Boxcar 平均器选件

The UHF-BOX option adds 2 independent 600 MHz boxcar averager units to the UHFLI Lock-in Amplifier, increasing the measurement speed and signal-to-noise ratio (SNR) for applications that use non-sinusoidal waveforms. Unlike the case of a digitizer or an oscilloscope, the measurement results from a boxcar averager are immediately available in the digital domain and as analog signals with user-defined offset and scaling factors.

A boxcar measurement is easily set up thanks to the LabOne^® user interface: the periodic waveform analyzer (PWA) displays a single period of the waveform, averaged to suppress noise and to highlight the features of interest. The boxcar window can be set graphically by placing the PWA cursors around the relevant part of the waveform; a second averaging window can be set to reduce baseline fluctuations and enable differential measurements. To achieve the best trade-off between measurement speed and SNR, the result can be averaged over consecutive periods between 1 and 1 million times.

Lock-in vs boxcar

Whereas lock-in amplifiers are ideal for analyzing sinusoidal signals and extracting specific components of a frequency spectrum, boxcar averagers are the tool of choice for low-duty-cycle signals (see figure). A typical input signal from a pulsed experiment has a pulse width T_p, repetition period of the pulses T_rep, and duty cycle d. In boxcar averaging, the input signal is multiplied with a boxcar function, also know as rectangular pulse train, with pulse width T_Box. In this way, noise contributions outside of the boxcar window are rejected (see panel c). Inside the boxcar gate, signal integration results in a single value per period later averaged over N periods.

Data extraction from low-duty-cycle signals requires information from the base frequency and many higher harmonics simultaneously. To capture this additional information, boxcar averagers need a signal input bandwidth that is many times larger than the base frequency, so that setting up a boxcar measurement requires careful control of more parameters compared to a lock-in measurement. The payoff usually comes in the form of shorter measurement times and higher SNR, which can make a big difference in areas such as imaging. Therefore, lock-in measurements and boxcar measurements are complementary tools for analyzing periodic signals.