Re: micro power square wave oscillator

James Arthur wrote:
On Jul 3, 11:26 pm, bill.slo...@xxxxxxxx wrote:
On Jul 4, 2:58 pm, James Arthur <bogusabd...@xxxxxxxxxxx> wrote:



bill.slo...@xxxxxxxx wrote:
On Jul 4, 10:24 am, James Arthur <bogusabd...@xxxxxxxxxxx> wrote:
bill.slo...@xxxxxxxx wrote:
On Jul 4, 3:03 am, Jim Thompson wrote:
http://analog-innovations.com/SED/EmitterCoupledOscillator.pdf
Not exactly a realistic circuit. Where is the OP going to get 500k
resistors? It isn't an E12 value, or even E24.
And a 0,265V voltage swing isn't all that useful. The classic two-
transistor emitter-coupled multivibrator has a free collector output,
usually used to drive a third - complementary - transistor as a
saturating switch to provide a rail-to-rail output.
And why use the 2N3904? The BFR92 has much lower internal capacitance
(and a much higher bandwidth) and could probably run with less than a
microamp in either leg. The BFT92 could serve as the saturating
switch.
Kvetch, kvetch, kvetch. Jim's circuit is cute; his
bias scheme saves a cap and a resistor over mine.
At the expense of any kind of useful output. An oscillator that won't
drive anything isn't all that useful.
I'm sure he used 2n3904s because--used carefully--
they're good enough and super-cheap. Don't you
like making neat things from jellybeans? I do.
Who doesn't? But Jim's effort doesn't really get to neat.
It's not like it really matters--the OP and his
vague wish list are long gone.
It might be fun to push things farther current-wise
using RF transistors but, why?
Lower power dissipation.
Ultimate low-power would dictate a high-Q tank,
probably a crystal and a FET or two.
You could presumably get a decent voltage swing out of Jim's circuit
by adding three more transistors - a long-tailed pair driven from one
of the emitters, and a saturating switch driven from one of the free
collectors. The tail wouldn't be all that long - only a quarter of a
volt - and you might tap the emitter resistor to trade off voltage
swing for extra DC bias.
I get 1.2v swing out of Jim's circuit with a simple
2uA class-A stage.
Biased how? And it might drive ECL and the like, but they aren't low-
power logic.
Biased with maximum cheese(iness): 22pF feeds the base
of a 2n3904, 2meg base-to-collector, 470k collector-to-rail.
I goofed twice though: it puts out just under a volt, and draws
3uA. Total circuit draw is still 9uA.
At 2V. 25uA at the OP's 5V.

I already spec'd a 2v regulated supply--don't make me make it
1.8v and save even more power!

And - now I come to think of it - the BFR92 and BFT92 are jelly bean
parts. Farnell stocks them in buckets. Joerg's 65GHz toy may yet
become another ...

The 2n3904 only shows about 4pF in LTSpice, so there's
really not much to save here with fancy-pants transistors.
I deem it more than good enough for our long-departed OP,
who never really needed any of this anyhow.


4pf at 100kHz and a couple of volts or so matters a whole lot. Unless you'd file a petition to revoke Ampere's, Coulomb's and Kirchhoff's laws or have them declared unconstitutional ;-)

--
Regards, Joerg

http://www.analogconsultants.com/

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