10mV ripple on ADCIN
Posted: Mon Nov 04, 2019 11:05 am
Hy, my dso has a 10mV ripple on ADCIN even without the analogboard plugged in.
When i measure VAC on 3.3V and GND i have no ripple
but on ADCIN and GND i do have 1.65V and 10mV ripple.
I thought about unstable 3.3v but since i have no ripple on 3.3v the problem could come from somewhere else.
As far as i have seen on the schematic ADCIN on the digital board is connected to a 2x 100kOhm voltage divider (R21 & R22) and nothing else. Where is that ripple comming from?
Measurements taken with a Fluke 87V
I have to add my digitalboard is modified.
* replaced Header J4 with a FFC connector,
* removed R4 (lcd backlight) and connected it with a smaller resistor to 3.3v
* basically V+ only powers the 3.3v Regulator
+ analogboard has its own filtered boost converter. but its not connected for testing.
When i measure VAC on 3.3V and GND i have no ripple
but on ADCIN and GND i do have 1.65V and 10mV ripple.
I thought about unstable 3.3v but since i have no ripple on 3.3v the problem could come from somewhere else.
As far as i have seen on the schematic ADCIN on the digital board is connected to a 2x 100kOhm voltage divider (R21 & R22) and nothing else. Where is that ripple comming from?
Measurements taken with a Fluke 87V
I have to add my digitalboard is modified.
* replaced Header J4 with a FFC connector,
* removed R4 (lcd backlight) and connected it with a smaller resistor to 3.3v
* basically V+ only powers the 3.3v Regulator
+ analogboard has its own filtered boost converter. but its not connected for testing.