Half power rail reference...

[Rickster C]

I recall a thread sometime in the last year that mentioned an idea for generating an accurate voltage at half the supply rail by switching an output at a 50/50 duty cycle to feed an RC. I can\'t seem to find that thread. I\'m wondering what the limitations might be on the accuracy. Obviously the difference in drive capability is a factor, but that can be mitigated by the external resistor.

i suppose there can be differences in the delay times for the two edges within the digital device. That can be mitigated by using a slower cycle. To get a 0.1% tolerance with a ±1 ns timing variation requires the waveform be 0.5 MHz.

Any ideas on other points that may be important? I suppose a quality integrating capacitor might be important as well. Also ceramic caps can be microphonic, so film caps will be needed. In fact I need to specify that all through the sensor power supply.

--

Rick C.

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

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:576a8f55-3fcb-4841-ac86-7d79cba1233eo@googlegroups.com...
I recall a thread sometime in the last year that mentioned an idea for
generating an accurate voltage at half the supply rail by switching an
output at a 50/50 duty cycle to feed an >RC. I can\'t seem to find that
thread. I\'m wondering what the limitations might be on the accuracy.
Obviously the difference in drive capability is a factor, but that can be
mitigated by the external resistor.

Unless you need a variable voltage then what\'s wrong with two resistors and
an op-amp voltage follower?

i suppose there can be differences in the delay times for the two edges
within the digital device. That can be mitigated by using a slower cycle.
To get a 0.1% tolerance with a ±1 ns timing variation requires the waveform
be 0.5 MHz.

Any ideas on other points that may be important? I suppose a quality
integrating capacitor might be important as well. Also ceramic caps can be
microphonic, so film caps will be needed. In fact I need to specify that
all through the sensor power supply.

--

Rick C.

 

[George Herold]

If you want a power supply reference, then why not just
use a resistor divider?
Or do you want a rail splitter power supply?
(In which case, what\'s the current/ voltage?)

George H.

 

[server]

On Monday, 2 November 2020 17:59:04 UTC, George Herold wrote:

If you want a power supply reference, then why not just
use a resistor divider?
Or do you want a rail splitter power supply?
(In which case, what\'s the current/ voltage?)

George H.

I don\'t think COG ceramics are microphonic to a significant extent.

John

 

[Rickster C]

On Monday, November 2, 2020 at 4:18:35 PM UTC-5, jrwal...@gmail.com wrote:

On Monday, 2 November 2020 17:59:04 UTC, George Herold wrote:
If you want a power supply reference, then why not just
use a resistor divider?
Or do you want a rail splitter power supply?
(In which case, what\'s the current/ voltage?)

George H.

I don\'t think COG ceramics are microphonic to a significant extent.

Yeah, if you can work with a small enough value. C0G aren\'t available much above what, 1000 pF or so?

--

Rick C.

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

 

[Lasse Langwadt Christensen]

tirsdag den 3. november 2020 kl. 03.26.08 UTC+1 skrev Rickster C:

On Monday, November 2, 2020 at 4:18:35 PM UTC-5, jrwal...@gmail.com wrote:
On Monday, 2 November 2020 17:59:04 UTC, George Herold wrote:
If you want a power supply reference, then why not just
use a resistor divider?
Or do you want a rail splitter power supply?
(In which case, what\'s the current/ voltage?)

George H.

I don\'t think COG ceramics are microphonic to a significant extent.

Yeah, if you can work with a small enough value. C0G aren\'t available much above what, 1000 pF or so?

you can get a few 100 nF for a couple of $, above that they get really expensive

 

[Robert Baer]

Rickster C wrote:

I recall a thread sometime in the last year that mentioned an idea for generating an accurate voltage at half the supply rail by switching an output at a 50/50 duty cycle to feed an RC. I can\'t seem to find that thread. I\'m wondering what the limitations might be on the accuracy. Obviously the difference in drive capability is a factor, but that can be mitigated by the external resistor.

i suppose there can be differences in the delay times for the two edges within the digital device. That can be mitigated by using a slower cycle. To get a 0.1% tolerance with a ±1 ns timing variation requires the waveform be 0.5 MHz.

Any ideas on other points that may be important? I suppose a quality integrating capacitor might be important as well. Also ceramic caps can be microphonic, so film caps will be needed. In fact I need to specify that all through the sensor power supply.

