Computer History MuseumSemiconductor History

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 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.



Contemporary Documents

Rudin, M. et al. "A Family of Linear Integrated Circuits for Data Systems," AFIPS Conference Proceedings, Fall Joint Computer Conference (1967) pp. 95-101.

Holloway, Peter and Norton, Mark. "A High-Yield Second-Generation 10-Bit Monolithic DAC," ISSCC Digest of Technical Papers (February 1976) pp. 106-107.

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.

Oral Histories

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.

More Information

Kress, Dave. "Highest Performance 10-bit IC DAC," Analog Dialogue Vol.11, No. 1 (1977) pp. 10-11.

Brokaw, A. Paul. "Complete Monolithic 10-bit A/D converter," Analog Dialogue Vol.12, No. 1 (1978) pp. 6-8.

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).