OrCAD

1. What is OrCAD?

1.1 What is OrCAD?

OrCAD is a proprietary electronic design automation (EDA) software suite developed by Cadence Design Systems, primarily used for schematic capture, PCB layout, and circuit simulation. It is widely adopted in academia, aerospace, telecommunications, and consumer electronics due to its robust toolset for designing high-speed digital, mixed-signal, and RF circuits. The suite integrates multiple modules, including:

Core Technical Capabilities

OrCAD’s simulation engine, PSpice, solves nonlinear differential equations using modified nodal analysis (MNA), enabling transient, AC/DC, and parametric sweeps. For a simple RC circuit, the transient response is governed by:

$$ V(t) = V_0 \left(1 - e^{-\frac{t}{RC}}\right) $$

where V(t) is the capacitor voltage, V0 is the input voltage, and RC is the time constant. PSpice discretizes this using the trapezoidal rule for numerical stability.

Historical Context

OrCAD originated in the 1980s as a DOS-based tool before Cadence acquired it in 1999. Its integration with Allegro (Cadence’s high-end PCB suite) allows seamless transition from prototyping to production, supporting industry standards like IPC-7351 for footprint generation.

Real-World Applications

In aerospace, OrCAD’s constraint manager ensures compliance with EMI/EMC requirements by enforcing trace spacing rules. For RF designs, its transmission line calculator optimizes impedance matching using:

$$ Z_0 = \sqrt{\frac{L}{C}} $$

where Z0 is the characteristic impedance, and L and C are distributed inductance and capacitance.

Performance Benchmarks

OrCAD’s Distributed Processing feature reduces simulation time for large circuits (e.g., 10,000+ nodes) by parallelizing matrix operations. A benchmark on a 16-core system showed a 6.8× speedup for a 4-layer DDR4 interface simulation compared to single-threaded execution.

1.2 Key Features of OrCAD

Advanced Schematic Capture

OrCAD Capture provides a hierarchical schematic design environment with support for multi-sheet designs, enabling complex circuit representation. Its Constraint Manager allows real-time electrical rule checks (ERC), ensuring design integrity before simulation or layout. Engineers leverage its parametric search for component selection, integrating directly with vendor databases for real-time availability and pricing.

High-Speed PCB Design

The OrCAD PCB Designer suite includes advanced routing algorithms for high-speed digital and mixed-signal layouts. Key capabilities include:

The Sigrity integration enables GHz-range signal analysis, solving transmission line effects via Telegrapher's equations:

$$ \frac{\partial^2 V}{\partial x^2} = LC\frac{\partial^2 V}{\partial t^2} + (RC + GL)\frac{\partial V}{\partial t} + RGV $$

Mixed-Signal Simulation

OrCAD PSpice combines SPICE3f5 and XSPICE engines for nanosecond-accurate simulations. Its Monte Carlo analysis handles component tolerance variations through statistical sampling:

$$ \sigma_{total} = \sqrt{\sum_{i=1}^n \left(\frac{\partial f}{\partial x_i}\sigma_i\right)^2} $$

The Behavioral Modeling feature supports Verilog-A integration for complex analog/digital boundary conditions.

Thermal and Power Analysis

OrCAD's Electro-Thermal Co-Simulation couples Joule heating with temperature-dependent material properties:

$$ P_{diss} = \int_V \sigma |\nabla \phi|^2 dV $$

where \(\sigma\) is temperature-dependent conductivity. The tool automatically derates components based on local thermal gradients.

Manufacturing Output Generation

The IPC-2581 and ODB++ export formats provide intelligent manufacturing data, including:

DFM rules are enforced through 3D clearance checking, preventing assembly conflicts down to 25μm resolution.

1.3 Applications in Electronics Design

OrCAD is a powerful suite of electronic design automation (EDA) tools widely used in the development of complex electronic systems. Its applications span across multiple domains, including analog and mixed-signal circuit design, high-speed digital systems, and printed circuit board (PCB) layout optimization.

