Hi Zack, thank you for these good tutorials! I have a question about the input impedence. Why is the input trace of isolate ADC wider than non-isolate ADC? I am a little confused about when i should control the impedance.
Those lines are the same width in the PCB layout. The reason the impedance is not controlled in this layout is two reasons: 1) The main reason is that these components do not have an input impedance specification that is controlled to a specific value like 50 Ohms, so you are not matching to a specific impedance. ADCs intended for sub-GHz signals have capacitive input impedance. 2) The frequencies at which this equipment will operate are assumed to be very low based on the sample rate of the ADC (kHz signal frequency range). So therefore the signal source only sees the ADC input as its load because the lines will most likely be electrically short. If these ADCs are only sampling a 10 kHz signal, then the wavelength of that signal will be very long, so the input impedance looking from the signal source to the ADC will be very close to the ADC input impedance. This means we ignore the coax input impedance and the trace impedance.
Thanks for always giving such good tutorials! Would you please talk about I2S as well for DAC?hardly find information for that layout. Should I2S have impedance control?length matched? Thanks again!
You don't need to split the ground plane in normal analog measurements. All you need to do proper separation of analog and digital regions. In high-resolution converters, you need to isolate the grounds with a moat. In this case, the ADC is isolated in nature but still, you can join the ground. I can explain the moat concept in the ground plane but it is hard to explain in writing🙂
You're right there is no requirement to split the ground plane in analog measurements, I've said that many times. The point of the isolated ADC is to have complete galvanic isolation between those two sides. Yes you can connect those grounds, but you don't have true galvanic isolation according to the strict definition of the term. