Re: RF circuit design.

Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Hello Rob,
>
>
>> I am trying to learn a bit of RF circuit design , mostly for interest
>> sake. I would like to model
>> some small signal amplifier circuits that I will be "designing" as it
>> were. ...
>
>
> Just my two cents: Place the emphasis on designing and building.
> Simulations are nice but their value is often inversely proportional to
> the frequency. At a GHz or so parasitic component values can render a
> SPICE simulation useless. Except when designing chips, but that's a
> whole other topic.
>
I've never subscribed to this philosophy. If you are designing for
1GHz, then you need a HUGE investment in signal generators, spectrum
analysers and network analysers. Whatever the potential pitfalls of
inaccurate spice models and insufficient modelling of the parasitics,
there are just as many pitfalls with the hands-on approach; you end up
measuring the noise-floor of your analyser, unexpected harmonics are
just down to the the IP2 of your analyser's front-end, you screwed up
the two-port cal of your VNA, etc.

Conversly, one of the wonders of simulating is that you can very easily
determine the effect (or otherwise) of lead-inductance, parasitic
capacitance, etc. on your design's performance. You've only got to
look at the literature to realise that, if you're careful, simulation
can agree very well with measurement, and the advantage of simulating
first is that it gives you some expectation of the performance of your
real circuit that you otherwise wouldn't have.

--
Rick

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