On Thu, 23 Dec 2021 01:06:39 -0500, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

>Lasse Langwadt Christensen wrote:
>> l&#4294967295;rdag den 18. december 2021 kl. 03.49.47 UTC+1 skrev
>> jla...@highlandsniptechnology.com:
>>> I need an isolated DAC. I could just generate a PWM thing, isolate
>>> it, and lowpass filter on the high side. But we could also generate a
>>> delta-sigma bit stream, which has advantages. If d-s, I might want to
>>> reclock it before lowpass filtering to get clean, fast edges.
>>>
>>> But then I could drive several d-flops.
>>>
>>> https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>>>
>>> The analog signal now has 16 levels instead of two, sorta random but
>>> still 16.
>>>
>>> Is this worth doing? It's hard to think about on a Friday night after
>>> pasta and beer.
>>>
>>
>> it is basically a FIR filter, so it's just an extra filter before
>> your filter
>>
>> if you are going to add a FF  anyway why not 8, like 74hc164
>
>This brings up a question that nags me but never came up in anything I 
>read.
>
>Don't you have to control the output voltages precisely?  The MSB 
>output's variability can swamp the outputs 6 bits down the line.

My suggestion isn't a resistive DAC in the classic sense. It's a
transversal filter.

Delta-sigma encodes a voltage as average duty cycle. Each resistor
contributes to the output in proportion to its duty cycle, so the
system is linear independent of resistor values.

-- 

If a man will begin with certainties, he shall end with doubts, 
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon

On Thursday, December 23, 2021 at 2:12:40 AM UTC-4, Tom Del Rosso wrote:
> Lasse Langwadt Christensen wrote: 
> > lørdag den 18. december 2021 kl. 03.49.47 UTC+1 skrev 
> > jla...@highlandsniptechnology.com: 
> >> I need an isolated DAC. I could just generate a PWM thing, isolate 
> >> it, and lowpass filter on the high side. But we could also generate a 
> >> delta-sigma bit stream, which has advantages. If d-s, I might want to 
> >> reclock it before lowpass filtering to get clean, fast edges. 
> >> 
> >> But then I could drive several d-flops. 
> >> 
> >> https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1 
> >> 
> >> The analog signal now has 16 levels instead of two, sorta random but 
> >> still 16. 
> >> 
> >> Is this worth doing? It's hard to think about on a Friday night after 
> >> pasta and beer. 
> >> 
> > 
> > it is basically a FIR filter, so it's just an extra filter before 
> > your filter 
> > 
> > if you are going to add a FF anyway why not 8, like 74hc164
> This brings up a question that nags me but never came up in anything I 
> read. 
> 
> Don't you have to control the output voltages precisely? The MSB 
> output's variability can swamp the outputs 6 bits down the line. 

You might see some high frequency noise from a supply to digital circuitry, but the voltage should be stable at lower frequencies even if not highly accurate.  Unless there is an excessively heavy load on the output, there won't be enough current to load the digital outputs.  If needed, the supply could be from a separate regulator with significant filtering on the input.  There's not enough indication of requirements to offer any truly constructive advice.  

-- 

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

On a sunny day (Thu, 23 Dec 2021 01:06:39 -0500) it happened "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote in
<sq140i$pe0$1@dont-email.me>:

>Lasse Langwadt Christensen wrote:
>> l&#4294967295;rdag den 18. december 2021 kl. 03.49.47 UTC+1 skrev
>> jla...@highlandsniptechnology.com:
>>> I need an isolated DAC. I could just generate a PWM thing, isolate
>>> it, and lowpass filter on the high side. But we could also generate a
>>> delta-sigma bit stream, which has advantages. If d-s, I might want to
>>> reclock it before lowpass filtering to get clean, fast edges.
>>>
>>> But then I could drive several d-flops.
>>>
>>> https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>>>
>>> The analog signal now has 16 levels instead of two, sorta random but
>>> still 16.
>>>
>>> Is this worth doing? It's hard to think about on a Friday night after
>>> pasta and beer.
>>>
>>
>> it is basically a FIR filter, so it's just an extra filter before
>> your filter
>>
>> if you are going to add a FF  anyway why not 8, like 74hc164
>
>This brings up a question that nags me but never came up in anything I 
>read.
>
>Don't you have to control the output voltages precisely?  The MSB 
>output's variability can swamp the outputs 6 bits down the line.

