OT: milestone, the x-Chapters

[Winfield Hill]

Jan Panteltje wrote...

As to 'starlight to sunlight',
have you ever used the Sony Super HAD cameras?
I have 3 for those as security camera, super picture with
only starlight and same in bright sunlight,
analog out NTSC/ PAL. 35 $ I think I payed for each ebay, 0.01 Lux...
Tested one once hanging out of the window looking straight
up in a cloudy sky, sees stars, satellites, planes...
has color. maybe something to monitor your Bs?

We badly need to add cameras to our bee hive sensors.
Since don't like flying in low light, ordinary cameras
can work for outside. Am installing the inside light
sensor today, we'll see how dark that gets.


--
Thanks,
- Win

 

[John Larkin]

On 24 Jun 2019 17:42:56 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Tom Gardner wrote...


Old school way of measuring voltage is with
a potential divider and a null meter.

So, the micro causes a current to be generated,
which is balanced against the photocurrent?

Accurate control of current over a wide range
achieved by PWM and filtering, as in modern
voltage calibrators.

Your "null meter" is going to hae 10nV DC offsets?

Your circuit is probably way better than is justified by the
photodiode. The response of a pd varies wildly with wavelength,
temperature, angle of illumination, and light distribution over the
surface. Big ones can be leaky too.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On 24 Jun 2019 23:19:47 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

John Larkin wrote...

The progressive-railing thing would be as good
as the parts you care to buy. 0.1% should be
possible.

OK, precision railing to say 1%, OK. But at
the highest gains, the fixed-value input-stage
feedback resistor, and the input offset ...
Explain that for us.

Is this an electronics discussion or a book promotion?


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Tom Del Rosso]

George Herold wrote:

Can you chain together TIA stages? Lowest gain first.


+---R2---+
| |\ |
+---R1---+-|-\ |
| |\ | >---+
I_in---+-|-\ .-|+/
| >---+ |/
Gnd-|+/
|/

I'm not sure that works.. and I have to do something when the 2nd TIA
rails... short it's inputs or something.

Here's a stupider question, since I'm no engineer. Wouldn't the second
stage be a regular opamp? I mean the TIA output is voltage, so....

 

[Tom Gardner]

On 25/06/19 15:05, John Larkin wrote:

On 24 Jun 2019 23:19:47 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

John Larkin wrote...

The progressive-railing thing would be as good
as the parts you care to buy. 0.1% should be
possible.

OK, precision railing to say 1%, OK. But at
the highest gains, the fixed-value input-stage
feedback resistor, and the input offset ...
Explain that for us.

Is this an electronics discussion or a book promotion?

A1: yes it is.
A2: does it matter?
A3: it is fun, who cares.

 

[George Herold]

On Tuesday, June 25, 2019 at 10:00:41 AM UTC-4, Tom Del Rosso wrote:

George Herold wrote:
Can you chain together TIA stages? Lowest gain first.


+---R2---+
| |\ |
+---R1---+-|-\ |
| |\ | >---+
I_in---+-|-\ .-|+/
| >---+ |/
Gnd-|+/
|/

I'm not sure that works.. and I have to do something when the 2nd TIA
rails... short it's inputs or something.

Here's a stupider question, since I'm no engineer. Wouldn't the second
stage be a regular opamp? I mean the TIA output is voltage, so....

Well the perhaps silly idea is to have to current go through R1 and R2.
Say R1 = 10 k and R2 = 1 Meg, and there is 1 uA of current, then ignoring
offset voltages the output of the second opamp should be 1.010 V,
and the first 10 mV... I guess I'll have to spice to check it.

I seem to recall some chained TIA circuits, but I couldn't find them
online, and forgot what they looked like.

George H.

 

[Winfield Hill]

Phil Hobbs wrote...

Winfield Hill wrote:
pcdhobbs@gmail.com wrote...

You aren't getting 0.1% over 8 decades
with 12 bits. Your step size is 0.45%.

The technique can do 1% of a 10^-8 signal.

