Digital is the most efficient form for manipulating many kinds of information. However, real world data is analog in nature and must be converted to digital form for processing. Integrated circuits incorporating analog and digital circuitry where signals are translated between these two modes are called mixed-signal devices. Numerous approaches are used to accomplish Analog to Digital (ADC) and Digital to Analog (DAC) conversion; each entails different trade offs between accuracy, speed, and cost.
Fairchild’s George Erdi designed one of the first ICs dedicated to data conversion applications, the µA722 10-bit Current Source, in 1968. In the 1970s many vendors including Analog Devices, AMD, Harris, Intersil, Motorola, National Semiconductor, Precision Monolithics (PMI), TI, and TRW developed families of devices that integrated specific portions of the data conversion function.
Using diffused resistors PMI's Dan Dooley designed the first fully integrated DAC, the 6-bit DAC01 in 1969. Motorola (MC1408) and PMI (DAC08) followed with 8-bit devices in 1975. The accuracy of data converters, expressed as bit resolution, is limited by the accuracy of a string of resistors. The larger the bit resolution, the higher the accuracy required of the resistors. In 1976 Peter Holloway at Analog Devices laser trimmed thin-film resistors on the wafers to achieve the required precision for the first single-chip 10-bit DAC, the AD561. Using integrated injection logic (I2L) bipolar circuit techniques, Paul Brokaw of Analog Devices designed the first monolithic ADC, the 10-bit AD571, in 1978. As ADCs require more circuit components than DACs, two-chip bipolar and CMOS solutions prevailed for 12-bit and higher functions through the early 1980s.
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