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- 1. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Colorado Technical UniversityPSpice, L-Edit Designed CMOS NAND Gate Analysis Lab 6 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: 7 June 2010 Completed: 11 June 2010 1
- 2. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Table of ContentsLab Objectives ........................................................................................................................................................................................ 3Requirements and Design Approaches/Trade-Offs................................................................................................................... 3L-Edit CMOS NAND Gate ................................................................................................................................................................... 4- CMOS NAND Gate Design Details................................................................................................................................. 4-5 CMOS NAND Gate Cross Sections .................................................................................................................................... 6 CMOS NAND Gate Design Rule Check ............................................................................................................................ 6 CMOS NAND Gate L-Edit Extracted NAND.SPC File .................................................................................................. 7 CMOS NAND Gate Modified SCNA.SPC File .................................................................................................................. 8 CMOS NAND Gate Test Plan .............................................................................................................................................. 8Fairchild Semiconductor CD4011BC Quad 2-Input NAND Buffered B Series Gate Characteristics .......................... 9 Table of Characteristics ................................................................................................................................................... 10Voltage Transfer Function of the L-Edit CMOS NAND Gate ................................................................................................ 11 Circuit Layout...................................................................................................................................................................... 12 PSpice Simulation Results......................................................................................................................................... 13-14 Truth Table Simulation Results .................................................................................................................................... 15 Truth Table .......................................................................................................................................................................... 16Propagation Delay and Rise/Fall Times of the CMOS NAND Gate .................................................................................... 17 Circuit Layouts.................................................................................................................................................................... 17 PSpice Simulation Results......................................................................................................................................... 18-19Summary of Results ........................................................................................................................................................................... 20Conclusion and Recommendations .............................................................................................................................................. 21 2