You mean \"half voltage\".

 

[Rickster C]

On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer wrote:

Rickster C wrote:
I recall a thread sometime in the last year that mentioned an idea for generating an accurate voltage at half the supply rail by switching an output at a 50/50 duty cycle to feed an RC. I can\'t seem to find that thread. I\'m wondering what the limitations might be on the accuracy. Obviously the difference in drive capability is a factor, but that can be mitigated by the external resistor.

i suppose there can be differences in the delay times for the two edges within the digital device. That can be mitigated by using a slower cycle. To get a 0.1% tolerance with a ±1 ns timing variation requires the waveform be 0.5 MHz.

Any ideas on other points that may be important? I suppose a quality integrating capacitor might be important as well. Also ceramic caps can be microphonic, so film caps will be needed. In fact I need to specify that all through the sensor power supply.

You mean \"half voltage\".

Thanks, but trying that both with and without the quotes didn\'t turn up the thread going all the way back to December. It couldn\'t have been that long ago could it? Seems like maybe three for four months back.

I\'m not sure how bad it would be to simply use a pair of 0.1% resistors. That would add error somewhere between 0.1% and 0.2% (not thinking about it too hard). There will be other sources of error from this same effect elsewhere (dividing the 5V signal source to 3.3 volts... or maybe not. Perhaps that can be mitigated by not using equal value resistors in the input and feedback paths.

It\'s funny that the other guys on the project don\'t seem to be able to think about this stuff. I guess they are mostly used to just plopping down chips. Heck, a new FPGA guy wanted to use a $20 Xilinx part instead of a $4-5 Gowin part!

I was happy to find I can get 10 nF C0G for under a nickle and 100 nF for around a dime. I thought they didn\'t come that large. They do get large!

--

Rick C.

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

 

[Jeroen Belleman]

On 2020-11-04 22:00, Rickster C wrote:

On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer
wrote:
Rickster C wrote:
I recall a thread sometime in the last year that mentioned an
idea for generating an accurate voltage at half the supply rail
by switching an output at a 50/50 duty cycle to feed an RC. I
can\'t seem to find that thread. I\'m wondering what the
limitations might be on the accuracy. Obviously the difference
in drive capability is a factor, but that can be mitigated by the
external resistor.

Maybe something along the lines of this?

If you want it accurate, use feedback to adjust the duty cycle.

Jeroen Belleman


Version 4
SHEET 1 880 680
WIRE 224 -16 -208 -16
WIRE 352 -16 224 -16
WIRE 400 -16 352 -16
WIRE 512 -16 400 -16
WIRE 400 16 400 -16
WIRE 224 32 224 -16
WIRE 512 32 512 -16
WIRE 176 48 -48 48
WIRE 176 96 96 96
WIRE -208 112 -208 -16
WIRE -48 160 -48 48
WIRE -16 160 -48 160
WIRE 96 160 96 96
WIRE 96 160 64 160
WIRE 128 160 96 160
WIRE 224 160 224 112
WIRE 224 160 208 160
WIRE 288 160 224 160
WIRE 400 160 400 80
WIRE 400 160 368 160
WIRE 512 160 512 112
WIRE 512 160 400 160
WIRE 608 160 512 160
WIRE 224 224 224 160
WIRE 512 224 512 160
WIRE 96 240 96 160
WIRE 176 240 96 240
WIRE 400 272 400 160
WIRE -48 288 -48 160
WIRE 176 288 -48 288
WIRE -208 368 -208 192
WIRE 224 368 224 304
WIRE 224 368 -208 368
WIRE 352 368 224 368
WIRE 400 368 400 336
WIRE 400 368 352 368
WIRE 512 368 512 304
WIRE 512 368 400 368
FLAG 608 160 0
FLAG 352 -16 Vp
FLAG 352 368 Vm
SYMBOL sw 224 16 R0
SYMATTR InstName S1WINDOW 3 243 28 VTop 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value PULSE(-1 1 10u 10n 10n 10u 20u)
SYMBOL res 224 144 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL cap 384 16 R0
SYMATTR InstName C1
SYMATTR Value 10u
SYMBOL cap 384 272 R0
SYMATTR InstName C2
SYMATTR Value 10u
SYMBOL res 496 16 R0
SYMATTR InstName R2
SYMATTR Value 10
SYMBOL res 496 208 R0
SYMATTR InstName R3
SYMATTR Value 100
TEXT -32 -96 Left 2 !.model switch sw(Ron=1 Roff=100k vt=0)
TEXT 568 -88 Left 2 !.tran 20m

