rickman wrote in :

Actually even single ended digital inputs don't have much hysteresis
unless they are designed for that.

Well, as a proportion if they only go high above soem fairly close approach
to V+, then low when close to 0V, then the dead band could be wide, the aim
was to eliminate false states so they ARE usually designed for it. I take
your point on very low volt systems, if the actual difference is small even
though proportionally it may not be.

Anyway, now I know that the supply is so small, your suggestion of discrete
transistors is almost certainly the way to go, unless there is enough similar
demand out there to have cause an off-shelf part to be made.

Normally I'd just look at how others are solving similar problems, so I guess
the question I can ask is: what is the signficant difference in this case
that prevents the nearest off-shelf answer from working?

On 10/29/2014 3:06 PM, Lostgallifreyan wrote:
rickman wrote in :

Actually even single ended digital inputs don't have much hysteresis
unless they are designed for that.

Well, as a proportion if they only go high above soem fairly close approach
to V+, then low when close to 0V, then the dead band could be wide, the aim
was to eliminate false states so they ARE usually designed for it. I take
your point on very low volt systems, if the actual difference is small even
though proportionally it may not be.

Anyway, now I know that the supply is so small, your suggestion of discrete
transistors is almost certainly the way to go, unless there is enough similar
demand out there to have cause an off-shelf part to be made.

Normally I'd just look at how others are solving similar problems, so I guess
the question I can ask is: what is the signficant difference in this case
that prevents the nearest off-shelf answer from working?

What off the shelf answer? I have not seen any all digital receivers
for any frequency. I think it may only be practical for this case and
I"m not sure of that. lol

This signal is very unique in that it has a very low data rate. This
allows integration in the digital domain over a large number of samples.
Theoretically the signal would be detectable with a negative SNR.
There are actually a number of issues I need to solve to get a prototype
working. The big one is being able to get a large enough signal that
even statistically it is noticeable at the receiver input.

--

Rick

rickman wrote in :

What off the shelf answer?

I just meant in terms of interfacing. Never mind, one of my other replies
might be far more useful. While you can integrate digitally, why do so? It
seems to me (if I haven't missed something I shouldn't) that you might get
away with much less gain before analog integration, then you can boost the
resulting slow signals with much less struggle with gand bandwidth products
and slew rates for low power and such. If you can do it this way, the
resulting slow pulses can be boosted with CMOS which at those speeds will be
pretty much nanopower.

On 10/29/2014 4:41 PM, Lostgallifreyan wrote:
rickman wrote in :

What off the shelf answer?

I just meant in terms of interfacing. Never mind, one of my other replies
might be far more useful. While you can integrate digitally, why do so? It
seems to me (if I haven't missed something I shouldn't) that you might get
away with much less gain before analog integration, then you can boost the
resulting slow signals with much less struggle with gand bandwidth products
and slew rates for low power and such. If you can do it this way, the
resulting slow pulses can be boosted with CMOS which at those speeds will be
pretty much nanopower.

Before integration comes demodulation. How would you demodulate and
integrate in the analog domain on a 100 uW power budget? The signal is
PSK. But that is not the real reason. My goal is to show it is
possible to do this entirely in the digital domain.

The devices I have available are not 100% optimized for low power at low
clock rates, but they are pretty good. If I can find devices that have
lower quiescent current the digital design has potential of being lower
power than the analog approach.

--

Rick

rickman wrote in :

Before integration comes demodulation. How would you demodulate and
integrate in the analog domain on a 100 uW power budget? The signal is
PSK. But that is not the real reason. My goal is to show it is
possible to do this entirely in the digital domain.


Low Vf diode in feedback loop of op-amp? I'm curious though, it's an
interesting thought, doing it all in digital equipment, but why? The main
drive behind me 'off-shelf' remark is that I suspect the best answer already
exists in many forms. I'm curious about what makes a need to keep searching.
I'm not denying it, far from it, there's usually more than one good way to
do something, I'm just not sure what the differentiating factor is in this
case.

