Thermal noise from long sense lines

A general treatment of the thermal noise produced by long, somewhat lossy sense lines of the type used in magnetic-film memories is presented. A graphical approach is described which can be used to determine the noise with arbitrary line termination. The comparison is made in a particular case for shorted versus matched resistive terminations, and it is found that the average noise is about the same in both cases although the spectra are different, especially at the lower frequencies. In calculations on a representative memory design it is shown how the 10 μV rms noise voltage caused by the sense line can dictate that the signal at the memory bit site must be of the order of 1 mV.