Novel Calibration Method for Switched Capacitor Arrays Enables Time Measurements with Sub-Picosecond Resolution

TL;DR

This paper presents a new calibration method for switched capacitor arrays that significantly improves time measurement resolution, achieving sub-picosecond accuracy by accurately determining sampling speeds and applying advanced analysis techniques.

Contribution

A novel calibration approach that accurately determines true sampling speeds in SCAs, enabling sub-picosecond time resolution in measurements.

Findings

Achieved less than 3 ps time resolution with linear interpolation.

Pushed resolution below 1 ps using advanced analysis techniques.

Calibration remains stable over time but sensitive to temperature variations.

Abstract

Switched capacitor arrays (SCA) ASICs are becoming more and more popular for the readout of detector signals, since the sampling frequency of typically several gigasamples per second allows excellent pile-up rejection and time measurements. They suffer however from the fact that their sampling bins are not equidistant in time, given by limitations of the chip process. In the past, this limited time measurements of optimal signals to standard deviations ({\sigma}) of about 4-25 ps in accuracy for the split pulse test, depending on the specific chip. This paper introduces a novel time calibration, which determines the true sampling speed of an SCA. Additionally, for two independently running SCA chips, the achieved time resolution improved to less than 3 ps ({\sigma}) independently from the delay for the split pulse test, when simply applying a linear interpolation. When using a more advanced analyzing technique for the split pulse test with a single SCA, this limit is pushed below 1 ps ({\sigma}) for delays up to 8 ns. Various test measurements with different boards based on the DRS4 ASIC indicate that the new calibration is stable over time but not over larger temperature variations.