On CMOS the output with high resistive load is rail to rail.
Yes supply voltage should be stable and ripple free of course.
I have done 8 bits R2R on FPGA output with analog video and it looked OK.
And yes I tested with a horizontal ramp for obvious errors.
Then again analog video composite was not so critical. 
But a real DAC is of course safer -)

Lasse Langwadt Christensen wrote:
> l�rdag den 18. december 2021 kl. 03.49.47 UTC+1 skrev
> jla...@highlandsniptechnology.com:
>> I need an isolated DAC. I could just generate a PWM thing, isolate
>> it, and lowpass filter on the high side. But we could also generate a
>> delta-sigma bit stream, which has advantages. If d-s, I might want to
>> reclock it before lowpass filtering to get clean, fast edges.
>>
>> But then I could drive several d-flops.
>>
>> https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>>
>> The analog signal now has 16 levels instead of two, sorta random but
>> still 16.
>>
>> Is this worth doing? It's hard to think about on a Friday night after
>> pasta and beer.
>>
>
> it is basically a FIR filter, so it's just an extra filter before
> your filter
>
> if you are going to add a FF  anyway why not 8, like 74hc164

This brings up a question that nags me but never came up in anything I 
read.

Don't you have to control the output voltages precisely?  The MSB 
output's variability can swamp the outputs 6 bits down the line.


-- 
Defund the Thought Police
Andiamo Brandon! 

On a sunny day (Sat, 18 Dec 2021 09:14:31 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
<dj5srgtk9f8b9fnbfb12f7hgthb12sosgd@4ax.com>:

>On Sat, 18 Dec 2021 15:56:51 GMT, Jan Panteltje
><pNaOnStPeAlMtje@yahoo.com> wrote:
>
>>On a sunny day (Fri, 17 Dec 2021 18:49:36 -0800) it happened
>>jlarkin@highlandsniptechnology.com wrote in
>><qfiqrghi0a53qhjqsn048smqah7ltqk895@4ax.com>:
>>
>>>I need an isolated DAC. I could just generate a PWM thing, isolate it,
>>>and lowpass filter on the high side. But we could also generate a
>>>delta-sigma bit stream, which has advantages. If d-s, I might want to
>>>reclock it before lowpass filtering to get clean, fast edges.
>>>
>>>But then I could drive several d-flops.
>>>
>>>https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>>>
>>>The analog signal now has 16 levels instead of two, sorta random but
>>>still 16.
>>>
>>>Is this worth doing? It's hard to think about on a Friday night after
>>>pasta and beer.
>>
>>No idea what your speed requirements are, but the i2c PCF8591 I have used
>>many times.
>>You would need to isolate sda and scl, also sda pulldown backwards.
>>It is an 8 bit ADC + DAC in one 16 pin DIL.
>>But then you can go 2 ways.
>
>There is one faction here that wants to put a uP up on the isolated
>side and use its DAC and ADC channels and let it close loops and such.
>OK, but we'd have to pick a chip that won't be EOL in a few years, and
>it would need its own program.

The reason I like Microchip PICs is thet even the old ones are still available.
Farnell has 18F14K22 (the one I use) in stock, 2 Euro 30 cents for 1.
It has hardware PWM, and 12 10 bit analog input channels,
and 2 analog comparators...
But the PIC istruction set is a bit different .. skip next instruction if true / false sort of thing.

jlarkin@highlandsniptechnology.com wrote:
> On Sat, 18 Dec 2021 15:56:51 GMT, Jan Panteltje
> <pNaOnStPeAlMtje@yahoo.com> wrote:
> 
>> On a sunny day (Fri, 17 Dec 2021 18:49:36 -0800) it happened
>> jlarkin@highlandsniptechnology.com wrote in
>> <qfiqrghi0a53qhjqsn048smqah7ltqk895@4ax.com>:
>>
>>> I need an isolated DAC. I could just generate a PWM thing, isolate it,
>>> and lowpass filter on the high side. But we could also generate a
>>> delta-sigma bit stream, which has advantages. If d-s, I might want to
>>> reclock it before lowpass filtering to get clean, fast edges.
>>>
>>> But then I could drive several d-flops.
>>>
>>> https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>>>
>>> The analog signal now has 16 levels instead of two, sorta random but
>>> still 16.
>>>
>>> Is this worth doing? It's hard to think about on a Friday night after
>>> pasta and beer.
>>
>> No idea what your speed requirements are, but the i2c PCF8591 I have used
>> many times.
>> You would need to isolate sda and scl, also sda pulldown backwards.
>> It is an 8 bit ADC + DAC in one 16 pin DIL.
>> But then you can go 2 ways.
> 
> There is one faction here that wants to put a uP up on the isolated
> side and use its DAC and ADC channels and let it close loops and such.
> OK, but we'd have to pick a chip that won't be EOL in a few years, and
> it would need its own program.
> 
> 
> 
Well, just pick one with 100k in stock at DK.  No, wait,....