Analog and Mixed-Signal Circuit Simulation

OrCAD PSpice provides industry-standard SPICE simulation capabilities, enabling engineers to model and analyze analog circuits with high precision. The tool supports:

For mixed-signal designs, PSpice seamlessly integrates analog behavioral modeling with digital event-driven simulation. This allows accurate prediction of interactions between analog front-ends and digital signal processing blocks.

$$ V_{out} = A_{OL}(V_+ - V_-) $$

High-Speed Digital Design

OrCAD Sigrity provides specialized tools for signal integrity analysis in high-speed digital systems. Key capabilities include:

The toolset enables prediction of signal degradation effects such as intersymbol interference (ISI) and crosstalk in multi-gigabit serial links. Eye diagram analysis provides quantitative measures of timing and voltage margins:

$$ J_{RMS} = \sqrt{\frac{1}{N}\sum_{i=1}^{N}(t_i - \bar{t})^2} $$

PCB Design and Manufacturing

OrCAD PCB Designer offers advanced features for physical implementation:

The tool's hierarchical design methodology supports team-based development of complex multilayer boards. Advanced via structures, including microvias and buried vias, can be implemented for high-density interconnect (HDI) designs.

RF and Microwave Circuit Design

For RF applications, OrCAD provides:

This enables design of impedance-matched networks and prediction of critical RF performance metrics such as noise figure and third-order intercept point (IP3). The Smith chart utility facilitates impedance matching network synthesis:

$$ \Gamma = \frac{Z_L - Z_0}{Z_L + Z_0} $$

Power Electronics Design

Specialized features for power electronics include:

The tool can predict efficiency metrics and thermal performance of switch-mode power supplies (SMPS) through coupled electrical-thermal simulations.

Signal Integrity Analysis in High-Speed Digital Design A diagram illustrating signal integrity concepts including an eye diagram, transmission line model, and signal degradation effects such as jitter, crosstalk, and reflections. Eye Diagram Jitter (J_RMS) Voltage Margin ISI Transmission Line Model Characteristic Impedance (Z0) Reflections Crosstalk Noise Time Voltage
Diagram Description: The section on high-speed digital design discusses signal integrity concepts like eye diagrams and transmission line effects, which are inherently visual.

2. Creating a New Project

2.1 Creating a New Project

Launching OrCAD Capture CIS presents the primary interface where all project development begins. The software architecture organizes designs hierarchically, with projects containing schematic folders, library references, and output configurations. For precision engineering applications, proper project initialization is critical to maintain design integrity throughout the development cycle.

Project Configuration Parameters

Select File → New → Project to initiate the project creation dialog. The configuration requires three essential parameters:

$$ \tau_{setup} = \frac{1}{f_{clock}} - t_{hold} - t_{prop} $$

Where $$t_{hold}$$ represents the minimum hold time for synchronous designs and $$t_{prop}$$ accounts for signal propagation delays through the schematic hierarchy.

Library Management System

The project creation wizard automatically generates:

Advanced users should configure the Library Manager before adding components. The recommended workflow:

  1. Navigate to Options → Design Template
  2. Set grid spacing to 0.1mm for precision analog designs
  3. Configure the net naming convention (IEEE 315-1975 recommended)
  4. Establish hierarchical block connectivity rules

Design Constraints Setup

For high-frequency or mixed-signal designs, configure the constraint manager immediately after project creation:


# Sample constraint file for DDR4 interface
set_constraint -net_type clock -max_length 1500um
set_constraint -net_group data_bus -min_spacing 3x
set_constraint -voltage_domain 1.2V -tolerance ±5%

The constraint manager uses a weighted optimization algorithm:

$$ \mathcal{L} = \sum_{i=1}^N w_i(f_i(x) - t_i)^2 $$

Where $$w_i$$ represents priority weights, $$f_i(x)$$ are measurable parameters, and $$t_i$$ are target values for each constraint.

Version Control Integration

For collaborative projects, configure the SVN/Git integration through:

The version control system maintains design integrity through SHA-256 hashing of schematic elements:

$$ H_{block} = \text{SHA-256}(G_{schematic} \parallel P_{properties} \parallel t_{timestamp}) $$

2.2 Placing and Editing Components

Component Placement in OrCAD

OrCAD's component placement system leverages a hierarchical library structure, where parts are stored in OLB (OrCAD Library) files. To place a component, navigate to Place > Part or use the shortcut P. The component browser allows filtering by name, footprint, or electrical characteristics. Advanced users can define custom search queries using wildcards (*, ?) or parameter-based filters.

For high-speed designs, component placement affects signal integrity. The Place > Component > Advanced menu provides options for controlled impedance routing constraints, thermal relief settings, and differential pair grouping. These parameters are stored in the component's properties and propagate to the PCB layout phase.

