Metastability in cmos pdf

This paper presents a detailed analysis of metastable behavior in cmos current mode logic cml latches. We perform a suitable generalization of metastability to the dynamic case, applying it. This all is possible by the scaling technology where the overall chip size get reduced but due to manufacturing and fabrication. Asic designed for a 28nm highperformance cmos process.

In section3 metastability dependence on the risefall time of the clock signal is derived. Cmos implementation of reliable synchronizer for multi. As shown in figure, when a clocked flipflop synchronizes an asynchronous input there is a small probability that the output exhibits an unpredictable response. Comparative analysis of metastability with d flip flop in cmos circuits manisha thakur nri institute of information and science technology, bhopal, india puran gaur nri institute of information and science technology, bhopal, india braj bihari soni nri institute of information and science technology, bhopal, india abstract. A study of metastability in cmos latches lehigh preserve. In digital logic circuits, a digital signal is required to be within certain voltage or current limits to represent a 0 or 1 logic level for correct circuit operation. Metastability is a phenomenon that can cause system failure in digital devices, including fpgas, when a signal is transferred between circuitry in unrelated or asynchronous clock domains.

The manual calculation serves as a first order approximation of the metastable voltage. The outcome is intermittent or random failures during operation. Ijca comparative analysis of metastability with d flip. Baumann, radiationinduced soft errors in advanced semiconductor technologies, eee trans. We conclude that it is possible to contain metastability to a limited part of the circuit instead of attempting to resolve, detect, or avoid it altogether. Metastability finite state machines electronics tutorial. The typical flipflops in figure 2 comprise master and slave latches and decoupling inverters. The understanding of the suitability of the flipflops and select the best topology for a given application is important to meet the need of the design to meet low power and high performance circuit subject. Yukawa, a cmos 8bit highspeed ad converter ic, jssc june 1985, pp. It can present a brief pulse at a flipflop output called a runt pulse or cause flipflop output oscillations. Comparative analysis of metastability with d flip flop in cmos circuits. We perform a suitable generalization of metastability to the dynamic case, applying it to a cmos dynamic dlatch. Fast digital trng based on metastable ring oscillator.

Digital logic metastability index output waveforms output waveforms due to signal timing da, db, dc da produces a normal output, as the data does not violate the setup or hold time of the device in relation to the clock. Comparative analysis of metastability with d flip flop in. Impact of technology scaling on metastability performance of cmos synchronizing latches maryam shojaei baghini, madhav p. Gain accuracy is the worst for resistive pullup as resistors poly, diffusion. Metastability of cmos masterslave flipflops circuits and systems. Analysis of metastable operation in a cmos dynamic dlatch. The variation of the latch delay is primarily caused by the finite current transition time, which in fact depends on the risefall times of the. One common way to demonstrate metastability is to supply two clocks that differ very slightly in frequency to the data and clock inputs topics. Using these parameters, calculations of mtbf under varying conditions are performed. Faster logic families oftenbut not alwayshave faster metastable resolutions. Albicki, analysis of metastable operation in rs cmos flipflops.

Dc analysis analyze dc characteristics of cmos gates by studying an inverter dc analysis dc value of a signal in static conditions dc analysis of cmos inverter egat lo vtupn i,nvi vout, output voltage single power supply, vdd ground reference. Comparator metastability analysis metastability 2 of 6 the designers guide community 1 metastability metastability is a problem that occurs in all latching comparators when the input is near the comparator decision point 3. The schematic of the measurement setup is shown in fig. Latched comparator eecs instructional support group home page. Metastability performance of clocked fifos texas instruments. Cmos technology introduction classification of silicon technology silicon ic technologies bipolar bipolarcmos mos junction isolated dielectric isolated oxide isolated cmos pmos aluminum gate nmos aluminum gate silicon gate aluminum gate silicon gate silicongermanium silicon 03121101 ece 4420 cmos technology 121103 page 2.

Figure 11 from analysis of metastability in pipelined adcs. Metastabilitysynchronizer metastability is a type of failure which occurs when digital circuits attempt to synchronize asynchronous digital data. Metastability of cmos latchflipflop semantic scholar. Design techniques for ultrahighspeed timeinterleaved. Metastability modelling although we have described metastability in terms of. Impact of technology scaling on metastability performance of.

A tutorial ran ginosar technion israel institute of technology metastability events are common in digital circuits, and synchronizers are a necessity to protect us from their fatal effects. The most common way to tolerate metastability is to add one or more successive synchronizing flipflops to the synchronizer. Robust metastabilitybased trng design in nanometer cmos with. Metastability analysis of cmos current mode logic latches. Abstract in this paper, we use circuit simulations to. A ball resting in a hollow on a slope is a simple example of metastability. Impact of technology scaling on metastability performance. If the ball is only slightly pushed, it will settle back into its hollow, but a stronger push may start the ball rolling down the slope. Metastability can appear as a flipflop that switches late or doesnt switch at all.

As previously explained, the latch behavior of a flipflop, can be described by a pair of static gates. Metastabilitycontaining circuits stephan friedrichs1,2, matthias fugger 3, and christoph lenzen1 1max planck institute for informatics, saarland informatics campus, germany email. Reliability analysis of synchronizers reliability of two flop synchronizer is based on probability of entering metastability and exiting from metastability. It explains how metastability mtbf is calculated, and highlights how various device and design parameters affect the result. The main metastability parameters of cmos latches are. An embedded 240mw 10b 50mss cmos adc in 1mm2, ieee jssc, vol. In physics, metastability is a stable state of a dynamical system other than the systems state of least energy. Ijca comparative analysis of metastability with d flip flop.

