strange ADC spikes

[olo]

Hello,

I'm experiencing voltage spikes on the output, but the strange thing
about that is these spikes are generated only if the input voltage
reaches certain levels and it doesn't matter how I "clock" the ADC
(2KHz to 40MHz).
(ADC is 8bit TDA8703) For example when the input constant signal is in
the middle D70=128 there are spikes to D70=255, another example
input signal should be convert to something about D70=150 but there
are spikes to the level of 170. There are several more levels where
these spikes are generated. At differentinput voltage levels spikes
have different amplitude, but constant for a certain levels. I assume
this is not a standard noise.

What's wrong with it ?

thanks in advance

Olo

 

[John Larkin]

On 5 Mar 2005 10:45:37 -0800, olo_666@wp.pl (olo) wrote:

Hello,

I'm experiencing voltage spikes on the output, but the strange thing
about that is these spikes are generated only if the input voltage
reaches certain levels and it doesn't matter how I "clock" the ADC
(2KHz to 40MHz).
(ADC is 8bit TDA8703) For example when the input constant signal is in
the middle D70=128 there are spikes to D70=255, another example
input signal should be convert to something about D70=150 but there
are spikes to the level of 170. There are several more levels where
these spikes are generated. At differentinput voltage levels spikes
have different amplitude, but constant for a certain levels. I assume
this is not a standard noise.

What's wrong with it ?

thanks in advance

Olo

It may be normal. Are you sampling the data at the proper "valid" time
relative to the clock? It has a right to do anything outside the
valid-data window.

But it's a discontinued part!

John

 

[olo]

John Larkin wrote in message news:

It may be normal. Are you sampling the data at the proper "valid" time
relative to the clock? It has a right to do anything outside the
valid-data window.

No, I've been taking samples at any time, but when I'm looking at
timing diagram I've been doing wrong . I'll check this out.

But it's a discontinued part!

yes, but quite cheap and easy to get in Poland

thanks for advice

olo