- 3. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Lab ObjectivesThe objective of this lab is to translate a usable CMOS NAND gate into a physical IntegratedCircuit (IC) design layout, useable by PSpice through the use of L-Edit software. The devicemust have a delay of less than 50 ns while carrying a 10 pF load capacitance. Finally, the L-Edit CMOS NAND gate must be compared and contrasted to the performancecharacteristics of a commercially available NAND gate (specifically Fairchild’s CD4011BCNAND gate). Since EE325 labs 3, 4, and 5 placed a heavily emphasis on the use andperformance of L-Edit, and PSpice as a circuit simulation tool, the intended audience of thisreport should already be knowledgeable in the use of L-Edit and PSpice and the methodsused in finding the L-Edit NAND gate models characteristics. Thus the detailed proceduresthat were offered in previous reports have been omitted from this report, although thegeneral simulation and circuit diagrams that were used are still included to allow a quickvisual guidance for further attempts at reconstructing this lab. Requirements and Design Approaches / Trade-offsThe requirements for this lab are to design a two-input NAND gate with appropriate sizesnecessary for handling a total propagation delay of less than 50 ns, while carrying a 10 pFload capacitance in PSpice. The design must use the MORBN20 design rules, and use thedefault 2 micron, N-Well, double-metal, 11-mask CMOS SCNA technology designconstraints. After the design pFET and nFET constraints are determined and the model isbuilt in L-Edit a design rule check must be completed with zero DRC errors. Finally thedevice must be extracted for use in PSpice and compared/contrasted against Fairchild’sCD4011BC NAND gate with a matching load resistance and capacitance. The finalbenchmarks should compare logic thresholds, noise margins, and propagation delays of theL-Edit modeled CMOS NAND gate against the Fairchild CD4011BC NAND gate, and showthat the above design constraints are met. 3
- 4. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate L-Edit CMOS NAND Gate Design DetailsIn order to achieve the design specifications required by this lab the followingprocedures/calculations were made in order to determine the required width and lengthsof the L-Edit CMOS NAND gate pFET and nFET devices. The design approach andcalculations follow as illustrated by figures 1 and 2. Figure 1: Hand drawn model of CMOS NAND gate and lab design objectives. It was determined that device resistances must be less than 1 kΩ, which provided a max channel current of 5 mA. 4
- 5. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND GateFigure 2: Hand Calculations used to determine the L-Edit pFET and nFET devices widths and lengths. L-Edit CMOS NAND Gate LayoutWith the results from the hand calculations the design phase began using the CMOS NANDgate model provided by page 5-9 of the 1995 book titled, “Physical Design of CMOSIntegrated Circuits Using L-Edit” by John P. Uyemura. Figure 3: L-Edit CMOS NAND gate design. The left side is the two pFETs (In parallel), the right side is the two nFETs (In series). Notice the pFETs device widths are approximately 3 times the nFETs. 5
- 6. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate L-Edit CMOS NAND Gate Cross SectionsObtaining the CMOS NAND Gates cross section was accomplished by clicking Tools/Cross-Section and clicking on the CMOS NAND Gate PMOS and NMOS sections by using the “Pick”button. Figure 4: L-Edit CMOS NAND Gate NMOS Cross Section. Figure 5: EE325 L-Edit CMOS NAND Gate PMOS Cross Section. L-Edit CMOS NAND Gate Design Rule Check Results -------------------- NAND_DRC.DRC --------------------- DRC Errors in cell Cell0 of file G:CMOS STUFF LAB 6LAB6. 0 errors. DRC Merge/Gen Layers Elapsed Time: 0.000000 seconds. DRC Test Elapsed Time: 0.000000 seconds. DRC Elapsed Time: 0 seconds. ------------------------------------------------------- 6
