hspice book hspice ch09 1 Thu Jul 23 19 10 43 1998 Chapter 9 AC Sweep and Signal Analysis This chapter describes performing an AC sweep and small signal analysis It covers the following topics Understanding AC Small Signal Analysis Using the AC Statement Using Other AC Analysis Statements Star Hspice Manual Release 1998 2 9 1 hspice book hspice ch09 2 Thu Jul 23 19 10 43 1998 Understanding AC Small Signal Analysis AC Sweep and Signal Analysis Understanding AC Small Signal Analysis The AC small signal analysis portion of Star Hspice computes see Figure 9 1 AC output variables as a function of frequency Star Hspice first solves for the DC operating point conditions which are used to develop linearized smallsignal models for all nonlinear devices in the circuit Simulation Experiment DC Op Point DC Transient Other AC analysis statements AC AC small signal simulation NOISE DISTO SAMPLE NETWORK Options Method DC options to solve operating point ABSH ACOUT DI MAXAMP RELH UNWRAP Figure 9 1 AC Small Signal Analysis Flow 9 2 Star Hspice Manual Release 1998 2 hspice book hspice ch09 3 Thu Jul 23 19 10 43 1998 AC Sweep and Signal Analysis Understanding AC Small Signal Analysis Capacitor and inductor values are converted to their corresponding admittances YC j C for capacitors and YL 1 j L for inductors Star Hspice allows resistors to have different DC and AC values If AC value is specified in a resistor statement the operating point is calculated using the DC value of resistance but the AC resistance value is used in the AC analysis This is convenient when analyzing operational amplifiers since the operating point computation can be performed on the unity gain configuration using a low value for the feedback resistance The AC analysis then can be performed on the open loop configuration by using a very large value for the AC resistance AC analysis of bipolar transistors is based on the small signal equivalent circuit as described in Using the BJT Models NPN and PNP on page 14 33 MOSFET AC equivalent circuit models are described in Chapter Introducing MOSFET The AC analysis statement permits sweeping values for Frequency Element Temperature Model parameter Randomized distribution Monte Carlo Optimization and AC design analysis Additionally as part of the small signal analysis tools Star Hspice provides Noise analysis Distortion analysis Network analysis Sampling noise Star Hspice Manual Release 1998 2 9 3 hspice book hspice ch09 4 Thu Jul 23 19 10 43 1998 Using the AC Statement AC Sweep and Signal Analysis Using the AC Statement You can use the AC statement in several different formats depending on the application as shown in the examples below The parameters are described below Syntax Single double sweep AC type np fstart fstop or AC type np fstart fstop SWEEP var starstop incr or AC type np fstart fstop SWEEP var type np start stop or AC var1 START param expr1 STOP param expr2 STEP param expr3 or AC var1 START start1 STOP stop1 STEP incr1 Parameterized sweep AC type np fstart fstop SWEEP DATA datanm or AC DATA datanm Optimization AC DATA datanm OPTIMIZE opt par fun RESULTS measnames MODEL optmod Random Monte Carlo AC type np fstart fstop SWEEP MONTE val The AC statement keywords and parameters have the following descriptions DATA datanm 9 4 data name referred to in the AC statement Star Hspice Manual Release 1998 2 hspice book hspice ch09 5 Thu Jul 23 19 10 43 1998 AC Sweep and Signal Analysis Using the AC Statement incr voltage current element or model parameter increment value Note If type variation is used the np number of points is specified instead of incr fstart starting frequency Note If type variation POI list of points is used a list of frequency values is specified instead of fstart fstop fstop final frequency MONTE val produces a number val of randomly generated values that are used to select parameters from a distribution The distribution can be Gaussian Uniform or Random Limit See Performing Monte Carlo Analysis on page 10 39 for more information np number of points per decade or per octave or just number of points depending on the preceding keyword start starting voltage current any element or model parameter value stop final voltage current any element or model parameter value SWEEP keyword to indicate a second sweep is specified in the AC statement TEMP keyword to indicate a temperature sweep type can be any of the following keywords DEC decade variation OCT octave variation LIN linear variation POI list of points var name of an independent voltage or current source any element or model parameter or the keyword TEMP indicating a temperature sweep Star Hspice supports Star Hspice Manual Release 1998 2 9 5 hspice book hspice ch09 6 Thu Jul 23 19 10 43 1998 Using the AC Statement AC Sweep and Signal Analysis source value sweep referring to the source name SPICE style However if parameter sweep a DATA statement and temperature sweep are selected a parameter name must be chosen for the source value and subsequently referred to in the AC statement The parameter name can not start with V or I Examples The following example performs a frequency sweep by 10 points per decade from 1 kHz to 100 MHz AC DEC 10 1K 100MEG The next line calls for a 100 point frequency sweep from 1 Hz to 100 Hz AC LIN 100 1 100HZ The following example performs an AC analysis for each value of cload which results from a linear sweep of cload between 1 pF and 10 pF 20 points sweeping frequency by 10 points per decade from 1 Hz to 10 kHz AC DEC 10 1 10K SWEEP cload LIN 20 1pf 10pf The following example performs an AC analysis for each value of rx 5 k and 15 k sweeping frequency by 10 points per decade from 1 Hz to 10 kHz AC DEC 10 1 10K SWEEP rx n POI 2 5k 15k The next example uses the DATA statement to perform a series of AC analyses modifying more than one parameter The parameters are contained in the file datanm AC DEC 10 1 10K SWEEP DATA datanm The following example illustrates a frequency sweep along with a Monte Carlo analysis with 30 trials AC DEC 10 1 10K SWEEP MONTE 30 When an AC statement is included in the input file Star Hspice performs an AC analysis of the circuit over the specified frequency range for each parameter value specified in the second sweep 9 6 Star Hspice Manual Release 1998 2 hspice book hspice ch09 7 Thu Jul 23 19 10 43 1998 AC Sweep and Signal Analysis Using the AC Statement For an AC analysis at least one independent AC source element statement must be in the data file for