Lab Getting Started with EDA Tools E3-238: Analog LSI Circuits INTRODUCTION The objective of this lab is to familiarize you with the Cadence irtuoso design environment. The irtuoso environment provides a set of tools to perform various operations in custom integrated circuit design, such as, design entry, simulation, extraction, and verification. This lab is focused on the schematic entry and circuit simulation. A subset of tools required for this lab is listed in Table. The problems in this lab are given to serve as a starting point for you to explore the capabilities and limitations of the tools. Table Tools for custom integrated circuit design. Tool Cadence irtuoso (IC67) Library Manager Schematic Editor L Analog Design Environment (ADE) L isualization and Analysis (ia) L Spectre (MMSIM5) Purpose To create and edit design libraries and cells. For graphical entry of circuit topology and parameters. To setup design variables, analyses, and probes. For post simulation data visualization and analysis. For circuit simulation. INSTRUCTIONS. The required device models for this lab are given in Appendix and stored at /Shares/models/lab.scs location at the arslserver. Include this file in ADE- L setup to use the models. 2. Use the inverter cell given in the lab_ref library for Problem 3. To include this library, append the following line in your cds.lib file present in the current working directory (home folder): DEFINE lab_ref /Shares/libraries/lab_ref. Page of 5
Problem (DC analysis of linear network) Find out the DC operating point (node voltages) of the circuit shown in Figure by both handcalculation and simulation. R4 5 R probe 0 2 6 R2 3 A B C I.5 A I + R 3 2 2I 3 I 2 4 Figure Resistive network with dependent sources. Problem 2 (DC analysis of nonlinear circuit) D/ T Consider the circuit in Figure 2. Assuming the exponential model ( I I e ) for the diode, hand-calculate the exact voltage across the diode (up to four places after the decimal point) using an iterative method. Simulate the DC operating point of the circuit using mydiode model (given in Appendix), and compare the hand-calculated and simulated values. Rk D S D I D mydiode I S 0 fa, Figure 2 Circuit with nonlinear component. Page 2 of 5
Problem 3 (DC analysis of circuit with multiple operating points) For the cross-coupled inverter shown in Figure 3, there exists three DC operating points. Obtain both the stable and meta-stable DC operating points by simulation with the inverter circuit given in Figure 4. Without a prior knowledge of the circuit behavior, how would you determine the number of equilibrium states (DC solutions) and check their stability? in 2 out 2 A 2 out, out in2 Stable Solutions in out A out Metastable solution, in out2 Figure 3 Cross-coupled pair of inverting amplifiers and its transfer characteristics. DD 5 mypmos W / L0 m/m in out mynmos W / L0 m/m Figure 4 Circuit description of the inverting amplifier. Page 3 of 5
Problem 4 (Transient analysis) For the first-order RC network shown in Figure 5, simulate the behavior of this circuit subject to a 0 to step input having a rise time of no more than 0ns. Plot the voltage waveform across the resistor and capacitor. erify that voltage across the capacitor changes by 63% of its final value in a time of one time constant. Repeat the above experiment with the initial voltage of 0.5 across the capacitor, and observe that initial conditions affect the initial operating point (in transient analysis). Rk 0 in R C C F Figure 5 First order RC network Problem 5 (AC analysis) In AC analysis, the simulator computes the small-signal behavior using phasor analysis of a circuit by first linearizing the circuit about a DC operating point. Compute the frequency response of the series RLC network shown in Figure 6. Plot both the magnitude and phase behavior of the loop current and the voltage across resistor, capacitor and inductor over a frequency range of mhz to MHz. Use 0 points per decade in your plot. Also, observe the following and comment:. The frequency response does not change with the change in initial conditions of the capacitor and inductor which of course affects the DC operating point. Why is it so? 2. At resonant frequency (f 0 = /2π LC), the magnitude of the voltage across capacitor and inductor depends on the value of the resistor and can be greater than the source voltage magnitude. If so, can the circuit be used as a voltage amplifier? If yes, then what about its power gain? Rk C F in R C 0 L LH Figure 6 Series RLC network. Page 4 of 5
APPENDIX The content of the lab.scs model file is shown in Table 2. Table 2 Spectre models. model mydiode diode is=0e-5 n= model mynmos mos2 type=n vto = 0.775 tox = 400e-0 nsub = 8e+5 + xj = 0.5u ld = 0.20u uo = 650 ucrit = 0.62e+5 uexp = 0.25 + vmax = 5.e+4 neff = 4.0 delta =.4 rsh = 36 cgso =.95e-0 + cgdo =.95e-0 cj = 95u cjsw = 500p mj = 0.76 mjsw = 0.30 + pb = 0.8 model mypmos mos2 type=p vto = -0.75 tox = 400e-0 nsub = 6e+5 + xj = 0.05u ld = 0.20u uo = 255 ucrit = 0.86e+5 uexp = 0.29 + vmax = 3.0e+4 neff = 2.65 delta =.0 rsh = 0 cgso =.90e-0 + cgdo =.90e-0 cj = 250u cjsw = 350p mj = 0.535 mjsw = 0.34 + pb = 0.8 Page 5 of 5