A New Class of Instruments
The Periodic Waveform Analyzer (PWA) is a type of synchronous detector used for the analysis of periodic signals. Synchronous detection comes in different flavors, but is generally defined as a method to optimize the signal-to-noise ratio (SNR) when extracting signals from a noisy background. Distinct synchronous detection schemes all make use of the fact that the signal of interest is periodic and the associated frequency is a known reference. Lock-in detection and boxcar averaging are two examples of synchronous detection. Each of these schemes is tailored to a specific signal type: a sinusoidal signal for lock-in detection, a low duty-cycle signal for boxcar averaging.
The PWA enters this scenario by taking a continuous stream of samples and linking them synchronously to the phase of the reference oscillator. Additionally, the samples are averaged with previous samples displaying the same phase. Performing this operation over many periods of the reference frequency leads to a dense set of phase and sample pairs (where the phase is a value between 0 and 2π). This can be viewed as a digital signal averager for periodic signals. Plotting the averaged values with the phase on the X axis provides the phase-domain representation of the considered signal.
The PWA also overcomes the limit imposed by the physical sampling rate of the ADC by several orders of magnitude, similarly to what is achieved by a sampling oscilloscope.