How do high frequency applications like 5G affect signal integrity?
2022-02-09
5G's place on the electromagnetic spectrum
In this article, let's take a look at the impact of higher frequencies on PCB signal integrity and ways to mitigate these issues.
Why are 5G frequencies bad for signal integrity?
In circuit board design, an increase in frequency can have many adverse effects on signal integrity -- especially the effects of increased noise and attenuation.
noise
The first thing to consider about noise is that as the frequency of the system increases, signal reflections become more and more important. According to transmission line theory, reflection is directly related to the ratio of the length of the transmission line to the wavelength of the signal.
signal reflection
We also know that the signal wavelength decreases with increasing frequency (λ=v/f).
Therefore, as 5G introduces higher frequencies, designers must also consider the effects of signal reflections
Such as ringing or other distortions, which can cause more noise in the system and effectively reduce the SNR.
Capacitive and Inductive Coupling
Furthermore, since capacitance and inductance are related to the rate of change of voltage and current, respectively, the effects of capacitive and inductive coupling become more relevant. This also creates noise and distortion, which reduces SNR.
Attenuation and skin effect
With regard to attenuation, an important consideration is the so-called skin effect. Essentially it shows that as the frequency of the signal increases, the penetration depth of the signal within the conductor decreases.
skin effect
The important implication of the skin effect is that as higher frequencies pass through a smaller area, they encounter greater resistance and cause greater IR losses. This loss also reduces SNR.
Ways to Improve SNR in 5G Designs
In high-speed designs, there are many factors that affect signal integrity. So, what can designers of 5G PCBs do?
Control Board Impedance
An important step in mitigating signal reflections and attenuation is controlling board impedance. Having properly terminated lines and a well-designed impedance matching network is critical to preventing signal reflections and delivering maximum power to the circuit block.
Focus on Impedance in Manufacturing: mSAP
Impedance control issues can also be addressed when manufacturing circuit boards.
Traditional PCB manufacturing processes have the disadvantage of creating traces with trapezoidal cross-sections. These cross-sections change the impedance of the traces themselves, severely limiting 5G applications.
One solution is to use mSAP (semi-additive manufacturing process) technology, which allows manufacturers to create traces with greater precision. Controlling the geometry of the lines can also help mitigate the skin effect and the loss of signal power due to it.
Place Components and Traces
When mitigating effects such as coupling, the most important thing is to judiciously place components and traces relative to each other and to ground.
For example, a multilayer PCB with buried ground and power planes can be a useful solution.
Placing sensitive wires close to the ground plane forces capacitive coupling to ground (as opposed to other wires) and provides a low-inductance return path for high-speed signals.
More Considerations for 5G Design
While this article does not address an exhaustive list of all problems or solutions, we review some high-level issues with signal integrity for 5G frequencies and possible design solutions to address them.
Clearly, 5G will present signal integrity challenges for PCB engineers, as both the frequency-dependent effects of noise and attenuation degrade SNR.
Some factors not considered in this article, such as the choice of dielectric and substrate materials, are equally important for a successful 5G design.
Spectrum analyzer, do you really know how to use it?
Analysis of the development trend of RF front-end
Related Article
The development of the bandwidth and technology of ZD power amplifier modules
ZD Power Amplifier Module Development
Antennas are an indispensable part of radio communication systems. Although the tasks of various radio equipment are different, the functions of antennas are basically the same. One is to radiate and receive electromagnetic waves; the other is to convert energy, converting the high-frequency oscillating current of the transmitter into high-frequency electromagnetic waves for radiation, and vice versa when receiving. The higher the antenna gain, the higher the conversion efficiency.
Some Trivia About Antennas