Wrong. Keep thinking, you can, if you use
multiple channels. OK, let me think and
calculate more carefully. The starlight-
to-sunlight version, with 15 parts, is a
simplified version, it's good to about 1%,
degrading somewhat at the bottom of a range.
OK, another hint, there are simultaneously-
overlapping ranges. But no range changing.

TIAs with input resistors can share photocurrent
-- the current just divides according to the
conductance of the various paths. But that's
super slow and noisy.

We try to drive the SJ conductance to infinity.
One can imagine a scheme where an extra factor
is picked up, but it's hard to imagine getting
10^8 or 10^10 operating range, you pick a number.

This fellow's creation can do that. OK, time for
another hint, if it isn't obvious by now, there's
one input amp, and one feedback resistor chain.

The entire circuit has output ranges, yes, but
multiple ranges are simultaneously active. You
can have as many ranges, with whatever scaling
factors, 10, 30, 100, 300, etc., as you like.
We picked 300 for star-to-sunlight, save parts.

Your ranges could go from 100fA to 10 amps.


--
Thanks,
- Win

 

[Winfield Hill]

George Herold wrote...

Tom Del Rosso wrote:
George Herold wrote:

Can you chain together TIA stages? Lowest gain first.


+---R2---+
| |\ |
+---R1---+-|-\ |
| |\ | >---+
I_in---+-|-\ .-|+/
| >---+ |/
Gnd-|+/
|/

I'm not sure that works.. and I have to do something when
the 2nd TIA rails... short it's inputs or something.

Here's a stupider question, since I'm no engineer. Wouldn't
the second stage be a regular opamp? I mean the TIA output
is voltage, so....

Well the perhaps silly idea is to have to current go through
R1 and R2. Say R1 = 10 k and R2 = 1 Meg, and there is 1 uA
of current, then ignoring offset voltages the output of the
second opamp should be 1.010 V, and the first 10 mV...
I guess I'll have to spice to check it.

When the current is high enough in R2 to rail the 2nd opamp,
how can the first one go to its proper value? But, yes, the
current has to go through both R1 and R2, at least for low
currents (oops, another hint).


--
Thanks,
- Win

 

[Winfield Hill]

Tom Del Rosso wrote...

Winfield Hill wrote:
Winfield Hill wrote...

* A neat TIA amplifier with an 8-decade dynamic
range, 12-bit precision, not a log converter!
Example use: a starlight to sunlight digitizer.

Let's see, 10V out, precision feedback resistor,
10uV input opamp voltage offset, 6-decade range,
with 100% error at the bottom. Raise output to
100V with amp, feedback resistor there, 7-decades.
How get 8 decades with 1% precision (10-decades)?

Maximum current 5mA, minimum FS = 50pA, for 1%
max Ioffset 0.5pA, check!

Maximum Voffset 100V/10^10 = 0.01uV, no way!
Change range resistors, not allowed? Sheesh!
We reveal the secret, a clever, easy-to-use
solution, but it wasn't our idea!

Isn't an idea like that patentable?

Yes, certainly, I'd say. But he'd have applied
for the patent in 2011, and it would have been
granted by now. He left the idea to all of us.


--
Thanks,
- Win

 

[Winfield Hill]

George Herold wrote...

Build 3 TIA's, different gains, when the
lowest rails you switch to the next one?

Yes, that would give you dynamic range, just
like range-switching the feedbackresistor.
But the cool thing about this design is,
there's no range switching. Multipule ranges
are active at the same time, so there's never
a momentary loss of data. BTW, it also works
going from positive to negative and back.


--
Thanks,
- Win

 

[George Herold]

On Tuesday, June 25, 2019 at 9:17:28 PM UTC-4, Winfield Hill wrote:

George Herold wrote...

Tom Del Rosso wrote:
George Herold wrote:

Can you chain together TIA stages? Lowest gain first.


+---R2---+
| |\ |
+---R1---+-|-\ |
| |\ | >---+
I_in---+-|-\ .-|+/
| >---+ |/
Gnd-|+/
|/

I'm not sure that works.. and I have to do something when
the 2nd TIA rails... short it's inputs or something.

