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- 1. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Colorado Technical UniversityPSpice, L-Edit Designed NMOS Inverter Analysis Lab 4 Report Submitted to Professor R. Hoffmeister In Partial Fulfillment of the Requirements for EE 325-CMOS Design By Loren Karl Robinson Schwappach Student Number: 06B7050651 Colorado Springs, Colorado Due: 17 May 2010 Completed: 26 May 2010 1
- 2. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Table of ContentsLab Objectives ..................................................................................................................................................................................................................................... 3Requirements and Design Approaches/Trade-Offs .................................................................................................................................................................. 3L-Edit NMOS Inverter........................................................................................................................................................................................................................ 4 NMOS Inverter Cross Section ...................................................................................................................................................................................... 4 NMOS Inverter Design Rule Check ............................................................................................................................................................................ 4 NMOS Inverter L-Edit Extracted NMOS.SPC File ................................................................................................................................................... 5 NMOS Inverter Modified SCNA.SPC File ................................................................................................................................................................... 5Characteristic Curves for the NMOS Inverter ............................................................................................................................................................................. 6 Circuit Layout .................................................................................................................................................................................................................. 6 PSpice Simulation Results............................................................................................................................................................................................ 8Voltage Transfer Function of the NMOS Inverter ..................................................................................................................................................................... 9 Circuit Layout ................................................................................................................................................................................................................10 PSpice Simulation Results..........................................................................................................................................................................................11 Truth Table ....................................................................................................................................................................................................................11Power Consumption of the NMOS Inverter ..............................................................................................................................................................................12 PSpice Simulation Results..........................................................................................................................................................................................12Small Signal Characteristics of the NMOS Inverter ................................................................................................................................................................13 Circuit Layout ................................................................................................................................................................................................................13 PSpice Simulation Results..........................................................................................................................................................................................14Frequency Response of the NMOS Inverter .............................................................................................................................................................................15 Circuit Layout ................................................................................................................................................................................................................15 PSpice Simulation