Waveform measurement using synchronous digital averaging: Design principles of accurate instruments

Averaging is frequently employed for waveform measurements in order to reduce the additive noise, but it becomes inaccurate if the averaged records are not coherent. This incoherence can be reduced if the waveform excitations and its acquisitions are clocked from the same source enabling synchronous digital averaging (SDA). Various aspects of an SDA instrument design are discussed in this paper: Architectures that perform averaging “on the fly”; impact of the master clock instability on the remaining incoherence; design of the mixed signal excitation stage; practical limitations on the number of averages, and how remaining incoherence of separate records is reduced as a result of averaging. Theoretical considerations are complemented by experimental results that show good agreement.