Did anyone test the noise free bits of msp430's ADC? I just want to know
that how many bits the ADC can reach?
eg, ADC12,the noise free bits can be 11 bits?
THANKS!
what about MSP430's ADC?
Started by ●December 29, 2008
Reply by ●December 29, 20082008-12-29
The noise you see from an ADC12 conversion will depend on the noise of
the source you are converting AND on the noise of your AVcc Supply.
I've seen students battling to reduce the noise of the analog signal
connected to the input, when in fact the noise they were seeing on the
ADC results was comming from the power supply connected to AVcc. If
your voltage reference is noisy, so will be the ADC conversion.
If I remember correctly, the internal voltage reference generator
generates less than 1/2 lsb when using the required 10uF and 0.1uF
capacitors (some people forget to use them!). In any case, there is
some info in the ADC12 chapter about the relationship between
frequency, input resistance and conversion noise.
In my experience, using AVcc as reference and sourcing it directly
from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
10-bit result with little effort, which is enought for many applications.
There are a lot more considerations to take into account when using
ADCs. Usually, you will have a low-pass filter on the ADC input for
anti-aliasing. A software filter might also be in order, but it does
not replace the analog filter.
If you don't know what 'Aliasing' means, then you need to read a good
book on analog to digital conversion, or search more info about ADCs
on the web.
Regards,
Michael K.
--- In m..., "380121850" <380121850@...> wrote:
>
> Did anyone test the noise free bits of msp430's ADC? I just want to
know that how many bits the ADC can reach?
> eg, ADC12,the noise free bits can be 11 bits?
> THANKS!
>
>
>
the source you are converting AND on the noise of your AVcc Supply.
I've seen students battling to reduce the noise of the analog signal
connected to the input, when in fact the noise they were seeing on the
ADC results was comming from the power supply connected to AVcc. If
your voltage reference is noisy, so will be the ADC conversion.
If I remember correctly, the internal voltage reference generator
generates less than 1/2 lsb when using the required 10uF and 0.1uF
capacitors (some people forget to use them!). In any case, there is
some info in the ADC12 chapter about the relationship between
frequency, input resistance and conversion noise.
In my experience, using AVcc as reference and sourcing it directly
from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
10-bit result with little effort, which is enought for many applications.
There are a lot more considerations to take into account when using
ADCs. Usually, you will have a low-pass filter on the ADC input for
anti-aliasing. A software filter might also be in order, but it does
not replace the analog filter.
If you don't know what 'Aliasing' means, then you need to read a good
book on analog to digital conversion, or search more info about ADCs
on the web.
Regards,
Michael K.
--- In m..., "380121850" <380121850@...> wrote:
>
> Did anyone test the noise free bits of msp430's ADC? I just want to
know that how many bits the ADC can reach?
> eg, ADC12,the noise free bits can be 11 bits?
> THANKS!
>
>
>
Reply by ●December 29, 20082008-12-29
Hello, u can try oversampling ADC in your code if u have time resources to do
that. I didnt tried ADC, but maybe this will help u.
Pozdrav Milan Baltic
--- On Mon, 29/12/08, 380121850 <3...@163.com> wrote:
From: 380121850 <3...@163.com>
Subject: [msp430] what about MSP430's ADC?
To: "msp430"
Date: Monday, 29 December, 2008, 9:38 AM
Did anyone test the noise free bits of msp430's ADC? I just want to know that how many bits the ADC can reach?
eg, ADC12,the noise free bits can be 11 bits?
THANKS!
Pozdrav Milan Baltic
--- On Mon, 29/12/08, 380121850 <3...@163.com> wrote:
From: 380121850 <3...@163.com>
Subject: [msp430] what about MSP430's ADC?
To: "msp430"
Date: Monday, 29 December, 2008, 9:38 AM
Did anyone test the noise free bits of msp430's ADC? I just want to know that how many bits the ADC can reach?
eg, ADC12,the noise free bits can be 11 bits?
THANKS!
Reply by ●December 29, 20082008-12-29
Thanks!
but if I used the internal voltage reference 1.5V,can I get more bits? and HOW about the effect on the internal voltage reference 1.5V with the noise of the AVcc?
Best Regards!
............The noise you see from an ADC12 conversion will depend on the noise of
the source you are converting AND on the noise of your AVcc Supply..........
.........If I remember correctly, the internal voltage reference generator
generates less than 1/2 lsb when using the required 10uF and 0.1uF
capacitors (some people forget to use them!). .......................
..............In my experience, using AVcc as reference and sourcing it directly
from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
10-bit result with little effort, which is enought for many applications.
