Fast modeling of core switching noise on distributed LRC power gridin ULSI circuits

As technology scales, power supply noise caused by core logic switching becomes critical. Shorter signal rise edge, high integration density, and necessity of using on-chip decoupling capacitors require that the on-chip power distribution should be modeled as an LRC transmission line network with millions of switching devices. In this paper, we propose a sophisticated power grid model consisting of distributed LRC elements excited by constant voltage sources and switching capacitors. Based on this, fast equations for core switching noise estimations were formulated. Full-chip noise distribution on the power grid with any topology was efficiently and accurately computed. SPICE simulations confirmed its efficiency and accuracy. Experimental results obtained on our benchmark circuits revealed that the proposed technique speeded up simulations by several orders of magnitude compared with SPICE, whereas typical relative error was between 0±5%. By integrating a packaging model, the new model predicts accurately the upper boundaries of noise level for power bounce, ground bounce, and differential-mode power noise. Meanwhile, locations of hot spots in the power network are precisely identified. The model is suitable for full-chip rapid simulations for on-chip power distribution design in advanced ultra large scale integration (ULSI) circuits, particularly for early stage analysis, in which global and local optimization such as topology selection, power bus sizing, and on-chip decoupling capacitor placement can be easily conducted     

Substrate noise generation in complex digital systems: efficient modeling and simulation methodology and experimental verification

More and more system-on-chip designs require the integration of analog circuits on large digital chips and will therefore suffer from substrate noise coupling. To investigate the impact of substrate noise on analog circuits, information is needed about digital substrate noise generation. In this paper, a recently proposed simulation methodology to estimate the time-domain waveform of the substrate noise is applied to an 86-Kgate CMOS ASIC on a low-ohmic epi-type substrate. These simulation results have been compared with substrate noise measurements on this ASIC and the difference between the simulated and measured substrate noise rms voltage is less than 10%. The simulated time domain waveform and frequency spectrum of the substrate noise correspond well with the measurements, indicating the validity of this simulation methodology. Both measurements and simulations have been used to analyze the substrate noise generation in more detail. It has been found that direct noise coupling from the on-chip power supply to the substrate dominates the substrate noise generation and that more than 80% of the substrate noise is generated by simultaneous switching of the core cells. By varying the parameters of the simulation model, it has been concluded that a flip-chip packaging technique can reduce the substrate noise rms voltage by two orders of magnitude when compared to traditional wirebonding.     

On the impact of on-chip inductance on signal nets under the influence of power grid noise

It has been well recognized that the impact of on-chip inductance on some critical nets, such as clock nets, is significant and cannot be ignored in delay modeling for these nets. However, the impact of on-chip inductance on signal nets in general is still not well understood. We present results of analyzing inductive effects on signal nets for ultradeep submicron technologies under the influence of power grid noise. The analysis is based on an Al-based 0.18-/spl mu/m CMOS process and a Cu-based 0.13-/spl mu/m CMOS process. The impact of on-chip inductance is shown to be insignificant if we assume a perfect power supply network around the interconnect routes. Otherwise, the impact of on-chip inductance can be significant. Furthermore, the results presented in this paper illustrate the impact of on-chip inductance one would expect from transitioning from an Al-based interconnect technology to a Cu-based interconnect technology. A heuristic method is proposed in the paper to account for the inductive coupling due to power grid noise in signal delay modeling and simulations.     

On the use of high-impedance power supplies to reduce the substrate switching noise in system-on-chips

This paper analyzes the generation and the propagation in system-on-chips of the switching noise due to embedded core logic blocks. Such disturbances contribute to degrade the performance of the other on-chip circuits and cause unwanted electromagnetic emission. These parasitic effects can be largely ascribed to the steep currents that flow into the power supply interconnects of the core logic blocks and to the parasitic coupling of the system-on-chip building blocks through the silicon substrate they share.In this work it is shown that the substrate voltage bounce due to the switching noise can be significantly attenuated if conventional low-impedance DC power supplies are replaced by high-impedance one. The effectiveness of the proposed approach is validated through computer simulations and experimental tests carried out on the digital core block of a test chip.     

Analysis of the PLL jitter due to power/ground and substrate noise

Phase-locked loops (PLL) in radio-frequency (RF) and mixed analog-digital integrated circuits (ICs) experience substrate coupling due to the simultaneous circuit switching and power/ground (P/G) noise which translate to a timing jitter. In this paper. an analysis of the PLL timing jitter due to substrate noise resulting from P/G noise and large-signal switching is presented. A general comprehensive stochastic model of the substrate and P/G noise sources in very large-scale integration (VLSI) circuits is proposed. This is followed by calculation of the phase noise of the constituent voltage-controlled oscillator (VCO) in terms of the statistical properties of substrate and P/G noise. The PLL timing jitter is then predicted in response to the VCO phase noise. Our mathematical method is utilized to study the jitter-induced P/G noise in a CMOS PLL, which is designed and simulated in a 0.25-/spl mu/m standard CMOS process. A comparison between the results obtained by our mathematical model and those obtained by HSPICE simulation prove the accuracy of the predicted model.     

