# Connecting Electrical Circuits for Multi-Board Schematic Capture

August 30, 2019

I have heard it said that “no man is an island.” Well, on some days it can certainly seem as though you are disconnected. This can be true despite the fact that many of your colleagues are mere feet away at another desk or in another cubicle or office. At times like this, I find it helpful to recall what Robert DeNiro, one of my favorite actors, attempts to relay to a table of friends and colleagues about baseball. In the movie “The Untouchables” he enthusiastically tries to remind them that each player is a member of a team; although, there are times that you must perform alone.

As a PCB designer, you are often in a similar situation. Although you may be designing a single circuit board alone, other circuits designed by others are required to complete a larger system of which your board is a part. According to KCL, all currents that enter and exit a node or connection point must balance to zero. And each complete current path is, in fact, a separate circuit and the larger system that consists of these multiple circuits also requires balance.

Thus, connecting electrical circuits and multiple PCBs correctly is a requirement for proper operation of the larger system. There are advantages to having this comprehensive system-level vantage point from which to evaluate your board. Before, we discuss these let’s delve more into connecting multiple PCBs during design or what can be referred to as multi-board schematic capture.

## What is Multi-board Schematic Capture?

PCB development is a three-stage process that includes design, manufacturing and testing. Each stage consists of steps that are distinctive for that particular stage. PCB design is the initial stage during which you create the circuit board architecture. For all but the simplest cases, PCB design consists of two primary tasks: schematic capture and specifying the PCB layout. The finalized PCB layout includes the information, data and graphics necessary for a contract manufacturer (CM) to physically build, fabricate, and mount the components on, assemble, your board.

As the design is the first stage of development, the quality of all subsequent stages relies upon it for accuracy and completeness. And within the design, the schematic capture serves as the blueprint for placing components and routing traces that dictate virtually all other PCB layout tasks. An example of schematic capture in progress is shown in the figure below.

Example of schematic capture

Schematic capture is the creative process of drawing a circuit diagram that represents the desired electrical operation required to achieve some performance objective. The diagram typically includes symbols, text and other imagery that represent the electrical components and the connections of the circuitry.

Multi-board schematic capture then can be defined as connecting electrical circuits, each of which will be fabricated and assembled on a separate PCB, such that a larger electrical drawing or schematic is created that is comprised of the interconnected circuits. It may not be apparent how this helpful for PCB design, but there are several advantages as discussed below.

## Advantages of Connecting Electrical Circuits for Multi-board Schematic Capture

Depending upon the complexity of the overall electronic device or product that you are developing, it may include many different circuit boards that perform different functions yet must operate seamlessly. Additionally, the schematic capture for these PCBs may be performed by different designers. And for highly complex systems, the designs may originate from different sources or be created in varying formats.

In these cases, PCB development can be challenging and time-consuming for design and manufacturing. However, by implementing multi-board schematic capture a number of advantages, as listed below, can be realized that will improve and perhaps optimize your development.

• Aid in designing SPI
SPI is a synchronous data transfer protocol, as shown above, for efficient communications between a processor and peripheral device. Peripherals are often separate electronic devices that require connection to the PCB that contains the processor. Any in many cases, there may be several such peripheral devices connected to a single processor board. By connecting these electrical circuits during schematic capture, analysis can be performed to verify communications and connection devices prior to board layout and manufacturing.

An example of an SPI interface

• Analyze system timing diagrams

For digital electronic systems, timing accuracy is critical for successful operation. The

ability to verify signal synchronization prior to board layout and manufacturing can not only reduce

cost but also save development man-hours and manufacturing waste for PCB respin. Utilizing multi-

board schematics in system timing allows for you to have a greater understanding of trouble areas

and signal hotspots early.

• Analyze inter-board signal and power integrity

The ability to analyze the entire electronic system is not a substitute for signal and power

Integrity (SI and PI) analyses that should be performed on the hardware system; however, it can

help identify actual and potential problems that can be corrected during design, ahead of

production. This saves time, effort, and makes the board layout process more reliable.

• More efficient collaborative design

When a team of designers are working on separate boards for a larger system it is

imperative that they are able to interact with their colleagues for efficient collaboration.

Failing to do so will undoubtedly extend the development process.

• Reduce the number of prototyping iterations

It is common for PCB development to require several design⇒build⇒test iterations to

make corrections and achieve the highest quality design. The ability to analyze boards

and systems during design can greatly reduce the number of changes needed and thus

the number of iterations required.

As shown above, there are many advantages to connecting electrical circuits for multi-board schematic capture. However, to fully capitalize on these time and cost-saving features requires the right PCB design package.

With the connection of multi-board circuits, you’ll most often find trouble with signal interference between low and high speed signals, improper or excessive voltage flow between vias or between connectors, and component density adding difficulties to traces and frequency domains.

Where PSpice comes in is giving you a reliable simulator that can simulate component interactivity based on an accurate, over 34,000 component model library, as well as providing voltage analysis for the power supply of the system, and running tolerance and cost analysis to determine which areas of the board need the least layout attention, saving money and increasing stability through to the end.

PSpice by Cadence gives you the capability to perform multi-board simulations to evaluate all aspects of SPI, SI and PI for fast and efficient PCB system design. Schematic capture and advanced signal simulation capability work seamlessly with Cadence’s PCB design platform for more efficient and high-quality designs the first time to minimize development time.