Results..........................................................................................................................................................................................16Propagation Delay and Rise/Fall Times of the NMOS Inverter ...........................................................................................................................................17 Circuit Layout ................................................................................................................................................................................................................17 PSpice Simulation Results................................................................................................................................................................................... 18-19Digital Frequency Response of the NMOS Inverter ................................................................................................................................................................20 PSpice Simulation Results................................................................................................................................................................................... 20-21Maximum Frequency of the circuit using the NMOS Inverter .............................................................................................................................................22 PSpice Simulation Results..........................................................................................................................................................................................22Summary of Results .........................................................................................................................................................................................................................23Conclusion and Recommendations .............................................................................................................................................................................................24 2
- 3. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Lab ObjectivesThis objective of this lab is to gain additional experience in the use and features of one of themost popular analog and digital simulation software packages; PSpice (specifically OrCADCapture CIS Demo Version 15.7). As an added objective, the user should complete this labassignment with a greater understanding of the common characteristics of N-channel MOSFET’s(NMOS) device, specifically the NMOS built for EE325 Lab 2 using L-Edit Student EditionVersion 7.2. The user should further be able to compare the characteristics of the NMOSinverter circuit against the IRF-150 Power MOSFET circuit analyzed during EE325 Lab 3. Thislab will evaluate/compare the L-Edit NMOS inverter characteristics against the IRF-150 resultsfrom Lab 3 by generating device characteristic curves, voltage transfer function, frequencyresponse diagram (bode plot), and time domain analysis of specific frequencies needed tocompute the characteristic rise/fall times, and propagation delays, and maximum frequency. Requirements and Design Approaches / Trade-offsThere are no specific design requirements for this project since it is not a design project, but aPSpice learning / inverter characteristic comparison lab. The primary objective of this lab is tolearn the procedures and methods in using the PSpice simulation software and to identify andanalyze key characteristics of the N-channel MOSFET (NMOS) inverter circuit while comparingthe results against the IRF-150 Power MOSFET inverter circuit analyzed for lab 3. The NMOSinverter circuit and data collected through this lab analysis will be compared again in lab 5. Tosuccessfully accomplish the PSpice analysis of the NMOS inverter, the user must havesuccessfully completed EE 325 lab 2 using L-Edit. The user must have extracted theNMOS.SPC file created during lab 2, the L-Edit SCNA.SPC file edited during lab 2, Cross-Section results from lab 2, DRC results from lab 2, and L-Edit NMOS Tanner Database Filefrom lab 2. These files should be compared against the figures / data presented on the followingpages. 3
- 4. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics L-Edit N-Channel MOSFET (NMOS) Inverter LayoutFigure 1: L-Edit NMOS Inverter created for EE325 Lab 2. A slight modification to Lab 2 NMOS left ActiveLayer and it’s contained Metal layers was accomplished, in order to eliminate the DRC errors created by Lab 2, due to the Drain, Gate, and Source Metal layers (had to be 3 µm apart). However this modification still allowed the NMOS W=18 µm and L = 6 µm. The layers used in the L-Edit design of this NMOS inverter are identified below... light purple = P-Select layer, teal = N-Select layer, red = Poly layer (width = 6µm), green = two Active layers {inside the (P / N)-Select layers} both heights = 18µm, blue = four Metal layers with assigned ports (Substrate, Source, Gate, and Drain), black = Contact layers (12 Active {inside Metal/Active layers}, and 1 Poly {Metal/Poly layer}. L-Edit NMOS Inverter Cross SectionObtaining the NMOS Inverters cross section was accomplished by clicking Tools/Cross-Section and clicking on the NMOS inverter using the “Pick” button. Figure 2: EE325 Lab 2 L-Edit NMOS Inverter Cross Section. L-Edit NMOS Inverter Design Rule CheckThe DRC errors were removed by increasing left Active/Metal layer spacing as shownabove. -------------------- NMOS.SPC --------------------- DRC Errors in cell Cell0 of file G:CMOS DesignLAB 4NMOS. 0 errors. DRC Merge/Gen Layers Elapsed Time: 0.000000 seconds. DRC Test Elapsed Time: 0.000000 seconds. DRC Elapsed Time: 0 seconds. ------------------------------------------------------- 4
