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Message from discussion GA144 polyForth
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Howerd  
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 More options Oct 15 2012, 2:03 pm
Newsgroups: comp.lang.forth
From: Howerd <howe...@yahoo.co.uk>
Date: Mon, 15 Oct 2012 11:03:30 -0700 (PDT)
Local: Mon, Oct 15 2012 2:03 pm
Subject: Re: GA144 polyForth
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On Oct 15, 1:54 am, rickman <gnu...@gmail.com> wrote:

> On 10/14/2012 5:00 AM, Howerd wrote:

> > On Saturday, October 13, 2012 11:30:44 PM UTC+2, rickman wrote:

> > Hi Rick,

> >> Then you are looking for resolution, not VCO speed.
> > I am looking for both - detection of very small signals and very small time intervals.

> In the GA144 the time interval will be determined by the CPU speed, I
> think the best you might get is around 10 ns, but I don't recall
> exactly, this might be for a clock timed loop that just takes the data
> and passes it on.  At that speed you will only get 4.3 ENOB (effective
> number of bits) theoretical max.  That's not very sensitive.

> >> Many other ADCs will give you very high resolution as well.
> > Digital resolution, yes, but analog resolution probably not.

> Uh, yeah...  right.  It's time to learn about electronics.  You can
> think that you are going to toss existing theory out the window, but
> this is not the area that needs to be reinvented in order to learn
> about... what was it you were exploring again?

> >> GA144 ADC for high resolution at very slow sample rates.
> > I think you are using "resolution" in two different ways - there is analog resolution ( ability to detect a given change in voltage ), and ADC resolution ( number of bits ).

> Yes, they are related by the gain of your amplifiers... uh, if you had
> amplifiers.  In the GA144 integrating ADC the analog resolution will be
> related to the sample rate...  if you have a sample rate.  The faster
> the sample rate the lower the analog resolution.  The 4.3 bits I mention
> above are over the analog range of about 1.2 volts, this is not well
> defined in the data sheet, so I'm not certain what this range is.  The
> ADC has a non-linear curve with more resolution in the center which is
> what I am assuming will be used.  Trying to get the full analog range of
> 1.8 volts uses the compressed ranges near the limits with very low
> analog resolution.

> The digital resolution is the number of bits.  The analog resolution is
> the analog range divided by the number of bits.  No magic, no new
> science to be invented.  The two are directly connected.  The only way
> to improve the analog resolution is to slow down the measurement to give
> longer integrations or to use an amplifier to get the same voltage range
> at the ADC input with a smaller range on the amplifier input.

> >> The rate of the VCO is not the sample rate of the ADC
> > It is if it is a 1-bit ADC, sort of.

> Ok, you can go ahead and think of this as a 1 bit ADC but that buys you
> the worst possible resolution at the highest sample rate.

> > Its the analog resolution that I am interested in. I presume that the GA144's VCO is just a handful of transistors, so the bottom bit of the VCO count represents some very small change in the charge at the input pin.

> No, the counter bits do NOT correspond to anything at the input.  The
> counter free runs at a rate between about 3.5 GHz and 5.5 GHz.  The raw
> readings just keep incrementing and the absolute values mean nothing.
> You get an ADC reading by SUBTRACTING one reading from the next.  This
> DIFFERENCE is proportional to the integral of the voltage at the input
> over the sample period.

> Actually, the range of the VCO in the linear area is only about 1.3 or
> 1.4 GHz rather than the 2 GHz I used to calculate the ENOB.  The
> frequency range is what determines the difference range and the ADC
> resolution.

> > Only with the GA144 do I get very sensitive analog inputs together with some fast processing, plus a high level (eForth or polyForth) IDE, all on chip.
> > I think this is magic :-)

> Yes, I expect it must seem like magic...  Or you could listen to people
> who don't see it as magic, but rather understand the details and can
> explain how it works as if it were engineering...

> I'm pretty sure you won't see anything in your signals using the GA144
> that you can't see as well if not better using other devices.  For
> example, how well will your readings be time correlated using multiple
> ADCs in the GA144?  I can't get an answer to questions like this.  Or
> even how long the GA144 nodes take to come out of sleep when the input
> clock transitions.  These are *very* important numbers when using the
> ADC for signal acquisition.  Random delays here cause signal
> distortion/noise.

> Rick

Hi Rick,

> You can think that you are going to toss existing theory out the window,...

Not at all - I am looking for observable effects predicted by existing
theory.

> The digital resolution is the number of bits.

Ageed.

> The analog resolution is the analog range divided by the number of bits.

Only in the most simplistic model, ignoring oversampling, compressed
sampling, and maybe some other effects.

What concerns me here is that you seem to have such confidence in your
theoretical models of what goes on in electronic circuits.
Surely any theory only covers the available data, and must be modified
when new data comes long that doesn't fit in.
I want to look for new data...

I think the discussion of the GA144's ADC is missing the point. Let me
try to explain by describing two circuits :

1. An antenna, RF amplifier, anti-aliassing filter, very fast ADC,
fast DSP. Say some electrons wander down the antenna - what does it
take to observe a change in the DSP's output?

2. An antenna connected to the VCO input of an F18. The VCO is
presumably very few FET's arranged to oscillate, clocking a line of
edge triggered flip-flops. Bit 0 of the counter is averaged at, say,
100 Mhz rate.

I predict that #2 would be more sensitive, i.e. it would take fewer
electrons to make a visible change. There is also significantly more
possibility of quantum coupling efects occuring over just a few
transistors than over circuit #1.

Also, if I do not find any interesting new effects using the GA144,
there is not much more to be done, besides going to a faster chip
process, since this looks to me like the absolute minimum number of
components to convert a signal at the antenna to something useable.

I have nothing against circuit #1 - it does exactly what it is
designed to do.

Here are some questions that might be answered experimentally by the
GA144 :

1. does electrical current flowing down a wire have oribital angular
momentum (OAM), and if so could this be useful?
2. if a radio wave containing OAM arrives at two antennas, can the OAM
be detected by two F18 VCO's ?
3. is it posible to demodulate RF signals using an GA144 by applying
simple fast algorithms?

> how well will your readings be time correlated using multiple ADCs in the GA144?

This interests me too. There are two F18's with analog pins next to
each other, so it would be possible to have one waiting for the other
with just the latching time of the ports between them. I would expect
jitter of around 10ns if the F18 cores are also doing something useful
with the data, but this is really just a guess.

> Or even how long the GA144 nodes take to come out of sleep when the input clock transitions.

As I understand this, the GA144 doesn't "go to sleep" - it is clocked
by receiving an instruction on one of its ports.
So no time at all.
The VCO-counting-ADC is free running, so any two would be independent.
You could synchronise reading them, but the read pulse would not be
connected to the VCO, so I would expect a lot of jitter. I think the
GA144's ADC's are good for audio maybe, but not for low jitter, high
speed, high resolution measurements.

In my experience, it is best never to use ADC's, but to convert the
signal you want to measure into a time period. The GA144 is good at
measuring time periods...

I'm sorry if this sounds like the classic Forth question and answer :
Q. how would you do X in Forth? A. don't do X, do Y.

Best regards,
Howerd


 
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