Editing Component Properties

Double-click any placed component to access its property editor. Key editable fields include:

For components with complex behavior, the Edit PSpice Model option opens a text editor for netlist modifications. This is particularly useful for defining nonlinear components like MOSFETs with BSIM models:

$$ I_{DS} = \mu C_{ox} \frac{W}{L} \left( (V_{GS} - V_{TH})V_{DS} - \frac{V_{DS}^2}{2} \right) $$

Advanced Placement Techniques

Use Place > Array for creating component patterns with mathematical spacing:

For RF circuits, the Match Group function ensures symmetrical placement of critical components like balanced amplifiers. This creates a persistent spatial relationship that updates during subsequent edits.

Cross-Probing with PCB Editor

OrCAD's Cross-Select mode (Ctrl+Shift+X) maintains bidirectional synchronization between schematic and PCB. Highlighting a component in either view automatically selects its counterpart, with visual feedback showing placement conflicts or DRC violations.

Automation via Scripting

Component manipulation can be automated using TCL scripts through OrCAD's Command Window. Example script for batch-updating resistor values:

foreach part [get_selected] {
  if {[get_property $$part REFDES] =~ "R*"} {
    set_property $$part VALUE "10k"
    set_property $part TOLERANCE "1%"
  }
}

This script iterates through selected components, updating all resistors to 10kΩ with 1% tolerance while preserving other properties.

2.3 Wiring and Netlisting

Netlist Generation in OrCAD

In OrCAD, a netlist serves as the bridge between schematic capture and simulation or PCB layout. The netlist is a structured text file that defines all components, their properties, and their interconnections. OrCAD generates this file automatically when the schematic is validated, but engineers must ensure proper wiring and net naming conventions to avoid errors.

$$ N = \sum_{i=1}^{k} C_i + \sum_{j=1}^{m} P_j $$

where N is the total number of nets, Ci represents component connections, and Pj denotes port connections.

Wiring Best Practices

Proper wiring ensures signal integrity and reduces post-layout corrections. Follow these guidelines:

Netlist File Structure

A standard OrCAD netlist contains these sections:

* Sample OrCAD netlist fragment
R1 1 2 10k
C1 2 0 100nF
VCC 3 0 DC 5V
.model NMOS NMOS (VTO=0.7 KP=110u)

Netlisting Errors and Debugging

Common netlisting failures stem from:

OrCAD's DRC (Design Rule Check) identifies these issues before netlist generation. For complex designs, cross-probing between the schematic and netlist viewer accelerates debugging.

Hierarchical Netlisting

For modular designs, hierarchical netlists maintain signal integrity across schematic blocks. Key considerations:

Block A Block B DATA[7:0]

2.4 Hierarchical Design Techniques

Hierarchical design in OrCAD allows complex schematics to be decomposed into manageable subcircuits, improving modularity and reusability. This technique is particularly valuable in large-scale projects such as multi-channel RF systems, power distribution networks, and mixed-signal ASIC designs, where flat schematics become unwieldy.

Block Diagram Abstraction

The hierarchical approach begins with a top-level block diagram, where each block represents a functional subcircuit. These blocks are implemented as Hierarchical Pins in OrCAD, which map directly to ports in lower-level schematics. The pin-to-port correspondence is strictly enforced during netlisting, ensuring signal integrity across hierarchy levels.

Parameter Inheritance

Global parameters propagate downward through the hierarchy, while local parameters remain confined to their subcircuits. The inheritance follows the relation:

$$ P_{child} = P_{parent} + \Delta P_{local} $$

where ΔPlocal represents parameter overrides at the child level. This is particularly useful for defining component tolerances or temperature coefficients that vary across subsystems.

Cross-Hierarchy Probing

OrCAD's Cross Probe feature maintains bidirectional navigation between hierarchical blocks and their implementations. When debugging, signals can be traced across multiple levels while preserving the physical layout context. The probing depth D follows:

$$ D = \log_2(N_{nets}) + C_{constraints} $$

where Nnets is the total network count and Cconstraints represents user-defined visibility rules.

Back Annotation Flow

After PCB layout, hierarchical designs require constrained back-annotation to prevent unintended modifications. OrCAD enforces these rules through:

Mixed-Signal Considerations

When combining analog and digital hierarchies, OrCAD's PSpice-AMS requires explicit interface definitions between domains. The conversion threshold Vth at hierarchical boundaries must satisfy:

$$ V_{th} \geq \max(3\sigma_{noise}, 0.1V_{DD}) $$

for reliable signal interpretation across abstraction levels. This constraint appears automatically when placing HDLs (Hierarchical Digital Blocks) adjacent to analog subcircuits.