- 5. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics L-Edit NMOS Inverter Extracted FileSome important things to not about this file, are the “Node Name Aliases”, these are the netaliases names that must be used in PSpice. Also mentioned are L=6 µm and W = 18 µm. -------------------- NMOS.CSE --------------------- * Circuit Extracted by Tanner Researchs L-Edit V7.12 / Extract V4.00 ; * TDB File: G:CMOS DesignLAB 4NMOS, Cell: Cell0 * Extract Definition File: C:LEditmosismorbn20.ext * Extract Date and Time: 05/25/2010 - 21:49 * WARNING: Layers with Unassigned AREA Capacitance. * <Poly Resistor> * <Poly2 Resistor> * <N Diff Resistor> * <P Diff Resistor> * <N Well Resistor> * <P Base Resistor> * WARNING: Layers with Unassigned FRINGE Capacitance. * <Pad Comment> * <Poly Resistor> * <Poly2 Resistor> * <N Diff Resistor> * <P Diff Resistor> * <N Well Resistor> * <P Base Resistor> * <Poly1-Poly2 Capacitor> * WARNING: Layers with Zero Resistance. * <Pad Comment> * <Poly1-Poly2 Capacitor> * <NMOS Capacitor> * <PMOS Capacitor> * NODE NAME ALIASES * 1 = Gate (12,33) * 2 = Drain (5,33) * 3 = Source (19,33) * 4 = Substrate (29,33) M1 Source Gate Drain Substrate NMOS L=6u W=18u AD=126p PD=50u AS=126p PS=50u * M1 DRAIN GATE SOURCE BULK (8 9 14 27) * Total Nodes: 4 * Total Elements: 1 * Extract Elapsed Time: 0 seconds .END ------------------------------------------------------- Edited SCNA.CSE File Required for L-Edit NMOS Inverter in PSpiceLines 2 and 11 of this file were edited to change CMOSN to NMOS and CMOSP to PMOS. -------------------- SCNA.SPC --------------------- * THESE ARE TYPICAL SCNA SPICE LEVEL 2 PARAMETERS .MODEL NMOS NMOS LEVEL=2 LD=0.250000U TOX=417.000008E-10 + NSUB=6.108619E+14 VTO=0.825008 KP=4.919000E-05 GAMMA=0.172 + PHI=0.6 UO=594 UEXP=6.682275E-02 UCRIT=5000 + DELTA=5.08308 VMAX=65547.3 XJ=0.250000U LAMBDA=6.636197E-03 + NFS=1.98E+11 NEFF=1 NSS=1.000000E+10 TPG=1.000000 + RSH=32.740000 CGDO=3.105345E-10 CGSO=3.105345E-10 CGBO=3.848530E-10 + CJ=9.494900E-05 MJ=0.847099 CJSW=4.410100E-10 MJSW=0.334060 PB=0.800000 * Weff = Wdrawn - Delta_W * The suggested Delta_W is -0.25 um .MODEL PMOS PMOS LEVEL=2 LD=0.227236U TOX=417.000008E-10 + NSUB=1.056124E+16 VTO=-0.937048 KP=1.731000E-05 GAMMA=0.715 + PHI=0.6 UO=209 UEXP=0.233831 UCRIT=47509.9 + DELTA=1.07179 VMAX=100000 XJ=0.250000U LAMBDA=4.391428E-02 + NFS=3.27E+11 NEFF=1.001 NSS=1.000000E+10 TPG=-1.000000 + RSH=72.960000 CGDO=2.822585E-10 CGSO=2.822585E-10 CGBO=5.292375E-10 + CJ=3.224200E-04 MJ=0.584956 CJSW=2.979100E-10 MJSW=0.310807 PB=0.800000 * Weff = Wdrawn - Delta_W * The suggested Delta_W is -1.14 um -------------------------------------------------------- 5
- 6. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Characteristic Curves for the NMOS Inverter CircuitIn order to begin analyzing the L-Edit NMOS inverter, you must have OrCAD 15.7 Demoinstalled (or a later, working variant). Next open OrCAD Capture CIS and create a newproject using Analog / Mixed (A/D). After the project space is ready a design schematicshould be built as shown in figure 3 below. Building a schematic is as simple as layingdown parts and connecting the components with wire. The main PSpice parts/componentswe will use in this lab are (Rectangle {acts as a virtual holder for the L-Edit NMOS inverter},VDC, VAC, VPULSE, 0Ground, C/ANALOG, R/ANALOG, and Net Alias). A rectangle wasdrawn to act as a virtual placeholder for the L-Edit NMOS inverter device. Once you haveeverything pieced together, and you have to place the correct net aliases consistent withthe L-Edit NMOS inverter {Gate, Drain, Substrate, and Source} as in figure 3, you are readyto run a PSpice simulation. First, create a new simulation profile. You must include the L-Edit NMOS inverter “NMOS.SPC” (extracted) and modified “SCNA.SPC” (L-Edit directory)files by locating them and clicking “Add to Design” under the “Configuration Files” tab(figure 4). Next, set the simulation settings to use a DC Sweep, with a Primary Sweep of“Vdrain” from 0 V to 5 V in small 1 mV increments (figure 5), and a Secondary Sweep of“Vgate” from 0 V to 5 V in 1 V increments (figure 6). The result of this simulation is seenin figure 7. Vdrain 5Vdc 0 Drain Gate NMOS (Extracted) Device Substrate W / L = 18 / 6 Vgate 5Vdc Source RS 0 1 0 0 Circuit used for generating the L-Edit NMOS inverter (Id - Vd) curves. Figure 3: PSpice circuit used for the L-Edit NMOS inverter Id-Vd curves. 6
