Bruce Jacob - - Circuit Integrity Research
Circuit Integrity Research: OverviewCircuit integrity refers to a large class of problems that can cause circuits to misbehave, including lack of signal integrity. Due to the pronounced trends of reduced feature sizes, reduced operating voltage levels, and increased operating frequencies (in which a significant portion of the signal time is spent in transition between levels), modern digital systems are becoming more susceptible to elecromagnetic emissions (noise), thermal effects, and voltage fluctuations. I bundle these issues all together and call the field Circuit Integrity, a term that I stole from the field of electrical cabling. In that field it means "the completeness or intactness of an electrical wire or circuit," but here I use it to mean the correct behavior of all the components necessary for the correct operation of a typical digital system (clock network, data/control signals, power/ground references).
The main issues on which our research group is focusing include EMI (electromagnetic interference) and temperature gradients. EMI is problematic because RF that couples to wires and devices in a system can be interpreted by that system as a valid signal, thereby disrupting the correct function of the circuit. Temperature gradients are problematic because temperature differentials across a chip cause separate regions of the chip to slow down at different rates (the hotter a circuit gets the slower it propagates signals). In a synchronous system, where all components are expected to operate in lock-step, such speed differentials spell certain disaster.
To date, we have developed an EMI-resistant microarchitecture called TERPS that allows a microprocessor to continue even in the face of severe (intentional) EMI; we have performed RF studies, physical experiments of the effects that injected RF has on digital circuits; and we have developed a test chip to perform temperature experiments (shown at the top of the page).
If you have any questions, please contact me.
TERPS: The Embedded Reliable Processing SystemElectromagnetic Interference (EMI) can have an adverse effect on commercial electronics. As feature sizes of integrated circuits become smaller, their susceptibility to such EMI increases. In light of this, integrated circuits will face substantial problems in the future either from electromagnetic disturbances or intentionally generated EMI from a malicious source (intentional EMI). In this work we introduce a fault tolerant architecture, TERPS, which can significantly reduce the threat of intentional EMI in computer systems. By employing a checkpoint and rollback recovery mechanism tied with 3D IC technology, TERPS can recover from substantial EMI without having to shutdown or reboot. In the face of such EMI, only a loss in performance dictated by the strength and duration of the interference and the frequency of checkpointing will be seen. We present the TERPS architecture and its functionality. The assumptions and experimental setup are described in detail. Various ways chips can fail under EMI are discussed. Finally performance impacts are provided along with future work.
This work is detailed in the following papers:
RF Effects on Digital CircuitsRadio frequency interference (RFI) can have adverse effects on commercial electronics. Current properties of high performance integrated circuits (ICs), such as very small feature sizes, high clock frequencies, and reduced voltage levels, increase the susceptibility of these circuits to RFI, causing them to be more prone to smaller interference levels. Also, recent developments of mobile devices and wireless networks create a hostile electromagnetic environment for ICs. Therefore, it is important to measure the susceptibility of ICs to RFI. In this study, we investigate the susceptibility levels to RFI of the clock network of a basic digital building block. Our experimental setup is designed to couple a pulse modulated RF signal using the pin direct injection method. The device under test is an 8-bit ripple counter, designed and fabricated using AMI 0.5um technology. Our experiments showed that relatively low levels of RFI (e.g., 16.8 dBm with carrier frequency of 1GHz) could adversely affect the normal functioning of the device under test.
This work is detailed in the following paper:
Highly Integrated, Heterogeneous Systems-on-Chip
(note: this section is cross-listed with the Embedded Systems page)It is clear from the decades-long trends of miniaturization and integration that future systems-on-chip will combine all technologies currently found in modern embedded systems -- including digital, analog and MEMS components. We are working to develop interfaces, models, and basic understanding to make this integration possible. Current (published) work focuses on integrating digital signal processing with MEMS sensors, and developing high-level power models for (digital) SoC components such as cores, memories, I/O controllers, and busses. Other work includes topologies and protocols for networks-on-chip and related issues in circuit integrity.
Details can be found in the following papers:
Temperature StudiesAs mentioned, we have developed a temperature-gradient Device-Under-Test (shown at top of page) ... the test is currently under development. Results by end of 2005, we hope.