- 7. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate L-Edit CMOS NAND Gate 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 PMOS and NMOS lengthsand widths. Note that the PMOS width must be about 2.8 times the NMOS width. -------------------- NAND.SPC --------------------- * Circuit Extracted by Tanner Researchs L-Edit V7.12 / Extract V4.00 ; * TDB File: G:CMOS STUFF LAB 6LAB6, Cell: Cell0 * Extract Definition File: C:LEditmosismorbn20.ext * Extract Date and Time: 06/02/2010 - 15:00 * 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 = Vout (17.5,35.5) * 2 = VA (23.5,-8.5) * 3 = VDD (-65.5,17.5) * 4 = GND (67.5,-2.5) * 5 = VB (32.5,-8.5) M1 VDD VB Vout VDD PMOS L=2u W=70u AD=1.05n PD=310u AS=560p PS=156u * M1 DRAIN GATE SOURCE BULK (-57.5 8.5 12.5 10.5) M2 Vout VA VDD VDD PMOS L=2u W=70u AD=560p PD=156u AS=1.05n PS=310u * M2 DRAIN GATE SOURCE BULK (-57.5 18.5 12.5 20.5) M3 GND VB 6 GND NMOS L=2u W=23u AD=161p PD=60u AS=184p PS=62u * M3 DRAIN GATE SOURCE BULK (42.5 8.5 65.5 10.5) M4 6 VA Vout GND NMOS L=2u W=23u AD=184p PD=62u AS=184p PS=62u * M4 DRAIN GATE SOURCE BULK (42.5 18.5 65.5 20.5) * Total Nodes: 6 * Total Elements: 6 * Extract Elapsed Time: 0 seconds .END ------------------------------------------------------- 7
- 8. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Edited SCNA.CSE File Required for using L-Edit CMOS NAND GateLines 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 -------------------------------------------------------- CMOS NAND Gate Test PlanNow that the L-Edit CMOS NAND gate device has been created, passed its DRC, andextracted. The next phase is to import the design files as accomplished previously in lab 5,to test the device constraints in PSpice. However, first we must have a good commerciallyavailable NAND gate to compare our L-Edit NAND gate to. Next, the characteristics of thecommercial NAND gate must be compared against the L-Edit model to include logicthresholds, noise margins, and propagation delays. Conclusions will be based upon howwell our design first accomplishes our original goal (total propagation delay < 50 ns), andhow well our L-Edit NAND gate competes against the commercial NAND gate. 8
- 9. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Fairchild Semiconductor CD4011BC Quad 2-Input NAND Buffered B Series Gate CharacteristicsThe commercial NAND gate chosen for comparison against our L-Edit NAND gate wasFairchild’s CD4011BC Quad 2 input buffered NAND gate. This is a low power, TTL,monolithic complementary MOS (CMOS) NAND gate constructed with n-channel and p-channel enhancement mode transistors with equal source and sink current capabilities,and symmetric output characteristics. Fairchild’s CD4011BC NAND gate further featuresbuffered outputs which improve the devices characteristics by providing a very high gain.The datasheet used for comparing this NAND gate against our L-Edit gate can bedownloaded from: http://www.fairchildsemi.com/ds/CD/CD4001BC.pdf. Figure 6: Fairchild CD4011BC Quad 2 Input NAND Gate DC Electrical Characteristics. Figure 7: Fairchild CD4011BC Quad 2 Input NAND Gate AC Electrical Characteristics. 9
- 10. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate CD4011BC Characteristic Parameter Ideal NAND Gate Procedure +25˚ C Transfer Char. Vthreshold 2.5 V 2.5Minimum HIGH input voltage VIH 2.5 3.5Maximum LOW input voltage VIL 2.5 1.5Minimum HIGH output voltage VOH 5 4.95Maximum LOW output voltage VOL 0 0.05 Noise NMH = VOH -VIH 2.5 V 1.45 V Margins NML = VIL - VOL 2.5 V 1.45 V Typ: 90ns Rise Time tLH 0s Max: 200ns Typ: 90ns Fall Time tHL 0s Max: 200ns Typ: 120ns tPHL 0s Max: 250ns Typ: 85ns tPLH 0s Propagation Delays Max: 250ns tP = Typ: 106.5ns 0s .5 * (tPHL + tPLH) Max: 250ns Table 1: CD4011BC NAND Gate quick reference table for Lab 6. 10