SYMATTR Value switch
SYMBOL sw 224 208 R0
SYMATTR InstName S2
SYMATTR Value switch
SYMBOL voltage -208 96 R0
SYMATTR InstName V1
SYMATTR Value 30V
SYMBOL ind 272 176 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName L1
SYMATTR Value 100u
SYMBOL voltage 80 160 R90
WINDOW 0 -32 56 VBottom 2

 

[Jeroen Belleman]

On 2020-11-04 22:56, Jeroen Belleman wrote:

On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer
wrote:
Rickster C wrote:
I recall a thread sometime in the last year that mentioned an
idea for generating an accurate voltage at half the supply rail
by switching an output at a 50/50 duty cycle to feed an RC. I
can\'t seem to find that thread. I\'m wondering what the
limitations might be on the accuracy. Obviously the difference
in drive capability is a factor, but that can be mitigated by the
external resistor.

Maybe something along the lines of this?

If you want it accurate, use feedback to adjust the duty cycle.

Jeroen Belleman

Sorry, I seem to have messed that up. Let\'s try again...

Jeroen Belleman


Version 4
SHEET 1 880 680
WIRE 224 -16 -208 -16
WIRE 352 -16 224 -16
WIRE 400 -16 352 -16
WIRE 512 -16 400 -16
WIRE 400 16 400 -16
WIRE 224 32 224 -16
WIRE 512 32 512 -16
WIRE 176 48 -48 48
WIRE 176 96 96 96
WIRE -208 112 -208 -16
WIRE -48 160 -48 48
WIRE -16 160 -48 160
WIRE 96 160 96 96
WIRE 96 160 64 160
WIRE 128 160 96 160
WIRE 224 160 224 112
WIRE 224 160 208 160
WIRE 288 160 224 160
WIRE 400 160 400 80
WIRE 400 160 368 160
WIRE 512 160 512 112
WIRE 512 160 400 160
WIRE 608 160 512 160
WIRE 224 224 224 160
WIRE 512 224 512 160
WIRE 96 240 96 160
WIRE 176 240 96 240
WIRE 400 272 400 160
WIRE -48 288 -48 160
WIRE 176 288 -48 288
WIRE -208 368 -208 192
WIRE 224 368 224 304
WIRE 224 368 -208 368
WIRE 352 368 224 368
WIRE 400 368 400 336
WIRE 400 368 352 368
WIRE 512 368 512 304
WIRE 512 368 400 368
FLAG 608 160 0
FLAG 352 -16 Vp
FLAG 352 368 Vm
SYMBOL sw 224 16 R0
SYMATTR InstName S1
SYMATTR Value switch
SYMBOL sw 224 208 R0
SYMATTR InstName S2
SYMATTR Value switch
SYMBOL voltage -208 96 R0
SYMATTR InstName V1
SYMATTR Value 30V
SYMBOL ind 272 176 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName L1
SYMATTR Value 100u
SYMBOL voltage 80 160 R90
WINDOW 0 -32 56 VBottom 2
WINDOW 3 243 28 VTop 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value PULSE(-1 1 10u 10n 10n 10u 20u)
SYMBOL res 224 144 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL cap 384 16 R0
SYMATTR InstName C1
SYMATTR Value 10u
SYMBOL cap 384 272 R0
SYMATTR InstName C2
SYMATTR Value 10u
SYMBOL res 496 16 R0
SYMATTR InstName R2
SYMATTR Value 10
SYMBOL res 496 208 R0
SYMATTR InstName R3
SYMATTR Value 100
TEXT -32 -96 Left 2 !.model switch sw(Ron=1 Roff=100k vt=0)
TEXT 568 -88 Left 2 !.tran 20m

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:98143f21-2150-49c8-9681-8916353ffb8ao@googlegroups.com...
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer wrote:
Rickster C wrote:
[snip]

It\'s funny that the other guys on the project don\'t seem to be able to
think about this stuff.

Could that be because they never get to know exactly what you\'re trying to
achieve or why you\'re trying to achieve it?

> Rick C.

