After long-term practice and summary, hardware circuit design has formed a number of fixed design modules. Mastering these modules is extremely beneficial for hardware system design, as it can significantly improve design efficiency and reduce the probability of errors. The key modules of hardware circuit design mainly include the power supply module, storage module, display module, and external interface module.
After long-term practice and summary, hardware circuit design has formed a number of fixed design modules. Mastering these modules is extremely beneficial for hardware system design, as it can significantly improve design efficiency and reduce the probability of errors. The key modules of hardware circuit design mainly include the power supply module, storage module, display module, and external interface module.
1. Power Supply Module
The power supply is the lifeblood of a system, and sufficient cost investment is recommended—it is crucial for product stability and passing various certifications.
- Adopt π-type filtering as much as possible with an additional 10uH inductor, and connect a 104 bypass capacitor to the power pin of each chip;
- Use varistors or transient voltage suppressor diodes to suppress surges;
- Separate analog and digital grounds, as well as high-current and low-current ground loops, and isolate them with magnetic beads or zero-ohm resistors;
- Design with margin to prevent overheating of power supply chips; attach heat sinks when the power consumption reaches 50% of the rated value.
2. IO Port Design
Pull up the input IO ports; calculate the driving capability for the output IO ports.
3. Operational Amplifier Circuit Design
Do not directly connect a capacitor to the output of an operational amplifier (op-amp).
In DC signal amplification circuits, a decoupling capacitor is sometimes directly connected to the op-amp output to reduce noise. Although the amplified signal is DC, this practice is highly risky. When a step signal is input or the power is turned on, the op-amp output current will be relatively large, and the capacitor will change the phase characteristics of the loop, leading to circuit self-oscillation—which is undesirable.
A proper decoupling capacitor should form an RC circuit: connect a resistor in series with the op-amp output first, then connect the decoupling capacitor in parallel. This method can greatly reduce the instantaneous output current of the op-amp without affecting the loop phase characteristics, thus avoiding oscillation.
4. High-Speed IO Port and Differential Signal Design
For long traces of high-speed IO ports, use a 33Ω resistor to suppress reflection; a matching resistor is usually added between the differential pair at the receiving end, and its value should be equal to the differential impedance to improve signal quality.
5. Level Matching Between Chips
When signals or power supplies are transmitted between interconnected PCBs (e.g., power or signals from Board A to Board B), an equal amount of current will flow back to Board A through the ground layer (Kirchhoff's Current Law). The current on the ground layer will take the path of least resistance. Therefore, at the interfaces where power supplies or signals are interconnected, the number of pins allocated to the ground layer should not be too small to reduce impedance and ground layer noise.
In addition, analyze the entire current loop (especially for high-current sections), and adjust the grounding layer or ground wire connection to control the current path (e.g., create a low-impedance path to direct most current through it), thereby reducing interference to other sensitive signals.
6. Switching Device Design
Avoid the overshoot characteristic of transistors during switching.
7. Testable Circuit Design for Single Boards
Design the single board with testable circuits to complete functional testing independently.
8. Test Point Layout on Circuit Boards
Add test points on the circuit board. In principle, test points should be as small as possible (while meeting the requirements of test equipment) and their branches as short as possible. Ensure the presence of test points for key signals and ground points.
9. High-Frequency Interference Suppression
The basic idea of suppressing high-frequency interference is to minimize the electromagnetic interference of high-frequency signal fields (so-called crosstalk). This can be achieved by increasing the distance between high-speed signals and analog signals, or adding ground guard/shunt traces next to analog signals. Pay extra attention to the noise interference of digital ground on analog ground.
If the above nine points are carefully checked in each schematic and PCB design, the success rate of product design will be improved, the number of modifications reduced, and the design cycle shortened.
The above are the nine core circuit modules for hardware engineers in circuit design. Mastering more circuit modules helps to complete design and iteration quickly.
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