Concept and implementation of a low-cost and accurate jitter measurement equipment for magnetic speed sensors

摘要

The purpose of this work is to develop a low-cost and accurate hardware concept of a jitter measurement system for magnetic speed sensors. A typical jitter measurement setup is analysed to achieve this purpose. To define the boundary conditions of such a measurement system, comparison measurements of typical measurement systems are done. These measurements provide information about the minimal storage size and sampling rate to measure jitter accurately. The concept is based on a microcontroller and a field programmable gate array (FPGA). With the new system the time for a characterization process of magnetic speed sensors can be shortened. The FPGA on the finished implemented jitter measurement tool measures timestamps with an effective sampling frequency of 400MHz, due to dual data rate (DDR) sampling. These timestamps are sent to the microcontroller over an interrupt-based protocol. The controller can store up to 14.000 timestamps and communicates with the host over a command-based USB protocol. Compared to existing measurement devices, the worst-case absolute error of the jitter measurement tool is about 2.25% and the amount of measurement time is decreased. The material costs for a complete system amount to approximately 200 euro which is extremely cheaper than the devices buyable on the open market.