Dynamic operation is provided in sub-array ultrasound imaging. Rather than using fixed or Euclidian distance relative timing, an approximation determines the relative timing. The dynamic timing relationship is approximated with log(x), arctan(x), or 1/x relationships. Adders, registers, counters, comparators, or other simple circuitry is used to calculate the timing relationship. For example, a portion of the circuit featuring a digital comparator and counter produces a reciprocal relationship.
