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Hardware driven timing signals

The conventional but somewhat awkward way to align sampling to a reference timing signal, using a sampling rate different from the reference pulse rate, is to use a clock multiplier scheme. A local oscillator generates a stable sequence of digital timing pulses, and counts them. The local oscillator pulses are used to clock the analog-to-digital converter hardware. In the meantime, if pulses count per timing cycle is inconsistent with the reference clock pace, some kind of comparator and a feedback heuristic will attempt to appropriately adjust the oscillator rate. This can work very well, but isn't perfect. Control loop accuracy and stability are sometimes an uneasy tradeoff, so good equipment often comes at a price.

A processing-based alternative

The Time Base Synchronization module supports a synchronization scheme that does not need the extra rate multiplier and control hardware. This scheme uses an abundance of samples — known as oversampling — for all signals, including the timing signal. Taking timing data and "measured signal data" side-by-side, a precise mathematical relationship can be constructed on-the-fly. This mathematical association can then be expanded to determine where samples are needed from each measured signal to be consistent with the rate defined by the time reference. Digital Signal Processing (DSP) techniques are then applied to evaluate the samples.

The illustration below shows the relationship between the high resolution hardware sampling, the sampled data that you want, and the time base signal.  

Time Base Synchronization Module (TBRESAMP)

Time Base Synchronization

When processing must be distributed among two or more measurement stations, maintaining precisely synchronized operation is tricky. The usual idea for synchronized sampling is to drive every station with the same sampling clock. However, distributing high-rate digital signals that are sufficiently clean and undistorted is not easy, even with hosts a few inches apart in the same rack. When stations must be physically separated by larger distances, this kind of solution rarely succeeds.

Things work much better when all of the stations operate autonomously and independently, aligning their sampling rate to a common reference clock, but not driving the sampling process directly. Some very good products can produce timing signals that are accurate and stable, but typically not well-suitable for sampling control. For example, a GPS receiver: it can produce a clean TTL-compatible timing pulse, but the rate is fixed at one pulse per second.

The Time Base and Time Synchronization Module (TBTSM) offers one possible strategy for time alignment with a much higher degree of flexibility.