Performance Optimization

Hierarchical designs introduce parasitic RLC networks at block interfaces. The impedance discontinuity Zd between levels is minimized by:

$$ Z_d = \sqrt{\frac{L_{interconnect}}{C_{port}}} $$

OrCAD's Constraint Manager automatically flags violations when Zd exceeds 20% of the characteristic impedance.

OrCAD Hierarchical Design Structure Block diagram showing hierarchical relationships in OrCAD, including top-level block, child blocks, hierarchical pins, parameter propagation, and cross-probe paths. Top-Level Block P_parent Child Block A ΔP_local Child Block B ΔP_local Cross Probe Hierarchical Pins Hierarchical Pins Z_d
Diagram Description: The section describes hierarchical block relationships, parameter inheritance flows, and cross-hierarchy signal tracing which are inherently spatial concepts.

3. Importing Schematics to PCB Designer

3.1 Importing Schematics to PCB Designer

Preparing the Schematic for PCB Layout

Before importing a schematic into OrCAD PCB Designer, ensure the schematic is fully annotated and error-free. Run a Design Rules Check (DRC) in OrCAD Capture to verify electrical connectivity, component references, and netlist integrity. Critical issues such as unconnected pins, duplicate reference designators, or invalid footprints must be resolved at this stage.

The netlist, which defines electrical connections between components, must be generated in a format compatible with PCB Designer. OrCAD Capture exports this as a .mnl (Allegro netlist) file, containing:

Netlist Generation and Validation

Navigate to Tools > Create Netlist in OrCAD Capture and select the Allegro PCB Designer option. The generated netlist must be validated using the Allegro Netlist Reader utility to ensure no syntax errors or missing footprints exist. Common pitfalls include:

Importing into PCB Designer

Launch OrCAD PCB Designer and create a new board file (.brd). Use the File > Import > Logic command to load the netlist. The import process maps schematic components to physical footprints and establishes connectivity based on the netlist. Critical post-import checks include:

Handling Complex Hierarchical Designs

For multi-sheet schematics, ensure hierarchical blocks are flattened during netlist generation. PCB Designer treats each subsheet as a logical unit, but physical placement requires manual or automated optimization. Use Room Definitions to group related components (e.g., power supply sections, RF modules) for efficient placement.

$$ \text{Placement Efficiency} = \frac{\sum \text{Connected Net Lengths}}{\text{Total Board Area}} $$

Design Synchronization

OrCAD supports bidirectional synchronization between schematic and PCB. Changes made in Capture (e.g., added decoupling capacitors) can be pushed to the board using Design > Update PCB. Conversely, PCB modifications like renamed nets propagate back to the schematic if Back Annotation is enabled.

Practical Considerations

High-speed designs require additional setup before layout:

3.2 Component Placement Strategies

Efficient component placement in OrCAD is critical for minimizing signal integrity issues, reducing parasitic effects, and optimizing manufacturability. Advanced users must consider electromagnetic compatibility (EMC), thermal dissipation, and high-speed signal routing constraints during placement.

Hierarchical Placement for Complex Designs

Modular placement improves reusability and simplifies debugging. Group related components (e.g., power supplies, RF sections) into functional blocks with clear boundaries. Use OrCAD’s Room feature to enforce placement constraints:

Signal Integrity-Driven Placement

Prioritize critical signal paths by placing components to minimize trace length and discontinuities. For a transmission line with impedance Z0, the maximum allowable untuned stub length lmax is:

$$ l_{\text{max}} = \frac{c}{10f\sqrt{\epsilon_r}} $$

where c is the speed of light, f is the signal frequency, and ϵr is the substrate’s dielectric constant. Place drivers and receivers symmetrically to avoid phase mismatches in differential pairs.

Thermal and Power Distribution Considerations

High-power components (e.g., LDOs, MOSFETs) require thermal relief vias and copper pours. The thermal resistance θJA between a component and ambient is minimized by:

Manufacturing-Driven Optimization

Component orientation affects pick-and-place machine efficiency. Follow these guidelines:

Driver Receiver Differential pair length ≤λ/10
Component Placement Strategies in OrCAD Top-down view of a PCB layout showing functional blocks, differential pairs, thermal vias, and fiducial markers with annotations for placement strategies. Analog Block Digital Block Room Boundary Room Boundary Differential Pair Z0 = 100Ω Thermal Via θJA Path Fiducial Fiducial Component Placement Strategies in OrCAD
Diagram Description: The section discusses spatial relationships and placement strategies that are inherently visual, such as room definitions, differential pair alignment, and thermal via placement.

