You are here

How to eliminate SPS noise from SAR ADC appearing on PCB wire? | Cypress Semiconductor

How to eliminate SPS noise from SAR ADC appearing on PCB wire?

Summary: 8 Replies, Latest post by Bob Marlowe on 15 Feb 2017 03:52 AM PST
Verified Answers: 3
Last post
Log in to post new comments.
eleci's picture
User
6 posts

I found there would be some noise appear on the pcb wire connecting to seq SAR ADC component The noise could be observed from OSC. the noise frequency is the same as the "sampe rate(SPS)" of ADC. so the voltage read from ADC is deviated, anyone can help to explain this? 

Attachments: 
eleci's picture
User
6 posts

append: my device type is : CY8C5467LTI-LP003

user_242978793's picture
User
1485 posts

Please post your code so we can check it.

eleci's picture
User
6 posts

Hi Bobgoar,

I use the project as bootable project, you can remove the bootable component.

Thanks for your reply.

user_242978793's picture
User
1485 posts

Okay I checked your SAR setting and found this issue. No vadc_ref  connection see below.  So I changed the input to this but too many DAC's I disabled one of yours and it still doesn't work.  I am sure this is the issue. pictue. I did this because the data sheet says this pin must be driven by an internal DAC.

eleci's picture
User
6 posts

Hi bobgoar,

I use external voltage reference which connect to vadc_ref. The voltage is 2.048v.

Thanks for your reply.

user_1377889's picture
User
10803 posts

I would suggest to check the buffering of the external reference which should be at least 1µF.

 

Bob

eleci's picture
User
6 posts

Hi Bob,

I use the reference chip: LTC6652-2.048(2.048v) connecting to the external ref pin and with 2.2uF*2 (X7R) non-polar capacitors bypass near the pin. (The SAR datasheet suggest capacitor 0.1u~10uF). So Could I say that the internal reference is better than external in this situation?

user_1377889's picture
User
10803 posts

I cannot say which reference is "better". You probably need to check noise on the Vref pin and on the supply rail. Of course you may try using the internal buffered reference.

 

Bob

Log in to post new comments.
RSS Back to Top
Topic locked