An03 dws


Published on

Published in: Technology, Business
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

An03 dws

  1. 1. FM 1990-2009 AN 03 DWS & DWV MODELING AND SIMULATION OF SEMICUSTOM CMOS CHIPSOne of the problems in the silicon (considering slow-wave at transistor level by means of DWSdevelopment of new semicustom effects) is about 150ps/cm, the macro models (Fig. 2).CMOS arrays and families is the on problem has to be approached using The static transfer functions of thischip power distribution. In fact, theswitching noise caused by thesimultaneous activation of a large power pads power pads 101number of output buffers at the 201 301same time (for example an n-bits 401 81bus) can be dangerous for the core 16mA 16mAlogic timing. We present an 16mA 16mAapproach to the problem based on driv. rec. rec.transmission line modeling (TLM). 2 4This methodology shows goodresults in the current technology, 9 nor ring osc. IVIVIVIVwhere the transition time is 90comparable with the propagation 7 9delay of the interconnection on rec. rec.chip. The results show the impact 403of TLM methodology about noise 303margin analysis and propagation 203delay evaluation. Also slow-wave 103 power pads power padspropagation and package effects areconsidered. Fig. 1: CMOS integrated circuit scheme (transmission line model).INTRODUCTION transmission line modeling. The simple model (STF, STF1 and slow-wave effect is due to a STF2) have been optimized byThe increasing complexity of the propagation mode typical of MIS simulating the DWS modelnew semicustom CMOS families (Metal Insulator Semiconductor) behavior and comparing theand the increasing speed of the structures. This effect causes 2-3 waveforms to similar SPICEcurrent submicron technology are times increase in the delay time. simulation. STF models theemphasizing switching noise Moreover, also the rise time quadratic dependence of the drainproblems. In fact, CMOS circuitry increases due to the dispersion of current versus the gate sourceproduces more noise than the the frequency because the slow- voltage in saturation conditionbipolar equivalent. Taking in wave factor is not linear with while STF1 models the transitionaccount these issues is becoming frequency. between linear and saturationmore and more important for the The simulations reported in this region.development of new families, for document refer to the model shown Fig. 1 shows a typical semicustompower and ground topology and I/O in Fig. 1, and have been performed standard cell topology with abuffers and packages compatibility using the simulator DWS and his couple of external power andevaluation. Because the faster graphic environment DWV. All the ground rings for I/O buffers andtransition times are now around waveforms displayed are referred to input protection and another couple200ps, and the propagation delay on an external ground node. The cells of internal rings for pre buffer and described in the device are modeled logic core. A 9-nor ring oscillator
  2. 2. D Cgs b) two couples of effect has been noted, due to the VDD and GND common interconnection through G pads used at the package. STF TD1 TD2 STF 2 Cds opposite corner The simulations show the voltage Vgs of the chip; transients on both power and c) four couples ground rings probed at two opposite Cgs STF1 of VDD and corners of the chip. Fig. 3a shows Vds GND pads used, that it is possible to have different one for each values of the power ( V 0.3V) at corner of the the same time and different chip. locations due to noise wave A double propagation within the rings. This Ids k k1 bonding has been effect decreases with the increasing S considered for of the pads number for power and N_channel Vgs Vds k*Ids both VDD and ground on chip and their uniform GND signals. For distribution around the chip STF STF1 STF2 double bonding boundary. Ids k k1 is intended a Due to the ring structure of power normal procedure and ground distribution, and the P_channel Vgs Vds k*Ids sometimes used periodic occurrence of the noise in the definition stimulus, some areas on the chip are STF STF1 STF2 of the bonding noisier than others, due to noise diagram wave interference. This stationaryFig. 2: Example of macro model structure for MOS transistor with (connection chip- behavior depends on noisethe p-channel and n-channel static transfer function. package) in order frequency, on time constants to reduce the presented by the power ringoperating at about 40 MHz is used number of package pins dedicated distribution and power padsas core noise generator. Four 16mA for power and ground. Using this location (that causebus drivers (with 50pF external procedure, two different power discontinuities). It is interesting toload) are used as I/O switching pads on chip, related to internal and note that, for this particular case,noise generator. external power ring pads, are the configuration b) shows lessAll the internal connections are bonded to the same package cavity peak-to-peak noise than themodeled by means of transmission pin. As result, the two power configuration c).lines, as well as the package pins (a distributions for logic core andPGA has been modeled in this output buffers are decoupled on OUTPUT WAVEFORMScase). chip but a not-negligible couplingA first level of clock treedistribution is used to evaluate theeffects of the noise caused by the 7.00 V V(101)simultaneous switching of the 6.10 V V(201)peripheral output drivers on the V(103) 7.00 Vinternal signals (in the logic core) 5.20 V V(203) V(81) chip_1.gin terms of skew on jitter. 