Zero dead time acquisition for a digital storage oscilloscope

Abstract

A zero dead time acquisition system for a digital storage oscilloscope (DSO) has an input buffer that stores an initial value from an acquisition memory for each sample interval of an input analog signal. The input analog signal is oversampled and digitized so that there are multiple digitized samples of the analog signal for each sample interval. At the beginning of a sample interval the initial value from the input buffer is transferred to an accumulation register, the output of which is compared with the multiple samples of the analog signal during the sample interval. If any of the multiple samples falls outside the limit determined by the value in the accumulation register, in a save on delta mode a latch is set to generate an error signal that terminates further acquisition cycles. In an envelope mode the comparison result causes the value in the accumulation register to be replaced with the sample value that fell outside the limit to establish a new limit, either maximum or minimum. At the end of the sample interval the value in the accumulation register is transferred to the acquisition memory while a new initial value is transferred to the accumulation register. In this manner both envelope and save on delta modes are implemented directly in the acquisition memory without requiring digital processing time so that the hold-off time after the acquisition cycle may be reduced to zero, producing 'zero dead time.'