The boxcar operation is defined by a trigger delay, a gate width and the number of trigger events (i.e., samples) that are averaged over in the buffer. The principle of operation can be understood as a two-step process: signal integration over the desired gate width and averaging the integrated signal over a defined amount of periods/trigger events Considering a simple implementation of the core circuitry looks like regular RC
low-pass filter that can be gated by a switch S. Provided the filter
time constant τ = RC is set to sufficiently large values with respect to the gate width, the output voltage is to a good approximation the integral of the input signal with a signal bandwidth of B = 1/(4RC). The output of this filter can then be subjected to another analog circuit for subsequent averaging. After each trigger event this sampling circuit has to be set back before receiving the next pulse. The time it takes for this reset is one of the major speed limitations for analog implementations, where maximum trigger rates of a few 10
kHz are typical even though the gate width itself can be as low as a few ten picoseconds and delay is set to zero. == History ==