Analog to digital converter

Abstract

Since the computers are the heart of all data processing, we must convert our analog signals to numbers. The process of converting a continuous analog signal to a series of numbers representing the signal at discrete intervals is called analog to digital conversion and is performed with analog to digital converters (ADC). Figure 4.1 shows a signal, where the amplitude is measured at regular intervals δt. In its simplest form, we could simply envisage measuring the amplitude of a slowly changing signal with an analog voltmeter and write down the numbers. Alternatively, if we have an analog plotted signal like in Figure 4.1, we just measure the amplitudes with a ruler and enter the numbers into a computer. In principle, this way of getting digital data is used when older paper seismograms are digitized manually, except that the process is automated by using a digitizing table, which automatically reads the position of a cursor on a table. The process of analog-digital conversion involves two steps: First the signal is sampled at discrete time intervals, then each sample is evaluated in terms of a number (usually integer, but in any case with finite resolution) and output in form of a code.