- 7. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Figure 4: PSpice Simulation Settings: Configuration Files requires for analyzing the L-Edit NMOS Inverter in PSpice.Figure 5: DC Sweep, Primary Sweep Config. Figure 6: DC Sweep, Secondary Sweep Config. 7
- 8. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics 1.0mAI Characteristic Curves for the L-Edit NMOS InverterD Primary Sweep: Vdrain (0-5 Vdc), .001 V increment V_Vgate = 5 Vr Secondary Sweep: Vgate (0-5 Vdc), 1 V increment Note: Lab 3 IRF-150 curve at V_Vgate = 5 V flattened ata approx. (2 V, 7 A) vs L-Edit NMOS (3 V, 950 uA)i Notice NMOS curves flatten out at largern voltages than the IRF-150 curves but also at much smaller currents than the IRF-150 curves. V_Vgate = 4 V 0.5mA Note: Lab 3 IRF-150 curve at V_Vgate = 4 V flattened at approx. (1 V, 2 A) vs L-Edit NMOS (2.4 V, 570 uA) V_Vgate = 3 V V_Vgate = 2 V V_Vgate = 1 V Note: V_Vgate < 1V curve is not visible 0A 0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0V -I(Vdrain) V_Vdrain Figure 7: Characteristic curves for the L-Edit NMOS Inverter. (0-5 V Sweeps).Noted in figure 7 above, the L-Edit NMOS inverter curves flattened out at larger Vdrainvoltages than the IRF-150 Power MOSFET curves (3 V {NMOS} vs. 2 V {IRF-150} whenV_Vgate = 5 V) but at a much lower Vdrain currents (950 µA {NMOS} vs. 7 A {IRF-150}when V_Vgate = 5 V). 8
- 9. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Voltage Transfer Function for the NMOS Inverter CircuitTo generate the voltage transfer function (Vout vs. Vin) of the L-Edit NMOS inverter, thecircuit design was updated to include a 50 kΩ resister after the VDC source “Vdrain”, and a1 pF capacitor after the 50 kΩ resister going to ground. Two net aliases “Vout” and “Vin”were then added until the circuit finally matched the circuit shown by figure 8.Next the circuit simulation settings were again adjusted. After the Secondary Sweep wasremoved, the Primary Sweep was updated to sweep “Vgate” from 0 V to 5 V in small 1mVincrements (figure 9). The new simulation was run with the results shown by the bottomhalf of figure 10. You may need to add a trace of “V(Vout)” if you didn’t attach a voltageprobe to Vout.Next, a line with a slope of 1 was drawn originating from (0 V, 0 V) to (3 V, 3 V). Theintersection of this line with the voltage transfer function graph of V(Vout) was noted asthe L-Edit NMOS inverters logic threshold or switching point. This threshold voltage is thepoint where Vin = Vout, and was determined to be approximately 1.8299 V (-27% of Ideal).The Ideal inverters Logic Threshold is V DD/2 – 0 = 2.5 V. The IRF-150 Power MOSFET’slogic threshold was approx 2.86 V (+15% of Ideal).Next a new plot was added to graph the slope (derivative) of “Vout” (Top half of figure 10).Creating a new plot is as simple as clicking plot/new plot and giving the new plot a trace(In this case d(V(Vout))). The points where the new slope = -1 are used to define the noisemargins of this inverter. An easy way to find these locations is by using the searchcommand and typing “search forward level(-1)”. Using this technique twice to find bothlocations where the slope = -1 the following could be defined. Once found you can identifythe specific x-value with the “search forward xvalue(###)” command, where ### is the x-value you are searching for. After adding these coordinates the following data wasobtained. L-Edit NMOS Noise Margin Comparison Table NMOS IRF-150 NMOS Noise Magin Comparison Ideal IRF-150 NMOS abs. diff in % % error % error Parameter Inverter Inverter Inverter error (vs. Ideal) (vs. Ideal) (vs. IRF-150) Logic Threshold or Switching Point 2.5 V 2.8682 V 1.8299 V +15% -27% 12% worse VIH = minimum HIGH input voltage 2.5 V 2.8965 V 2.1214 V +16% -15% 1% better VIL = maximum LOW input voltage 2.5 V 2.8311 V 941.732 mV +13% -62% 49% worse VOH = minimum HIGH output voltage 5V 4.9886 V 4.9105 V 0% -2% 2% worse VOL = maximum LOW output voltage 0V 32.908 mV 711.519 mV N/A N/A N/A Noise Margin Low = NML = VIL – VOL 2.5 V 2.798 V 230 mV +12% -91% 79% worse Noise Margin High = NMH = VOH – VIH 2.5 V 2.092 V 2.7891 V -16% 12% 4% better Table 1: L-Edit NMOS Noise Margin Comparison Table, all percentages are rounded, last column is a difference comparison of the IRF-150’s % error to ideal to the L-Edit NMOS inverter %error to ideal. 9
- 10. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Vdrain 5Vdc 0 R1 50k Vout Drain Vin Gate NMOS (Extracted) Device Substrate CL W / L = 18 / 6 1pF Vgate 5Vdc Source RS 0 1 0 0 0 Circuit used for generating the L-Edit NMOS inverter voltage transfer function (Vout vs. Vin)Figure 8: PSpice circuit for generating the L-Edit NMOS inverter voltage transfer function (Vout vs. Vin). Notice the addition of R1 (50 kΩ), CL (1 pF), and Net Aliases Vout, and Vin. Figure 9: PSpice simulation setup parameters for the NMOS inverter voltage transfer function. 10
