A Minimal-Component 100 MHz Full-Duplex Digital Link Over a Single Coaxial Cable for Laboratory Instrumentation

TL;DR

This paper introduces a simple, low-component, full-duplex digital communication system over a single coaxial cable, suitable for laboratory use, with experimental validation showing reliable high-speed data transmission.

Contribution

It presents a minimal-component, passive hybrid-based full-duplex digital link that requires no active calibration or transformers, enabling efficient bidirectional communication over coaxial cables.

Findings

Peak-to-peak timing error below 1 ns for 6 m cables

Reliable 250 MBaud full-duplex data transmission demonstrated

Good agreement between simulations and experimental jitter measurements

Abstract

We present a minimal-component bidirectional digital interconnect that enables simultaneous transmission and reception of baseband logic signals over a single coaxial cable. The circuit consists of a passive resistive hybrid providing matched line termination and directional separation, a single CMOS logic gate as driver, and a commercial LVDS receiver used as a differential comparator. No active echo cancellation, calibration, or transformer coupling is required. An analytical treatment of the hybrid network is used to determine the system parameter that maximizes the received signal amplitude. SPICE simulations predict deterministic timing errors caused by incomplete separation of transmitted and received signals. Experimental measurements confirm the predicted deterministic jitter and show good agreement with the simulation results. For typical laboratory coaxial cables up to 6 m, the measured peak-to-peak edge timing error remains below 1 ns. A bidirectional transmission experiment with randomized data at 250 MBaud demonstrates a clearly open eye diagram and confirms reliable full-duplex operation. Due to its simplicity and compatibility with existing coaxial infrastructure, the proposed approach may be useful in laboratory and detector environments where cable routing or feedthrough density is constrained.