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Sat, 18 Dec 2021 23:24:42 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

>On 18/12/2021 13:49, jlarkin@highlandsniptechnology.com wrote:
>> I need an isolated DAC. I could just generate a PWM thing, isolate it,
>> and lowpass filter on the high side. But we could also generate a
>> delta-sigma bit stream, which has advantages. If d-s, I might want to
>> reclock it before lowpass filtering to get clean, fast edges.
>> 
>> But then I could drive several d-flops.
>> 
>> https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>> 
>> The analog signal now has 16 levels instead of two, sorta random but
>> still 16.
>> 
>> Is this worth doing? It's hard to think about on a Friday night after
>> pasta and beer.
>
>Probably not much advantage to it.
>
>You might need slightly less filtering after it, but that isn't likely 
>to save you much.
>
>With all of the resistors the same value (since you labelled them all R) 
>you will only get 5 levels, not 16, since there will be 0,1,2,3 or 4 
>flipflops high.
>
>If you have a longer chain of flipflops (or even just for 4 of them), 
>you would be better off not weighting them all the same, but weight the 
>conductance (1/R) as raised cosine or gaussian or something that will 
>filter better than a flat-top impulse response.
>

With R..2R.. resistors I'd get 16 levels, but have choices of where to
put the resistors. That's too hard to think about.

Might be a thesus or something.



-- 

I yam what I yam - Popeye

On Sat, 18 Dec 2021 11:41:07 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>> I need an isolated DAC. I could just generate a PWM thing, isolate it,
>> and lowpass filter on the high side. But we could also generate a
>> delta-sigma bit stream, which has advantages. If d-s, I might want to
>> reclock it before lowpass filtering to get clean, fast edges.
>> 
>> But then I could drive several d-flops.
>> 
>> https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>> 
>> The analog signal now has 16 levels instead of two, sorta random but
>> still 16.
>> 
>> Is this worth doing? It's hard to think about on a Friday night after
>> pasta and beer.
>> 
>> 
>> 
>Sure, that works.  It's a species of transversal filter.
>
>You can also make a waveform generator using one or more HC4018 counters 
>and weighted resistors.  We had a discussion with George a few years 
>back about that.
>
>Cheers
>
>Phil Hobbs

Here's one idea for a floating programmable ac/dc load. It's
constant-current, but if we have voltage and current sensors we could
fake constant resistance or constant voltage modes. V1 would be our
isolated DAC.

Given lots of channels on a board, we want to minimize the size and
cost of per-channel isolation. A load doesn't have to be especially
accurate.

