A method that includes deriving a first power spectral density function of a signal input to a ripple cancellation filter; deriving a second power spectral density function of a signal concurrently output from the ripple cancellation filter; frequency shaping the first power spectral density according to a spectral rejection image of the ripple cancellation filter to obtain a test power spectral density; and indicating a degraded performance of the ripple cancellation filter in the event that the test and second power spectral density functions fail to match within pre-determined criteria.