Beginning of Presentation CDEEP EE 705/707 NGSPICE - Demo - PowerPoint PPT Presentation

IIT Bombay Beginning of Presentation CDEEP EE – 705/707 NGSPICE - Demo Presented By: Sandeep Kasliwal (TA) Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 1 Introduction  NGSPICE is a general-purpose circuit simulation program for nonlinear dc, nonlinear transient, and linear ac analysis.  Circuits may contain resistors, capacitors, inductors, mutual inductors, independent voltage and current sources, four types of dependent sources, lossless and lossy transmission lines, switches, uniform distributed RC lines, and the 5 most common semiconductor devices: diodes, BJTs, JFETs, MESFETs, and MOSFETs. Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 2 Types Of Analysis  DC  AC Small Signal  Transient  Pole-Zero  Small Signal Distortion  Sensitivity  Noise Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 3 DC Analysis  It determines the dc operating point of the circuit with inductors shorted and capacitors opened.  It’s options are specified on the .DC, .TF, and .OP command lines.  The dc small-signal value of a transfer function, input resistance, and output resistance can also be computed.  The dc analysis can also be used to generate dc transfer curves. Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 4 AC Analysis  It computes the ac output variables as a function of frequency (user-specified range).  The program first auto. computes the dc operating point of the circuit and determines linearized, small- signal models for all of the nonlinear devices in the circuit.  The desired output of an ac small-signal analysis is usually a transfer function (voltage gain, trans- impedance, etc.). Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 5 Transient Analysis  It computes the transient output variables as a function of time over a user-specified time interval.  The initial conditions are auto. determined by a dc analysis.  All sources which are not time dependent (for example, power supplies) are set to their dc value.  The transient time interval is specified on a “.TRAN “ command line. Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay IIT Bombay Slide 6 NGSPICE – Example Inverter Circuit Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 7 Netlist & Commands * Script file is shown below (comment starts with *) * The following line includes MOS model file *”spice_tsmc_model.txt” .include spice_tsmc_model.txt * Declaring m1 and m2 instances of pmos and nmos m1 vout vin vdd vdd CMOSP L = 0.18u W = 0.72u m2 vout vin 0 0 CMOSN L = 0.18u W = 0.18u * Here L = a and W = b overwrites default values of L & W *mentioned in model file. Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 8 Cont… * Electrical sources used * In Inverter Example: input voltage source and supply * voltage Vinput vin 0 dc 0 Vsupply vdd 0 dc 1.8 * The following line directs ngspice to perform dc analysis .dc vinput 0 1.8 0.01 * ngspice execution commands are * between ”.control” & ”. endc ” commands. Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 9 Cont… .control * Running the script file run * ”print v(N)” prints the voltage at node ”N” print v(vout) * plot the voltage of input(vin) & output(vout) nodes, * & plot ”0.9” line on the output plot plot v(vout) v(vin) (0.9) (1.62) (.18) * Create inv_dc_char.ps file of output plot set hcopydevtype = postscript hardcopy inv_dc_char.ps v(vout) v(vin) (0.9) (1.62) (.18) .endc .end Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Slide 10 Execution Of Script File  Save the script file as ” filename.spice ” or “filename.cir”  ”.spice” or ”.cir” extention is not compulsory but it is a good practice.  The following command in linux terminal will execute the script file, > ngspice filename.spice Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay IIT Bombay Slide 11 Output Plot Autumn 2009 Prof. Maryam Shojaei Baghini

IIT Bombay IIT Bombay Slide 12 References  http://newton.ex.ac.uk/teaching/CDHW/Electroni cs2/userguide/ Autumn 2009 Instructor : Prof. Maryam Shojaei Baghini

IIT Bombay Thank you