Integrating ADC

An integrating ADC is a type of analog-to-digital-converter that converts an unknown input voltage into a digital representation through the use of an integrator. In its most basic implementation, the unknown input voltage is applied to the input of the integrator and allowed to ramp for a fixed time period (the run-up period). Then a known reference voltage of opposite polarity is applied to the integrator and is allowed to ramp until the integrator output returns to zero (the run-down period). The input voltage is computed as a function of the reference voltage, the constant run-up time period, and the measured run-down time period. The run-down time measurement is usually made in units of the converter's clock, so longer integration times allow for higher resolutions. Likewise, the speed of the converter can be improved by sacrificing resolution.

Converters of this type (or variations on the concept) are able to achieve high resolutions (8.5 digits, or 28 bits, in the case of the Agilent 3458A digital multimeter), but often do so at the expense of speed. The Agilent 3458A, for example, only achieves its highest resolution at a rate of six samples per second. For this reason, these converters are not found in audio or signal processing applications. Their use is typically limited to digital voltmeters and other instruments requiring highly accurate measurements.

The First Electronic Computer: The ENIAC

In 1946, John Mauchly and John Presper Eckert developed the ENIAC I (Electrical Numerical Integrator and Calculator). The U.S. military sponsored their research; they needed a calculating device for writing artillery-firing tables (the settings used for different weapons under varied conditions for target accuracy). The Ballistics Research Laboratory heard about John Mauchly's research at the University of Pennsylvania's Moore School of Electrical Engineering. Mauchly had previously created several calculating machines, some with small electric motors inside. In 1942 he had begun designing a better calculating machine based on the work of John Atanasoff, which would use vacuum tubes to speed up calculations.