Analog-to-Digital Conversion（模拟数字转换）.pdf

CHEM 411L Instrumental Analysis Laboratory Revision 1.0 Analog-to-Digital Conversion In this laboratory exercise we will construct an Analog-to-Digital Converter (ADC) using the staircase technique. In todays world ADCs can be obtained as Integrated Circuits on a single chip. Instead of simply purchasing a pre-packaged ADC, we will instead construct an ADC from more fundamental components so as to better understand how these circuits operate. This will illustrate the issues associated with interfacing instrumentation with digital computers. The output of most analytical instrumentation is an analog signal. To process this signal using a digital computer requires that we convert this analog output into a digital input for a computer or digital storage device. An ADC operates by periodically querying the output voltage of am instrument, converting the numeric voltage level to its binary equivalent and then presenting this binary equivalent as output. The ADCs output is then connected to an appropriate data port of a computer. Working in tandem, the computer will query its data port and latch the output of the ADC into a buffer from where it can be retrieved and then processed into the computers memory. The computer is then ready for another signal from the ADC. P a g e |2 Sprott explains: … circuits in which the voltages and currents are allowed to have only two rather different values … are called digital circuits. With digital circuits, the exact values of the voltages are of no consequence so long as one can unambiguously determine which of the two states the circuit is in. The two states are variously referred to as on/off, true/false, yes/no, high/low, or one/zero. Digital circuits