A system and circuit for constructing a synchronous signal diagram from asynchronous sampled data provides a low cost and production-integrable technique for providing a signal diagram. The data signal is edge-detected and asynchronously sampled (or alternatively a clock signal is latched). The data signal or a second signal is compared to a settable threshold voltage and sampled. The edge and comparison data are folded according to a swept timebase to find a minimum jitter period. The crossing of the signal diagram edges is determined from a peak of a histogram of the folded edge data. A histogram of ratios of the sample values versus displacement from the position of the crossing location is generated for each threshold voltage. The technique is repeated over a range of settable threshold voltages. Then, the ratio counts are differentiated across the histograms with respect to threshold voltage, from which a signal diagram is populated.