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Development Needs for High-Frequency Signals
With the advancement of technology, high-frequency signals are increasingly used in various fields such as communications, networks, and automobiles. The PCBs we manufacture play the role of transmitting high-frequency signals. Any PCB transmission exceeding 50 MHz is considered high-speed transmission. Future signal transmission is expected to develop towards higher frequencies and lower power consumption.
What is a High-Frequency Signal?
1. In the process of signal transmission, a signal with a higher oscillation frequency per second is called high-frequency or high-speed, while one with fewer oscillations per second is referred to as low-frequency or low-speed. Higher frequency signals have smaller amplitudes and shorter wavelengths.
2. Signals can be categorized into analog sine waves and digital square waves.
Wireless communication primarily uses analog sine wave signals, such as in base stations, automotive collision avoidance systems, broadcasting, mobile phones, radar, and remote control devices.
Wired communication primarily uses digital square wave signals, such as in mainframe computers, network communication products, and internal signal transmission in mobile phones.
Research and Analysis of Square Wave Signals: Time Domain
& Frequency Domain
1. Time Domain:
Describes the relationship between a mathematical function or physical signal and time. For example, the time domain waveform of a signal shows how the signal changes over time. In time domain analysis, an oscilloscope is often used to convert the signal into its time domain waveform.
2. Frequency Domain:
A coordinate system used to describe the characteristics of a signal in terms of frequency. In electronics, control system engineering, and statistics, frequency domain graphs display the amount of signal within each given frequency band over a range of frequencies. Spectrum analyzers are commonly used to convert actual signals into their frequency domain spectra.
Time Domain: The horizontal axis represents time, and the vertical axis represents the changes in the signal.
Frequency Domain: The horizontal axis represents frequency, and the vertical axis represents the amplitude of the signal at that frequency.
Functions or signals can be converted between time and frequency domains through a pair of mathematical operators. Fourier Transform is used to decompose a square wave into multiple sine waves and display them in a histogram of amplitude and frequency, known as a frequency spectrum. This describes the relationship between frequency and amplitude changes.
Signal Integrity
1. What is Signal Integrity?
In communication, signals can be presented in forms such as images, sounds, and commands. Signal integrity refers to the completeness of the signal received at the receiving end after being transmitted through a conductor (carrier) from the transmitting end. During signal transmission, the quality of the conductor can cause signal loss or distortion.
2. Insertion Loss:
Refers to the signal loss that occurs during the transmission of high-frequency signals from the transmitting end, through the carrier (PCB), to the receiving end. Insertion loss should be minimized.
Excessive signal loss causes signal distortion and transmission leakage (insertion loss).
Factors Contributing to Insertion Loss
1) Factors
A. Dielectric Loss: Material properties (Dk & Df)
B. Conductor Loss: Conductor resistivity
C. Radiation Loss: Radiation from the operating environment, such as electromagnetic fields and mobile phones
D. Leakage Loss: Interference from signal transmission in adjacent lines (minimal loss, can be ignored)
2) Impact of Factors
A. Dielectric Loss (αD) accounts for about 40%.
B. Conductor Loss (αC) accounts for about 57%. Together, they account for 97% of the total loss.
C. Radiation Loss (αR) accounts for about 3%.
D. Leakage Loss (αL) can be ignored.
Therefore, the main factors affecting insertion loss are dielectric loss and conductor loss.
How Dielectric Loss Occurs
1. The dielectric layer is composed of many polar molecules (dipoles). The stronger the polarity, the higher the Dk. When square waves propagate rapidly, they cause the numerous dipole molecules in the dielectric to move, wasting energy.
2. The dipole molecules in the dielectric are influenced by the square wave electric field, causing slight “jitter or oscillation” and “stretching or pulling” due to positive and negative attraction, leading to energy loss.
3. The energy temporarily used for “positive and negative attraction” is called Er or Dk. The energy consumed by jittering and pulling is converted into heat and is lost permanently, known as Df or dielectric loss.
This blog is the introduction to a white paper called Introduction to High Frequency Signal Insertion Loss. Click the button below to request the full white paper. The white paper has additional sections on measure to improve dielectric loss, how conductor loss occurs, measure to improve conductor loss, and insertion loss testing methods.