- 11. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Voltage Transfer Function for the CMOS NAND Gate CircuitUsing the same approach that was used in labs 3, 4, and 5 our first step in comparing our L-Edit NAND gate design against the CD4011BC NAND gate is to verify the Voltage TransferFunction (Logic Threshold, and Noise Margins) of our NAND gate. To accomplish this thecircuit shown by figure 8 was built and simulation settings were set as illustrated byfigures 9 and 10. First the logic threshold for input B was taken by sweeping input B, nextthe logic threshold, and circuit noise margins were calculated against by sweeping input A.Results are shown in figures 11 and 12. 0 0 VA VB 5Vdc 5Vdc VA VB VDD L-Edit CMOS NAND Gate R1 0 VDD P-CH W/L = 70/2 um GND 0 5Vdc N-CH W/L = 23/2 um 1 Vout V RL 200k CL 50pF 0 Circuit used for generating the L-Edit CMOS NAND Gate Voltage Transfer Characteristics.Figure 8: PSpice circuit for generating the L-Edit CMOS NAND Gate voltage transfer function (Vout vs. Vin). Figure 9: Simulation Settings (DC Sweep) used for obtaining the voltage transfer function. 11
- 12. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Figure 10: Configuration files needed to correctly run simulation of L-Edit NAND gate in PSpice. 5.0VVo Logic Threshold for Input Bltage 2.5V (2.4917,2.4917) Logic Threshold / Switching Point 0V 0V 1.0V 2.0V 3.0V 4.0V 5.0V V(VOUT) V_VB/1 V_VB Figure 11: Logic threshold graph for Input B. 12
- 13. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate 0 S l o p (2.2918,-1.0000) (3.1167,-1.0000) e Slope = -1 Slope = -1 -10 -20 -30 D(V(Vout)) 5.0V V o l t (2.2918,4.4912) a VIL, VOH g e Noise Margins and Logic Threshold For Input A 2.5V NML = 1.827443 V NMH = 1.3745 V (2.6238,2.6238) Logic Threshold / Switching Point VIH, VOL (3.1167,464.357m) SEL>> 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_VA/1 V_VA Figure 12: Logic Threshold and Noise Margins for input A. Results are in table below. CMOS Winner Noise Margin Comparison Ideal CD4011BC NAND Gate % error Parameter NAND Gate NAND Gate Input A (vs. Ideal) unless noted Input A: 2.6238 V Logic Threshold or Switching Point 2.5 V 2.5 V CD4011BC Input B: 2.4917 V VIH = minimum HIGH input voltage 2.5 V 3.5 V 3.1167 V L-EDIT NAND VIL = maximum LOW input voltage 2.5 V 1.5 V 2.2918 V L-EDIT NAND VOH = minimum HIGH output voltage 5V 4.95 V 4.4912 V CD4011BC VOL = maximum LOW output voltage 0V .05 V 464.357 mV L-EDIT NAND Noise Margin Low = NML = VIL – VOL 2.5 V 1.45 V 1.827443 V L-EDIT NAND Noise Margin High = NMH = VOH – VIH 2.5 V 1.45 V 1.3745 V CD4011BC Table 2: L-Edit NMOS Noise Margin Comparison Table, all percentages are rounded.From these results it can be seen that that our nFET and pFET devices have different logicthresholds. This is due to the different operating characteristics and current mobility of then and p channel devices. The noise margins define how well the NAND gates withstandelectrical noise. The results show that our L-Edit NAND has a better NM L than theCD4011BC NAND but a worse NMH. 13
- 14. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate 0 0 V1 = 0 V1 = 0 V2 = 5 VA VB V2 = 5 TD = 0 TD = 0 TR = 10ps TR = 10ps TF = 10ps TF = 10ps PW = 100ns PW = 50ns PER = 200ns PER = 100ns V V VA VB VDD L-Edit CMOS NAND Gate R1 0 VDD P-CH W/L = 70/2 um GND 0 5Vdc N-CH W/L = 23/2 um 1 Vout V RL 200k CL 50pF 0 Circuit used for verifing the L-Edit CMOS NAND Gate truth table. VA pulse = 5MHz, VB pusle = 10MHz Figure 13: PSpice circuit for verifying the L-Edit CMOS NAND Gate truth table.The PSpice circuit was again modified as illustrated by figure 13, to allow us to perform atruth table verification of our NAND gate circuit. This was accomplished by setting upinput A as a 5 MHz pulse (PER = 200ns) and input B as a 10 MHz pulse (PER = 100ns), bothinputs pulsing from 0V to 5V. Figure 14: Simulation Settings for verifying L-Edit NAND gate truth table. 14