3.3 Manual and Automatic Routing

Manual Routing Techniques

Manual routing in OrCAD provides fine-grained control over trace placement, essential for high-speed or RF designs where impedance matching and signal integrity are critical. The process involves:

Automatic Routing Strategies

OrCAD’s autorouter (CBR, or Constraint-Based Router) leverages predefined design rules to optimize trace paths. Key considerations:

Mathematical Basis for Autorouting

The autorouter’s pathfinding algorithm uses a modified A* search with a cost function:

$$ C = \sum_{i=1}^{n} \left( w_l \cdot L_i + w_v \cdot V_i + w_d \cdot D_i \right) $$

where \( L_i \) is trace length, \( V_i \) is via count, \( D_i \) is deviation from preferred layer, and \( w \) are user-defined weights.

Hybrid Routing Approaches

For complex designs, combine manual and automatic routing:

Design Rule Checks (DRC) Post-Routing

After routing, validate the layout using Tools → Quick Check to detect violations such as:

Figure: Manual vs. autorouted traces (blue) with critical nodes (red).
Manual vs. Autorouted Traces Comparison A side-by-side comparison of manual and autorouted PCB traces with critical nodes and layer transition points highlighted. Manual Routing Autorouting Manual routing path Autorouting path Critical nodes Layer transition
Diagram Description: The diagram would physically show a comparison between manual and autorouted traces with critical nodes highlighted, illustrating spatial relationships and routing patterns.

3.4 Design Rule Checks (DRC)

Design Rule Checks (DRC) in OrCAD serve as a critical validation step to ensure a PCB layout adheres to manufacturing constraints, electrical clearances, and signal integrity requirements. Unlike schematic-level checks, DRC operates on the physical layout, verifying geometric and electrical compliance before fabrication.

DRC Categories and Constraints

OrCAD’s DRC engine evaluates multiple constraint classes:

Constraints are defined in the Constraint Manager, which hierarchically organizes rules by net class, layer, or component type. For example, a 100Ω differential pair might require:

$$ Z_{diff} = 2Z_0 \sqrt{\frac{1 - k}{1 + k}} $$

where k is the coupling coefficient between traces.

DRC Execution Workflow

  1. Rule Import: Load predefined rules from IPC standards or foundry specifications.
  2. Custom Rule Creation: Define layer-specific clearances or high-speed constraints via algebraic expressions (e.g., @CLK_NET.length <= 1500mil).
  3. Batch Processing: Run DRC across the entire board or selected regions with parallel computation.
  4. Error Visualization: Violations are highlighted in 3D view with severity levels (critical/warning/informational).

Advanced DRC Techniques

For RF/microwave designs, electromagnetic rule checks (ERC) supplement traditional DRC by evaluating:

$$ \oint_S \mathbf{J} \cdot d\mathbf{s} = -\frac{\partial}{\partial t} \int_V \rho \, dv $$

DRC results export to machine-readable formats (CSV, XML) for integration with yield analysis tools. False positives are mitigated by marking exempted regions or nets as DRC-ignored.

Real-World Case Study

A 24-layer server motherboard design used OrCAD’s DRC to detect a 3μm copper imbalance in power delivery networks (PDNs), which would have caused a 12% voltage droop during transient loads. The error was traced to an incorrect via antipad definition in the constraint template.

4. PSpice Simulation Setup

4.1 PSpice Simulation Setup

Circuit Schematic Preparation

Before initiating a PSpice simulation, ensure the schematic is correctly constructed in OrCAD Capture. All components must have valid PSpice models assigned. Passive elements (resistors, capacitors, inductors) should include appropriate tolerances if Monte Carlo or sensitivity analysis is required. For active components (transistors, op-amps), verify that the model parameters align with the intended operating conditions.

Critical checks include:

Simulation Profile Configuration

Create a new simulation profile via PSpice > New Simulation Profile. The key analysis types include:

$$ \text{Transient Analysis: } x(t) = \int_{0}^{t} f(\tau) \, d\tau $$
$$ \text{AC Sweep: } H(j\omega) = \frac{V_{\text{out}}(\omega)}{V_{\text{in}}(\omega)} $$

For transient analysis, set the Run to time parameter to at least 5 times the circuit's dominant time constant. For AC sweeps, use a logarithmic decade scale with sufficient points per decade (typically 100) to capture resonant peaks accurately.