6.00 V 4.30 V V(81) 5.00 V chip_2.gPOWER AND GROUND 3.40 V V(81) 4.00 VSIMULTANEOUS SWITCHING chip_4.gNOISE WITHIN THE CHIP 2.50 V 3.00 V 1.60 V 2.00 VFig. 3 shows the simulated powerand ground noise for the following 0.70 V 1.00 Vpower distribution topology: 0.00 V -0.20 Va) only a couple of VDD and GNDpads used; -1.10 V -1.00 V a b -2.00 V -2.00 V c 200.00 -3.00 V 210.00 220.00 230.00 240.00 250.00 260.00 270.00 280.00 290.00 300.00 300.00 310.00 320.00 330.00 340.00 350.00 360.00 370.00 380.00 390.00 400.00 TIME[nS] TIME[nS] Fig. 3a: Power & ground voltage noise (1 P&G couple) Fig. 4: Output driver voltage (a=1 P&G couple, b=2 P&G couples, c=4 P&G couples)
  3. 3. 7.00 V V(101) V(201) 6.10 V V(103) 5.20 V V(203) An internal clock signal (Fig. 6a 4.30 V and 6b) has been analyzed at the 3.40 V driver output and at the input of 2.50 V two far receivers; the signals are displayed using eye-diagrams. It 1.60 V is possible to see that the 0.70 V propagation shows about 1ns of delay, 500ps of skew between the -0.20 V receiving taps and 500ps of jitter -1.10 V due to simultaneous switching -2.00 V noise. Simulations performed 200.00 210.00 220.00 230.00 240.00 250.00 260.00 270.00 280.00 290.00 300.00 using the RC (lumped or TIME[nS] distributed) model for the same Fig. 3b: Power & ground voltage noise (2 P&G couples) clock tree interconnection showed a delay evaluation which Due to the ground bouncing effects and GND package pins for I/O and is 30% lower than the result the output signals present an logic core. It is possible to note the obtained using TLM models. overshoot and undershoot of about noise shape and level differences on 2 V (Fig. 4). Increasing the number internal power and ground rings CONCLUSION of power pads, the slew-rate (nodes 301 and 401) for the two increases, so that the signals show configurations. In particular, in the The increasing speed of semicustom IC technologies leads7.00 V V(101) to a growing impact on system V(201) performance of on-chip signal6.10 V V(103) integrity issues related to both V(203)5.20 V signal interconnection and power4.30 V bouncing effects. Accurate models of interconnecting paths are needed3.40 V in order to get reliable results from2.50 V simulations and choose the best on-1.60 V chip interconnect structure. TLM0.70 V for both lossy slow-wave interconnect and for package-0.20 V effects is needed. This in turn-1.10 V requires the use of next generation-2.00 V simulation tools which are able to 200.00 210.00 220.00 230.00 240.00 250.00 260.00 270.00 280.00 290.00 300.00 deal with a large number of TIME[nS] transmission lines at very small Fig. 3c: Power & ground voltage noise (4 P&G couples) time-step (in the range of 5ps for CMOS technology). In this way the IC designer can more noise (no slew-rate control first case, the noise is mainly quickly evaluate several design has been assumed for the buffers correlated to the noise source in the alternatives for power supply, used). core. signal interconnections and The signal V(90) is the ring packaging issues. Transmission line BONDING AND INTERNAL oscillator output and it is shown as propagation on both signal and NOISE reference for noise correlation of noise paths frequently leads to ring bounces. difficult to predict or unexpected Fig. 5 shows the differences effects that can have a major impact between a chip supplied by double CLOCK SKEW AND NOISE on choosing the internal chip bonded pads (first four MARGIN EVALUATION architecture. simulations), or independent VDD
  4. 4. 1.16 V V(101) -1.14 V chip_2.g 6.10 V V(201) 3.96 V chip_2.g 1.14 V V(301) -1.12 V chip_2.g 5.88 V V(401) 3.94 V chip_2.g 1.41 V V(101) -1.18 V chip_2_spt.g 6.10 V V(201) 3.71 V chip_2_spt.g 0.91 V V(301) -1.17 V chip_2_spt.g 5.97 V V(401) 4.21 V chip_2_spt.g 5.59 V V(90) -0.75 V chip_2.g 100.00 130.00 160.00 190.00 220.00 250.00 280.00 310.00 340.00 370.00 400.00 TIME[nS] Fig. 5: Power and ground noise with double or single bonding6.00 V V(2)-1.00 V6.00 V V(7)-1.00 V6.00 V V(9)-1.00 V 110.00 112.00 114.00 116.00 118.00 120.00 122.00 124.00 126.00 128.00 130.00 TIME[nS] Fig. 6a: Internal clock signal: eye diagrams (2 P&G couples, single bonding) 5.75 V V(2) -0.82 V 5.73 V V(7) -0.76 V 5.69 V V(9) -0.72 V 110.00 112.00 114.00 116.00 118.00 120.00 122.00 124.00 126.00 128.00 130.00 TIME[nS] Fig. 6b: Internal clock signal: eye diagrams (2 P&G couples, double bonding)