Version 4
SHEET 1 2092 1028
WIRE 592 -96 496 -96
WIRE 688 -96 592 -96
WIRE 896 -96 768 -96
WIRE 992 -96 896 -96
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WIRE 496 464 496 384
WIRE 992 464 992 384
FLAG 496 464 0
FLAG -224 336 0
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FLAG 208 320 V+
FLAG 416 112 G1
FLAG 432 256 S1
FLAG -96 96 IN
FLAG 592 -96 D1
FLAG 992 464 0
FLAG 1072 112 G2
FLAG 1056 256 S2
FLAG 896 -96 D2
FLAG 1568 96 IN
FLAG 64 176 V+
FLAG 1440 176 V+
FLAG 96 64 0
FLAG 1408 64 0
SYMBOL Opamps\\UniversalOpamp2 32 112 M180
WINDOW 0 -77 53 Left 2
SYMATTR InstName U1
SYMBOL nmos 448 32 R0
WINDOW 0 98 37 Left 2
WINDOW 3 83 74 Left 2
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SYMATTR Value BSC240N12NS3
SYMBOL res 400 96 R90
WINDOW 0 -41 58 VBottom 2
WINDOW 3 -36 58 VTop 2
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SYMATTR Value 100
SYMBOL res 480 288 R0
WINDOW 0 54 43 Left 2
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SYMATTR Value 1
SYMBOL voltage -224 192 R0
WINDOW 0 49 75 Left 2
WINDOW 3 28 114 Left 2
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WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value SINE(0.2 0 100)
SYMBOL voltage 144 336 R0
WINDOW 0 51 55 Left 2
WINDOW 3 58 84 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 8
SYMBOL res 400 240 R90
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SYMBOL voltage 672 -96 R270
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WINDOW 3 -100 -7 VRight 2
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SYMATTR Value SINE(0 10 10)
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SYMBOL nmos 1040 32 M0
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WINDOW 3 83 74 Left 2
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SYMATTR Value BSC240N12NS3
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WINDOW 0 -41 58 VBottom 2
WINDOW 3 -36 58 VTop 2
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WINDOW 3 64 74 Left 2
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SYMATTR Value 1
SYMBOL res 1088 240 M90
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WINDOW 3 75 54 VTop 2
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SYMATTR Value 1K
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SYMATTR Value 100p
SYMBOL cap 1280 160 R0
WINDOW 0 -47 8 Left 2
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SYMATTR InstName C2
SYMATTR Value 100p
TEXT 680 416 Left 2 !.tran 100m
TEXT 624 256 Left 2 ;Programmable Load
TEXT 640 304 Left 2 ;JL  Nov 17  2021
TEXT 696 216 Left 2 ;Bipolar
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TEXT 376 448 Left 2 ;common




-- 

I yam what I yam - Popeye

On Sat, 18 Dec 2021 17:24:39 +0100, Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>18.12.21 03:49, jlarkin@highlandsniptechnology.com wrote:
>>I need an isolated DAC. I could just generate a PWM thing, isolate it,
>>and lowpass filter on the high side. But we could also generate a
>>delta-sigma bit stream, which has advantages. If d-s, I might want to
>>reclock it before lowpass filtering to get clean, fast edges.
>>
>>But then I could drive several d-flops.
>>
>>https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>>
>>The analog signal now has 16 levels instead of two, sorta random but
>>still 16.
>>
>>Is this worth doing? It's hard to think about on a Friday night after
>>pasta and beer.
>>
>>
>You could use an Icoupler. They have 10ns ish propagation delay and comes with ability to generate supply also. Then filter the PWM and you are done

If I want analog accuracy, I'd prefer to run the PWM or D-S through a
fast gate or flop that's powered by some good reference, dropped down
from whatever isolated supply. A resistor and an LM4040 type thing
would do.





-- 

I yam what I yam - Popeye

On Sat, 18 Dec 2021 15:56:51 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

>On a sunny day (Fri, 17 Dec 2021 18:49:36 -0800) it happened
>jlarkin@highlandsniptechnology.com wrote in
><qfiqrghi0a53qhjqsn048smqah7ltqk895@4ax.com>:
>
>>I need an isolated DAC. I could just generate a PWM thing, isolate it,
>>and lowpass filter on the high side. But we could also generate a
>>delta-sigma bit stream, which has advantages. If d-s, I might want to
>>reclock it before lowpass filtering to get clean, fast edges.
>>
>>But then I could drive several d-flops.
>>
>>https://www.dropbox.com/s/0d7x6l6isyoldva/ML_DS_Dac.jpg?raw=1
>>
>>The analog signal now has 16 levels instead of two, sorta random but
>>still 16.
>>
>>Is this worth doing? It's hard to think about on a Friday night after
>>pasta and beer.
>
>No idea what your speed requirements are, but the i2c PCF8591 I have used
>many times.
>You would need to isolate sda and scl, also sda pulldown backwards.
>It is an 8 bit ADC + DAC in one 16 pin DIL.
>But then you can go 2 ways.

There is one faction here that wants to put a uP up on the isolated
side and use its DAC and ADC channels and let it close loops and such.
OK, but we'd have to pick a chip that won't be EOL in a few years, and
it would need its own program.



-- 

I yam what I yam - Popeye