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With the development of integrated circuit process technology, the operation speed of multi-chip components is getting higher and higher, and the processing of high-speed signals has become the key to the success of MCM circuit design. When the rising or falling edge of the clock signal is small, the transmission line effect is caused, that is, signal integrity problems occur.
Combine an actual DSP high-speed image data acquisition system to illustrate the generation of signal integrity problems and specific solutions.
At present, the increasingly fine semiconductor process makes the transistor size smaller and smaller, so the signal transition of the device is faster and faster, the fast slope transient of the high-speed digital system and the extremely high operating frequency, and the large circuit density. This has led to signal integrity issues and electromagnetic compatibility issues in the field of high-speed digital circuit system design. Destroying signal integrity directly leads to signal distortion, timing errors, and incorrect data, address, and control signals, which can cause misoperations and even system crashes. Therefore, signal integrity issues have increasingly attracted the attention of high-speed digital circuit designers.
When the impedances don't match, what are the ways to match it? First, consider using a transformer for impedance conversion, as in the example in the TV above. Second, consider using series/parallel capacitors. Or inductive methods, which are often used when debugging RF circuits. Third, consider the use of series/parallel resistors. Some drivers have lower impedance and can be connected in series with a suitable resistor to match the transmission line, such as high-speed signal lines, sometimes A series of resistors of several tens of ohms will be connected in series. The input impedance of some receivers is relatively high. The method of parallel resistors can be used to match the transmission line. For example, 485 bus receivers often have a matching resistor of 120 ohms in parallel at the data line terminal.
The so-called input impedance mainly considers the power consumed by the circuit itself (can be understood as meaningless loss). For a voltage-driven circuit, the larger the impedance, the smaller the current, the smaller the P=I*I*R, and the smaller the current. In terms of the driving circuit, the smaller the impedance, the smaller the P=I*I*R, and the smaller the power consumption, so that for the latter circuit, more power can be output.
1. Signal Integrity: refers to the quality of the signal in the circuit system. If the signal can be transmitted from the source to the receiver without distortion in the required time, we call the signal complete.
As data rates continue to increase, signal integrity issues have become the most critical factor for design engineers to consider. This exponential increase in data rate can be seen in applications such as handheld mobile devices and consumer display products to high-bandwidth routers/switches. Jitter (noise) is the primary reason for reducing the level of signal integrity in a design. In addition to signal integrity enhancement techniques using layout, impedance matching, and more expensive materials, designers can simply add jitter cancellers such as equalizers to the design to solve jitter problems. This way designers don't have to focus on signal integrity issues, but focus on the core design of the system.
12. What is the pin-to-pin delay (delay)?
1. What is Signal Integrity?
1. EMC, EMI. 2. Routing skills for high-speed differential signals
Signal integrity (SI) issues are becoming a growing concern for digital hardware designers. Due to the increased data rate bandwidth in wireless base stations, wireless network controllers, wired network infrastructure, and military avionics systems, board design has become increasingly complex.
This article focuses on signal integrity challenges involving high-speed interface design (the main features of RapidIO switching support these high-speed interface designs), and the ability to optimize RapidIO switching is designed to achieve high signal integrity in high-speed designs.
9 basic knowledge discussions about grounding technology
The advantage of Protel is that it is more popular in the Chinese market. As long as the PCB is Protel, any file can make a board. Southern China is more likely to accept the OrCAD format.
The main cause of electromagnetic interference caused by the ground line is the impedance of the ground line. When the current flows through the ground line, a voltage is generated on the ground line. This is the ground line noise. Driven by this voltage, ground loop current is generated, causing ground loop interference. When two circuits share a ground line, a common impedance coupling is formed. The method for solving the ground loop interference is to cut the ground loop, increase the impedance of the ground loop, and use a balanced circuit. The solution to the common impedance coupling is to reduce the impedance of the common ground portion or to use a parallel single-point grounding to completely eliminate the common impedance.
The ways to control the effects of transmission line effects from the following aspects.
When the system is operating at 50MHz, transmission line effects and signal integrity issues will occur; when the system clock reaches 120MHz, PCBs based on traditional methods will not work unless high speed circuit design knowledge is used. Therefore, high-speed circuit design technology has become a design tool that electronic system designers must adopt. The controllability of the design process can only be achieved by using the design techniques of high-speed circuit designers.
As circuit design becomes more complex and high-speed, how to ensure the integrity of various signals (especially high-speed signals), that is, to ensure signal quality, becomes a problem. At this time, it is necessary to analyze by means of the transmission line theory, and the characteristic impedance matching of the control signal line becomes the key. The non-strict impedance control will cause considerable signal reflection and signal distortion, resulting in design failure. Common signals, such as PCI bus, PCI-E bus, USB, Ethernet, DDR memory, LVDS signals, etc., require impedance control. Impedance control ultimately needs to be realized through PCB design, and higher requirements are also imposed on the PCB board process.
26. When there are multiple digital/analog function blocks in a PCB board, the conventional practice is to separate the digital/analog grounds. What are the reasons?
Can you introduce some foreign technical books and materials on high-speed PCB design?