A time-to-amplitude converter with constant fraction timing discriminators for short time interval measurements

Abstract

The construction and the performance of a time-to-amplitude converter equipped with constant fraction discriminators is described. The TAC consists of digital and analog parts which are constructed on two printed circuit boards, both of which are located in a single width NIM module. The dead time of the TAC for a start pulse which is not followed by a stop pulse within the time range of the device (∼ 100 ns) is only ∼ 100 ns, which enables one to avoid counting rate saturation even with a high random input signal rate. The differential and integral nonlinearities of the TAC are better than ± 1.5% and 0.0.5%, respectively. The resolution for input timing pulses of constant shape is 20 ps (fwhm), and less than 10 ps (fwhm) with a modification in the digital part. The walk error of the constant fraction timing discriminators is presented and various parameters affecting it are discussed. The effect of the various disturbances in linearity caused by the fast ECL logic and their minimization are also discussed. The time-to-amplitude converter has been used in positron lifetime studies and for laser range finding.