----- Original Message -----
From: "Matthias Weingart" <msp430@msp4...>
To: <msp430@msp4...>
Sent: Tuesday, May 24, 2005 7:45 PM
Subject: Re: [msp430] ADC noise created by external crystal oscillator
> On Wed, May 18, 2005 at 11:30:11PM -0000, Joel
Acevedo wrote:
>
>> How should I connect the crystal oscillator, could this be the cause?
>>
>> Does anyone know the cause of this and how can I solve it?
>
> 1. Switch the XTAL off during ADC sampling.
> or
> 2. Do not connect the XTAL capacitors to the GND-plane
> use a single wire to the GND pin of the MSP430 instead
> (should not be in series with any AGND current path)
I always connect the crystal that way on any board I design. I never have
any ADC problems, even on single-sided PCBs.
Leon
--
Leon Heller, G1HSM
http://webspace.webring.com/people/jl/leon_heller/
On Wed, May 18, 2005 at 11:30:11PM -0000, Joel Acevedo wrote:
> How should I connect the crystal oscillator, could
this be the cause?
>
> Does anyone know the cause of this and how can I solve it?
1. Switch the XTAL off during ADC sampling.
or
2. Do not connect the XTAL capacitors to the GND-plane
use a single wire to the GND pin of the MSP430 instead
(should not be in series with any AGND current path)
Matthias
Reply by Joel Acevedo●May 18, 20052005-05-18
Hello:
I'm using the MSP430F149 ADC unit to sample a signal generated by a
waveform generator (a sine wave). Whenever I run the program a high
frequency sinusoid is added to the input sinusoid resulting in noisy
signal. I noticed that the frequency of the noise sinusoid is 4.8 MHz
which is the exact frequency of the external crystal oscilator I am
using as system clock. If I use the MSP internal clock and turn the
external oscilator off, the 4.8MHz sinusoid disappears. Still, I get
some noise (with a lower frequency) in the input signal
caused ,aparently ,by the internal system clock.
How should I connect the crystal oscillator, could this be the cause?
Does anyone know the cause of this and how can I solve it?
Any ideas will be really appreciated.
Joel