Logic signal extraction

Abstract

Methods for producing logic signal displays for an instrument known as a 'logic oscilloscope' are disclosed. A digital input signal is first sampled as an analog signal to produce multi-bit digital samples that are representative of the amplitude of the input signal over time. The multi-bit digital samples are then processed using interpolative techniques to ascertain when the input signal crossed a hypothetical logic level threshold or pair of thresholds and when the signal was in one logic state or the other. The resulting transition times and logic states are then used as the basis for generating a variety of digital displays, including logic timing diagrams, state table displays, and cursor readouts similar to those available in a logic analyzer. Setup and hold time violations and measurements may also be obtained using this information. In a pseudo-synchronous mode of operation, one logic signal is treated as a virtual clock signal, so that the states of other (data) signals are determined at times controlled by the active transitions of this clock signal. A cursor provides a digital readout of the logic value of one or more signals, whether they are displayed in analog form or logic timing diagram form or not shown on the screen at all.