...........................
发件人： tintronic
发送时间： 2008-12-29 23:52:46
收件人： msp430
抄送：
主题： [msp430] Re: what about MSP430's ADC?
The noise you see from an ADC12 conversion will depend on the noise of
the source you are converting AND on the noise of your AVcc Supply.
I've seen students battling to reduce the noise of the analog signal
connected to the input, when in fact the noise they were seeing on the
ADC results was comming from the power supply connected to AVcc. If
your voltage reference is noisy, so will be the ADC conversion.
If I remember correctly, the internal voltage reference generator
generates less than 1/2 lsb when using the required 10uF and 0.1uF
capacitors (some people forget to use them!). In any case, there is
some info in the ADC12 chapter about the relationship between
frequency, input resistance and conversion noise.
In my experience, using AVcc as reference and sourcing it directly
from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
10-bit result with little effort, which is enought for many applications.
There are a lot more considerations to take into account when using
ADCs. Usually, you will have a low-pass filter on the ADC input for
anti-aliasing. A software filter might also be in order, but it does
not replace the analog filter.
If you don't know what 'Aliasing' means, then you need to read a good
book on analog to digital conversion, or search more info about ADCs
on the web.
Regards,
Michael K.
--- In m..., "380121850" <380121850@...> wrote:
>
> Did anyone test the noise free bits of msp430's ADC? I just want to
know that how many bits the ADC can reach?
> eg, ADC12,the noise free bits can be 11 bits?
> THANKS!
>
>
>
>
>
>
>
>
>
but if I used the internal voltage reference 1.5V,can I get more bits? and HOW about the effect on the internal voltage reference 1.5V with the noise of the AVcc?
Best Regards!
............The noise you see from an ADC12 conversion will depend on the noise of
the source you are converting AND on the noise of your AVcc Supply..........
.........If I remember correctly, the internal voltage reference generator
generates less than 1/2 lsb when using the required 10uF and 0.1uF
capacitors (some people forget to use them!). .......................
..............In my experience, using AVcc as reference and sourcing it directly
from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
10-bit result with little effort, which is enought for many applications.
...........................
发件人： tintronic
发送时间： 2008-12-29 23:52:46
收件人： msp430
抄送：
主题： [msp430] Re: what about MSP430's ADC?
The noise you see from an ADC12 conversion will depend on the noise of
the source you are converting AND on the noise of your AVcc Supply.
I've seen students battling to reduce the noise of the analog signal
connected to the input, when in fact the noise they were seeing on the
ADC results was comming from the power supply connected to AVcc. If
your voltage reference is noisy, so will be the ADC conversion.
If I remember correctly, the internal voltage reference generator
generates less than 1/2 lsb when using the required 10uF and 0.1uF
capacitors (some people forget to use them!). In any case, there is
some info in the ADC12 chapter about the relationship between
frequency, input resistance and conversion noise.
In my experience, using AVcc as reference and sourcing it directly
from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
10-bit result with little effort, which is enought for many applications.
There are a lot more considerations to take into account when using
ADCs. Usually, you will have a low-pass filter on the ADC input for
anti-aliasing. A software filter might also be in order, but it does
not replace the analog filter.
If you don't know what 'Aliasing' means, then you need to read a good
book on analog to digital conversion, or search more info about ADCs
on the web.
Regards,
Michael K.
--- In m..., "380121850" <380121850@...> wrote:
>
> Did anyone test the noise free bits of msp430's ADC? I just want to
know that how many bits the ADC can reach?
> eg, ADC12,the noise free bits can be 11 bits?
> THANKS!
>
>
>
>
>
>
>
>
>
Reply by ●December 29, 20082008-12-29
the internal voltage reference is only accurate to 4 or 5 bits.
don't know if you are interested in absolute accuracy or just
relative accuracy
the a/d itself is very good with a good external reference, which is
the limiting factor.
Now a days it's fairly easy to get a 16 bit a/d to toggle only one
bit even when powered by a noise switcher (with proper filtering and
layout)
--- In m..., "380121850" <380121850@...> wrote:
>
> Thanks!
> but if I used the internal voltage reference 1.5V,can I get
more bits? and HOW about the effect on the internal voltage reference
1.5V with the noise of the AVcc?
>
> Best Regards!
>
> ............The noise you see from an ADC12 conversion will depend
on the noise of
> the source you are converting AND on the noise of your AVcc
Supply..........
> .........If I remember correctly, the internal voltage reference
generator
> generates less than 1/2 lsb when using the required 10uF and 0.1uF
> capacitors (some people forget to use
them!). .......................