- 11. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics 0 S l (941.732m,-1.0000) Graph of V(Vout)s Slope o Interesting points are where Slope = -1 Slope of V(Vout) = -1 p (2.1214,-1.0000) These points determine Vin(low) and Vin(high) e -2.5 Slope of V(Vout) = -1 Used for finding NML and NMH -5.0 D(V(Vout)) 5.0V V NMOS Voltage Transfer Function (Vout vs. Vin {V_Vgate}) o u NMOS NML = Vin(low) - Vout(low) = 230mV (941.732m,4.9105) Logic Threshold or Switching Point t NMOS NMH = Vout(high) - Vin(high) = 2.7891V Vin (low), Vout (high) (1.8299,1.8299) 2.5V Ideal NML = 2.5 V, IRF-150 NML = 2.798 V Vin (high), Vout (low) Ideal NMH = 2.5 V, IRF-150 NMH = 2.092 V (2.1214,711.519m) So.. NML is approx -91% of Ideal, -92% of IRF-150 So.. NMH is approx +12% of Ideal, +33% of IRF-150 SEL>> This is a simple strait line (slope = 1) 0V 0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0V V(Vout) V_VgateFigure 10: PSpice simulation results displaying voltage transfer characteristics of the L-Edit NMOS invertercircuit. The top plot is a graph of the slope of V(Vout) the points where slope = -1 identify the points neededto calculate the noise thresholds of the device. You can see from the graph of Vout vs. Vin that the L-EditNMOS NML is -91% of the Ideal NML (the IRF-150 was +12% of the Ideal NML), while the L-Edit NMOSNMH is +12% of the Ideal NMH (the IRF-150 was -16% of the Ideal NML). So the while the L-Edit NMOSinverters NMH is closer to the ideal (abs diff. of 4% better), the NML is much farther (abs diff. of 79% worse).This means the L-Edit NMOS inverter will work well for Logic (low) inputs < 941 mV and Logic (high)inputs > 2.121 V. The IRF-150 Power MOSFET inverter worked well with Logic (low) inputs < 2.8311 V andLogic (high) inputs > 2.8965 V. Vin Vout 0 1 1 0 Table 2: Truth table for the L-Edit NMOS inverter.After analyzing figure 10 the truth table above (table 2) can be developed. It is obviousfrom this truth table that this circuit is acting as an inverter, although with a much lowerNML than the IRF-150 Power MOSFET’s NML. A Vin < 941 mV (Low) results in a Vout of4.91 V (High), while a Vin > 2.12 V (High) results in a Vout of 711 mV (Low). 11
- 12. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Power Consumption of the NMOS Inverter CircuitModifications to the circuit used in generating the voltage transfer function (figure 8) arenot required (other than switching the V-probe at “Vout” for a W-probe at “Vdrain”) forfinding the power consumed, nor are modifications to the simulation settings. By running asimulation using a W-probe at “Vdrain” the following results were obtained as shown byfigure 11. 500uW P o L-Edit NMOS Inverter w Power Consumed as a function of Vin e (5.0000,480.613u) r (2.1214,428.848u) Power = 481uW Minimum (High) Input voltage = 2.12 V C Max Power = 481uW Power = 429uW o n s u m 250uW e Min Power = 24pW (1.8299,317.004u) d Previously Determined Logic Threshold, Switching Point Power = 317uW Power = 8.9uW Maximum (Low) Input voltage = 942mV (941.732m,8.9472u) IRF-150 Min Power = 56 uW (2.3M times higher) Power = 24pW IRF-150 Max Power = 25 mW (52 times higher) (0.000,24.255p) 0W 0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0V -W(Vdrain) V_VgateFigure 11: PSpice simulation results showing power consumed by the L-Edit NMOS inverter circuit.As observed from figure 11, minimum power (24 pW) is consumed when the transistor isinverting an input (Vin) logic Low (0) into an output (Vout) logic High (1), howevermaximum power (481 µW) is consumed when the transistor is inverting an input (Vin)logic High (1) into an output (Vout) logic Low (0). The power consumed at Vin = 0 V is 24pW, while the power consumed at Vin = 5 V is 481 µW. The IRF-150 consumed a minimumof 56 µW (2.3M times more power) to invert a low input into a high output, and consumed25 mW (52 times more power) to invert a high input into a low output.A complex logic circuit composed of 2000 such NMOS inverters, where half have a logic 0,and the other half have a logic 1 could consume approx 481 mW of power (1000 * 24 pW +1000 * 481 µW = 481 mW). This is much smaller (approx. 52 times less) than the powerrequired for accomplishing this same feat using only IRF-150 inverters (requires approx.25W). So for low power (digital) applications the NMOS inverter is much better suited as alogic inverter. 12
- 13. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Small Signal Characteristics of the NMOS Inverter CircuitIn order to find the small signal characteristics of the L-Edit NMOS inverter, the VDC powersource “Vgate” voltage was changed (see figure 12) to the threshold voltage determined byfigure 11. Next circuit simulation settings were adjusted for Bias Point analysis, and thecheck box for calculating small-signal DC gain was checked. “Vgate” was used as thesimulation input source and “V(Vout)” was provided as an Output variable name asillustrated in figure 13. Vdrain 5Vdc 0 R1 50k Vout Drain Vin Gate NMOS (Extracted) Device Substrate CL W / L = 18 / 6 1pF Vgate 1.8299Vdc Source RS 0 1 0 0 0 Circuit used for generating the L-Edit NMOS inverter small signal characteristics. Vgate is now at threshold voltage. Figure 12: PSpice circuit used to find the small signal characteristics of the NMOS inverter. Figure 13: PSpice simulation settings for finding small signal characteristics. 13