Advanced Parameter Sweeps

PSpice allows parametric sweeps of component values or model parameters. To analyze a filter's cutoff frequency dependence on resistance:

.PARAM Rval = 1k
.STEP PARAM Rval LIST 1k 2k 5k
R1 OUT 0 {Rval}

Monte Carlo and Worst-Case Analysis

For statistical simulations, define component tolerances in the model properties:

Configure the Monte Carlo setup with at least 100 runs for Gaussian distribution validation. Worst-case analysis requires specifying MAX or MIN deviation modes for each parameter.

Convergence and Accuracy Settings

PSpice uses iterative methods to solve nonlinear circuits. Adjust these parameters in Simulation Settings > Options:

For oscillators or circuits with regenerative feedback, enable Skip initial transient solution (SKIPBP) to bypass DC operating point calculation.

Post-Simulation Data Analysis

PSpice Advanced Analysis tools enable:

Use measurement expressions (e.g., Bandwidth(V(OUT),3)) to automatically extract metrics like rise time or phase margin.

PSpice Simulation Analysis Types Three panels illustrating different PSpice simulation analysis types: transient analysis, AC sweep, and parameter sweep. Transient Analysis Amplitude (V) Time (s) AC Sweep Gain (dB)/Phase (°) Frequency (Hz) Gain Phase Parameter Sweep Amplitude (V) Rval R1 R2 PSpice Analysis Types Transient AC Sweep Parametric
Diagram Description: The section involves voltage waveforms, transformations, and time-domain behavior which are highly visual concepts.

4.2 Transient and AC Analysis

Transient Analysis

Transient analysis in OrCAD solves time-domain differential equations to simulate circuit behavior over a specified time interval. The analysis computes nodal voltages and branch currents by numerically integrating the system of nonlinear differential-algebraic equations (DAEs) derived from Kirchhoff's laws and component models. The trapezoidal or Gear integration methods are typically employed for stability and accuracy.

The governing equation for a capacitor in transient analysis illustrates the numerical approach:

$$ I_C(t) = C \frac{dV_C(t)}{dt} $$

Discretized using the backward Euler method:

$$ I_C(t_{n+1}) = C \frac{V_C(t_{n+1}) - V_C(t_n)}{\Delta t} $$

where Δt is the time step. OrCAD dynamically adjusts Δt to balance accuracy (smaller steps during rapid transitions) and computational efficiency (larger steps in quasi-static regions).

AC Small-Signal Analysis

AC analysis linearizes the circuit around the DC operating point and computes the frequency response. The system is solved in the phasor domain, with complex matrices representing impedance and admittance:

$$ \mathbf{Y}(\omega)\mathbf{V}(\omega) = \mathbf{I}(\omega) $$

where Y(ω) is the nodal admittance matrix, V(ω) the phasor voltages, and I(ω) the phasor current sources. OrCAD sweeps the frequency range specified by the user (e.g., 1Hz to 1GHz with logarithmic spacing) and stores the magnitude/phase of all node voltages and branch currents.

Practical Considerations

Advanced Techniques

For RF/microwave circuits, enable harmonic balance analysis (available in OrCAD PSpice Advanced Analysis) when transient analysis becomes impractical due to widely separated time constants. This solves the circuit in the frequency domain while accounting for nonlinear effects through iterative spectral methods.

The SVG below conceptually illustrates the relationship between time-domain and frequency-domain analyses:

Transient Analysis AC Analysis Fourier Transform

OrCAD Implementation


* Transient analysis example
V1 1 0 PULSE(0 5 0 1n 1n 10n 20n)
R1 1 2 1k
C1 2 0 1p
.TRAN 0.1n 50n
  

* AC analysis example
V1 1 0 AC 1
R1 1 2 1k
C1 2 0 1p IC=5
.AC DEC 10 1k 1G
Time-Frequency Domain Relationship Dual-panel technical diagram showing a time-domain pulse waveform and its corresponding frequency spectrum with labeled harmonics and integration steps. Time-Frequency Domain Relationship Time Domain 0 Δt Time (s) V_C(t) I_C(t) Frequency Domain Frequency (Hz) Magnitude (dB) 1st 2nd 3rd 4th 5th Fourier Transform
Diagram Description: The section covers time-domain vs. frequency-domain transformations and numerical integration methods, which benefit from visual representation of waveforms and spectral relationships.

