Keywords: Express PCB, High Speed PCB

Every year, the demand for reliable High Speed PCB and the need for high-speed digital circuits is increasing. With many other components, power supply, and microprocessors, the digital PCB circuits are packed compactly. These components operate at frequencies over 1 GHz easily. This article focuses on such issues and the methods to follow while designing PCB to avoid any issues.

High Speed PCB’s Application

The heart of computational devices such as smartphones, computers, and many more is High-speed PCB. These devices have a complex nature. Hence, the Express PCB is very reliable and robust. In the fields of IoT, aerospace, and communications, Applications of high-speed circuits are growing. While designing board layouts for high-speed circuits, understanding the considerations that are needed to be followed is essential with the criticality of the application in mind.

Considerations of Design for High Speed PCB

In designing High-speed PCBs, the following are considered as the go-to techniques for achieving high-speed operation in a low-power environment.

• Packaging all the components in Floor planning
• Minimization of onboard noise from the power network
• Optimization and Clock selection
• Decreasing reflection of a signal
• Minimization of cross-talk between traces of signal
• Proper line termination and impedance matching
• Optimizing the system for self-coupling and EMI from the environment

Board Material Selection for High Speed PCB

The loss tangent and dielectric constant of the material determine the choice of board material. When an electromagnetic wave passes through it, the energy lost from the material is Loss tangent. The energy lost is more when the loss tangent is higher.

• Ground plane design

In minimizing stray capacitance, heat dissipation, shielding, and a common reference voltage, Ground planes in a PCB helps. In a low impedance path, the current in a circuit tends to be lower. At very high frequencies to the ground plane, fast raising signal edges are coupled. In the ground plane, this creates a current spike. The analog performance of the PCB is damaged by this current spike. As the input stray capacitance increases, high-speed op-amps are affected by the presence of the ground plane below further. Between the ground plane, analog devices, and digital devices proper distance is maintained to avoid these conditions.

• Microstrip Design

The behavior of the Signal trace on planes of a single ground resembles that of a layout of a microstrip line and as a stripline layout, signal trace in between two ground planes acts similarly.

Floor planning for High Speed PCB

By means of parasitic capacitance, parasitic resistance, and parasitic inductance, passing through the lead and connecting lines, Floor packing and planning have a significant impact on communication delay, noise, frequency response, and edge rate. Along with the schematic design, board-level design, packaging design, and Silicon design must be done. To floor plan the circuit, Software simulations can be used before physical deployment. The designer can ensure that the design will work in an intended way if specification regarding the component locations and signal routing is done from the beginning itself. The rework time and lowers cost is decreased by this. Thus, the cycle time of the product is minimized.

Power supply and clock design for High Speed PCB

In the PCB circuit, the premium source of onboard low-frequency noise is the Power supply. By connecting the power plane to the ground plane by using parallel capacitors, Power integrity in a high-speed system can be ensured. Low ac impedance is ensured by Parallel capacitors of different values across a wide band of frequencies. For analog and digital devices, Separate power planes shall be used to reduce noise coupling. To ensure that all signals on the PCB layout are arriving at the proper time, Clock selection is crucial in relation to the clock signal.

EMI optimization for High Speed PCB

Mutually coupling or self-coupling from the other electronic devices in the surroundings can result in EMI affecting a device. In high-speed circuits using certain techniques, EMI can be optimized.

• Matching and routing

Reflection can be induced by unterminated or unmatched signal traces. Signal ringing back to the source is caused by this. This is a kind of self EMI. Removal of signal ringing is ensured by proper matching. Self-coupled EMI is reduced by proper routing.

• EMI filter and shielding

Using an elongated ground plane, Shielding in a PCB is done. External EMI that causes signal disturbance in the circuit is decreased by skin effect on the conductive surface of the ground plane. To couple it to the ground after filtering out ambient EMI noise, EMI filters are implemented. You can use a simple decoupling capacitor setup as an EMI filter.

Signal Integrity for High Speed PCB

A variety of signals of varying frequency, both analog and digital is present in a PCB. To coupling and noise, these signals are sensitive. To ensure signal integrity, Proper care in matching, impedance, shielding, and routing has to be taken.

• Routing

During routing, certain guidelines that must be observed are as follows: 

• The high-frequency clock traces as routed as straight as possible. As compared to right-angled bends, arc bends are preferred in case of the need for bends to avoid signal loss due to discontinuity.
• Clock signals Termination. The reflection is reduced with this.
• High isolation is needed by Signal traces that are sensitive. So, on separate layers, they must be routed.
• As they can increase inductance and cause impedance mismatch, Multiple via are avoided.

• Impedance matching

A direct impact on the integrity of signals is posed by impedance matching between the receiver and transmitter. Signal loss and signal reflection is produced by improperly matched lines. The impedance of the load and the impedance of the trace must equal the impedance of the source. Signal integrity and matching are ensured by Proper termination of a transmission line.

Conclusion

Planning everything is imperative in High Speed PCB design before starting the process of physical layout. The foundation for a good layout is a good schematic. During the PCB design, factors like impedance matching, routing, power supply location, and signal integrity are the crucial considerations to be made. The robustness and reliability of the PCB will be enhanced by efficient implementation and design.