> ..............In my experience, using AVcc as reference and
sourcing it directly
> from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
> 10-bit result with little effort, which is enought for many
applications.
> ...........................
>
>
>
>
>
>
> 件人： tintronic
> 送时间： 2008-12-29 23:52:46
> 件人： msp430
> 抄送：
> 主题： [msp430] Re: what about MSP430's ADC?
>
> The noise you see from an ADC12 conversion will depend on the noise
of
> the source you are converting AND on the noise of your AVcc Supply.
> I've seen students battling to reduce the noise of the analog signal
> connected to the input, when in fact the noise they were seeing on
the
> ADC results was comming from the power supply connected to AVcc. If
> your voltage reference is noisy, so will be the ADC conversion.
> If I remember correctly, the internal voltage reference generator
> generates less than 1/2 lsb when using the required 10uF and 0.1uF
> capacitors (some people forget to use them!). In any case, there is
> some info in the ADC12 chapter about the relationship between
> frequency, input resistance and conversion noise.
> In my experience, using AVcc as reference and sourcing it directly
> from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
> 10-bit result with little effort, which is enought for many
applications.
> There are a lot more considerations to take into account when using
> ADCs. Usually, you will have a low-pass filter on the ADC input for
> anti-aliasing. A software filter might also be in order, but it does
> not replace the analog filter.
> If you don't know what 'Aliasing' means, then you need to read a
good
> book on analog to digital conversion, or search more info about ADCs
> on the web.
>
> Regards,
> Michael K.
>
> --- In m..., "380121850" <380121850@> wrote:
> >
> > Did anyone test the noise free bits of msp430's ADC? I just want
to
> know that how many bits the ADC can reach?
> > eg, ADC12,the noise free bits can be 11 bits?
> > THANKS!
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>
>
>
>
>
don't know if you are interested in absolute accuracy or just
relative accuracy
the a/d itself is very good with a good external reference, which is
the limiting factor.
Now a days it's fairly easy to get a 16 bit a/d to toggle only one
bit even when powered by a noise switcher (with proper filtering and
layout)
--- In m..., "380121850" <380121850@...> wrote:
>
> Thanks!
> but if I used the internal voltage reference 1.5V,can I get
more bits? and HOW about the effect on the internal voltage reference
1.5V with the noise of the AVcc?
>
> Best Regards!
>
> ............The noise you see from an ADC12 conversion will depend
on the noise of
> the source you are converting AND on the noise of your AVcc
Supply..........
> .........If I remember correctly, the internal voltage reference
generator
> generates less than 1/2 lsb when using the required 10uF and 0.1uF
> capacitors (some people forget to use
them!). .......................
> ..............In my experience, using AVcc as reference and
sourcing it directly
> from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
> 10-bit result with little effort, which is enought for many
applications.
> ...........................
>
>
>
>
>
>
> 件人： tintronic
> 送时间： 2008-12-29 23:52:46
> 件人： msp430
> 抄送：
> 主题： [msp430] Re: what about MSP430's ADC?
>
> The noise you see from an ADC12 conversion will depend on the noise
of
> the source you are converting AND on the noise of your AVcc Supply.
> I've seen students battling to reduce the noise of the analog signal
> connected to the input, when in fact the noise they were seeing on
the
> ADC results was comming from the power supply connected to AVcc. If
> your voltage reference is noisy, so will be the ADC conversion.
> If I remember correctly, the internal voltage reference generator
> generates less than 1/2 lsb when using the required 10uF and 0.1uF
> capacitors (some people forget to use them!). In any case, there is
> some info in the ADC12 chapter about the relationship between
> frequency, input resistance and conversion noise.
> In my experience, using AVcc as reference and sourcing it directly
> from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
> 10-bit result with little effort, which is enought for many
applications.
> There are a lot more considerations to take into account when using
> ADCs. Usually, you will have a low-pass filter on the ADC input for
> anti-aliasing. A software filter might also be in order, but it does
> not replace the analog filter.
> If you don't know what 'Aliasing' means, then you need to read a
good
> book on analog to digital conversion, or search more info about ADCs
> on the web.
>
> Regards,
> Michael K.
>
> --- In m..., "380121850" <380121850@> wrote:
> >
> > Did anyone test the noise free bits of msp430's ADC? I just want
to
> know that how many bits the ADC can reach?
> > eg, ADC12,the noise free bits can be 11 bits?
> > THANKS!