Inductance model and analysis methodology for high-speed on-chip interconnect

With operating frequencies entering the multi-gigahertz range, inductance has become an important consideration in the design and analysis of on-chip interconnects. In this paper, we present an accurate and efficient inductance modeling and analysis methodology for high-performance interconnect. We determine the critical elements for a PEEC based model by analyzing the current flow in the power grid and signal interconnect. The proposed model includes distributed interconnect resistance, inductance and capacitance, device decoupling capacitances, quiescent switching currents in the grid, pad connections, and pad/package inductance. We propose an efficient methodology for extracting these elements, using statistical models for on-chip decoupling capacitance and switching currents. Simulation results show the importance of various elements for accurate inductance analysis. We also demonstrate the accuracy of the proposed model compared to the traditional loop-based inductance approach. Since the proposed model can consist of hundreds of thousands of RLC elements, and a fully dense mutual inductance matrix, we propose a number of acceleration techniques that enable efficient analysis of large interconnect structures.     

Modeling techniques for energy-efficient system-on-a-chip signaling

In order to tackle noise, delay, and power in the deep-submicron age, the most efficient approach is to design power-efficient and robust signaling techniques that allow for reliable communication between CMOS gates. This is referred to as energy-efficient on-chip-signaling. To design, optimize, and compare different signaling schemes, it is important to properly model on-chip wires. This article describes several techniques used in interconnect modeling. It focuses on the efficient modeling of on-chip wires, investigates the impact of inductive and capacitive coupling on the quality of the signal and the wire-load model, and contains a quantification of the impact of the wire model on the design of efficient signaling techniques.     

Performance degradation of LC-tank VCOs by impact of digital switching noise in lightly doped substrates

In mixed analog-digital designs, digital switching noise is an important limitation for the performance of analog and RF circuits. This paper reports a physical model describing the impact of digital switching noise on LC-tank voltage-controlled oscillators (VCOs) in lightly doped substrates. The model takes into account the propagation from the source of substrate noise to the different components in the VCO and the resulting modulation of the oscillator frequency. The model is validated with measurements on a 3.5-GHz LC-tank VCO designed in 0.18-/spl mu/m CMOS. It reveals that for this VCO, impact occurs mainly via the nonideal metal ground lines for lower frequencies and low tuning voltage and via the integrated inductors for higher frequencies and high tuning voltage. To make the design immune to substrate noise, the parasitic resistance of the on-chip ground interconnect has to be kept as low as possible and inductors have to be shielded. Hence, the developed model allows investigating the dominant mechanisms behind the impact of substrate noise on a VCO, which is crucial information for achieving a substrate noise immune design.     

Simultaneous switching noise in on-chip CMOS power distribution networks

Simultaneous switching noise (SSN) has become an important issue in the design of the internal on-chip power distribution networks in current very large scale integration/ultra large scale integration (VLSI/ULSI) circuits. An inductive model is used to characterize the power supply rails when a transient current is generated by simultaneously switching the on-chip registers and logic gates in a synchronous CMOS VLSI/ULSI circuit. An analytical expression characterizing the SSN voltage is presented here based on a lumped inductive-resistive-capacitive RLC model. The peak value of the SSN voltage based on this analytical expression is within 10% as compared to SPICE simulations. Design constraints at both the circuit and layout levels are also discussed based on minimizing the effects of the peak value of the SSN voltage.     

Modeling of On-Chip Bus Switching Current and Its Impact on Noise in Power Supply Grid

In this paper, an analytical model for the current draw of an on-chip bus is presented. The model is combined with an on-chip power supply grid model in order to analyze noise caused by switching buses in a power supply grid. The bus is modeled as distributed resistance–inductance–capacitance (RLC) lines that are capacitively and inductively coupled to each other. Different switching patterns and driver skewing times are also included in the model. The power supply grid is modeled as a network of RLC segments. The model is verified by comparing it to HSPICE. The error was below 8%. The model is applied to determine the influence of driver skewing times on maximum power supply noise.      

