On Thu, 6 Nov 2014, rickman wrote:

On 11/6/2014 10:04 AM, Jerry Stuckle wrote:
On 11/5/2014 1:29 PM, rickman wrote:
On 11/4/2014 9:42 PM, Jerry Stuckle wrote:
On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?


I agree with Jim. We need many more specifics to provide a meaningful
answer. There are a lot of micropower opamps out there now, but the
devil is in the details.

I've only found one detail that is giving me the devil. That is the
bandwidth. The signal is 60 kHz. I can't think of any other issues I
would have with any amp capable of amplifying this signal with a low
power level. What more info do you feel is needed? Can you ask
questions? Better yet, just point me to any amp that will meet my two
stated requirements!


The other posts you made had the info - things like impedance and gain
are important, as is frequency of operation (but we already know that).

A couple of things to consider, however. The higher the impedance, the
more susceptible it will be to ambient noise pickup. You're starting
with a very small signal and may need to add shielding to limit external
noise.

The other problem is you're asking for low impedance output. Low
impedance limits noise pickup, but increases current drain. So how low
of an impedance do you want?

I don't follow on this. How does a low output impedance drive the current
drain?

If you use a large resister in the collector, you'll get high impedance
output. But load it down with a low impedance, and there won't be a proper transfer of the
signal.

So you use a low value collector resistor, current goes up because it
pushes more current through the device, but you get your lower impedance.

I thought generally people wanted more current into preamps, because that
helped them in handling strong signals. So take a look at WWVB
preamps/receivers from the seventies. Certainly they'd be using bipolar
transistors, but one might think they might be reasonably low current. On
the other hand, I can't remember why you need low current for this, and
something like a WWVB receiver usually doesn't need to fuss about being
extra low current. So I suspect those projects never tried to be
ultra-low current.

My Casio Waveceptor watch does, but I have no idea what kind of circuitry
is in there, and even if I opened the watch, I bet it would be difficult
to trace.

On the other hand, I have a Radio Shack "atomic clock" that runs for years
on one AAA or AA battery, so someone figured out how to receive WWVB with
low current and low voltage. But then, the WWVB front end is likely a
module, which is another way to solve the problem, just buy a module, or
strip one out of an existing clock. But again, I can't remember why you
are needing this, so I suspect there's some reason why these options
aren't being used.

Is a preamp really going to be low current compared to the later
circuitry's needs? Once you add the rest, maybe it's not worth pursuing
ultra-low current for the preamp.

Michael