1968: Dedicated Current Source IC Integrates a Data Conversion Function

The precision manufacturing requirements of combining analog and digital capability on one chip made them one of the last product areas to yield to monolithic solutions.

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 untrimmed diffused resistors PMI's Dan Dooley and process engineer Jerry Bresee built a fully integrated DAC, the 6-bit DAC01 in 1969. Their 1970 aimDAC100 offering 10-bit accuracy over the full military operating temperature range in a two-chip solution was followed by a single chip device, the monoDAC02 in 1972. Also in 1972 John Bowers used aimDAC100 chips to build an A to D convertor in a standard DIP package to replace bulky multichip modules. PMI announced the lower cost 8-bit DAC08 that became an industry standard design copied by Motorola and others in 1975. At Analog Devices, Peter Holloway designed a 10-bit DAC, the AD561 using laser trimmed thin film resistors in 1976 and Paul Brokaw designed a monolithic 10-bit ADC 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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  • Brokaw, A. Paul. "A Monolithic 10-Bit A/D Using I2L and LWT Thin-Film Resistors," IEEE Journal of Solid-State Circuits, Vol. SC-13 (December 1978) pp. 736-745.
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  • Timko, Mike and Holloway, Peter. "Complete 12-bit, 2-Chip IC A/D Converter" Analog Dialogue Vol.12, No. 3 (1978) pp. 3-6
  • Kester, Walt. The Data Conversion Handbook. (Reed/Elsevier, 2005).
  • Paul Brokaw: Analog Devices. The Silicon Genesis Interviews (6.15.2006), Department of Special Collections, Stanford University Libraries, Stanford, California.
  • Ray Stata: Analog Devices. The Silicon Genesis Interviews (6.28.2006), Department of Special Collections, Stanford University Libraries, Stanford, California.