Ultra-Wideband Differential Line-to-Balanced Line Transitions for Super-High-Speed Digital Transmission

Abstract

A conventional differential line (DL), commonly used on typical digital circuit boards for transmitting high-speed digital data, has fundamental limitations on the maximum signal bandwidth (~10 GHz), mainly due to signal skew, multiple line coupling, and EM interference. Therefore, to support super-high-speed digital data transmission, especially for beyond 5G communications, a practical high-performance transmission structure for digital signals is required. Balanced lines (BLs) can transmit the differential signals with multiple advantages of ultra-wide bandwidth, common-mode rejection, reduced crosstalk, phase recovery, and skew reduction, which enable super-high-speed transmission. In order to utilize the BLs in the DL-based digital circuit, connecting structures between a DL and BLs are required, but the DL-to-BL transition structures dominate the operating bandwidth and signal properties. Therefore, in this paper, properties, and design methods for two ultra-wideband DL-to-BL transitions, i.e., DL-to-CPS (coplanar stripline) and DL-to-PSL (parallel stripline) transitions, are presented. Both implemented DL-to-CPS and DL-to-PSL transitions provide high-quality performance up to 40 GHz or higher, significantly enhancing the frequency bandwidth for the transmission of digital signals while providing compatibility with the DL-based PCBs. The fabricated DL-to-CPS transition performs well from DC to 40 GHz with an insertion loss of less than 0.86 dB and a return loss of more than 10 dB, and the fabricated DL-to-PSL transition also provides good performance from DC to 40 GHz, with an insertion loss of less than 1.34 dB and a return loss of more than 10 dB. Therefore, the proposed DL-to-BL transitions can be applied to achieve super-high-speed digital data transmission with over 40 GHz bandwidth, which is more than four times the bandwidth of the DL, supporting over 200 Gbps of digital data transmission on PCBs for the next generation of advanced communications.

Compact Ultra-Wideband Wilkinson Power Divider in Parallel Stripline with Modified Isolation Branches

“…where i = 1, 2, 3 (stage number). When a signal is applied at Port 1, the total ABCD matrix can be calculated by sequentially multiplying the corresponding ABCD matrices, as shown in (4). Here, the subscripts (m,i) represent each even-mode (e,i) or odd-mode (o,i) shunt circuit for the stage number i.…”

Ultra-Wideband Vertical Transition in Coplanar Stripline for Ultra-High-Speed Digital Interfaces

“…The BB ′ -CC ′ and FF ′ -GG ′ sections of the proposed CPS-based vertical transition in Figure 4 represent the DL-to-CPS transition. The analytical design formulas for the characteristic line impedance of this transition were described in [17], but the dielectric regions are slightly modified in this paper. To derive the analytical formula for the capacitance of each cross-section of the transition using the conformal mapping method, it is assumed that quasi-TEM or TEM electromagnetic fields are formed at each cross-section of the transition.…”

“…On the other hand, in order to significantly enhance the digital transmission speed, ultra-wideband transmission lines and structures were proposed, enabling the sustenance of signal integrity in high-speed digital data transmission without incurring additional power consumption, thus making it a favorable solution [17]. For ultra-high-speed digital data transmission on typical PCBs, ultra-wideband transitions from a DL to a balanced line (BL), such as a coplanar stripline (CPS) and parallel stripline (PSL), were proposed.…”

“…For ultra-high-speed digital data transmission on typical PCBs, ultra-wideband transitions from a DL to a balanced line (BL), such as a coplanar stripline (CPS) and parallel stripline (PSL), were proposed. These BL-based transmission lines, which support differential signaling, provide effective noise rejection, common-mode signal elimination, and self-phase recovery properties [17]. Here, a CPS is a transmission line with only two signal lines placed on the same plane and is often utilized as a balanced antenna balun [18].…”

“…Sensors 2024, 24, 3233 3 of 15 noise rejection, common-mode signal elimination, and self-phase recovery properties [17].…”