- 14. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter CharacteristicsSmall data capture from the bottom of PSpice simulation output file…--------------------------------------------------------------------------------------------------------------------- **** SMALL-SIGNAL CHARACTERISTICS V(DRAIN)/V_Vgate = -5.730E+00 INPUT RESISTANCE AT V_Vgate = 1.000E+20 OUTPUT RESISTANCE AT V(DRAIN) = 4.792E+04---------------------------------------------------------------------------------------------------------------------So the gain is approximately 5.73 (IRF-150 gain was 113.7, 19.8 times lower), inputresistance is approximately 100 EΩ (exa-ohms) or higher, due to PSpice limits (Same asIRF-150), and output resistance is approximately 47.92 kΩ (IRF-150 was 997.8 Ω, 48 timeshigher). At this point it seems that this circuit has a good gain, extremely high inputimpedance and low output impedance. So the IRF-150 Power MOSFET inverter circuitprovides a higher gain than the L-Edit NMOS inverter circuit, with a smaller outputresistance. One of the main contributors to this large output resistance is the 50 kΩresister “R1” located after “Drain” (The IRF-150 circuit used a 1 kΩ resister). 14
- 15. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Frequency Response of the NMOS Inverter CircuitTo find the frequency response of the circuit using the L-Edit NMOS Inverter a VAC source(with 1 VAC, and the threshold voltage VDC) was swapped for the VDC source “Vgate” asshown in figure 14. Simulation settings were then adjusted to provide a good bode plotdiagram showing frequencies from 1Hz to 10GHz (plotted logarithmically) at 10 points perdecade as shown by figure 15. The results shown by figure 16 indicated the circuit wasbehaving like a low pass filter with a corner (f * 3 dB) frequency of 2.426 MHz. You mayneed to add a trace of “DB(V(Vout))” This indicates that frequencies less than the cornerfrequency will respond better (larger gains realized) than frequencies greater than thecorner frequency (less gain realized, until eventually the NMOS inverter is unable to keepup with the large frequencies and is non-functional. Vdrain 5Vdc 0 R1 50k Vout Drain Vin Gate NMOS (Extracted) Device Substrate CL W / L = 18 / 6 1pF V1 1Vac Source 1.8299Vdc RS 0 1 0 0 0 Circuit used for finding the L-Edit NMOS inverter frequency response. Vgate is now a VAC source (1 VAC) at threshold DC voltage. Figure 14: PSpice circuit used for finding the NMOS circuits frequency response. Figure 15: PSpice simulation settings for creating a bode plot of the circuit’s frequency response. 15
- 16. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics 50 V Bode plot for L-Edit NMOS inverter Corner Frequency (Max -3 dB) g frequency response This is the frequency at which a the power out is reduced to 1/2 of max i and the voltage gain is reduced .707 of max n Estimation of Corner Freq. = 2.426 MHz ( (2.4262M,12.164) d B ) .1 * f( 3 dB ) = 242.6 kHz f( 3 dB ) = 2.426MHz 0 10 * f( 3 dB ) = 24.26 MHz (1.3757M,13.064) Estimation of Max Freq. = 1.376 MHz This was found by adding seperate Vout trace Max freq. is the frequency where Vout reaches 90% of Vdd (4.5 V) Will check this out at later time. IRF-150 Corner Freq. = 56.410 kHz (43 times less ) Note: The NMOS inverter acts like a LP Filter (Approx -14dB / decade) -50 1.0Hz 10Hz 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHz 1.0GHz 10GHz DB(V(Vout)) FrequencyFigure 16: PSpice simulation results (bode plot) of circuits frequency response. Corner freq = 2.4262 MHz(43 times the value of the IRF-150’s corner freq.). You should observe that frequencies below 1.3 MHzreceive great gain and allow the IRF-150 switching speeds to approximate that of an ideal inverter.You can see from the results displayed in figure 16 the L-Edit NMOS inverter has a larger cutofffrequency than the IRF-150 Power MOSFET inverter (Approx 2.43 MHz vs. 56 kHz). Thisallows the NMOS inverter to work in a much larger, although still limited (frequencies in theGHz range, are widely used today) realm of engineering circuits. This fact tied together with thepower consumption requirements of the NMOS circuit vs. IRF-150 make the NMOS design asure win over the IRF-150 in the realm of low power digital circuitry. However, it pales incomparison to a CMOS inverter, especially in the power consumption category. 16
- 17. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Propagation Delays of the NMOS Inverter CircuitThe circuit was again modified by replacing the VAC source “Vgate” with a Vpulse source asshown by figure 17. This figure was used in conjunction with the variable values used intable 3 for analyzing the circuits propagation delay (current) and digital frequencyresponse (upcoming) sections of this report. For each simulation a Time Domain Analysiswas performed to allow the user to see 3 to 5 periods (run to time = 3 to 5 * PER), and stepsize < 1/1000 (I used 1ps for simplicity) of each period as shown by figure 18. Simulationresults are shown on figure 19. Vdrain 5Vdc 0 R1 50k Vout V Drain Vin Gate NMOS (Extracted) Device Substrate CL V1 = 0 V2 = 5 W / L = 18 / 6 1pF Vgate TD = 0 TR = 1ps Source TF = 1ps PW = 206.1ns PER = 412.2ns RS 0 1 0 0 0 Circuit used for finding the L-Edit NMOS inverter digital frequency response and propagation delays. Vgate is now a Vpulse source (TR, TF, PW, PER) are set using table. Figure 17: PSpice circuit for finding the L-Edit NMOS inverter circuits propagation delays and digital frequency response at f( 3 dB ), .1 * f( 3 dB ), 10 * f( 3 dB ). V1 = 0, V2 = 5, TD = 0, and TR/TF/PW/PER come from Table ?. Vpulse : Variables used for NMOS PSpice schematic Time-Rise Pulse & Period Frequency (Hz) Width Time-Fall (PER) (s) (PW) (s) (TR & TF) (s) f3db = 2.426 MHz 412.2 ns 206.1 ns 1 ps .1 * f3db = 242.6 kHz 4.122 µs 2.061 µs 1 ps 10 * f3db = 24.26 MHz 41.22 ns 20.61 ns 1 ps Table 3: Variables used by PSpice circuit figure 17. 17
