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This file type includes high resolution graphics and schematics when applicable. | This provides a measure of the period of U7's output, which is inversely proportional to its frequency. Because that frequency was proportional to the input's period, the value latched by U9 and U10 is directly proportional to the input frequency, but at much higher resolution, and can be measured much more quickly. U11 and U12 generate all of the needed timing signals. Different frequencies can be chosen, depending on the range to be measured.
An example helps illustrate the process. For f(in) = 4 Hz and f1 = 4000 Hz, U1 will count to 1000 before being latched by U2 and U3. This will cause rate multipliers U4 to U6 to generate 1000 × f2/4096, or 1 MHz for f2 = 4.096 MHz. U7 divides this down to 244 Hz, and U8 measures the period as f3/244 Hz, or 524 for f3 = 128 kHz.
Therefore, we have multiplied the input frequency by a factor of 131 (524 Hz/4 Hz), so the circuit can resolve to 0.0076 Hz in one second. This would otherwise take two minutes using the original 4-Hz input.
Karen Hunsberger, an independent consultant, holds a B.Sc (Hon) from the University of Waterloo and a B.Ed. from the University of Western Ontario. She enjoys working on alternative energy and farm/garden designs.