NOISE IN (DOUBLE) RELAXATION OSCILLATION SQUIDS

We have modelled the effect of two intrinsic noise sources on the flux noise spectral density of (Double) Relaxation Oscillation SQUIDs ((D) ROSs) based on hysteretic Josephson tunnel junctions. An important noi se source is the spread in the critical current of the SQUID due to th ermal fluctuations. Critical current noise mainly determines the noise on the average output voltage of DROSs with high flux to voltage tran sfer. A second noise source is the spread in the relaxation frequency due to the random interaction between the Josephson oscillations and t he relaxation oscillations during switching to the zero-voltage state. This effect can dominate the voltage noise of a ROS.