- 18. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Figure 18: PSpice simulation settings for finding the NMOS inverter propagation delays and digital responses. Run to times should be 3-5 * PER, and step size should be = TR / TF. 5.0VV Rise / Fall Times and Propagation Delayso Frequency = f(3dB) = 2.426 MHzl (824.400n,4.9140)t t(LH) rise = 111.861 nsa t(HL) fall = 7.298 nsg (735.402n,4.5000) (824.871n,4.5000)e prop. delay (LH) = 34.976 ns prop. delay (HL) = 2.742 ns t(LH) rise t(HL) fall tP (Prop Delay Time) = 18.859 ns .1 Vdd to .9 Vdd .9 Vdd to .1 Vdd 2.5V (653.454n,2.5000) (827.142n,2.5000) Max Switching Freq = 8.392 MHz This result is not always very accurate Parasitic Capacitance (623.541n,500.000m) tp(LH) = time to rise from 0 to 2.5V tp(HL) = time to fall from 5 to 2.5V (832.169n,500.000m) (618.478n,10.673m) (840.000n,206.254m) 0V 600ns 650ns 700ns 750ns 800ns 850ns V(Vout) TimeFigure 19: PSpice simulation results showing rise time, fall time and propagation delays of circuit at input freq. = 2.426 MHz = f(3dB). 18
- 19. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics From the results obtained by figure 19 above we can calculate the following (table 4)..Note a small %error in tPHL and tPLH may be the parasitic capacitance and resistance of the NMOS inverter. NMOS Inverter Rise/Fall Times and Propagation Delay Comparison Parameter Ideal IRF-150 NMOStHL = the time it takes output voltage to drop from 4.5 V to .5 V 0s 21 ns 7.3 nstLH = the time it takes output voltage to rise from .5 V to 4.5 V 0s 4.453 µs 111.9 nstPLH = the time it takes output voltage to rise from 0 to 2.5 V 0s 1.774 µs 35nstPHL = the time it takes output voltage to fall from 5 V to 2.5 V 0s 13 ns 2.7 nstP = Propagation delay time = .5 * ( tPLH + tPHL ) 0s 831 ns 18.9 nsMax Switching Frequency (calculated) = 1/( tLH + tHL ) ∞ 223.5 kHz 8.389 MHz*Note: Calculated result is usually far off from actual result. Not yetMax Switching Frequency (observed/actual) ∞ 100 kHzknown at this point. Table 4: NMOS Inverter Rise/Fall times and Propagation Delay Comparisons.From figure 19 and table 4’s results, the NMOS circuit’s propagation delays and rise/falltimes are much smaller than the IRF-150’s propagation delays and rise/fall times. Thisfurther stakes the previous claim, that the NMOS inverter circuit is the better inverter toutilize, for high frequency, low power (digital) applications. 19
- 20. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Digital Frequency Response of the NMOS Inverter CircuitNow the NMOS inverter circuits digital response is analyzed using the circuit from theprevious section (figure 17) and substituting for the frequencies provided by table 3. Thedigital response is checked first at the corner frequency of 2.426 MHz (as done previously),then at 242.6 kHz, and finally at 24.26 MHz. The results follow (Note, you will need to readthe captions next to each figure for an understanding of the results)… 5.0V V o l (411.409n,4.9116) (890.939n,5.0000) Frequency = f(3dB) = 2.426 MHz t a g e 2.5V (206.102n,14.327m) (716.852n,0.000) 0V 0.03us 0.20us 0.40us 0.60us 0.80us 1.00us 1.20us 1.40us 1.60us 1.80us V(Vout) V(Vin) TimeFigure 20: PSpice simulation results showing digital response of output at frequency of 2.426 MHz. Note thered is the input square pulse (Vin), and the green is the output inverted response (Vout). This is acting as anOK inverter since the output reaches over 90% of the operating range within a pulse width, however thisresponse should improve with a lower input frequency. It is noted that the NMOS low is approx .2 V not 0 V. 5.0V V Frequency = .1 * f(3dB) = 242.6 kHz o l (9.2857u,5.0000) (3.1393u,5.0000) t a g e 2.5V (5.2831u,197.759m) (11.519u,0.000) (8.9559u,197.820m) 0V 2us 4us 6us 8us 10us 12us 14us 16us 18us 19us V(DRAIN) V(GATE) Time Figure 21: PSpice simulation results showing digital response of output at frequency of 242.6 kHz (.1 * corner). Notice the digital response is much cleaner now and is nearly that of an ideal inverter. 20