On 10/30/2014 1:02 PM, Lostgallifreyan wrote:
rickman wrote in :

Before integration comes demodulation. How would you demodulate and
integrate in the analog domain on a 100 uW power budget? The signal is
PSK. But that is not the real reason. My goal is to show it is
possible to do this entirely in the digital domain.


Low Vf diode in feedback loop of op-amp? I'm curious though, it's an
interesting thought, doing it all in digital equipment, but why? The main
drive behind me 'off-shelf' remark is that I suspect the best answer already
exists in many forms. I'm curious about what makes a need to keep searching.
I'm not denying it, far from it, there's usually more than one good way to
do something, I'm just not sure what the differentiating factor is in this
case.

I don't know about "best" but you can buy a time code receiver chip that
spits out a demodulated signal to be decoded by an MCU. At that point
the data rate is pretty low so an MCU can run at very low power levels,
likely dominated by the quiescent current.

When you suggest an op amp, we already covered that ground and they
aren't low power enough. I'm curious how they amplify the signal in the
receiver chip with the whole circuit drawing a very low power level.

--

Rick

On 10/30/2014 01:27 PM, rickman wrote:
On 10/30/2014 1:02 PM, Lostgallifreyan wrote:
rickman wrote in :

Before integration comes demodulation. How would you demodulate and
integrate in the analog domain on a 100 uW power budget? The signal is
PSK. But that is not the real reason. My goal is to show it is
possible to do this entirely in the digital domain.


Low Vf diode in feedback loop of op-amp? I'm curious though, it's an
interesting thought, doing it all in digital equipment, but why? The main
drive behind me 'off-shelf' remark is that I suspect the best answer already
exists in many forms. I'm curious about what makes a need to keep searching.
I'm not denying it, far from it, there's usually more than one good way to
do something, I'm just not sure what the differentiating factor is in this
case.

I don't know about "best" but you can buy a time code receiver chip that
spits out a demodulated signal to be decoded by an MCU. At that point
the data rate is pretty low so an MCU can run at very low power levels,
likely dominated by the quiescent current.

When you suggest an op amp, we already covered that ground and they aren't
low power enough. I'm curious how they amplify the signal in the receiver
chip with the whole circuit drawing a very low power level.

Motorola's app notes on the old 4000 series CMOS included
various analog circuits, including use of a CMOS inverter
as an amplifier. I'm enough of a packrat that I keep those
things.

4000 series may not be useful in your case, but the circuits
or variants of them may apply in newer CMOS implementations.

'Course calling it all digital may be just a game if your
input stage is a digital circuit biased to operate in an
analog mode.

George

rickman wrote in :

The signal is PSK.

I missed that bit. I thought it would be simple AM.. If the integrated
signal (after feedback diode demod) differ enough in amplitude (or AC
content) with frequency, threshold detection might be enough. I'm just
pondering it though, I have no idea if it can be done with less power than
you can give it.

On 10/30/2014 1:23 PM, Lostgallifreyan wrote:
rickman wrote in :

The signal is PSK.

I missed that bit. I thought it would be simple AM.. If the integrated
signal (after feedback diode demod) differ enough in amplitude (or AC
content) with frequency, threshold detection might be enough. I'm just
pondering it though, I have no idea if it can be done with less power than
you can give it.

The signal is also AM, but the PSK is supposed to be detectable at lower
signal levels.

--

Rick

rickman wrote in :

The signal is PSK.

My sight isn't very good. That's Psk, not Fsk... Phase? What did I miss.
I've been hung up on the notion that this is an MSF time signal thing, and I
just looked at the spec for the UK one which is a simple switch on/off of a
carrier, so easy to detect efficiently. Yours is something else entirely, but
what? You may need to lay a lot more cards down before you find an answer you
can use, unless you hunt in the dark. (No reason not to, I usually do, on
most things I do, as the net usually makes some light at greatest need).