Re: micro power square wave oscillator

On Wed, 02 Jul 2008 16:12:15 -0700, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

<snip>
First, low voltage. A fresh silver cell is just 1.55V. Then the clock
never really feeds anything except the input of a divider chain within
the chip. They'll probably do their darndest to keep its capacitance to
a minimum.

It does seem clear that's important.

A square wave oscillator won't be a nice resonant architecture. So
you'll have to muscle capacitive charges around and it will consume more
power. It's like wanting to rapidly move the pendulum of a grandfather's
clock between its end points. This is why the OP might want to think
about whether it really has to be a square wave.

That was helpful. Do you imagine that they may use an LC, though, and
attemp to retain as much energy there as possible? Or, as you seem to
suggest to me, graduate the transfer of charge more trapezoidally and
not use magnetic field storage, at all?

I kind of imagine that the usual crystal model most of us are likely
to use has also been tremendously refined by watchmakers into a very,
very proprietary one -- one that models the physics much better -- and
that they use that in combination with thoughtful design. But I have
to say that everytime I think about trying to do a 32kHz oscillator at
very low power using discrete parts I just learn to appreciate how
much good work has gone into what is now a very cheap watch.

Jon
.

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