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>
>
>
>
>
Reply by ●December 29, 20082008-12-29
Actually, the internal reference can go to 1/2LSB but it is, of course, relative
because each band gap comes
with slight different value because silicon processing. So, to compensate the differences between each MSP430
you need a calibration procedure using an external calibrated source for measuring the top value (and using GND
to measure bottom). Then with simple math you can add an offset and multiply by a factor to get all MSPs
reading the same value down to 1/2LSB in the full 12 bit range.
I cannot recall if 1/2LSB works for 1.5V reference. It does work very well for 2.5V in my designs. The 10uF cap
at Vref is mandatory. Use Tantalum for better stability.
If you need an input buffer (with any AmpOp of your choice) use a small negative power supply in this AmpOp to
compensate the input offset (to be able to reach zero with 0V input).
-Augusto
---------- Cabelho original -----------
De: m...
Para: m...
Cia:
Data: Tue, 30 Dec 2008 02:18:30 -0000
Assunto: [msp430] Re: what about MSP430's ADC?
>
> the internal voltage reference is only accurate to 4 or 5 bits.
>
> don't know if you are interested in absolute accuracy or just
> relative accuracy
>
> the a/d itself is very good with a good external reference, which is
> the limiting factor.
>
> Now a days it's fairly easy to get a 16 bit a/d to toggle only one
> bit even when powered by a noise switcher (with proper filtering and
> layout)
>
>
> --- In m..., "380121850" <380121850@...> wrote:
> >
> > Thanks!
> > but if I used the internal voltage reference 1.5V,can I get
> more bits? and HOW about the effect on the internal voltage reference
> 1.5V with the noise of the AVcc?
> >
> > Best Regards!
> >
> > ............The noise you see from an ADC12 conversion will depend
> on the noise of
> > the source you are converting AND on the noise of your AVcc
> Supply..........
> > .........If I remember correctly, the internal voltage reference
> generator
> > generates less than 1/2 lsb when using the required 10uF and 0.1uF
> > capacitors (some people forget to use
> them!). .......................
> > ..............In my experience, using AVcc as reference and
> sourcing it directly
> > from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
> > 10-bit result with little effort, which is enought for many
> applications.
> > ...........................
> >
> >
> >
> >
> >
> >
> > 件人： tintronic
> > 送时间： 2008-12-29 23:52:46
> > 件人： msp430
> > 抄送：
> > 主题： [msp430] Re: what about MSP430's ADC?
> >
> > The noise you see from an ADC12 conversion will depend on the noise
> of
> > the source you are converting AND on the noise of your AVcc Supply.
> > I've seen students battling to reduce the noise of the analog signal
> > connected to the input, when in fact the noise they were seeing on
> the
> > ADC results was comming from the power supply connected to AVcc. If
> > your voltage reference is noisy, so will be the ADC conversion.
> > If I remember correctly, the internal voltage reference generator
> > generates less than 1/2 lsb when using the required 10uF and 0.1uF
> > capacitors (some people forget to use them!). In any case, there is
> > some info in the ADC12 chapter about the relationship between
> > frequency, input resistance and conversion noise.
> > In my experience, using AVcc as reference and sourcing it directly
> > from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
> > 10-bit result with little effort, which is enought for many
> applications.
> > There are a lot more considerations to take into account when using
> > ADCs. Usually, you will have a low-pass filter on the ADC input for
> > anti-aliasing. A software filter might also be in order, but it does
> > not replace the analog filter.
> > If you don't know what 'Aliasing' means, then you need to read a
> good
> > book on analog to digital conversion, or search more info about ADCs
> > on the web.
> >
> > Regards,
> > Michael K.
> >
> > --- In m..., "380121850" <380121850@> wrote:
> > >
> > > Did anyone test the noise free bits of msp430's ADC? I just want
> to
> > know that how many bits the ADC can reach?
> > > eg, ADC12,the noise free bits can be 11 bits?
> > > THANKS!
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> >
> >
> >
> >
> >
> >
> >
>
>
>
with slight different value because silicon processing. So, to compensate the differences between each MSP430
you need a calibration procedure using an external calibrated source for measuring the top value (and using GND
to measure bottom). Then with simple math you can add an offset and multiply by a factor to get all MSPs
reading the same value down to 1/2LSB in the full 12 bit range.
I cannot recall if 1/2LSB works for 1.5V reference. It does work very well for 2.5V in my designs. The 10uF cap
at Vref is mandatory. Use Tantalum for better stability.
If you need an input buffer (with any AmpOp of your choice) use a small negative power supply in this AmpOp to
compensate the input offset (to be able to reach zero with 0V input).
-Augusto
---------- Cabelho original -----------
De: m...
Para: m...
