Guys,
How accurate do you think the ADCs of ARM controllers are?? I am currently
working with LPC2103 and LPC2362. The ADC values are close to the analog
input but not accurate. The sensors I am going to use are quite costly, cost
because of there accuracy, but the ADCs in ARM don't seem to be that
accurate. Can I use any external circuitry to reduce the errors? Any ideas
are welcome...
--
With Regards,
Nishant Agrawal
LPC ADC issue
Started by ●April 22, 2010
Reply by ●April 22, 20102010-04-22
I am currently using LPC175x and LPC176x and used some LPC21xx family mcu.
They are not very good in absolute sense but their adc are good in mcu
sense... so, are you sure you can't do filter them better by hw and by
sw before telling they are so bad? It is not so important the cost of
your sensor/adc/mcu it is more important to know their accuracy and
resolutions and also if they are well interfaced and filtered by hw and
then by sw.
So, in my experience adc inside NXP ARM mcu are quite good (also
compared with other vendors) also if a bit slower for some applications
and I normally achieve their accuracy and resolution parameters without
no much problems.
If you need some help may be helpful describing better your application.
Nishant Agrawal ha scritto:
>
> Guys,
> How accurate do you think the ADCs of ARM controllers are?? I am
> currently working with LPC2103 and LPC2362. The ADC values are close
> to the analog input but not accurate. The sensors I am going to use
> are quite costly, cost because of there accuracy, but the ADCs in ARM
> don't seem to be that accurate. Can I use any external circuitry to
> reduce the errors? Any ideas are welcome...
>
> --
> With Regards,
> Nishant Agrawal
>
They are not very good in absolute sense but their adc are good in mcu
sense... so, are you sure you can't do filter them better by hw and by
sw before telling they are so bad? It is not so important the cost of
your sensor/adc/mcu it is more important to know their accuracy and
resolutions and also if they are well interfaced and filtered by hw and
then by sw.
So, in my experience adc inside NXP ARM mcu are quite good (also
compared with other vendors) also if a bit slower for some applications
and I normally achieve their accuracy and resolution parameters without
no much problems.
If you need some help may be helpful describing better your application.
Nishant Agrawal ha scritto:
>
> Guys,
> How accurate do you think the ADCs of ARM controllers are?? I am
> currently working with LPC2103 and LPC2362. The ADC values are close
> to the analog input but not accurate. The sensors I am going to use
> are quite costly, cost because of there accuracy, but the ADCs in ARM
> don't seem to be that accurate. Can I use any external circuitry to
> reduce the errors? Any ideas are welcome...
>
> --
> With Regards,
> Nishant Agrawal
>
Reply by ●April 22, 20102010-04-22
What kind of inaccuracy are you facing? Absolute? Non-linear? Noise? What
is your target performance?
Have you ensured that your Analog input supply is very well decoupled? Or
even driven by a separate linear regulator? And the Vref?
I get 1% accuracy, which is good enough for me. I know I can get better,
but I just don't need it. I use the LPC1765, by the way.
Of course, if you need accuracy and resolution way beyond this (like 16-bit
resolution with appropriate repeatability) you could use an external ADC
with an SPI or I2C serial link to the processor.
-Ahmad
2010/4/22 M. Manca
> I am currently using LPC175x and LPC176x and used some LPC21xx family mcu.
> They are not very good in absolute sense but their adc are good in mcu
> sense... so, are you sure you can't do filter them better by hw and by
> sw before telling they are so bad? It is not so important the cost of
> your sensor/adc/mcu it is more important to know their accuracy and
> resolutions and also if they are well interfaced and filtered by hw and
> then by sw.
> So, in my experience adc inside NXP ARM mcu are quite good (also
> compared with other vendors) also if a bit slower for some applications
> and I normally achieve their accuracy and resolution parameters without
> no much problems.
> If you need some help may be helpful describing better your application.
>
> Nishant Agrawal ha scritto:
>
> >
> > Guys,
> >
> >
> > How accurate do you think the ADCs of ARM controllers are?? I am
> > currently working with LPC2103 and LPC2362. The ADC values are close
> > to the analog input but not accurate. The sensors I am going to use
> > are quite costly, cost because of there accuracy, but the ADCs in ARM
> > don't seem to be that accurate. Can I use any external circuitry to
> > reduce the errors? Any ideas are welcome...
> >
> > --
> > With Regards,
> > Nishant Agrawal
> >
>
is your target performance?
Have you ensured that your Analog input supply is very well decoupled? Or
even driven by a separate linear regulator? And the Vref?
I get 1% accuracy, which is good enough for me. I know I can get better,
but I just don't need it. I use the LPC1765, by the way.
Of course, if you need accuracy and resolution way beyond this (like 16-bit
resolution with appropriate repeatability) you could use an external ADC
with an SPI or I2C serial link to the processor.
-Ahmad
2010/4/22 M. Manca
> I am currently using LPC175x and LPC176x and used some LPC21xx family mcu.
> They are not very good in absolute sense but their adc are good in mcu
> sense... so, are you sure you can't do filter them better by hw and by
> sw before telling they are so bad? It is not so important the cost of
> your sensor/adc/mcu it is more important to know their accuracy and
> resolutions and also if they are well interfaced and filtered by hw and
> then by sw.
> So, in my experience adc inside NXP ARM mcu are quite good (also
> compared with other vendors) also if a bit slower for some applications
> and I normally achieve their accuracy and resolution parameters without
> no much problems.
