Protel 99 SE high frequency PCB design research - Power Circuits - Circuit Diagram

Probe for domestic high-frequency needles like JKT-50L with three probes.

Full range of MOS power ICs.

Shunluo high-frequency inductors, parallel stack inductors, and authorized agents for winding inductors.

Industrial router crystal 3.2x2.5mm 3225 26M (26.000MHz) with 12PF, 10PPM, 20PPM, and 30PPM options.

With the rapid development of electronic technology, printed circuit boards (PCBs) have become increasingly complex and versatile. Designers working on high-frequency PCBs must possess a solid theoretical foundation and extensive practical experience. Both the schematic design and the PCB layout should consider the high-frequency working environment to create an optimal design. This article focuses on the issues encountered in high-frequency PCB design using Protel99SE, particularly in manual layout and wiring.

1. Layout Design

Although Protel99SE offers an auto-layout function, it often falls short of meeting the demands of high-frequency circuits. Manual layout techniques are frequently required to optimize component positions before combining them with automated layout processes. A well-thought-out layout significantly impacts the product's lifespan, stability, and electromagnetic compatibility (EMC). Thus, factors such as overall board layout, wiring feasibility, manufacturability, mechanical structure, heat dissipation, electromagnetic interference (EMI), reliability, and signal integrity must all be carefully considered.

Generally, components tied to mechanical dimensions are positioned first, followed by larger and more specialized components, and finally smaller ones. Wiring requirements should always be taken into account, with high-frequency components grouped closely together and signal lines kept as short as possible to minimize cross-talk.

1.1 Placement of Positioning Inserts Related to Mechanical Dimensions

Power sockets, switches, connectors between PCBs, and indicators are examples of components tied to mechanical dimensions. These components are usually placed at the edges of the PCB, leaving a 3mm to 5mm gap from the board’s edge. Indicators such as LEDs should be placed precisely according to their intended use. Switches and fine-tuning components like adjustable inductors or resistors should be positioned near the board’s edge for easy access. Components that require frequent replacement should be placed in areas that are easier to reach.

1.2 Placement of Special Components

High-power transistors, transformers, and rectifiers generate significant heat during operation at high frequencies. Proper ventilation and heat dissipation must be considered during layout. These components should be placed in areas of the PCB where airflow is optimal. High-power rectifiers and regulators should be equipped with heatsinks and kept away from transformers. Heat-sensitive components like electrolytic capacitors should also be kept away from heat-generating devices to avoid increased resistance and degraded performance.

Components prone to failure, such as regulators, electrolytic capacitors, and relays, should be placed for ease of maintenance. Test points that need frequent measurement should be arranged so that the probes can easily access them.

Since 50Hz leakage magnetic fields can interfere with low-frequency amplifiers, these components should be isolated or shielded. Amplifier stages should ideally follow the schematic diagram in a straight line. This arrangement ensures that the ground current of each stage is confined to that stage, preventing interference with other circuits. Input and output stages should be as far apart as possible to minimize parasitic coupling interference.

Considering the signal transmission relationships between functional circuit units, low-frequency and high-frequency circuits should be separated. Analog and digital circuits should also be kept apart. Integrated circuits should be placed in the center of the PCB to facilitate wiring to other devices.

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