IEEE Solid-State Circuits Magazine - Summer 2015 - 25

(TTL), the first ADCs offered used all
discrete devices.
The early high-speed ADCs produced by Computer Labs were
primarily used in research and
development projects associated
with radar receiver development by
companies such as Raytheon, General Electric, and MIT Lincoln Labs.
In the mid-1960s, development of
lower speed instruments, PC-boards,
and modular ADCs was pioneered by
such companies as Analogic (founded
by Bernard M. Gordon) and Pastoriza
Electronics (founded by James Pastoriza). Other companies in the data
converter business were Adage, Burr
Brown, General Instrument Corporation, Radiation, Inc., Redcor Corporation, Beckman Instruments, Reeves
Instruments, Texas Instruments, Raytheon Computer, Preston Scientific,
and Zeltex, Inc. Many of the data converters of the 1960s took the form of
digital voltmeters that used integrating architectures, although Adage
introduced an 8-bit, 1-Ms/s sampling
ADC, the Voldicon VF7, in the early
1960s [47].
In addition to the widespread
proliferation of discrete transistor
circuits in the 1960s, various IC building blocks became available, which
led to size and power reductions in
data converters. In 1964 and 1965,
Fairchild introduced two famous Bob
Widlar IC designs: the μA709 op-amp
and the μA710/μA711 comparators.
These were quickly followed by a
succession of linear ICs from Fairchild and other manufacturers. The
7400-series of TTL and high-speed
emitter-coupled-logic (ECL) also
emerged during this period as well
as the 4000-series CMOS logic from
RCA in 1968. In addition to these
devices, Schottky diodes, Zener
reference diodes, field-effect transistors (FETs) suitable for switches,
and matched dual junction-gate FETs
also made up some of the building
blocks required in data converter
designs of the period.
In 1965 Ray Stata and Matt Lorber
founded Analog Devices, Inc. (ADI)
in Cambridge, Massachusetts. The

2.3 W
US$800

74 and
74H Logic
Soon to Be Replaced
by 2502, 2503, 2504
SAR Logic ICs from
AMD and National

"MINIDAC"

µA710
Comparator

Figure 10: The ADC-12U, a 12-bit, 10-n s successive-approximation ADC from the Pastoriza
Division of Analog Devices, 1969.

initial product offerings were high
performance modular op-amps, but
in 1969 ADI acquired Pastoriza Electronics, a leader in data converter
products, thereby making a solid
commitment to both data acquisition and linear products.
Pastoriza had a line of data acquisition products; Figure 10 shows a
photograph of a 1969 12-bit, 10-μs
general purpose successive-approximation ADC, the ADC-12U, that
sold for approximately US$800. The
architecture was successive approximation, and the ADC-12U utilized a
μA710 comparator, a modular 12-bit
"MiniDAC," and 14 7400-series logic
packages to perform the successiveapproximation conversion algorithm.
The MiniDAC module was actually constructed from quad-switch

ICs (AD550) and a thin film network
(AD850) as shown in Figure 11.
Figure 12 shows details of the famous
quad switch patented by James Pastoriza [60].
Notice that in the ADC-12U, the
implementation of the successive
approximation algorithm required
14 logic packages. In 1958 Bernard
Gordon had filed a patent on the
logic to perform the successive
approximation algorithm [43], and
in the early 1970s, Advanced Micro
Devices and National Semiconductor
introduced commercial successiveapproximation register logic ICs:
the 2502 (8-bit, serial, not expandable), 2503 (8-bit, expandable), and
2504 (12-bit, serial, expandable).
These were designed specifically
to perform the register and control

Logic Inputs
R
i
AD550 "µDAC"
Quad Switch,
Quad Current
Source

AD550 "µDAC"
Quad Switch,
Quad Current
Source

Vout

AD850
Current Setting
Precision Thin-Film Resistor Network

Reference
Circuit

Figure 11: A 1969-vintage 12-bit MiniDAC using quad current switches, a thin film resistor
network, a voltage reference, and an op-amp.

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