4.3 Monte Carlo and Sensitivity Analysis

Monte Carlo Analysis

Monte Carlo analysis is a statistical method used to assess the impact of component tolerances on circuit performance. It operates by running multiple simulations with randomized parameter values within specified tolerance bounds, typically following Gaussian (normal) or uniform distributions. The resulting output distribution provides insight into yield probabilities and worst-case performance scenarios.

$$ \sigma_{total} = \sqrt{\sum_{i=1}^{n} \left( \frac{\partial f}{\partial x_i} \sigma_i \right)^2 } $$

Where σtotal is the standard deviation of the output, ∂f/∂xi represents the sensitivity of the output to parameter xi, and σi is the standard deviation of parameter xi. In OrCAD, this is implemented by:

Sensitivity Analysis

Sensitivity analysis complements Monte Carlo by quantifying how much each component variation contributes to output variance. OrCAD calculates normalized sensitivity coefficients:

$$ S_{x_i} = \frac{x_i}{f} \cdot \frac{\partial f}{\partial x_i} $$

A sensitivity of 0.5 indicates a 1% change in the component produces a 0.5% change in the output. Critical components (|S| > 1) require tighter tolerances for stable performance.

Practical Implementation in OrCAD

To configure these analyses: 


* Monte Carlo Setup
.MC 1000 DC V(OUT) YMAX 
+ R1(R=1k DEV=5%) C1(C=10n DEV=20%)

* Sensitivity Analysis
.SENS V(OUT) 
+ RANGE 1k 10k STEP 100

Key interpretation metrics include:

Advanced Applications

In RF and high-speed designs, these techniques predict:

For accurate results, correlation between parameters (e.g., matched resistor pairs) must be specified using the CORREL statement in the model definitions.

5. Creating Custom Components and Footprints

5.1 Creating Custom Components and Footprints

Custom Component Creation in OrCAD Capture

OrCAD Capture allows the creation of custom schematic symbols for components not available in default libraries. The process begins with defining the symbol’s graphical representation and electrical properties. Open the Part Editor from the Tools menu and select New Part. Define pin configurations, ensuring correct electrical types (input, output, power, etc.) and pin numbering.

For complex components like multi-part ICs, use the Homogeneous or Heterogeneous partitioning options. Homogeneous parts are identical (e.g., op-amp channels), while heterogeneous parts differ (e.g., a microcontroller with separate analog and digital sections). Pin visibility and grouping must adhere to the device datasheet.

Footprint Design in OrCAD PCB Editor

Footprints define the physical layout of components on the PCB. Start by selecting File → New → Library in PCB Editor, then create a new footprint. Critical parameters include:

For precision, derive pad coordinates from the component’s datasheet. For example, a QFN-16 package with 0.5 mm pitch requires pad centers spaced at 0.5 mm intervals. The pad width should be 0.25 mm to allow solder wetting while avoiding bridging.

Linking Symbols to Footprints

In Capture, assign footprints via the PCB Footprint property in the part properties dialog. Use the exact footprint name from the PCB Editor library. Verify compatibility by cross-referencing pin numbers between the schematic symbol and footprint. Mismatches here cause netlist errors during PCB layout.

Advanced Techniques: Parametric Footprints

For reusable designs, leverage OrCAD’s Parametric Footprint Generator. Define variables for pad dimensions, pitch, and row spacing. For example, a BGA footprint can be generated dynamically using:

$$ \text{Pad Pitch} = \text{Ball Pitch} - \text{Solder Ball Diameter} + \text{Tolerance} $$

This ensures scalability for different package sizes. Scripting via Skill language further automates footprint generation for high-pin-count devices.

Design Rule Checks (DRC) and Validation

Before finalizing, run DRC in PCB Editor to detect overlaps, missing pads, or incorrect clearances. Use the 3D Viewer to inspect mechanical fit. Export the footprint to a STEP file for verification in CAD tools if enclosure integration is critical.

Real-World Application: High-Frequency Components

Custom footprints for RF components (e.g., antennas, filters) require controlled impedance and minimal parasitics. Use tapered traces and ground vias adjacent to signal pads to reduce inductance. For a 50 Ω transmission line, calculate the pad width (W) using the microstrip formula:

$$ Z_0 = \frac{87}{\sqrt{\epsilon_r + 1.41}} \ln\left(\frac{5.98h}{0.8W + t}\right) $$

where \(h\) is substrate height, \(t\) is trace thickness, and \(\epsilon_r\) is the dielectric constant.