> If you need some help may be helpful describing better your application.
>
> Nishant Agrawal ha scritto:
>
> >
> > Guys,
> >
> >
> > How accurate do you think the ADCs of ARM controllers are?? I am
> > currently working with LPC2103 and LPC2362. The ADC values are close
> > to the analog input but not accurate. The sensors I am going to use
> > are quite costly, cost because of there accuracy, but the ADCs in ARM
> > don't seem to be that accurate. Can I use any external circuitry to
> > reduce the errors? Any ideas are welcome...
> >
> > --
> > With Regards,
> > Nishant Agrawal
> >
>
Reply by ●April 22, 20102010-04-22
On Thursday 22 April 2010 05:56:06 am Nishant Agrawal wrote:
> How accurate do you think the ADCs of ARM controllers are?? I am currently
> working with LPC2103 and LPC2362. The ADC values are close to the analog
> input but not accurate. The sensors I am going to use are quite costly,
> cost because of there accuracy, but the ADCs in ARM don't seem to be that
> accurate. Can I use any external circuitry to reduce the errors? Any ideas
> are welcome...
Make sure that you are properly buffering your analog signal before presenting
it to the ADC, and match the output impedance of the buffer to what the ADC is
designed for.
Also keep in mind that the ADC has a reference limit of 3.3V. If you are
expecting 8 bits of accuracy, that's 13mV/bit. If you want the full 10 bits on
the 2103, that's 3mV. Your buffer, VDDa, traces and all that good stuff have to
be taken into account if you want accurate results.
Also note that if you're simply tying VDDa to VDD, you will have to contend
with digital noise in your ADC results.
-A.
> How accurate do you think the ADCs of ARM controllers are?? I am currently
> working with LPC2103 and LPC2362. The ADC values are close to the analog
> input but not accurate. The sensors I am going to use are quite costly,
> cost because of there accuracy, but the ADCs in ARM don't seem to be that
> accurate. Can I use any external circuitry to reduce the errors? Any ideas
> are welcome...
Make sure that you are properly buffering your analog signal before presenting
it to the ADC, and match the output impedance of the buffer to what the ADC is
designed for.
Also keep in mind that the ADC has a reference limit of 3.3V. If you are
expecting 8 bits of accuracy, that's 13mV/bit. If you want the full 10 bits on
the 2103, that's 3mV. Your buffer, VDDa, traces and all that good stuff have to
be taken into account if you want accurate results.
Also note that if you're simply tying VDDa to VDD, you will have to contend
with digital noise in your ADC results.
-A.
Reply by ●April 22, 20102010-04-22
--- In l..., Nishant Agrawal wrote:
>
> Guys,
>
> How accurate do you think the ADCs of ARM controllers are?? I am currently
> working with LPC2103 and LPC2362. The ADC values are close to the analog
> input but not accurate. The sensors I am going to use are quite costly, cost
> because of there accuracy, but the ADCs in ARM don't seem to be that
> accurate. Can I use any external circuitry to reduce the errors? Any ideas
> are welcome...
>
> --
> With Regards,
> Nishant Agrawal
>
Hi,
using the 2103 or the 2362 I would expect slightly better performance of the LPC2362 because the analog supply pins are available for a filtered reference / supply voltage. Check your voltage on the analog supply pins for ripple and do not expect the accuracy of the ADC to be better than the supply voltage the ADC gets. e.g. if you see ripple of 20 mV on the supply voltage you might also get 20mV jitter in your ADC results which is 6-7 LBS at 3V and 10-bit.
Also watch your Vss for the same ripple and make sure both are as clean as you expect your result to be.
If external supplies are nice and clean, there is still the option to switch to a 17xx instead of the LPC2362. The 1700 series has an improved ADC.
Hope this provides some ideas where to look.
Cheers, Bob
btw. may be in the future you can use the LPC1102 instead of the LPC2103, it is REALLY tiny.
Check here: http://tech.groups.yahoo.com/group/lpc2000/message/49062
>
> Guys,
>
> How accurate do you think the ADCs of ARM controllers are?? I am currently
> working with LPC2103 and LPC2362. The ADC values are close to the analog
> input but not accurate. The sensors I am going to use are quite costly, cost
> because of there accuracy, but the ADCs in ARM don't seem to be that
> accurate. Can I use any external circuitry to reduce the errors? Any ideas
> are welcome...
>
> --
> With Regards,
> Nishant Agrawal
>
Hi,
using the 2103 or the 2362 I would expect slightly better performance of the LPC2362 because the analog supply pins are available for a filtered reference / supply voltage. Check your voltage on the analog supply pins for ripple and do not expect the accuracy of the ADC to be better than the supply voltage the ADC gets. e.g. if you see ripple of 20 mV on the supply voltage you might also get 20mV jitter in your ADC results which is 6-7 LBS at 3V and 10-bit.
Also watch your Vss for the same ripple and make sure both are as clean as you expect your result to be.
If external supplies are nice and clean, there is still the option to switch to a 17xx instead of the LPC2362. The 1700 series has an improved ADC.
Hope this provides some ideas where to look.
Cheers, Bob
btw. may be in the future you can use the LPC1102 instead of the LPC2103, it is REALLY tiny.
Check here: http://tech.groups.yahoo.com/group/lpc2000/message/49062
