Re: micro power square wave oscillator

On Jul 2, 1:10 am, nukeymusic <NuKeyMu...@xxxxxxxxx> wrote:
I'm looking for a schematic for a square wave oscillator which draws
around 10uA, powered by 2 to 5V and oscillates at around 100kHz with a
50% duty cycle. I tried out some schematics around a 4007 but none can
meet all the requirements.

A simple two transistor astable multivibrator should do the job. You'd
need low capacitance transistors - the SD214 is one part that might
just do the job

http://www.datasheetcatalog.org/datasheet/linearsystems/SD214.pdf

The BFR92 5GHz broad-band transistor would walk it, since it is an
appreciably lower capacitance part

http://www.nxp.com/acrobat_download/datasheets/BFR92_CNV_2.pdf

but you'd need to put some 22R of low inductance (surface mount)
resistor in series with each base to stop them oscillating at a GHz or
so on the stray inductances and capacitances around your layout. A
ferrite chip (non-wound) inductor might do the same job - they weren't
widely available back when I was playing with the BFR92 and it's PNP
complement.

Note the base of the BFR92 can't take more than 2V of reverse voltage
- on a 5V supply you have to be careful that your circuit doesn't
destroy the transistor when it turns it off. You should really build
and test the circuit in LTSpice before you risk blowing up real parts
(not that they are all that expensive - a dollar or so each).

--
Bill Sloman, Nijmegen
.

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