- 15. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate The results from the simulation are shown in figure 15 below. From the results our L-Edit NAND gate is working as expected and only outputting 0V (low) when both inputs A and B are 5V (high). Otherwise “Vout” is 5V (high). 5.5VV Sim results for verifying truth table VA = 5MHz pulse (0-5V), VB = 10MHz pulse (0-5V)olt VA = 5V VA = 5V VB = 5V Vout = 1Va VB = 5V Vout = 1V Vout = 1Vge 4.0V 2.0V Notice: Vout only = 0V when VA = 5V, and VB = 5V Both Inputs are logic 1 VA = 0V VB = 0V Vout = 0V VB = 0V VA = 0V 0V 0s 20ns 40ns 60ns 80ns 100ns 120ns 140ns 160ns 180ns 200ns V(VOUT) V(VA) V(VB) Time Figure 15: PSpice simulation results for truth table verification. 15
- 16. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate L-Edit CMOS NAND Truth Table Input Output A B Vout 0 0 1 0 1 1 1 0 1 1 1 0 Table 3: Truth table for the L-Edit CMOS NAND Gate.The results from figure 15 and table 3 have successfully shown that our L-Edit NAND gateis performing as a NAND gate should. Next PSpice circuit and simulation settings will beadjusted to verify that our circuit is meeting our original design specifications (propagationdelay < 10 ns) and finally our NAND gate will be compared against the commercial NANDgate. 16
- 17. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Propagation Delays of the CMOS NAND Gate CircuitThe rise/fall times and propagation delay times of our L-Edit NAND gate will be measuredas was accomplished similarly in labs 3, 4, and 5. Two circuit designs were used, the first(figure 16) was used to find the propagation delay against a capacitive load of 10 pF (ouroriginal design specification), and the second (figure 17) was used to find the propagationdelay against a capacitive load of 50 pF (for accurate comparison against Fairchild’sCD4011BC NAND gate). Input A was setup as a 7.5 MHz pulse as requested by theinstructor (use a frequency between 5MHz and 10MHz). 0 0 V1 = 0 V2 = 5 VA TD = 0 TR = 10ps VB TF = 10ps 5Vdc PW = 66.666ns PER = 133.333ns VA VB VDD L-Edit CMOS NAND Gate R1 0 VDD P-CH W/L = 70/2 um GND 0 5Vdc N-CH W/L = 23/2 um 1 Vout V RL 200k CL 10pF 0 Circuit used for verifing the L-Edit CMOS NAND Gate propogation delays at VA freq = 7.5MHz, CL = 10pF Figure 16: PSpice circuit for finding the L-Edit CMOS NAND Gate circuits propagation delays and digital frequency response at frequency 7.5MHz with 10pF load capacitance (CL). 0 0 V1 = 0 V2 = 5 VA TD = 0 TR = 10ps VB TF = 10ps 5Vdc PW = 66.666ns PER = 133.333ns VA VB VDD L-Edit CMOS NAND Gate R1 0 VDD P-CH W/L = 70/2 um GND 0 5Vdc N-CH W/L = 23/2 um 1 Vout V RL 200k CL 50pF 0 Circuit used for verifing the L-Edit CMOS NAND Gate propogation delays at VA freq = 7.5MHz, CL = 50pF Figure 17: PSpice circuit for finding the L-Edit CMOS NAND Gate circuits propagation delays and digital frequency response at frequency 7.5MHz with 50pF load capacitance (CL). 17
- 18. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Figure 18: PSpice simulation setting used to find propagation delay times of 7.5MHz input. 5.5VV Propogation Delays for VA pulse = 7.5MHz with 10pF load capacitanceolta (203.036n,4.9992) (266.818n,5.0060)ge (200.601n,4.5000) (266.928n,4.5000) 4.0V tLH (rise) is from .1 Vdd to .9 Vdd tHL (fall) is from .9 Vdd to .1 Vdd pHL is time to (rise) from 0 to 2.5V pLH is time to (fall) from 5 to 2.5V (200.228n,2.5000) (267.256n,2.5000) 2.0V tLH (rise) = 515 ps tHL (fall) = 813 ps pLH = 438 ps pHL = 170 ps tp = 304 ps (200.086n,500.000m) (267.741n,500.000m) 0V (200.058n,18.072m) (269.294n,18.072m) 195ns 200ns 210ns 220ns 230ns 240ns 250ns 260ns 270ns 275ns V(VOUT) Time Figure 19: PSpice simulation results of circuit with 10pF load. Circuit correctly meets design specifications with all rise/fall times and propagation delays less than 10 ns. 18
