Forums

LPC2000 ADC/DAC

Started by jdauchot December 11, 2007
Hi All

Can someone explain why NXP has liminted the bit resolution to 10 bits
on the ADC and DAC in their chips?

Regards

Jean-Jacques

An Engineer's Guide to the LPC2100 Series

--- In l..., "jdauchot" wrote:
>
> My application requires at least 16 bits ADC for the load cells I have
> to measure.
>
> Regards
>
> Jean-Jacques
It would be a really rare occurance to find a 96dB signal to noise
ratio( 16 bit resolution ) inside a primarily digital chip. They are
doing pretty well if they are actually getting the 60dB or better
needed for 10 bit resolution. An external A/D would probably fit your
requirements better?

--Dave
----- Original Message -----
From: "jdauchot"
To:
Sent: Tuesday, December 11, 2007 5:46 PM
Subject: [lpc2000] LPC2000 ADC/DAC
> Hi All
>
> Can someone explain why NXP has liminted the bit resolution to 10 bits
> on the ADC and DAC in their chips?

Cost?

Leon
On 12/12/07, jdauchot wrote:
> Hi Leon
>
> That does not make sense. Why make chip with 4 cans , 2 uart and
> numerous other interfaces and only provide 10bits ADC/DAC ?
>
> My application requires at least 16 bits ADC for the load cells I have
> to measure.

Depening on the speed, you can take a look at Analog Device.
ADI has some ARM7 MCUs with integrated 16bit ADCs.
If you want high performance, look at Silicon Labs. For
example, C8051F06x series provide 16bit SAR ADCs
with up to 1Msps throughput. It is not that cheap though.

The main stream ARM MCU vendors like NXP/Atmel/ST
do not offer good ADCs.

Xiaofan
--- In l..., "jdauchot" wrote:
>
> Hi Leon
>
> That does not make sense. Why make chip with 4 cans , 2 uart and
> numerous other interfaces and only provide 10bits ADC/DAC ?
>
> My application requires at least 16 bits ADC for the load cells I
have
> to measure.
>
> Regards
>
> Jean-Jacques

Sure, but you are going to build an analog section on your PCB with
very deliberate noise control and highly specialized grounding (guard
rings, etc).

It doesn't make sense to try to build this inside a digital device
with heavy switching transients. The noise would overwhelm the
additional bits.

Richard
Hi Leon

That does not make sense. Why make chip with 4 cans , 2 uart and
numerous other interfaces and only provide 10bits ADC/DAC ?

My application requires at least 16 bits ADC for the load cells I have
to measure.

Regards

Jean-Jacques
--- In l..., "Leon" wrote:
>
> > Hi All
> >
> > Can someone explain why NXP has liminted the bit resolution to 10
bits
> > on the ADC and DAC in their chips?
>
> Cost?
>
> Leon
>
----- Original Message -----
From: "jdauchot"
To:
Sent: Tuesday, December 11, 2007 6:27 PM
Subject: [lpc2000] Re: LPC2000 ADC/DAC
> Hi Leon
>
> That does not make sense. Why make chip with 4 cans , 2 uart and
> numerous other interfaces and only provide 10bits ADC/DAC ?
>
> My application requires at least 16 bits ADC for the load cells I have
> to measure.

ADCs are quite difficult things to put on a chip, and going from 10 bits
to16 is very expensive in terms of chip area and processing. There aren't
very many MCUs with 16 bit ADCs.

Also, it can be quite difficult designing a board for a 16 bit ADC that
enables you to use the added precision; this can be easier with an external
ADC.

Leon
jdauchot Wrote
>That does not make sense. Why make chip with 4 cans , 2 uart and
>numerous other interfaces and only provide 10bits ADC/DAC ?

Notice that those are all digital devices. Digital and analog process's
are quite different. Analog tends to take more die space. Digital tends
to make more noise.

>My application requires at least 16 bits ADC for the load cells I have
>to measure.

That sounds like a ratiometric app. Potentially easier and shouldn't need
a lot of speed. How about these for a starting point?

http://focus.ti.com/docs/prod/folders/print/ads1255.html
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1155,C1001,C1152,P37
907

Robert
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