 

[Rickster C]

On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman wrote:

On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer
wrote:
Rickster C wrote:
I recall a thread sometime in the last year that mentioned an
idea for generating an accurate voltage at half the supply rail
by switching an output at a 50/50 duty cycle to feed an RC. I
can\'t seem to find that thread. I\'m wondering what the
limitations might be on the accuracy. Obviously the difference
in drive capability is a factor, but that can be mitigated by the
external resistor.

Maybe something along the lines of this?

If you want it accurate, use feedback to adjust the duty cycle.

Jeroen Belleman


Sorry, I seem to have messed that up. Let\'s try again...

Sorry, I don\'t understand. The inductor is grounded on the end that looks like it should be the output. The waveforms are all sloped square waves. What am I missing?

Not sure how I would determine how to apply feedback. What would be the measurement to use to set the feedback? I don\'t have a way to measure the voltage. That\'s the point, to provide a reference voltage at Vcc/2 without active monitoring or control. As someone said, a pair of resistors would do the job, but with ~0.2% accuracy using 0.1% resistors. Using a 50/50 output with a single 0.1% resistor should provide ~0.1% accuracy which should be pretty good.

This is the reference voltage for delta-sigma ADCs. The input signal is being stepped down from a 0-5V signal to a 3.3V input with a pair of 0.1% resistors. I wonder if it might make sense to drop the input signal in the same manner with a single resistor and a 2:1 timing cycle. So 5V -> 3.33V giving 0.1% on the dropping circuit. The accuracy of the sensor is ballpark 1%, but there are numerous additions to this error and keeping them all small is useful. But maybe I\'m over thinking this one. It\'s just that we can always take out something we find is not needed. But if we don\'t put it into the design it will be hard to add for testing when we find it might be useful.

--

Rick C.

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

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman wrote:

On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer
wrote:
Rickster C wrote:

The accuracy of the sensor is ballpark 1%,

That makes me wonder what the sensor is sensing, how it is interfaced, how
quickly it needs to sense, etc.
If you want help then I think a schematic or part of a schematic would be
much better than trying to describe the system in words.

--

Rick C.

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer
wrote:
Rickster C wrote:

The accuracy of the sensor is ballpark 1%,

That makes me wonder what the sensor is sensing, how it is interfaced,
how
quickly it needs to sense, etc.
If you want help then I think a schematic or part of a schematic would be
much better than trying to describe the system in words.

Here is a link to the entire project, every bit of anything we have
generated other than the latest schematics and software which recently was
hosted on github. OpenVentBristol

https://drive.google.com/drive/folders/1F87dkECYyU-Lrm9mpBsMEJ7y3rBM_GSt?usp=sharing

When I buy an ADC chip I\'m pretty sure they didn\'t know my requirements
when they designed it. Yes, I just checked and we have not given access to
any semiconductor makers.

Was that an attempt at sarcasm?

I appreciate any advice, but I don\'t have a full set of design documents to
share. This is early days on the ADC design. I\'m happy to share a verbal
description with numbers, but it ain\'t that complicated.

If it ain\'t complicated then a schematic drawn on the back of an enveleope
and put in a scanner is the way I would likely convey the information.
You may prefer to use a schematic capture tool which is fine.
A simplified schematic showing the intended ADC interface circuitry is all
that\'s needed.

The stuff being sensed is slow. The accuracy requirement is 3% if I
recall. As I said, I\'m looking to design the very tiny analog portion of
this circuit to preserve as much accuracy as I can.

I really don\'t get why you would need to understand every aspect of the
sensors.

Well if I were designing an interface from a sensor to an ADC then some of
the things which might go through my mind are:

What is the source impedance and voltage or current range coming in from the
sensor?
Single ended or differential?
What bandwidth do I need?
What is the input impedance of the ADC and what voltage range is needed?

If you already have an intended circuit for that then it should easily fit
on the back of an envelope.

One of them is a differential pressure sensor for an orifice based flow
rate sensor with a 0 to 6 kPa range with a 5 volt Vdd and an output scaled
to Vdd. The signal being sensed is the human breath with a cycle time of 2
seconds minimum. Not sure of the upper frequency limit, but the initial
edges start off rater steeply, so perhaps 100 Hz.

Ok well 100 Hz is not the hardest frequency to deal with so do you already
have an intended interface schematic from this sensor to your ADC?

?Does any of that help?

A little. A schematic would help a lot more than a Google drive with so many
documents that there\'s no way I would know which, if any, is relevant.

