R68-32 The IADIC: A Hybrid Computing Element

O. Serlin
1968 IEEE transactions on computers  
This paper describes an Integrating Analog-to-Digital Converter whose principle of operation is as follows. The output of an analog integrator is monitored by two comparators for positive and negative overflows with respect to a given level q. The comparators drive a bidirectional counter. After every overflow, a pulse of current is added to the integrator input; the polarity, magnitude, and duration of this pulse are calculated to offset the output of the integrator by the amount q. The
more » ... concept lies somewhere between that of the "hybrid integrator"' and that of the continuous ADC (analog-to-digital converter)2; both ideas have been discussed extensively. What is new, perhaps, is the authors' suggestion that the IADIC, by combining the operations of integration and AD conversion, is the AD counterpart of the MDAC (multiplying digital-to-analog converter) and should be as useful at the AD end of a hybrid system as the M DAC is at the DA end. Three reasons are given to support this proposition: 1) by using a multiplicity of IADICs instead of a conventional ADC, analog sample-hold circuits are not required, 2) the multiplexer is eliminated, and 3) the ADC is not required. These arguments are, at best, of questionable validity. The sample-hold amplifiers ahead of the conventional multiplexer-ADC are needed to assure that all analog values crossing the AD interface refer to the same point in time. This fact greatly simplifies the digital program. With a multiplicity of converters, either conventional or IADICs, sampling is still necessary but must be done digitally with dual-buffered outputs. Multiplexing is primarily a reflection of the digital computer architecture: even with multiple AD converters, the digitized information must be funneled through a limited number of I/O channels (usually just one). Multiplexing with IADICs will then be digital rather than analog in nature, and the cost differential is not large. Of course, it is entirely possible that digital computers that are essentially parallel in structure (e.g., SOLOMON, ILLIAC IV, parallel DDA) may be able to take advantage of a multiplicity of AD converters.
doi:10.1109/tc.1968.227416 fatcat:vdlx3sk7kffzjlmindxzjkhcrm