Neil said:
ha ha...ha, boat huh? you mean train don't you? Looks like your going
have to ask him(Robert Pease, National Engineer),he has spoke openly
about his views on spice at seminars accross United States,
Yes, I know all about Bob. He is misguided on this.
I read
some of his articles, I tend to agree. May be you should read the
book I mentioned in my POST, and make your own opinion.
I have made my own opinion. Its based on being both an analogue ic and
board designer for er.. some years, and knowing how its actually done in
practise.
I use to
trust spice too..........
Of courses Spice has its limitations, just as a screwdriver does.
However, this doesn't mean that Spice shouldn't be used as the
fundamental design tool for analogue design.
You are obviously a newbie on this so I'll point out one or two issues.
Lets take analogue ic design. How do you propose to design a 1000
transistor circuit? A 10,000 transistor circuit? What's the fab cost?
Turn around time? You reckon that you can solve the equations by hand?
This is the deal. 10,000s of analogue ic designers, that is *all* of
them use spice as *the* number one de-facto method of designing
circuits. Period. It cant be any other way, today. Its simply not
possible to reliably design such circuits without spice. The designs are
two large and complex and cost too way much to fab. Its typically a 40
hour day, 5 days a week of solid simulation. This *is* the way it is.
Its quite common for people to design large analogue circuits, and have
them work 100% with first pass silicon. Some even get a $50k bonus on
that condition. Those that suggest that Spice is a side line tool, are
on a par to claiming that a Bible is just a superficial add-on to the
x-tian religion. They are quite oblivious to what practising analogue ic
designers use as a matter of course on a daily basis.
For the most part, designs don't work because of simply neglecting to do
a specific simulation, rather then the simulation itself not reflecting
real life. Its hard to think of all operating conditions. However, most
spices have various feature that allow worst case analysis to be
performed and other such multyruns. One might typically do 10,000
variations of a circuit. How do you propose to do such checking in the
real world?
Spice is like anything else, GIGO. Realistically, there is no
alternative. Even a 1 transistor circuit has no exact analytical
solution. The key is getting good models, and understanding the model
failings and compensating for that in the design.
Of course designs have to be physically checked on the bench, but if you
do know what you are doing this checking can be very, very, minimal.
Down to just producing a data sheet for example. I am sure Jim T. could
give us a few examples of right first time
Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.