Re: micro power square wave oscillator

Jonathan Kirwan wrote:
On Tue, 01 Jul 2008 18:05:58 -0700, D from BC
<myrealaddress@xxxxxxxxx> wrote:

<snip>
I was thinking of loading too..
Mmmmm....
1/100Khz = 10uS

Let's say a risetime and falltime of 1uS.
Say supply = 5V

By
I = C dv/dt
And assuming a 100% efficient circuit..

10uA = C 5V/1uS

C = 2pF !!

With those assumptions and if I did the math right, it suggests you
can't even drive a typical scope probe without going over the supply
current spec.

I suppose you are right. Dispels the PUJT relaxation thingy, I think,
as it dumps the charge each cycle and I think the 2n6028 has 100's of
pF, roughly. Not good.

Trapezoidal rise/fall, then? ;) Or perhaps draw some charge at first
and then just move it back and forth in an LC + xtl tank with high Q,
replacing losses?

How do the watch folks do it? There must be some serious remodeling
of crystals for simulation work there (vastly more complex
understanding of them) in order to design something as efficient as
I've seen from them. Anyone know the details here?


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.

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.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
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