Noise generation,propagation and effects on RF components in system-on-a-chip packaging

Substrate coupling noise effects in wireless receiver systems in terms of the crosstalk power spectral density induced from the fast switching digital circuits is the center of study in this paper. Deterioration in performance of a low noise amplifier is plotted against various values of die-attach inductance, inductance on digital ground pins, physical separation between the analog and digital circuits on-chip, number of simultaneous switching output buffers, etc. Different Ball Grid Array Packages, both the wire bonded and flip-chip attached versions have been studied. The return loss and insertion loss for paths from the on-chip wire bond pad to connect pads on the printed circuit boards have been plotted. Results show that noise reduces by a greater amount for reduction in die-attach inductance as compared to a reduction in inductance on the digital ground pin.     

Modeling and measurement of simultaneous switching noise coupling through signal via transition

The signal via is a heavily utilized interconnection structure in high-density System-on-Package (SoP) substrates and printed circuit boards (PCBs). Vias facilitate complicated routings in these multilayer structures. Significant simultaneous switching noise (SSN) coupling occurs through the signal via transition when the signal via suffers return current interruption caused by reference plane exchange. The coupled SSN decreases noise and timing margins of digital and analog circuits, resulting in reduction of achievable jitter performance, bit error ratio (BER), and system reliability. We introduce a modeling method to estimate SSN coupling based on a balanced transmission line matrix (TLM) method. The proposed modeling method is successfully verified by a series of time-domain and frequency-domain measurements of several via transition structures. First, it is clearly verified that SSN coupling causes considerable clock waveform distortion, increases jitter and noise, and reduces margins in pseudorandom bit sequence (PRBS) eye patterns. We also note that the major frequency spectrum component of the coupled noise is one of the plane pair resonance frequencies in the PCB power/ground pair. Furthermore, we demonstrate that the amount of SSN noise coupling is strongly dependent not only on the position of the signal via, but also on the layer configuration of the multilayer PCB. Finally, we have successfully proposed and confirmed a design methodology to minimize the SSN coupling based on an optimal via positioning approach.     

Scaling trends of on-chip power distribution noise

The design of power distribution networks in high-performance integrated circuits has become significantly more challenging with recent advances in process technologies. As on-chip currents exceed tens of amperes and circuit clock periods are reduced well below a nanosecond, the signal integrity of on-chip power supply has become a primary concern in the integrated circuit design. The scaling behavior of the inductive and resistance voltage drops across the on-chip power distribution networks is the subject of this paper. The existing work on power distribution noise scaling is reviewed and extended to include the scaling behavior of the inductance of the on-chip global power distribution networks in high-performance flip-chip packaged integrated circuits. As the dimensions of the on-chip devices are scaled by S, where S>1, the resistive voltage drop across the power grids remains constant and the inductive voltage drop increases by S, if the metal thickness is maintained constant. Consequently, the signal-to-noise ratio decreases by S in the case of resistive noise and by S/sup 2/ in the case of inductive noise. As compared to the constant metal thickness scenario, ideal interconnect scaling of the global power grid mitigates the unfavorable scaling of the inductive noise but exacerbates the scaling of resistive noise by a factor of S. On-chip inductive noise will, therefore, become of greater significance with technology scaling. Careful tradeoffs between the resistance and inductance of the power distribution networks will be necessary in nanometer technologies to achieve minimum power supply noise.     

CAD-oriented equivalent-circuit modeling of on-chip interconnectson lossy silicon substrate

A new, comprehensive CAD-oriented modeling methodology for single and coupled interconnects on an Si-SiO₂ substrate is presented. The modeling technique uses a modified quasi-static spectral domain electromagnetic analysis which takes into account the skin effect in the semiconducting substrate. Equivalent-circuit models with only ideal lumped elements, representing the broadband characteristics of the interconnects, are extracted. The response of the proposed SPICE compatible equivalent-circuit models is shown to be in good agreement with the frequency-dependent transmission line characteristics of single and general coupled on-chip interconnects     

Electromagnetic interference (EMI) of system-on-package (SOP)

Electromagnetic interference (EMI) issues are expected to be crucial for next-generation system-on-package (SOP) integrated high-performance digital LSIs and for radio frequency (RF) and analog circuits. Ordinarily in SOPs, high-performance digital LSIs are sources of EMI, while RF and analog circuits are affected by EMI (victims). This paper describes the following aspects of EMI in SOPs: 1) die/package-level EMI; 2) substrate-level EMI; 3) electromagnetic modeling and simulation; and 4) near electromagnetic field measurement. First, LSI designs are discussed with regard to radiated emission. The signal-return path loop and switching current in the power/ground line are inherent sources of EMI. The EMI of substrate, which work as coupling paths or unwanted antennas, is described. Maintaining the return current path is an important aspect of substrate design for suppressing EMI and for maintaining signal integrity (SI). In addition, isolating and suppressing the resonance of the DC power bus in a substrate is another important design aspect for EMI and for power integrity (PI). Various electromagnetic simulation methodologies are introduced as indispensable design tools for achieving high-performance SOPs without EMI problems. Measurement techniques for near electric and magnetic fields are explained, as they are necessary to confirm the appropriateness of designs and to investigate the causes of EMI problems. This paper is expected to be useful in the design and development of SOPs that take EMI into consideration.     