Custom Footprint Design for QFN-16 Package Top-down view of a QFN-16 footprint with labeled pads, pitch measurements, silkscreen outline, and assembly layer markings. 0.5 mm 0.5 mm 0.25 mm U1 Solder Pads Thermal Pad Silkscreen Assembly
Diagram Description: The section involves spatial relationships in footprint design and parametric calculations, which are highly visual.

5.2 Scripting and Automation with OrCAD

Introduction to OrCAD Scripting

OrCAD provides robust scripting capabilities through its OpenAccess API and Skill programming language, enabling automation of repetitive tasks, custom design rule checks, and batch processing. The scripting environment integrates directly with the OrCAD Capture and PCB Designer workflows, allowing engineers to streamline complex design processes.

Skill Language Fundamentals

Skill, a Lisp-derived language, is the primary scripting tool for OrCAD. Key features include:

$$ \text{Example Skill function: } \quad (defun add\_resistor (value) \ (create\_inst "R" value)) $$

Automating Schematic Tasks

Common automation use cases in OrCAD Capture include:


; Skill script to rename all capacitors
(let ( (caps (get_components "^C")) )
  (foreach cap caps
    (set_instance_property cap "Reference" (strcat "C" (itoa (index cap))))
  )
)

PCB Designer Automation

In Allegro PCB Designer, scripting enables:

The axl API namespace provides access to PCB-specific functions:


; Skill script to highlight nets with length > 100mm
(axlClearSelSet)
(foreach net (axlGetNets)
  (when (> (axlDBGetNetLength net) 100.0)
    (axlHighlightObject net)
  )
)

Performance Optimization

For large designs, consider:

Integration with External Tools

OrCAD scripts can interface with:


# Python COM example to export BOM
import win32com.client
orcad = win32com.client.Dispatch("OrCAD.Capture")
project = orcad.OpenProject(r"C:\design.opj")
project.ExportBOM(Format="CSV", File=r"C:\bom.csv")

Debugging Techniques

Effective debugging methods include:

5.3 Integration with Other CAD Tools

OrCAD’s interoperability with other CAD tools is critical for seamless design workflows, particularly in complex multi-disciplinary projects. The software supports bidirectional data exchange with mechanical CAD (MCAD), simulation tools, and enterprise PLM systems through standardized file formats and APIs.

Mechanical CAD (MCAD) Integration

OrCAD integrates with MCAD tools like SolidWorks, Autodesk Inventor, and PTC Creo via the IDX (Intermediate Data Exchange) format. This ensures accurate representation of PCB outlines, component heights, and keep-out zones in mechanical assemblies. The process involves:

Simulation Tool Interoperability

OrCAD’s SPICE engine (PSpice) supports co-simulation with MATLAB/Simulink for mixed-signal systems. The coupling is achieved through:

$$ \frac{dV_{out}}{dt} = \frac{1}{C} \int I_{PSpice} \, dt $$

where IPSpice is the current waveform exported from PSpice and integrated into Simulink’s solver. For finite-element analysis (FEA), OrCAD exports netlists to tools like ANSYS HFSS via the .SNP (Touchstone) format, enabling S-parameter extraction for high-frequency designs.

PLM/PDM System Integration

Enterprise integration with Windchill (PTC) or Teamcenter (Siemens) is facilitated through the ODBC database interface. Key features include:

Scripting and API Customization

OrCAD’s OpenAccess API allows Python or TCL scripts to automate cross-tool workflows. Example use cases:

import win32com.client
orcad = win32com.client.Dispatch("OrCAD.Application")
pcb = orcad.ActiveDocument
pcb.ExportIDX("C:/design.idx")  # Export to MCAD

For Altium Designer users, OrCAD provides schematic conversion via the .DSN to .SchDoc translator, though pin-to-pin equivalence must be manually verified for complex symbols.

Challenges and Best Practices

Cross-tool integration often faces discrepancies in:

Mitigation strategies include adopting IPC-2581 as a unified output format and using middleware like Cadence’s Integrate for real-time synchronization.

6. Official OrCAD Documentation

6.1 Official OrCAD Documentation

6.2 Recommended Books and Guides

6.3 Online Resources and Communities