--

Rick C.

 

[Rickster C]

On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde wrote:

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer
wrote:
Rickster C wrote:

The accuracy of the sensor is ballpark 1%,

That makes me wonder what the sensor is sensing, how it is interfaced,
how
quickly it needs to sense, etc.
If you want help then I think a schematic or part of a schematic would be
much better than trying to describe the system in words.

Here is a link to the entire project, every bit of anything we have
generated other than the latest schematics and software which recently was
hosted on github. OpenVentBristol

https://drive.google.com/drive/folders/1F87dkECYyU-Lrm9mpBsMEJ7y3rBM_GSt?usp=sharing

When I buy an ADC chip I\'m pretty sure they didn\'t know my requirements
when they designed it. Yes, I just checked and we have not given access to
any semiconductor makers.

Was that an attempt at sarcasm?

I appreciate any advice, but I don\'t have a full set of design documents to
share. This is early days on the ADC design. I\'m happy to share a verbal
description with numbers, but it ain\'t that complicated.

If it ain\'t complicated then a schematic drawn on the back of an enveleope
and put in a scanner is the way I would likely convey the information.
You may prefer to use a schematic capture tool which is fine.
A simplified schematic showing the intended ADC interface circuitry is all
that\'s needed.

The stuff being sensed is slow. The accuracy requirement is 3% if I
recall. As I said, I\'m looking to design the very tiny analog portion of
this circuit to preserve as much accuracy as I can.

I really don\'t get why you would need to understand every aspect of the
sensors.

Well if I were designing an interface from a sensor to an ADC then some of
the things which might go through my mind are:

What is the source impedance and voltage or current range coming in from the
sensor?
Single ended or differential?
What bandwidth do I need?
What is the input impedance of the ADC and what voltage range is needed?

If you already have an intended circuit for that then it should easily fit
on the back of an envelope.

One of them is a differential pressure sensor for an orifice based flow
rate sensor with a 0 to 6 kPa range with a 5 volt Vdd and an output scaled
to Vdd. The signal being sensed is the human breath with a cycle time of 2
seconds minimum. Not sure of the upper frequency limit, but the initial
edges start off rater steeply, so perhaps 100 Hz.

Ok well 100 Hz is not the hardest frequency to deal with so do you already
have an intended interface schematic from this sensor to your ADC?

?Does any of that help?

A little. A schematic would help a lot more than a Google drive with so many
documents that there\'s no way I would know which, if any, is relevant.

The 3.3V for Vcco is ratiod from the 5V sensor supply as the output value is a fraction of the sensor supply. Vref at Diff + input is half supply voltage. This may not be of value though. I\'m pretty tired and I have a hundred other things I\'m looking at. I don\'t think I work this hard when I get paid to do this stuff. But at least I get to do it on my own without having to get consensus from a dozen other people some of who don\'t even do hardware.

3.3V |
--- |
| |
+----| Vcco
|
+----| Sq Wave
| |
\\ |
Rb-C1 TC ~10 ms Rb / |
\\ |
/ |
Gnd C1 | |
|---||---+----| +
Vref |
+--\\/\\/-+ Gnd C2 |
5V | | |---||---+ |Diff In
Sensor +--|\\ | | |
|\\ | >--+---/\\/\\/----+----| -
| >--\\/\\/-+--|/ Ra | |
|/ | \\ |
\\ Ra / |
/ \\ |
\\ / |
/ | |
| +----| D-S Out
--- |
Gnd

I\'m not sure if I can eliminate the voltage divider on the output of the 5V sensor if I make the two Ra resistors different values. That would let me eliminate the op amp as well. Yeah, I\'m pretty sure I can. Put two Ra in series for the input and a single Ra from the D-S output and the input range should be 0 to 5V. The ADC output sample rate is 200 SPS with a clock of 33.556632 MHz. MEMS clocks are custom programmed at Digikey from blanks. Just as rapid delivery as stock crystals and they seem just as good, 25 ppm. I guess they laser a PN on them when they program them. Some table top machine I\'m sure. Keep the hopper filled and they can ship thousands per day.

There will be four or more ADC like this and they can all share the Vref signal. But I don\'t see that this is really much better than just a simple divider. Slightly better accuracy from the single resistor instead of two.

ASCII art was more fun than banging VHDL.

--

Rick C.