Here's a stupider question, since I'm no engineer. Wouldn't
the second stage be a regular opamp? I mean the TIA output
is voltage, so....

Well the perhaps silly idea is to have to current go through
R1 and R2. Say R1 = 10 k and R2 = 1 Meg, and there is 1 uA
of current, then ignoring offset voltages the output of the
second opamp should be 1.010 V, and the first 10 mV...
I guess I'll have to spice to check it.

When the current is high enough in R2 to rail the 2nd opamp,
how can the first one go to its proper value?

Right, you've got to short the inputs of the 2nd opamp
when it rails.. I guess you can do that with a fet and
signal from the uC.

George H.
But, yes, the

current has to go through both R1 and R2, at least for low
currents (oops, another hint).


--
Thanks,
- Win

 

[Tom Del Rosso]

Winfield Hill wrote:

George Herold wrote...

Build 3 TIA's, different gains, when the
lowest rails you switch to the next one?

Yes, that would give you dynamic range, just
like range-switching the feedbackresistor.
But the cool thing about this design is,
there's no range switching. Multipule ranges
are active at the same time, so there's never
a momentary loss of data. BTW, it also works
going from positive to negative and back.

And since there's only one input stage, that amp somehow never rails.

?

 

In x-ray systems the get those kind of dynamic ranges using CCO chips, Current Controlled Oscillators.


Steve

 

[Winfield Hill]

Tom Del Rosso wrote...

Winfield Hill wrote:
George Herold wrote...

Build 3 TIA's, different gains, when the
lowest rails you switch to the next one?

Yes, that would give you dynamic range, just
like range-switching the feedbackresistor.
But the cool thing about this design is,
there's no range switching. Multipule ranges
are active at the same time, so there's never
a momentary loss of data. BTW, it also works
going from positive to negative and back.

And since there's only one input stage, that
amp somehow never rails.

Correct. Tom, if you scratch the word, somehow,
then I'd think you know how it was done. You're
very close now to the answer.


--
Thanks,
- Win

 

[Tom Del Rosso]

Winfield Hill wrote:

Tom Del Rosso wrote...

Winfield Hill wrote:
George Herold wrote...

Build 3 TIA's, different gains, when the
lowest rails you switch to the next one?

Yes, that would give you dynamic range, just
like range-switching the feedbackresistor.
But the cool thing about this design is,
there's no range switching. Multipule ranges
are active at the same time, so there's never
a momentary loss of data. BTW, it also works
going from positive to negative and back.

And since there's only one input stage, that
amp somehow never rails.

Correct. Tom, if you scratch the word, somehow,
then I'd think you know how it was done. You're
very close now to the answer.

So the 2 opamps in the second stage produce 2 oututs that both go to an
ADC. A uP chooses an input but there is no other switching. There are
2 JFETS but they aren't used to change the gain of any stage.

Since there is no gain switching, is there some kind of feedback that
causes a change in "bias" on the input stage? But no, that would
oscillate.

 

[Jan Panteltje]

On a sunny day (Wed, 26 Jun 2019 04:48:16 -0400) it happened "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote in
<qevbgh$ont$1@dont-email.me>:

Winfield Hill wrote:
Tom Del Rosso wrote...

Winfield Hill wrote:
George Herold wrote...

Build 3 TIA's, different gains, when the
lowest rails you switch to the next one?

Yes, that would give you dynamic range, just
like range-switching the feedbackresistor.
But the cool thing about this design is,
there's no range switching. Multipule ranges
are active at the same time, so there's never
a momentary loss of data. BTW, it also works
going from positive to negative and back.

And since there's only one input stage, that
amp somehow never rails.

Correct. Tom, if you scratch the word, somehow,
then I'd think you know how it was done. You're
very close now to the answer.

So the 2 opamps in the second stage produce 2 oututs that both go to an
ADC. A uP chooses an input but there is no other switching. There are
2 JFETS but they aren't used to change the gain of any stage.

