frequency of 1 GHz. The electrical network is based on computationally efficient electrothermal macromodels of standard and custom cells. These are linked in a physically consistent manner with a detailed thermal network extracted from an OpenAccess layout file. Coupled with model-order reduction techniques, hierarchical dynamic electrothermal simulation of large 3DICs is shown to be tractable, yielding spatial and temporal selected transistor-level thermal profiles.

Physics-based compact electrothermal macromodels of standard cells are developed for fast dynamic simulation of three-dimensional integrated circuits (3DICs). Such circuits can have high thermal densities and thermal effects often limit their performance. The macromodels developed here use fewer state-variables than a discrete transistor-level implementation while retaining transistor-level accuracy. This results in significant speed-up over transistor-level simulation for large-scale circuits. The macromodel-based methodology enables robust and significantly faster dynamic electrothermal simulation over the long times required for thermal transients to subside. Consequently, transient junction temperature can be examined in the design phase. Simulated junction and measured surface thermal transients are compared.

A transient electrothermal simulation of a 3-D integrated circuit (3DIC) is reported that uses dynamic modeling of the thermal network and hierarchical electrothermal simulation. This is a practical alternative to full transistor electrothermal simulations that are computationally prohibitive. Simulations are compared to measurements for a token-generating asynchronous 3DIC clocking at a maximum frequency of 1 GHz. The electrical network is based on computationally efficient electrothermal macromodels of standard and custom cells. These are linked in a physically consistent manner with a detailed thermal network extracted from an OpenAccess layout file. Coupled with model-order reduction techniques, hierarchical dynamic electrothermal simulation of large 3DICs is shown to be tractable, yielding spatial and temporal selected transistor-level thermal profiles.

This article reports a new method for transient analysis of nonlinear circuits based on nonlinear device state variables and waves at their ports. The method is based on relaxation and thus does not require large matrix decompositions if time step is constant. The use of waves results in guaranteed convergence for any linear passive circuit and some types of nonlinear circuits. Additionally, the formulation using waves ensures that nonlinear devices are always excited with a physically meaningful input, i.e., the amount of power transmitted to nonlinear devices is bounded. The method was implemented in the fREEDA™ circuit simulator. The formulation, its properties, and a convergence analysis of the proposed method are presented first, followed by case studies. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2011.

A method for circuit-level modelling a physically realistic Esaki tunnel diode model is presented. A paramaterisation technique that transforms the strongly nonlinear characteristic of a tunnel diode into two relatively modest nonlinear characteristics is demonstrated. The introduction of an intermediate state variable results in a physically realistic mathematical model that is not only moderately nonlinear and therefore robust, but also single-valued.

This paper presents a dynamic simulation methodology using a reduced order compact macromodel of standard cells. The standard cell macromodels are formulated with a smaller number of state variables compared to an equivalent transistor-level implementation. This results in significant speed-ups over transistor-level simulation for large scale circuits. Such reduction in state variables also reduces memory usage. The macromodels are based on transistor equations, and simulation using these models produces results in excellent agreement (delay errors below 1%) with transistor-level simulation results. Various examples showing 1.5x−100x reduction in dynamic simulation time and 1.5x−2.8x reduction in memory usage are presented.

A combined transient simulation of a 300 MHz input, 20 MHz output RF radio transceiver system was performed using an industry standard FDTD simulator integrated with an open source state-variable based multi-physics simulator. The two simulators were interfaced at every time step and several nonlinear iterations were performed at each step in order to ensure simulation convergence of the system which contains strong nonlinearities and a wide range of signal strengths at different points in the system.