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

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer
wrote:
Rickster C wrote:

The 3.3V for Vcco is ratiod from the 5V sensor supply as the output value
is a fraction of the sensor supply. Vref at Diff + input is half supply
voltage. This may not be of value though. I\'m pretty tired and I have a
hundred other things I\'m looking at. I don\'t think I work this hard when I
get paid to do this stuff. But at least I get to do it on my own without
having to get consensus from a dozen other people some of who don\'t even do
hardware.

3.3V |
--- |
| |
+----| Vcco
|
+----| Sq Wave
| |
\\ |
Rb-C1 TC ~10 ms Rb / |
\\ |
/ |
Gnd C1 | |
|---||---+----| +
Vref |
+--\\/\\/-+ Gnd C2 |
5V | | |---||---+ |Diff In
Sensor +--|\\ | | |
|\\ | >--+---/\\/\\/----+----| -
| >--\\/\\/-+--|/ Ra | |
|/ | \\ |
\\ Ra / |
/ \\ |
\\ / |
/ | |
| +----| D-S Out
--- |
Gnd

Ok well if I wanted a 1.65V reference for a sensitive ADC circuit I\'d avoid
square waves unless there was some good reason why they couldn\'t be avoided.
Noise generated by fast transitions can easily end up in unexpected places.

I\'d be more likely to have a look here if an external reference was needed:
https://www.google.com/search?q=1.65V+precision+reference&tbm=isch

Assuming it wasn\'t sufficient to just use two resistors, or two resistors
and an op amp.

I\'m tired too and will be away for the next 24 hours.

What is D-S Out?

 

[Rickster C]

On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde wrote:

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer
wrote:
Rickster C wrote:

The 3.3V for Vcco is ratiod from the 5V sensor supply as the output value
is a fraction of the sensor supply. Vref at Diff + input is half supply
voltage. This may not be of value though. I\'m pretty tired and I have a
hundred other things I\'m looking at. I don\'t think I work this hard when I
get paid to do this stuff. But at least I get to do it on my own without
having to get consensus from a dozen other people some of who don\'t even do
hardware.

3.3V |
--- |
| |
+----| Vcco
|
+----| Sq Wave
| |
\\ |
Rb-C1 TC ~10 ms Rb / |
\\ |
/ |
Gnd C1 | |
|---||---+----| +
Vref |
+--\\/\\/-+ Gnd C2 |
5V | | |---||---+ |Diff In
Sensor +--|\\ | | |
|\\ | >--+---/\\/\\/----+----| -
| >--\\/\\/-+--|/ Ra | |
|/ | \\ |
\\ Ra / |
/ \\ |
\\ / |
/ | |
| +----| D-S Out
--- |
Gnd

Ok well if I wanted a 1.65V reference for a sensitive ADC circuit I\'d avoid
square waves unless there was some good reason why they couldn\'t be avoided.
Noise generated by fast transitions can easily end up in unexpected places.

I\'d be more likely to have a look here if an external reference was needed:
https://www.google.com/search?q=1.65V+precision+reference&tbm=isch

Assuming it wasn\'t sufficient to just use two resistors, or two resistors
and an op amp.

I\'m tired too and will be away for the next 24 hours.

What is D-S Out?

Do you see the circuit? Oh, you are asking about D-S out, so I guess not. Searching I see I didn\'t mention this is a sigma-delta ADC input. As I said, I\'m very tired at the moment.

Are you familiar with those? You should also note that I mentioned the bandwidth of the signal can be limited to 100 Hz with no ill effects which the capacitors should accomplish just fine.

Heck, the O2 sensor has a 90% rise time of 5 seconds. We\'ll run a low pass filter on the 200 Hz measurement to get lots of precision and low noise. The pressure sensors are the sort of signal you see on hospital TV shows.

I\'m off to have a bit of ice cream and bed. Tired am I.

--

Rick C.

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

 

[Jeroen Belleman]

On 2020-11-05 02:16, Rickster C wrote:

On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert
Baer wrote:
Rickster C wrote:
I recall a thread sometime in the last year that mentioned
an idea for generating an accurate voltage at half the
supply rail by switching an output at a 50/50 duty cycle to
feed an RC. I can\'t seem to find that thread. I\'m
wondering what the limitations might be on the accuracy.
Obviously the difference in drive capability is a factor,
but that can be mitigated by the external resistor.

