When a microcontroller or FPGA sends SPI control signals to a phase-locked loop (PLL) chip, it often requires a series connection of a 22 ohm or 33 ohm resistor. What is the reasoning behind this? Impedance discontinuities can cause electromagnetic wave reflections, which in turn can lead to signal distortion. Therefore, impedance matching is often … Read more
Technical Field: Electronic devices, particularly those with rigid-flexible circuit boards. More specifically, it relates to rigid-flexible circuit boards with signal lines and grounding areas on both sides and below some conductive layers in the flexible circuit board area to reduce impedance variation. Background Technology Overview: With the increasing integration of electronic devices and the popularity … Read more
In FPGA development, the design of the wiring for the UART interface, specifically the EIA/TIA-232 (commonly known as RS-232) interface, is crucial. A reasonable wiring layout not only enhances communication stability but also effectively reduces signal interference. Below are the key points for EIA/TIA-232 interface in FPGA UART development. 1. Signal Line Layout TX/RX Pair: … Read more
In PCB (Printed Circuit Board) design, factors such as signal transmission stability and impedance matching are typically considered. Choosing the appropriate stacking scheme is crucial to meet design requirements. In certain cases, especially when designing six-layer boards, a special design scheme known as ‘pseudo eight-layer’ may be adopted. The ‘pseudo eight-layer’ actually refers to a … Read more
Friends in “Vehicle Technology” should know that the CAN bus requires two 120 Ohm termination resistors at both ends, making the total line resistance 60 Ohms. This is a piece of knowledge that almost everyone knows, but very few can explain clearly. In most cases, we have the experience that adding a 120 Ohm resistor … Read more
In modern high-frequency microwave circuit design, vertical interconnect transition structures serve as critical paths for signal transmission between different layers of PCBs, and their performance directly affects the overall properties of the system. As communication systems advance into the millimeter-wave frequency band, traditional via structures can no longer meet the integrity requirements for high-frequency signals. … Read more
When testing a signal with an output impedance of 50Ω using a Pico oscilloscope, a 50Ω to 1MΩ direct terminal is required. Recently, during an on-site test with a client, I found that the waveform oscillated severely, as shown in Figure 1 (red box), making it impossible to conduct accurate data analysis. Figure 1 Severe … Read more
Click the blue text above to follow us The main reason for adding a 22Ω or 33Ω resistor in series when a microcontroller uses SPI to connect to a sensor or controller is to suppress reflections and ringing. 1 Principle of Reflection and Source Matching In high-speed digital signal transmission, when the signal driver (such … Read more
For more experience sharing, follow RF Engineer When a microcontroller or FPGA sends SPI control signals to a phase-locked loop chip, it often requires a series connection of a 22 ohm or 33 ohm resistor. What is the reason for this? Impedance discontinuities can cause electromagnetic wave reflections, which in turn lead to signal distortion. … Read more