Abstract: Methods and apparatus are provided for separating DC and AC components of a composite signal Is=Idc+Iac from a current source, e.g., a photodiode current source. Four current mirrors CM-1 . . . CM-4 are used with common branches and overlap. CM-1 through CM-3 mirror Is and CM-4 mirrors Idc where Iac has been removed by a frequency selective branch. Outputs of the Cm-3 and Cm-4 are combined at a node to provide a signal proportional substantially only to Iac. Complementary devices are used where Cm-1 and Cm-4 are of one type and Cm-2 and Cm-3 are of opposite type. The arrangement allows detection of AC signals (e.g., pulses) that are orders of magnitude smaller than the DC background. An I-to-V converter with a large feedback resistance is used at the output to produce a comparatively large voltage output proportional to Iac.

Abstract: A counter/divider apparatus employing an array of counters arranged in parallel. Each counter repeatedly counts through a sequence of a number of clock pulses. The number is different for each counter and the numbers are relatively prime numbers. The outputs of the counters are applied to a detector that recognizes a preset combination of output signals which is present after a predetermined number of clock pulses have been received. The detector then produces an output pulse which clears all the counters to their initial states, and the cycle is repeated. The apparatus thus divides the input clock pulses by the aforementioned predetermined number.