Maybe something along the lines of this?

If you want it accurate, use feedback to adjust the duty cycle.

Jeroen Belleman


Sorry, I seem to have messed that up. Let\'s try again...

Sorry, I don\'t understand. The inductor is grounded on the end that
looks like it should be the output. The waveforms are all sloped
square waves. What am I missing?

Not sure how I would determine how to apply feedback. What would be
the measurement to use to set the feedback? I don\'t have a way to
measure the voltage. That\'s the point, to provide a reference
voltage at Vcc/2 without active monitoring or control.[...]

You wanted this to provide a reference??? Sorry, I assumed you
wanted a power rail splitter.

Forget it then. You need a simple resistor divider, maybe
buffered with a unit gain amp.

Jeroen Belleman

 

[Rickster C]

On Thursday, November 5, 2020 at 2:37:38 AM UTC-5, Jeroen Belleman wrote:

On 2020-11-05 02:16, Rickster C wrote:
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert
Baer wrote:
Rickster C wrote:
I recall a thread sometime in the last year that mentioned
an idea for generating an accurate voltage at half the
supply rail by switching an output at a 50/50 duty cycle to
feed an RC. I can\'t seem to find that thread. I\'m
wondering what the limitations might be on the accuracy.
Obviously the difference in drive capability is a factor,
but that can be mitigated by the external resistor.

Maybe something along the lines of this?

If you want it accurate, use feedback to adjust the duty cycle.

Jeroen Belleman


Sorry, I seem to have messed that up. Let\'s try again...

Sorry, I don\'t understand. The inductor is grounded on the end that
looks like it should be the output. The waveforms are all sloped
square waves. What am I missing?

Not sure how I would determine how to apply feedback. What would be
the measurement to use to set the feedback? I don\'t have a way to
measure the voltage. That\'s the point, to provide a reference
voltage at Vcc/2 without active monitoring or control.[...]

You wanted this to provide a reference??? Sorry, I assumed you
wanted a power rail splitter.

Forget it then. You need a simple resistor divider, maybe
buffered with a unit gain amp.

Jeroen Belleman

The resistor divider has tolerance related error while the 50/50 thing powered from the same supply as the signal source canceling variations has rather near zero error. Advice is fine, but I was asking if anyone remembered the thread where it was already discussed in detail.

There must be someone who was involved in the thread who remembers the subject line.

--

Rick C.

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

 

[piglet]

On 04/11/2020 9:00 pm, Rickster C wrote:

On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer wrote:
Rickster C wrote:
I recall a thread sometime in the last year that mentioned an idea for generating an accurate voltage at half the supply rail by switching an output at a 50/50 duty cycle to feed an RC. I can\'t seem to find that thread. I\'m wondering what the limitations might be on the accuracy. Obviously the difference in drive capability is a factor, but that can be mitigated by the external resistor.

i suppose there can be differences in the delay times for the two edges within the digital device. That can be mitigated by using a slower cycle. To get a 0.1% tolerance with a ±1 ns timing variation requires the waveform be 0.5 MHz.

Any ideas on other points that may be important? I suppose a quality integrating capacitor might be important as well. Also ceramic caps can be microphonic, so film caps will be needed. In fact I need to specify that all through the sensor power supply.

You mean \"half voltage\".

Thanks, but trying that both with and without the quotes didn\'t turn up the thread going all the way back to December. It couldn\'t have been that long ago could it? Seems like maybe three for four months back.

I\'m not sure how bad it would be to simply use a pair of 0.1% resistors. That would add error somewhere between 0.1% and 0.2% (not thinking about it too hard). There will be other sources of error from this same effect elsewhere (dividing the 5V signal source to 3.3 volts... or maybe not. Perhaps that can be mitigated by not using equal value resistors in the input and feedback paths.

It\'s funny that the other guys on the project don\'t seem to be able to think about this stuff. I guess they are mostly used to just plopping down chips. Heck, a new FPGA guy wanted to use a $20 Xilinx part instead of a $4-5 Gowin part!

I was happy to find I can get 10 nF C0G for under a nickle and 100 nF for around a dime. I thought they didn\'t come that large. They do get large!

If you don\'t think the 0.1% resistive divider is good enough can\'t you
calibrate it out during power-on self test? Or even add a analog switch
mux upstream for sensor sanity checking?

piglet