Inductively Coupled Board-to-Board Connectors

Abstract

This paper discusses the potential application of inductive coupling elements as backplane connectors. Tradeoffs in the choice of inductive elements are discussed and a simple circuit model for electrically large board-to-board transformers is presented. Measured data for a 10mm outer diameter transformer shows an acceptable eye opening for 400Mbps NRZ data, and over 1GHz of bandwidth in the frequency domain. We also discuss how inductive connectors could find application in future long range FR4 backplanes.

Fine Pitch Inductively Coupled Connectors for Multi-Gbps Pulse Signaling

“…A real world transformer has leakage, parasitics, crossover capacitance (Cc) between the coils and it behaves more like a bandpass filter. This makes impedance matching hard and crossover capacitance (Cc) can be used to compensate for the high frequency roll-off in the forward transfer function and also to tune the return loss as discussed in [2]. Figure 2 shows that broadband SIt >= -1OdB for a transformer can be achieved through a combination of 50 ohm series termination and crossover capacitance.…”

“…In a high end laminate process with 50um trace width/space and 50um vias a 1.2nH inductance can be realized in a 400um diameter structure. Crosstalk constraints would drive the spacing between adjacent inductors to be 1/5th of the outer diameter [2]. This implies that we can build 480um pitch inductive connectors in a laminate technology and these can be single ended or even differential.…”

“…They can have application in level 2 and level 3 interconnections as well [2]. In our previous work we established a basic proof of concept for inductive connectors through RF and digital measurements of 2.5nmmO1mm outer diameter inductively coupled test-structures built on low cost printed circuit boards [2]. We demonstrated potential for 1.45Gbps pulse signaling and also demonstrated feasibility for NRZ signaling with bandlimited data at 3.3 Gbps.…”

“…Inductively coupled interconnects have shown potential for multi-Gbps signaling in chip to chip communication and 3D IC's [6,7]. They can have application in level 2 and level 3 interconnections as well [2]. In our previous work we established a basic proof of concept for inductive connectors through RF and digital measurements of 2.5nmmO1mm outer diameter inductively coupled test-structures built on low cost printed circuit boards [2].…”

A compact inductively coupled connector for mobile devices

“…Finally, a zero-insertion force backplane connector composed of transformers with diameters ranging from 1 to 10 mm on low-cost PCBs has been proposed [5]. It was determined that multi-Gbps signaling was achievable, though the relatively large minimum width and spacing of the PCB process resulted in a transformer which suffered from losses at high-frequency and therefore required coding of the data to achieve the highest data rates.…”