Eric Vittoz - IEEE

TECHNICAL LITERATURE
With the Swatch assembly concept, engineers
observed that the ultra-sound welding process
detuned the crystal, but then, the watch was already
sealed and its parts couldn't be directly accessed anymore.
The only way left to access the electronic circuitry
of the watch after the assembly process was
through the battery contact plates. EM's engineers
decided to replace the capacitor matching or trimming
principles with a digital tuning of the frequency
divider chain by means of non-volatile memory. For
this purpose, EM Microelectronic developed its own
EEPROM cells accessible over a dedicated 2-wire programming
protocol and they delivered the first nonvolatile
memory based CMOS watch ICs in 1984 to
ETA. IC design engineers, supported by the process
team designed the EEPROM cells which could be realized
with only one additional mask in EM Microelectronic’s
HCMOS process. The availability of this very
economic memory technology gave the company a
significant advantage in a number of non-watch
applications. It was essential already in early RFID
products and especially also in a number of sensor
interface circuits, which always needed trimming or
calibration functions. Compared to other external
processes, EM Microelectronic has since been able to
keep the number of additional masks for memory
(EEPROM or Flash) in its own semiconductor processes
at the lowest levels.
F. Resilience
Finally, robustness is also an issue in electronic
watches. The developed assembly and packaging
techniques have to withstand a very tough acceleration
test: the homologation process of an electronic
watch model includes a 5000G shock test to which,
the watch has to resist without damage. An integrated
circuit may well resist mechanically such a test, but
the designers didn’t imagine that the shock would
induce a voltage peak into the piezo-electric buzzer
used in some models. The first circuits were
destroyed and the subsequent versions would include
the needed over-voltage protection.
III. From Microprocessor Prototypes to
Microcontroller Products
A. Watch Microcontroller & Interface Functions
The electronic watch seems to be the first portable,
battery operated electronic mass market product in
history. On June 1, 2006, Swatch celebrated the 333
millionth Swatch, a time piece which has been produced
in several thousand models, with different
functions. Through its novel approach of watch production
and marketing, Swatch signaled that functionality
and time-telling were no longer the primary
selling points in a watch. Swatch was not so much
marketing time-telling as it was fun and fashion.
Functional diversity however remains a must to
meet diversity in customers' preferences, a point
which is not easy to conciliate with cost optimization
requirements of high volume industrial watch production.
Watch components (i.e., also semiconductor
components) should therefore be as generic
(reusable) as possible, while remaining as cost-effective
as possible: there is always a compromise or balance
to be found. Reusability across different models
limits development costs and increases flexibility in
an environment characterized by a high innovation
pace in functionality and design. Cost effectiveness in
semiconductor is essentially limiting chip size and
using cost-effective production process. The quest for
the right optimum especially affects watch microcontrollers
used in more complex or functionally rich
models. In theory, it would be ideal to have one
generic microcontroller chip applicable to every
watch model; in reality however watchmakers are
working with microcontroller families built around a
few dedicated microprocessor cores.
A microcontroller is generally considered as a digital
device. A watch microcontroller however is a
mixed-mode device with a digital microprocessor
core, memories and a set of mainly analog interfaces.
The most common interfaces are motor drivers with
adaptive control; there are up to 6 motor drivers on
microcontrollers for purely analog chronograph
watches. Other interfaces include LCD drivers for digital
displays, LED drivers for backlight, sensor interfaces
(touch, shock, acceleration, temperature, etc),
vibrating alarm and buzzer drivers, I 2 C or SPI interfaces,
button and crown rotation detection and more.
B. Technology Transfer and Diffusion
Almost all watch microcontrollers developed by EM
Microelectronic for Swatch Group products are based
on microprocessor cores designed by the Swiss Center
for Electronics and Microtechnology (CSEM).
CSEM was founded in 1984 out of the CEH and other
research labs and represents the continuation of the
original research initiatives of the Swiss watch-making
industry. As will be shown further down in this article,
the microprocessor example epitomizes the cultural
proximity and actual technology transfer process
between research institutes of the Neuchâtel area
(e.g., CSEM, Institute of Microtechnology of the University
of Neuchâtel) and the Swiss watch-making
industry. But it also underlines the key role of an
industrial semiconductor manufacturer in transforming
research and lab results into products ready for
mass-production. The microprocessor core has to be
optimized, design libraries need to be developed,
memory technologies have to be added, digital and
analog interfaces need to be defined. Finally, a microcontroller
remains useless without software development
tools (high level programming language, com-
34 IEEE SSCS NEWS Summer 2008