Conversion techniques, analog digital

HOESCHELE, D. F. Analog-to-Digital/Digital-to-Analog Conversion Techniques (Wiley, New York, 1968). 

Hoeschele, D. F., Jr. Analog-To-Digital Digital-To-Analog Conversion Techniques. New York Wiley, 1968. 

Flash A/D The fastest A/D conversion process available to date, also referred to as parallel A/D conversion. The analog signal is simultaneously evaluated by 2 — 1 comparators to produce an -bit digital code in one step. Because of the large number of comparators required, the circuitry for flash AID converters can be very expensive. This technique is commonly used in digital video systems. 

The techniques for analog-to-digital conversion can be classified into one of three fundamental principles they differ in conversion speed and sophistication of physical implementation. 

Word-at-a-time conversion. This technique (flash converters) converts an analog input signal in a very short step (5 to 200 nsec) into digital form by comparing the input signal with all possible values at a time. Therefore a high number of comparators (2" 1, for a resolution of n bits) is needed to produce the result. As the number of comparators increases exponentially, this technique is limited to moderate resolution (typically 8 bit). 

Results of on-line, real-time instrumental analyses are posted directly to the database, with or without processing, as soon as the instrument presents the analytical data. All results are available for review and validation immediately after being posted -a feature critical to effective laboratory management. Data is acquired from laboratory instrumentation of virtually any manufacturer or function. Instruments are interfaced to the computer via analog to digital conversion, RS-232C, current loop, IEEE-4888, binary coded decimal (BCD) or bit parallel techniques. 

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