Apparatus and method for solid state storage of episodic signals

Abstract

A method and apparatus for digitally storing episodic signals, such as, electrocardiogram signals is disclosed. In a preferred embodiment, the apparatus includes, for each signal channel, an input amplifier, an analog-to-digital converter, and a double data buffer. The incoming signal on each channel is converted to a multibit digital number a fixed sampling rate. Each multibit digital number is stored in a location in the double data buffer. When a fixed amount of data is stored in the buffer, a processor examines the data to determine the periods during which the signal is undergoing the most rapid rate of change. For these periods, both an indicator of the period, and a first number of data samples per unit time is stored in a bulk solid state memory. Preferably, the data stored is a number relating to the difference between the value of the sample and a number related to the value of the last sample. For other periods, having rates of data change high, but not as high as those of the first period, a smaller number of samples per unit time is stored. These samples are chosen to faithfully reproduce the minima and maxima of the waveform. For all other waveform periods, every Rth sample is stored. The storage media is preferrably dynamic random access memory, the refresh rate of which is determined by the temperature of the circuitry.