Boxcar Averager Option

As the first fully digital boxcar averager, the UHF-BOX Boxcar Averager unlocks new perspectives and innovative ways of analyzing non-sinusoidal signals with low duty cycles. It operates as a high-speed digitizer synchronized to an oscillator, so that it enables the capture of every sample without dead times while rejecting all non-periodic signal components. The LabOne^® toolset comprises a Periodic Waveform Analyzer (PWA) that visualizes the averaged signal over one or multiple periods and makes it straightforward to set the averaging windows for the signal and the baseline suppression. The UHF-BOX Boxcar Averager is an option for the UHFLI Lock-in Amplifier and contains 2 independent boxcar units with one PWA each.

Read more about Zurich Instruments' approach to boxcar averaging on the UHF-BOX Product Highlights page. For a discussion of the differences between digital boxcars and "old-school boxcar" models based on analog signal processing, look at the Basics of Boxcar Averaging page.

UHF-BOX upgrade and compatibility

• Field-upgradeable option
• Compatible with all other UHF options

Synchronous detection of signals with low duty cycles

Boxcar Averagers (also known as gated integrators and boxcar integrators) are designed to recover low duty cycle signals. The ratio between the average time over which a signal is present and the interval in which only noise is found can be as low as 10^-9. Even when the scenario is less extreme, it is clear that optimum signal-to-noise ratios cannot be achieved by simple averaging over all samples: it is necessary to reject all noise sources. As many experiments grappling with this challenge feature strictly repetitive signals with a fixed periodicity, Zurich Instruments designed its boxcar as a synchronous detection tool. This means that the boxcar averager does not rely on a point-by-point trigger-based extraction, but instead uses an internal or external reference frequency and so transfers the measurement into the frame of reference of the experiment. As in the case of lock-in detection, the synchronous detection performed by boxcar averaging rejects all signal components that are not linked to the frequency of interest.

Periodic Waveform Analyzer

To conveniently set the gating and the baseline windows, the Periodic Waveform Analyzer (PWA) displays a graphical average of the signal where cursors can be used to isolate the portions of the signal that truly matter. The PWA operates at a sampling rate of 450 MHz, and associates every input sample to one of the 1024 available bins depending on the phase of the reference oscillator. One or multiple periods can be displayed over either phase or time. The FFT of the signal reveals all harmonic components present in the signal – acting as a multi-harmonic analyzer. With this tool, users can immediately infer how much signal power is in found in individual harmonics. Phase and amplitude of up to 8 of each harmonic component can then be measured with the lock-in demodulators.

Baseline suppression

Boxcar averaging is a two-step process. First, the mean value of all samples within the measurement window is determined; subsequently, the mean of these results is calculated over a user-adjustable number of oscillator periods. The baseline suppression feature enables background subtraction based on a measurement taking place in a second window within the same period. This keeps the signal constant even if the signal offset changes. When tuning the reference frequency to half the experiment frequency, it is also possible to subtract subsequent signals that contain on-and-off-type of information, e.g. in pump-probe experiments.

Multi-channel boxcar

The multi-channel boxcar supports dual-timebase experiments. This applies to setups where a pulsed laser undergoes a slower modulation of the physical experiment, for instance. The multi-channel operation associates the measurement result of the fast pulses to the time bins according to the slow frequency. The result is the deconvoluted time series of the dual timebase. Asynchronous optical sampling (ASOPS) is a prominent example for such experiments, where two slightly detuned repetitive laser sources are used in a pump-probe scheme. The boxcar averager extracts the low duty cycle signal, and a PWA displays the boxcar results by associating these results according to the relative phase of the two lasers.