Freelance Years
Getting a new job after National wasn't easy - nobody wanted design managers
- and it took me a while to realise that's the impression my CV gave!
So, with time running out my only real choice was to go freelance, or
contracting.
Contract engineers in the UK
electronics industry are a bit of an oddity, not understood much by the
employed guys, and vice versa. My guess is that most of them, like me
after a while, distrusted employers and would rather be their own boss.
Having done both I think the advantages are illusory.
I got a month's work at Matrics,
a small design company in in Tetbury (antique city) in southern
Gloucestershire, doing layout at first. Not too challenging but very
enjoyable and it did keep the wolf from the
door.
After a while they let me have a go at design - my first pure CMOS
chip, which was to be the analogue part of a battery charger
controller. This used an unusual process (single poly EEPROM) from AWA
in Australia, which had
the advantage of tunnel oxide capacitors at quite high capacitance per
unit
area. I did a switched capacitor ADC which worked quite well; the only
problem
on the chip was the bandgap, which didn't always start up - major
lesson
here! CMOS bandgaps always need a start-up circuit (not many
books
tell you that - but it's worth reading stuff by Bob Pease on the
subject).
The project came to nothing - I think our customer sold snake oil.
Matrics was developing a reputation for being good at designing RFID
(Radio Frequency Identification) chips, often known as Tags. A key
customer for these
was Atmel, a fab based in Colorado with, at that time, no analogue
designers. I worked on a number of designs with all kinds of
challenges - especially things like low power, multiple supplies and
automatic switching between them
(that's really unpleasant stuff!)
Common reader to tag communications use 100% amplitude modulation,
which is easy for the tag to detect - but of course the net power
received by the tag is reduced, so you need a sizeable capacitor to
hold up the tag supply. Another scheme was cooked up which uses
10% modulation - now the
power at the tag is much better but the demodulator gets more
difficult. Essentially
you need a comparator with adaptive thresholds, which you can derive
from
leaky peak detectors. I developed a rather neat switched capacitor
design which was worthy
of a patent IMHO but didn't get beyond the thought stage - no money for
that! Anyway it has been used in a number of high volume designs.
We did a lot of mixed analogue-digital designs over the years:
interpolators
for precision metrology, water filters (a really low power RC
oscillator),
an Ethernet PHY, and various clever pad designs. Two memorable chips
were
a bipolar interface for automotive motor control - a very large
geometry
single layer metal design, and an even larger CMOS telephony chip
containing
many switched capacitor circuits for things like MF tone decoding. Both
worked
pretty well.
I spent two spells at Ericsson's design centre in Swindon (now sadly
defunct).
The buzz when I first went was Bluetooth; I was to join a new team
developing
the 2nd generation RF chip, the first having been done in Sweden with
Sven
Mattison, the "father" of Bluetooth, at the helm. I was lucky enough to
get
two patents on this project, one for a new take on a bipolar bandgap,
and
the other for what I considered to be a much neater idea, a trimmable
oscillator (US patents 6,310,510 and
6,326,859).
Later at Ericsson I got to do some higher frequency stuff with an
LNA and gmC filter for a DECT (digital cordless) phone chip. In my last
session
there I did a very low voltage (sub 1V) bandgap and a dB-linear VCA for
wide-band CDMA.
More to come, in time ...