Since there is no gain switching, is there some kind of feedback that
causes a change in "bias" on the input stage? But no, that would
oscillate.

It would oscillate, but you could only use the value that makes sense,
start:
nothing railed: use the higest gain
if 1 railed, use the next one up
else if 2 railed activate JFET1, test again
if still 2 railed also activate JFET2 and test again.
if still 2 railed sound the super-nova alarm
else use the one that is not railed .. .math.. output
go to start

?

 

[John S]

On 6/25/2019 9:21 AM, Tom Gardner wrote:

On 25/06/19 15:05, John Larkin wrote:
On 24 Jun 2019 23:19:47 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

John Larkin wrote...

The progressive-railing thing would be as good
as the parts you care to buy. 0.1% should be
possible.

OK, precision railing to say 1%, OK.  But at
the highest gains, the fixed-value input-stage
feedback resistor, and the input offset ...
Explain that for us.

Is this an electronics discussion or a book promotion?

A1: yes it is.
A2: does it matter?
A3: it is fun, who cares.

+1

 

[George Herold]

On Tuesday, June 25, 2019 at 9:57:01 PM UTC-4, Tom Del Rosso wrote:

Winfield Hill wrote:
George Herold wrote...

Build 3 TIA's, different gains, when the
lowest rails you switch to the next one?

Yes, that would give you dynamic range, just
like range-switching the feedbackresistor.
But the cool thing about this design is,
there's no range switching. Multipule ranges
are active at the same time, so there's never
a momentary loss of data. BTW, it also works
going from positive to negative and back.

And since there's only one input stage, that amp somehow never rails.

?

The first stage will have to lowest gain.. Still one could probably make it
rail with a laser. I want to see what the various step responses look
like.

Win, If we all promise to buy the X-chapters, will you post 'scope shots?
(or do I have to build it myself. :^)

George H.

 

[George Herold]

On Wednesday, June 26, 2019 at 5:22:41 AM UTC-4, Jan Panteltje wrote:

On a sunny day (Wed, 26 Jun 2019 04:48:16 -0400) it happened "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote in
qevbgh$ont$1@dont-email.me>:

Winfield Hill wrote:
Tom Del Rosso wrote...

Winfield Hill wrote:
George Herold wrote...

Build 3 TIA's, different gains, when the
lowest rails you switch to the next one?

Yes, that would give you dynamic range, just
like range-switching the feedbackresistor.
But the cool thing about this design is,
there's no range switching. Multipule ranges
are active at the same time, so there's never
a momentary loss of data. BTW, it also works
going from positive to negative and back.

And since there's only one input stage, that
amp somehow never rails.

Correct. Tom, if you scratch the word, somehow,
then I'd think you know how it was done. You're
very close now to the answer.

So the 2 opamps in the second stage produce 2 oututs that both go to an
ADC. A uP chooses an input but there is no other switching. There are
2 JFETS but they aren't used to change the gain of any stage.

Since there is no gain switching, is there some kind of feedback that
causes a change in "bias" on the input stage? But no, that would
oscillate.

It would oscillate, but you could only use the value that makes sense,
start:
nothing railed: use the higest gain
if 1 railed, use the next one up
else if 2 railed activate JFET1, test again
if still 2 railed also activate JFET2 and test again.
if still 2 railed sound the super-nova alarm
else use the one that is not railed .. .math.. output
go to start

?

Right something like that.. but you could use the signal from the lower
gain stage to see if the upper one has 'unrailed'.
GH

 

[John S]

On 6/25/2019 9:05 AM, John Larkin wrote:

On 24 Jun 2019 23:19:47 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

John Larkin wrote...

The progressive-railing thing would be as good
as the parts you care to buy. 0.1% should be
possible.

OK, precision railing to say 1%, OK. But at
the highest gains, the fixed-value input-stage
feedback resistor, and the input offset ...
Explain that for us.

Is this an electronics discussion or a book promotion?

John, you are usually not so unkind.