The use of computer simulation to validate electronic circuit designs is now a way of life throughout the electrical and computer engineering world. Effective use of computer-aided design (CAD) can significantly reduce the length and number of design cycles, thereby reducing production costs and time-to-market.Key factors in the ultra-competitive electronics and computer industries.SPICE (Simulation Program with Integrated Circuit Emphasis), orginally developed at the University of California, Berkeley. There are many variants of SPICE available on both Windows PC and Unix workstation platforms.

PSpice provides a complete simulation environment including simulation, waveform analysis with cross-probing,

and bias results display on the schematic. The latest version of PSpice Studio has evolved from the combination of PSpice A/D with advanced analyses, which verifies a design for operational correctness beyond the basic analog simulation capability.

Features include new Sensitivity and Monte Carlo analysis, an entirely redesigned Optimizer with multiple engines, and Smoke (stress) analysis, which guides the user on how to improve design performance, cost-effectiveness, and reliability. These features, widely accepted and used, are based on the Cadence® Analog Workbench architecture and are now available to PSpice users with a simplified user interface designed exclusively for the Windows platform. An additional set of Analog Workbench model libraries is now supported within the PSpice simulation environment as parameterized models.

At the core of the PSpice engine is a sophisticated, native mixed-signal simulator used to simulate mixed-signal designs of any size, containing analog and digital parts ranging from IGBTs and pulse width modulators to DACs and ADCs. View your simulation results, both analog and digital, in the same window and on the same time axis.

### Key Features

- Improves simulation times, reliability and convergence on larger designs with new performance technology
- Provides flexible design entry options using either Capture or Concept HDL depending on circuit or PCB design needs.
- Prevents board failures by determining which components are over stressed using Smoke analysis or observing component yields using Monte Carlo.
- Prevents board failures by determining which components are over stressed using Smoke analysis or observing component yields using Monte Carlo.
- Prevent board failures using Smoke analysis to determine which components are over stressed and using Monte Carlo to observe component yields.
- Identifies and simulates functional blocks of complex circuitry using mathematical expressions and functions

### Advanced Analysis

#### Measurements

A measurement is a numerical value that represents a specific performance characteristic of the circuit, based on the simulation results. For example, specifications like bandwidth and maximum gain are measurements that are evaluated from the gain curve. When a measurement is successfully evaluated on simulation data, PSpice stores the precise expression used [e.g. max(V(1))-min(V(2))] so that it can quickly re-evaluate it after subsequent simulations of that circuit. Measurement evaluations appear in an optional Measurement Results table below the plots. PSpice includes a library of ready-to-use pre-defined measurements, such as risetime, overshoot, bandwidth, gain margin, etc. Users can also create custom measurements from scratch, or by copying and modifying an existing one.

Figure 1. Probe plot in PSpice with measurement display enabled

#### Sensitivity Analysis

From top to bottom in Figure 2, the window panes are parameter/sensitivity table, specification (measurement) table, and the output window. Sensitivity analysis is used to identify the critical components in the design. These critical components should be specified with tighter tolerances, and are the best candidates for optimization. Likewise, the least critical components can be identified, which make good candidates for cost reduction if their preciseness does not critically affect design performance or yield. The sensitivity analysis window will automatically load all circuit parameters with tolerances.

Figure 2. Advanced Analysis with the Sensitivity window displayed

#### Monte Carlo Analysis

Monte Carlo Analysis is used to predict yield and statistical performance of a design. The new Advanced Monte Carlo Analysis is also based on PSpice measurements. Prior to running the simulation profile(s) for each Monte Carlo run, each component parameter is randomly varied based on its probability distribution and tolerance range. After each simulation, the enabled measurements are evaluated, and the results are stored for statistical analysis.

Figure 3. Monte Carlo Analysis window displaying a Cumulative Distribution Function (CDF)

#### Optimizer

The new Optimizer in PSpice Advanced Analysis is a major improvement over the previous PSpice Optimizer*. It allows an unlimited number of parameters and specifications. Specifications are based on measurements and can be imported from PSpice. No extra work is required to setup the parameters in the schematic editor; they can be selected from a list in the Optimizer, or sent to the Optimizer from the Sensitivity analysis window or the schematic editor. Parameters can also be “cross-probed" from the Optimizer to find their source in the Schematic.

The Optimizer offers four search engines to optimize the design:

- LSQ uses a least squares, gradient-based algorithm for finding the lowest total error
- Modified LSQ is also gradient-based, but can handle goal and constraint driven optimization. It also tries to optimize with fewer simulations
- Random repeatedly performs simulations with random sets of parameters, so that the best cases can be used for the gradient-based engines
- Discrete looks up the nearest available value for the parameters by searching through tables provided with Advanced Analysis (e.g. Resistor-5%), or arbitrary tables created by users

Figure 4. Optimizer window

#### Smoke Analysis

Smoke analysis provides information on component stress during circuit operation. It uses the transient analysis simulation results to calculate measurements that correspond to specified safe operating limits, then compares the measurements against the limits and displays the results in a table that can easily be ordered to show the biggest violations first.

Figure 5. Smoke analysis window

### PSpice 9.1 Student Version

The **PSpice 9.1 Student Version** lets you test drive these products:

- PSpice A/D
- Capture
- Schematics
- PSpice Optimizer

The Student Version of PSpice is intended for use by college students and professors who are interested in learning about analog and mixed-signal simulation. It is not intended to demonstrate the capabilities of any product other than PSpice. Because it is distributed freely, certain limitations have been imposed on the libraries and functionality.

Zbynek Soban

soban@ hw.cz

### Links

- PSpice 9.1 Student Version - Download Files from Cadence
- PSpice Studio - http://www.cadence.com/products/si_pk_bd/pspice_studio
- Using PSpice - http://www.orcadpcb.com/pspice

### Related articles

- EPROM Simulator - http://www.hw-server.com/constrc/epsi.html
- The IEEE 802.3af-Compliant Power-Over-Ethernet power-suplly ICs - http://www.hw-server.com/news/maxpoeics.html