IEEE Solid-State Circuits Magazine - Summer 2015 - 24

Datrac was the first commercial ADC
suitable for digitizing ac waveforms,
such as speech.
During the same period, a few other companies manufactured lower
speed ADCs suitable for digital voltmeter measurement applications,
and there were offerings of optical
converters based on coded discs for
measuring the angular position of
shafts in avionics applications [44].
Converters of the middle to late
1950s used a combination of vacuum
tubes, solid-state diodes, and transistors to implement the conversion
process. A few of the companies in
the data converter business at the
time, in addition to Epsco, were NonLinear Systems, Inc., J.B. Rea, and
Adage. To gain further insight to the
converters of the 1950s, [42], [44]-
[47] are excellent sources.

Commercial Data Converters
of the 1960s Drivers: Industrial,
PCM, and Defense
During the mid-1950s through the
early 1960s, electronic circuit designs
began to migrate from vacuum tubes
to transistors, thereby opening up
many new possibilities in data conversion products. As indicated earlier,
the silicon transistor was responsible
for the increased interest in solidstate designs. There was more and
more interest in data converter products, as indicated in survey articles
published in 1964 [47] and 1967 [48].
Because these devices were basically
unfamiliar to new customers, efforts

19 in × 15 in × 26 in
500 W
150 lb
US$8,500
Figure 8: 1954 Epsco Datrac 11-bit, 50-kSPS
vacuum tube ADC designed by Bernard
M. Gordon of EPSCO. (Reproduced with the
permission of Analogic Corporation, Peabody,
Massachusetts.)

were begun to define specifications
and testing requirements for converter products [49]-[58].
The IBM-360 mainframe computer
and solid-state minicomputers (such
as the Digital Equipment Corporation's Programmed Data Processor
series starting in 1963) added to
the general interest in data analysis
applications. Other driving forces
requiring data converters in the
1960s were industrial process control, measurement, PCM, and military systems.
Efforts continued during the 1960s
at Bell Labs to develop high speed

19 in Rack-Mounted,
150 W, US$10,000
Installation of 12 ADCs
in Experimental Digital
Radar Receiver
Figure 9: The HS-810, an 8-bit, 10-Ms/s ADC released by Computer Labs in 1966.

s u m m E r 2 0 15

IEEE SOLID-STATE CIRCUITS MAGAZINE

converters (e.g., 9 bits, 5 Ms/s) for
PCM applications [59], and the military division of Bell Labs began work
on developing hardware and software
for an anti-ballistic missile system.
In 1958 the U.S. Army began the
development of the Nike-Zeus antiballistic missile system, with Bell
Labs responsible for much of the
hardware design. This program was
replaced by Nike-X in 1963, which was
the first program to propose a digitally controlled phased-array radar
for guiding the short- and long-range
interceptor missiles. The objective
of the system was to intercept and
destroy incoming Soviet nuclear warheads above the atmosphere, thereby
protecting U.S. population centers.
The program continued under the
Johnson administration as Sentinel
and under the Nixon administration
as Safeguard, until it was terminated
after the SALT talks in 1975.
Key to the Nike-X/Sentinel/Safeguard systems was the use of digital
techniques to control the phasedarray radar and perform other command and control tasks. The logic was
resistor-transistor-logic mounted in
hybrid packages. Also important to
the system were the high-speed ADCs
used in the phased-array radar receiver. Early prototypes for the required
8-bit 10-Ms/s ADC were developed by
John M. Eubanks and Robert C. Bedingfield at Bell Labs between 1963 and
1965. In 1966, these two pioneers in
high speed data conversion left Bell
Labs and founded Computer Labs-a
company based in Greensboro, North
Carolina-and introduced a commercial version of this ADC.
The 8-bit, 10-Ms/s converter was
rack-mounted, contained its own linear power supply, dissipated nearly
150 W, and sold for approximately
US$10,000 (see Figure 9). The same
technology was used to produce 9-bit,
5-Ms/s and 10-bit 3-Ms/s versions.
Although the next generation of Computer Labs' designs would take advantage of modular op-amps (Computer
Labs OA-125 and FS-125), ICs such as
the Fairchild μA710/711 comparators,
and 7400 transistor-transistor logic

Table of Contents for the Digital Edition of IEEE Solid-State Circuits Magazine - Summer 2015