- 21. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics 5.0VV Frequency = 10 * f(3dB) = 24.26 MHzol (48.514n,5.0000)tage 2.5V 41.366n,1.6905) (59.332n,198.101m) (78.702n,0.000) 0V 20.5ns 40.0ns 60.0ns 80.0ns 100.0ns 120.0ns 140.0ns 160.0ns 180.0ns V(DRAIN) V(GATE) Time Figure 22: PSpice simulation results showing digital response of output at frequency of 24.26 MHz (10 *corner). Notice the digital response is horrible now. The NMOS inverter simply cannot switch fast enough to follow the input signal. This is now a non-functional inverter.As observed from figures 20 thru 22 above, the lower the frequency is with respect to thecorner frequency the better the NMOS inverter circuit performs. As the frequenciesincrease much higher than the corner frequency, the NMOS inverter cannot switch fastenough to follow the input signal (the rising edge time constant is too long per theswitching speed.). This is mostly due to the large (50 k) load resistance and partially due tothe internal capacitance of the NMOS inverter. However, as already stated, the NMOSinverter performs as a digital logic inverter much better than the IRF-150 Power MOSFET.The NMOS inverter can work with higher frequencies, requires a lot less power, andswitches much faster. 21
- 22. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Maximum Frequency of the NMOS InverterThe maximum frequency is the frequency at which the output just reaches 90% or 10% ofthe operating range within a pulse width. Finding the maximum frequency is done througha little trial and error. Using the corner frequency as a starting position the frequency wasincrementally increased until the output reached 90% of VDD = 4.5 V. This was found to beapproximately 4.3 MHz, as shown in figure 23 below. The components that limit thefrequency response of the NMOS inverter circuit are the circuit and NMOS deviceresistances, and the circuit 1pF and NMOS parasitic capacitances. 5.0V V o Approximation of Max Frequency Response l Output reaches approx. 90% of operating range t By slowly increasing frequencies this freq. was found a Frequency = 4.3 MHz g e (232.514n,4.5129) Approx 4.5V -> 90% of 5V 2.5V 0V 100ns 120ns 140ns 160ns 180ns 200ns 220ns 240ns 260ns V(DRAIN) TimeFigure 23: PSpice simulation results of testing freq. = 4.3 MHz as maximum frequency. Notice outputreaches approx 4.5 V (90% of 5 V). 22
- 23. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics LAB 4: Summary of Results Winner IRF-150 NMOS Evaluation Ideal IRF-150 Parameter Inverter Inverter Procedure Inverter vs NMOS Circuit Circuit Circuit Transfer Char. VThreshold 2.5 V 2.8682 V 1.8299 V IRF-150 Noise NMH 2.5 V 2.092 V 2.7891 V IRF-150 Margins NML 2.5 V 2.798 V 230 mV IRF-150 P@0V 0W 56 µW 24 pW NMOS Power P@5V 0W 25 mW 481 uW NMOS PMax 0W 25 mW 481 uW NMOS Rise Time tLH 0s 4.453 µs 111.9 ns NMOS Fall Time tHL 0s 21 ns 7.3 ns NMOS tPHL 0s 13 ns 2.7 ns NMOSPropagation Delays tPLH 0s 1.774 µs 35 ns NMOS tP 0s 831 ns 18.9 ns NMOS Small Signal Gain Av ∞ 113.7 5.73 IRF-150 Rin ∞ ∞ ∞ Tie Impedances Rout 0 997.8 Ω 47.92 kΩ IRF-150 3dB Corner 2.4262 f3dB N/A 56.23 kHz NMOS Frequency MHz Maximum fMax ∞ 100 kHz 4.3 MHz NMOS Frequency Table 5: Summary of results for Lab 4 23
- 24. EE325, CMOS Design, Lab 4: L-Edit NMOS Inverter Characteristics Conclusion and RecommendationsAs mentioned in previous sections for an ideal inverter (VIL =VIH=Vdd/2=2.5 V, V OH = Vdd=5 V,VOL=0 V, Noise margins = 2.5 V) and as displayed in the tables above, the NMOS invertercircuit NML is -91% of the Ideal NML (The IRF-150 is +12% of the Ideal NML), while theNMOS inverter circuit’s NMH is +12% of the Ideal NM H (The IRF-150 is -16% of the IdealNMH). Furthermore, the NMOS inverter circuit has a voltage threshold of 1.8299 V whilethe IRF-150 Power MOSFET circuit had a Voltage Threshold of 2.8682 V. In addition, theIRF-150 circuit design had a small signal output impedance of 997.8 Ω (due to the small 1 kΩoutput resister), while the NMOS design had a small signal output impedance of 47.92 kΩ (due tothe large 50 kΩ output resister). These numbers initially suggested that the IRF-150 was abetter choice as an inverter due to closer realization of an ideal switching point. However,by the end of the lab the additional analysis and comparison of the NMOS inverter againstthe IRF-150 circuit revealed a completely different story (on numerous levels). First, and ofgreat importance, the IRF-150 is a Power MOSFET and demands much larger amounts ofpower than the NMOS inverter circuit. The IRF-150 consumed a minimum of 56 µW (2.3Mtimes more power than the NMOS) to invert a low input into a high output, and consumed25 mW (52 times more power than the NMOS) to invert a high input into a low output.This is a tremendous loss for the IRF-150, since power is of the utmost importance intoday’s digital world. However the IRF-150 also provides a much larger gain than theNMOS circuit (113.7 vs. 5.73). This is another reason why the IRF-150 is a Power MOSFET.Last but not least, the IRF-150 circuit’s rise/fall times, and propagation delay times aremuch slower than the NMOS circuit’s. This means the IRF-150 switches too slow to act as asufficient inverter at high frequency applications. While the NMOS circuit was also not abeast in this area, the NMOS circuit could handle maximum frequencies 43 times that of theIRF-150 Power MOSFET circuit. In summary, the IRF-150 design from lab 3 is insufficientas a high frequency, low power, large scale, digital inverter when up against the NMOSdesign. In such cases the NMOS inverter wins hands down. 24

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