An M-sequence reflection measurement system

For the realization of an m-sequence-based reflectometer, a correlator performing a pulse compression is necessary in order to determine the impulse response function (IRF) of a device under test (DUT). Using a hardware correlator, a time delayed version of the m-sequence transmit signal is required. In this contribution, a concept for the generation of two m-sequences with a fast and precisely adjustable time lag between them is presented. Programmable linear feedback shift registers (LFSRs) are used for generating the m-sequences. The desired time lag is realized by using different initial states of the LFSRs. To guarantee that the time lag is set within one clock period, a select pulse generator (SPG) has been designed and implemented into the system. The concept has been validated by means of measurements using a realized demonstrator setup. According results show the fast time lag adjustment. Furthermore, reflection measurements have been performed with different coupler architectures and a coaxial cable with a length of 20m. Results obtained with two different couplers are compared regarding the achievable dynamic range.