Non-blocking programmable delay line with minimal dead time and tens of picoseconds jitter

TL;DR

This paper introduces a non-blocking, high-resolution digital delay line using FPGA logic primitives, achieving adjustable delays from 23 ns to 1635 ns with 10 ps resolution, minimal dead time, and manageable jitter for photonic network applications.

Contribution

The authors present a novel asynchronous circuit design for a programmable delay line with optimized resolution, delay range, and dead time, addressing key issues like thermal stability and pulse spreading.

Findings

Delay range from 23 ns to 1635 ns with 10 ps resolution

Timing jitter ranges from 7 ps to 165 ps, increasing linearly with delay

Dead time achieved between 4 ns and 22.5 ns

Abstract

We report a non-blocking high-resolution digital delay line based on an asynchronous circuit design. Field programmable gate array logic primitives were used as a source of delay and optimally arranged using combinatorial optimization. This approach allows for an efficient trade-off of the resolution and a delay range together with minimized dead time operation. We demonstrate the method by implementing the delay line adjustable from 23 ns up to 1635 ns with a resolution of 10 ps. We present a detailed experimental characterization of the device focusing on thermal instability, timing jitter, and pulse spreading, which represent three main issues of the asynchronous design. We found a linear dependence of the delay on the temperature with the slope of 0.2 ps/K per a logic primitive. We measured the timing jitter of the delay to be in the range of 7 ps - 165 ps, linearly increasing over the dynamic range of the delay. We reduced the effect of pulse spreading by introducing pulse shrinking circuits, and reached the overall dead time of 4 ns - 22.5 ns within the dynamic range of the delay. The presented non-blocking delay line finds usage in applications where the dead time minimization is crucial, and tens of picoseconds excess jitter is acceptable, such as in many advanced photonic networks.