Cia:
Data: Tue, 30 Dec 2008 02:18:30 -0000
Assunto: [msp430] Re: what about MSP430's ADC?
>
> the internal voltage reference is only accurate to 4 or 5 bits.
>
> don't know if you are interested in absolute accuracy or just
> relative accuracy
>
> the a/d itself is very good with a good external reference, which is
> the limiting factor.
>
> Now a days it's fairly easy to get a 16 bit a/d to toggle only one
> bit even when powered by a noise switcher (with proper filtering and
> layout)
>
>
> --- In m..., "380121850" <380121850@...> wrote:
> >
> > Thanks!
> > but if I used the internal voltage reference 1.5V,can I get
> more bits? and HOW about the effect on the internal voltage reference
> 1.5V with the noise of the AVcc?
> >
> > Best Regards!
> >
> > ............The noise you see from an ADC12 conversion will depend
> on the noise of
> > the source you are converting AND on the noise of your AVcc
> Supply..........
> > .........If I remember correctly, the internal voltage reference
> generator
> > generates less than 1/2 lsb when using the required 10uF and 0.1uF
> > capacitors (some people forget to use
> them!). .......................
> > ..............In my experience, using AVcc as reference and
> sourcing it directly
> > from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
> > 10-bit result with little effort, which is enought for many
> applications.
> > ...........................
> >
> >
> >
> >
> >
> >
> > 件人： tintronic
> > 送时间： 2008-12-29 23:52:46
> > 件人： msp430
> > 抄送：
> > 主题： [msp430] Re: what about MSP430's ADC?
> >
> > The noise you see from an ADC12 conversion will depend on the noise
> of
> > the source you are converting AND on the noise of your AVcc Supply.
> > I've seen students battling to reduce the noise of the analog signal
> > connected to the input, when in fact the noise they were seeing on
> the
> > ADC results was comming from the power supply connected to AVcc. If
> > your voltage reference is noisy, so will be the ADC conversion.
> > If I remember correctly, the internal voltage reference generator
> > generates less than 1/2 lsb when using the required 10uF and 0.1uF
> > capacitors (some people forget to use them!). In any case, there is
> > some info in the ADC12 chapter about the relationship between
> > frequency, input resistance and conversion noise.
> > In my experience, using AVcc as reference and sourcing it directly
> > from DVcc (with a 100nF btpass cap), you can obtain a 'noise-free'
> > 10-bit result with little effort, which is enought for many
> applications.
> > There are a lot more considerations to take into account when using
> > ADCs. Usually, you will have a low-pass filter on the ADC input for
> > anti-aliasing. A software filter might also be in order, but it does
> > not replace the analog filter.
> > If you don't know what 'Aliasing' means, then you need to read a
> good
> > book on analog to digital conversion, or search more info about ADCs
> > on the web.
> >
> > Regards,
> > Michael K.
> >
> > --- In m..., "380121850" <380121850@> wrote:
> > >
> > > Did anyone test the noise free bits of msp430's ADC? I just want
> to
> > know that how many bits the ADC can reach?
> > > eg, ADC12,the noise free bits can be 11 bits?
> > > THANKS!
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> >
> >
> >
> >
> >
> >
> >
>
>
>
Reply by ●December 30, 20082008-12-30
The 12bit adc of the MSP430 is a pretty good one. Possibly the best
we have found in any microcontroller. It is very usable. Best with an
external reference, of course, but it is decent with the internal one
as well. How many bits you can resolve depends heavily on the whole
circuit. With a good layout, appropriate filtering, a low impedance
source on the analog input of the adc, etc... you can obtain 10bit
stable single readings, taken at random time, which is pretty good.
What we normally do, however, is to average a fair number of
readings, that will greately improve the result. In certain
applications we found that a properly tuned "system" can achieve the
equivalent of 13-14 bits of useful resolution. So the the number of
useful bits available depends on the application: fast conversion
approx. 10 bit, slow averaged conversion up to 14.
we have found in any microcontroller. It is very usable. Best with an
external reference, of course, but it is decent with the internal one
as well. How many bits you can resolve depends heavily on the whole
circuit. With a good layout, appropriate filtering, a low impedance
source on the analog input of the adc, etc... you can obtain 10bit
stable single readings, taken at random time, which is pretty good.
What we normally do, however, is to average a fair number of
readings, that will greately improve the result. In certain
applications we found that a properly tuned "system" can achieve the
equivalent of 13-14 bits of useful resolution. So the the number of
useful bits available depends on the application: fast conversion
approx. 10 bit, slow averaged conversion up to 14.
