|Time interval measurement based on excitation of a surface acoustic wave filter|
|Petr Pánek, Ph.D.|
Time measurement plays a key role in modern technologies, since the
measurement of many quantities is transferred to the measurement of
time interval. Current methods of time measurement allow to achieve a
very high resolution of the interpolation between the time marks of
the reference time scale. The measured event triggers a suitable
deterministic process which is then observed in the instants of time
marks. Based on these observations, one can determine the instant of
the event. The key problem in the design of a time interpolator is
creating a mechanism that would generate a perfectly predictable
We have developed and theoretically analyzed a new method for time-interval measurement [1,2,3] that makes use of a time interpolator based on a surface acoustic wave (SAW) transversal filter. This filter when excited by a short pulse generates a signal of finite length, whose spectrum is concentrated in a limited band. It follows from the sampling theorem that if this signal is sampled with an appropriate frequency, it can be exactly reconstructed from a finite number of samples. By comparing two reconstructed filter responses, we can determine the time interval between the two exciting pulses. The developed method provides excellent accuracy in relation to the period of reference time marks. In first experiments we have achieved an accuracy of 25 ps rms at a clock frequency of 16 MHz. Our analysis has shown that by employing the state-of-the-art components currently used in mobile communications, we can expect an accuracy on the order of 0.1 ps.
Fig. 1. A SAW-filter-excitation time-interval meter developed at ÚRE has been used for the first time in the GPS GTR50 timing receivers also developed at ÚRE (the two light-colored instruments on the upper left-hand side).