- 19. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate From the results obtained by figure 19 above our L-Edit CMOS NAND gate’s total propagation delay of 304 ps is well below our original requirement of a total propagation delay less than 50 ns using a load capacitance of 10pF. After adjusting the circuit load capacitance to 50 pF to match the Fairchild CD4011BC NAND gate load capacitance our final simulation was ran for a final apples to apples comparison between NAND gates. 5.5VVo Prop delays for VA pulse = 7.5MHz with a 50pF load capacitancelta (203.036n,4.9998) tLH is the time to (rise) from .1Vdd to .9Vdd (266.818n,5.0060)ge tHL is the time to (fall) from .9Vdd to .1Vdd (200.601n,4.5000) pHL is the time to (rise) from 0 to 2.5V (266.928n,4.5000) 4.0V pLH is the time to (fall) from 5 to 2.5V Comparison L-Edit CMOS NAND Gate CD4011BC NAND Gate tLH = 515 ps tLH = 90 ns (200.228n,2.5000) (267.257n,2.5000) tHL = 814 ps tHL = 90 ns pHL = 171 ps pHL = 120 ns 2.0V pLH = 439 ps pLH = 85 ns tp = 305 ps tp = 106.5 ns (200.086n,500.000m) (267.742n,500.000m) 0V (200.057n,6.0241m) (269.465n,18.072m) 195ns 200ns 210ns 220ns 230ns 240ns 250ns 260ns 270ns 275ns V(VOUT) Time Figure 20: PSpice simulation results of circuit with 50pF load. The L-Edit CMOS NAND gate clearly out performs the Fairchild CD4011BC NAND gate. Table 4 contrasts these results. From the results obtained by figure 20 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 CMOS NAND Gate. 19
- 20. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate L-Edit CMOS CD4011BC Parameter Ideal NAND Gate Winner NAND Gate (CL = 50 pF) L-EdittHL = the time it takes output voltage to drop from 4.5 V to .5 V 0s 90 ns 814 ps NAND L-EdittLH = the time it takes output voltage to rise from .5 V to 4.5 V 0s 90 ns 515 ps NAND L-EdittPLH = the time it takes output voltage to rise from 0 to 2.5 V 0s 85 ns 439 ps NAND L-EdittPHL = the time it takes output voltage to fall from 5 V to 2.5 V 0s 120 ns 171 ps NAND L-EdittP = Propagation delay time = .5 * ( tPLH + tPHL ) 0s 106.5 ns 305 ps NANDMax Switching Frequency (calculated) = 1/( tLH + tHL ) L-Edit ∞ 5.55 MHz 752 MHz*Note: Calculated result is usually far off from actual result. NAND Table 4: CMOS NAND Gate Rise/Fall times and Propagation Delay Comparisons.Clearly our L-Edit NAND gate is capable of switching much faster than the FairchildCD4011BC NAND gate due to the shorter propagation delays and rise/fall times making it aclearer choice for higher frequency applications. L-Edit CMOS Winner Evaluation Ideal CD4011BC NAND Parameter % error Procedure NAND NAND Input A, unless (vs. Ideal) noted. Input A: 2.6238 V Transfer Char. VThreshold 2.5 V 2.5 V CD4011BC Input B: 2.4917 V Noise NMH 2.5 V 1.45 V 1.3745 V CD4011BC Margins NML 2.5 V 1.45 V 1.827443 V L-Edit NAND Rise Time tLH 0s 90 ns 515 ps L-Edit NAND Fall Time tHL 0s 90 ns 814 ps L-Edit NAND tPHL 0s 120 ns 171 ps L-Edit NAND Propagation Delays tPLH 0s 85 ns 439 ps L-Edit NAND tP 0s 106.5 ns 305 ps L-Edit NAND Table 5: Summary of results for Lab 6. 20
- 21. EE325, CMOS Design, Lab 6: L-Edit CMOS NAND Gate Conclusion and RecommendationsThe L-Edit CMOS NAND gate clearly met all device specifications and delay requirements asdemonstrated by this report and table 5. Furthermore, the L-Edit CMOS NAND gate offerssuperior frequency response in comparison to the Fairchild’s CD4011BC Quad 2 inputbuffered NAND gate. This makes the L-Edit NAND gate a competitive gate for higherfrequency applications. The logic threshold and noise margin results showed that theFairchild NAND gate operated very close to our L-Edit designed NAND gate with a betterhigh noise margin and logic threshold but a worse low noise margin. However, due to theslow switching speed of the Fairchild CD4011BC NAND gate our L-Edit design would stillmake a good design alternative, especially for higher frequency applications.This was an excellent lab at demonstrating the powerful versatility offered through customdesign modeling of CMOS logic gates using L-Edit, and showed that alternative CMOSdesigns can sometimes perform better than commercial alternatives. 21

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