Nmos pullup suffers from body effect, affecting gain setting accuracy. Pdf metastability analysis of cmos current mode logic. Metastability in digital systems occurs when two asynchronous signals combine in such a way that their resulting output goes to an indeterminate state. Request pdf metastability analysis of cmos current mode logic latches this paper presents a detailed analysis of metastable behavior in cmos current mode logic cml latches.

When the clock skewslew is too much rise and fall time are more than the tolerable values. A comprehensive approach to modeling, characterizing and. However, if the input is around the vs2 point when the latch samples, theres a possibility the latch will. Characterization and reduction of metastability errors in cmos interface circuits clemenz lenard portmann technical report no. Introducing an asynchronous signal into a digital synchronized system, using flipflops. Analysis of metastability in pipelined adcs sedigheh hashemi, behzad razavi the allen institute for ai proudly built by ai2 with the help of our collaborators using these sources. In this paper, we use circuit simulations to characterize the effects of technology scaling. Robust metastabilitybased trng design in nanometer cmos with subvdd precharge and hybrid selfcalibration vikram b. Metastability characteristics depend on circuit factors, such as internal gainbandwidth product. Pdf metastability requirements for a 2 ghz cmos modulator. This paper presents the design of a second order, single bit, cmos, continuoustime analog to digital delta sigma modulator m which samples at 2 ghz, consumes 18 mw at 1. Metastability of cmos latchflip flop abstract this paper presents the optimal device size, aspect ratio, and configurations for the design of the metastable hardened cmos latchflipflop by using the ac smallsignal analysis in the frequency domain instead of the usual timedomain approach.

For example, the material in ref 1 measures a t of 0. In this work, we demonstrate that dynamic memory cells present an anomalous behavior referred to as metastable operation with characteristics similar to those of static latches. While this chapter focuses uniquely on the cmos inverter, we will see in the following chapter that the same methodology also applies to other gate topologies. Metastability arises at the moment the latch samples.

Robust metastability based trng design in nanometer cmos with subvdd precharge and hybrid selfcalibration vikram b. Semiconductor cmos logic and to transistor behavior under intermediate input voltage levels. Using these data the designer can determine the influence of metastable states in an application and take any necessary countermeasures. Metastability is a widespread phenomenon and errors may occur in any synchronous circuit where an input signal can change randomly with respect to a reference signal 1 4. For a simple cmos latch, valid data must be present on the input for a specified period of time before the. Stable state 0 stable state 1 metastable state figure 1. Edn keep metastability from killing your digital design. This paper presents the design of a second order, single bit, cmos, continuoustime analog to digital delta sigma modulator m which samples. Our investigation in cmos technology showed that such a circuit could be implemented on an inverter. The new technologies are giving the advance systems which are capable to perform multiple operations simultaneously. Metastability synchronizer metastability is a type of failure which occurs when digital circuits attempt to synchronize asynchronous digital data. Metastability in electronics is the ability of a digital electronics system to persist for an unbounded time in an unstable equilibrium or metastable state.

Metastability gain settling time smallsignal bw, slew rate overdrive recovery memory cmrr power consumption. This approach allows for an entire clock period except for the setup time of the second flipflop for metastable events in the first synchronizing flipflop to resolve themselves. Originally, synchronizers were requiredwhen reading an asynchronous input that is, an input not synchronized with. Digital logic metastability and flip flop mtbf calculation.

As we have seen that whenever setup and hold violation time occurs, metastability occurs, so we have to see when signals violate this timing requirement. Cmos layout and simulation is shown in fig 16 and fig 17. Understanding metastability in fpgas july 2009, ver. Metastability of cmos latchflipflop solidstate circuits. Request pdf impact of technology scaling on metastability performance of cmos synchronizing latches. Dc analysis analyze dc characteristics of cmos gates by studying an inverter dc analysis dc value of a signal in static conditions dc analysis of cmos inverter egat lo vtupn i,nvi vout, output voltage single power supply, vdd ground reference find vout fvin voltage transfer characteristic. Section2 briefly describes the operation of the cml latch.

A circuit simulator can give us a more precise calculation. If the input is a stable high or low voltage when the latch samples, then it will work properly. Robust metastabilitybased trng design in nanometer. Pmos pullup has no body effect, but is subject to pn matching. The cmos inverter quantification of integrity, performance, and energy metrics of an inverter optimization of an inverter design 5. Metastability ability to make correct decisions overdrive recovery memory power consumption. This paper presents a detailed analysis of the metastable behavior in the cml latches.

This paper describes metastability in fpgas, explains why the phenomenon occurs, and discusses how it can cause design failures. Latched comparator eecs instructional support group. Metastability of cmos latchflipflop custom integrated. Mechanical metastability in flipflops, metastability means indecision of whether the output should be. The single latch analysis can then be easily extended to a cascade of latches such as found in a masterslave. International journal of computer applications 10316. Srikanth jagannathan, shijiewen, richard wong performance, metastability, and softerrorrobustness tradeoffs for flipflops in 40 nm cmos ieee transactions on circuits and systemsi. May 10, 2014 2the most common way to tolerate metastability is to add one or more successive synchronizing flipflops to the synchronizer. Thus, it is required to build a circuit with the ability to be put into a metastable state. Statistical modeling of metastability in adcbased serial io.