Analysis and experimental verification of digital substrate noisegeneration for epi-type substrates

Substrate coupling in mixed-signal IC's can cause important performance degradation of the analog circuits. Accurate simulation is therefore needed to investigate the generation, propagation, and impact of substrate noise. Recent studies were limited to the time-domain behavior of generated substrate noise and to noise injection from a single noise source. This paper focuses on substrate noise generation by digital circuits and on the spectral content of this noise. To simulate the noise generation, a SPICE substrate model for heavily doped epi-type substrates has been used. The accuracy of this model has been verified with measurements of substrate noise, using a wide-band, continuous-time substrate noise sensor, which allows accurate measurement of the spectral content of substrate noise. The substrate noise generation of digital circuits is analyzed, both in the time and frequency domain, and the influence of the different substrate noise coupling mechanisms is demonstrated. It is shown that substrate noise voltages up to 20 mV are generated and that, in the frequency band up to 1 GHz, noise peaks are generated at multiples of the clock and repetition frequency. These noise signals will strongly deteriorate the behavior of small signal analog amplifiers, as used in integrated front-ends     

Design strategies and decoupling techniques for reducing theeffects of electrical interference in mixed-mode IC's

A key issue in the successful integration of analog circuits is a stable analog power supply. Traditional on-chip decoupling methods exhibit transients in the supply or voltage drops and power losses. This paper introduces the RLC decoupling method that features an enhanced transient response while being especially suited for low-power, low voltage applications. Both a theoretical and a practical approach are presented together with measurement results. As the benefits of a stable local power supply can be lost by the inadequate connection of two subcircuits with relative variations on the local grounds, a differential approach of signal transfer is proposed. Furthermore, the effect of a good local decoupling can be deteriorated by substrate noise, so some attention is given to this problem too     

On-chip inductance cons and pros

Provides a high level survey of the increasing effects of on-chip inductance. These effects are classified into desirable and nondesirable effects. Among the undesirable effects of on-chip inductance are higher interconnect coupling noise and substrate coupling, challenges for accurate extraction, the required modifications of the infrastructure of CAD tools, and the inevitably slower CAD tools as compared to RC-based tools. Among the desirable effects is lower power consumption, less need for repeaters, faster signal rise time, and less delay uncertainty. The viability of design methodologies considering on-chip inductance is briefly discussed.     

An all-band TV tuner IC with 10-GHz 100-V mixed analog/digital Sibipolar technology

An all-band TV tuner IC with an on-chip PLL and a high-voltage output stage is developed. The use of a self-aligned bipolar technology called high-voltage compatible sidewall base contact structure (HV-SICOS) allows the integration of 1-GHz analog circuits, 1-GHz low-power ECL-I²L PLL circuits, and a 0.5- to 30-V tuning diode bias current on the same chip. The analog block has a VCO and mixer pair for the VHF/CATV and another pair for the UHF bands, a UHF input amplifier, an IF amplifier, and a VCO signal switching circuit. To suppress the digital noise level for mixed analog/digital mode operation, the PLL is constructed with high-speed ECL circuits for divide-by-four and dual modulus prescalers, and low-power I²L circuits. An isolation area is placed between the analog and digital blocks. Conversion gain of 24 dB for VHF/CATV and 33 dB for UHF, a noise figure of 10 dB, and 1% cross modulation of 95 dB-μV are obtained. This IC operates with a total power dissipation of 200 mW on a 3-mm×4-mm chip     

Noise considerations for mixed‐signal RF IC transceivers

This paper discusses design tradeoffs for mixedsignal radio frequency integrated circuit (RF IC) transceivers for wireless applications in terms of noise, signal power, receiver linearity, and gain. During air wave transmission, the signal is corrupted by channel noise, adjacent interfering users, image signals, and multipath fading. Furthermore, the receiver corrupts the incoming signal due to RF circuit nonlinearity (intermodulation), electronic device noise, and digital switching noise. This tutorial paper gives an overview of the design tradeoffs needed to minimize RF noise in an integrated wireless transceiver. Fundamental device noise and the coupling of switching noise from digital circuits to sensitive analog sections and their impact on RF circuits such as frequency synthesizers are examined. Methods to minimize mixedsignal noise coupling and to model substrate noise effects are presented.