Electronic Circuit Design With OrCAD X

Key Takeaways

• OrCAD X has a complete and comprehensive solution for every aspect of electronic design, from schematic creation to production.

• Because the design platform shares a common UI/UX interface, moving between different levels of the design is quick and straightforward.

• Additional considerations for layout optimization like EMI, power integrity, and MCAD integration can also benefit from in-design analysis to accelerate design turnaround time.

Electronic circuit design produces complex electronics with an established, bottom-up workflow.

Electronic circuit design occurs in cascading design phases. What’s essential to keep in mind is that these design phases are often bidirectional – a change to the schematic impacts the placement and routing of the components and may prompt a response back at the schematic level. Like an unwanted signal reflection returning to the source, alterations late in the design can become exceptionally cumbersome to correct. Electronics development will consider each design phase independently and holistically to minimize these impacts on engineering change orders (ECOs). OrCAD X aids this process by giving designers a wealth of tools at each design stage for a seamless workflow that’s as malleable as the design itself.

A Brief Overview of Electronic Circuit Design

A Walkthrough of Electronic Circuit Design

Prototyping a design begins with workable specifications. As electronic circuit design is often a race against time when turning prototypes into production, vision is critical to success. However, designs rarely proceed straightforwardly from initial conception to final product. Instead, designers should expect revisions to come about – whether driven by supply chain issues, manufacturing demands, or changes in product goals; adaptability will be vital to minimizing turnaround time when revision conditions arise.

1. Schematic Drawing

The benefit of working in the schematic for simulation is that users can save progress on their design as they execute and tweak simulation analysis. In this piecewise manner, even small circuit blocks can grow to encompass a complicated design involving thousands of components. There’s additional work in marrying the disparate functionalities of the circuit, but the general scope will focus on adding passive elements for power integrity and active elements for signal conditioning. These ancillary circuits ensure power delivery remains constant and maintain optimal communication between different sub-circuits of the design. The final step for the schematic will be associating the correct footprints to their corresponding schematic symbol, establishing consistency between the symbolic logic and physical pinout.

The panel to the left of the schematic workspace shows the file hierarchy and circuit blocks.

2. Planning to Simulation

Circuit floorplanning starts with partitioning the design into smaller circuit block diagrams that isolate functionality from the greater system performance (e.g., the power distribution network or PDN). This task typically falls to the engineer, but designers have much to lean on: manufacturer’s datasheets often include circuit layouts for simulation with parameters that can, at the very least, provide insight after deciding upon the base circuit topography.

OrCAD X Capture allows users to quickly place general and manufacturer-specific symbols with PSpice parts for quick simulation. Users can also import PSpice models from licensed third-party vendor sources or create their simulation models.

PSpice integration in OrCAD X Capture allows designers to simulate circuit response rapidly.

3. PCB Layout

After finalizing the schematic, designers initiate the PCB layout by transferring the component footprints to the board file through the schematic netlist. The circuit layout is a science, but there’s an art to managing board space between placement and routing for optimal performance. This design stage is the earliest point where mechanical considerations emerge: connectors must orient correctly, edge clearance requires observation, and other factors constrain the design. While sometimes challenging, these constraints are beneficial because they initially guide component placement.

The first task will be shaping the Design Rule Checks (DRCs) that prevent the designer from producing designs that are difficult or impossible to manufacture without drastically affecting quality. Designers can use a standard organization database file (.dsn) with OrCAD X Capture to preconfigure the Constraint Manager and then adjust as necessary or fill out the table individually for each design. Additionally, the board’s physical stackup and its effect on manufacturing processes will offer substantial insight into forming the design rules.

Users can import Design Rules set in the Constraint Manager from OrCAD X Capture to OrCAD X Presto or vice versa.

Designers should then define the outline of the rigid board or flex/rigid-flex assembly. From there, any component placement with defined x and y locations (relative to mounting holes, board edge, etc.) requires immediate placement. Then, designers should look at their circuit blocks and any supporting datasheets to optimize the near layout. Regarding board placement, prioritize circuit blocks with many fanouts toward the center of the board; connectors (predominantly horizontal) should move toward the board edges unless otherwise specified by the engineer.

Placement is only one-half of the layout: designers must route copper traces, shape pours, and create other features that provide electrical and thermal conductivity. Routing will take the bulk of the design time, but proper placement will expedite the process while improving the performance of the printed circuit. Much like the placement, the initial routing should focus on the critical nets – think clocks, differential pairs, data lines, etc. – where signal integrity issues can rapidly propagate throughout the board, creating runtime errors. EM simulation of the design and post-production testing will be necessary to ensure the printed circuit remains electrically compatible with its surroundings.

Designers can simplify layout workflow in OrCAD X Presto PCB Editor with automatic fanout, among other features.

4. Prototyping

With the complexities inherent to PCB design, revisions are nearly impossible to avoid. Sometimes, even a perfectly functional design simply has to adjust to market forces, whether that’s component availability or a broadening of the scope of the design. Revisions can be planned refinements to test prototypes using production quality and unsuitable components for high-volume lots. Whatever the case, OrCAD X Presto PCB Editor and its 3DX canvas offer design teams a fast and powerful method to visualize MCAD-ECAD integration, including 3D placement/ routing and bending of flex regions. Even as designs evolve, users can easily stay on top of new ECOs and incorporate changes.

The new 3DX canvas in OrCAD X Presto PCB Editor simplifies MCAD design integration.

Best Practice Tips for Circuit Designers

Space Allocation

Demand for smaller form factors is high in consumer electronics, yet users don’t want to sacrifice performance or functionality appreciably. The designer is responsible for optimizing the rigid board/flex assembly layout without compromising on factors like profitability, interference, and heat dissipation. When working on a flex/rigid-flex printed circuit or an enclosed product, ensure the design fits into the enclosure before producing the actual PCB. Collaborate closely with the mechanical engineers or product designers during this design phase.

Component Placement Considerations

Analog components should have a reasonable clearance from their high-speed digital counterparts. The same applies to power management components, which should be in an isolated layout region. Besides functionality, component placement should consider serviceability, like for industrial control panels that require regular maintenance. Use strategic wire-to-board connector placement to make servicing and troubleshooting easier. 

Electromagnetic Interference (EMI)

With less space and higher speeds, EMI can rapidly undermine an otherwise effective PCB design. To reduce the possibility of EMI issues with a PCB, take note of the ground plane and current return path.  A good separation of ground planes, especially for high-speed signals, helps minimize interference that couples through the ground copper. It’s also essential to verify high-speed signals have the shortest return path to prevent the signal from interfering with other components.

Power Delivery Network (PDN)

No matter how sophisticated a layout is, a poor-performing power module design can render it meaningless. Besides choosing the right power-regulating components or battery, you’ll want to ensure that the traces are sufficient for the current density.  Proper decoupling capacitor size and placement (keep small capacitance capacitors closest to matching power net pins) prevents issues caused by unintended under-voltage or current limiting conditions.

Cadence Is on the Cutting-Edge of Circuit Design Solutions

Electronic circuit design is a deep and broad topic spanning multiple disciplines, fields, and levels of expertise; it’s easy for newcomers to get overwhelmed. Fortunately, designers have the new OrCAD X Presto PCB Editor to assist them throughout the layout with an easy-to-use, customizable UI that prioritizes the workspace. Designers can download the new OrCAD X free trial and see how easy and powerful a circuit layout can be. Looking to take a design to the next level? Cadence’s PCB Design and Analysis Software products offer unparalleled and industry-recognized performance.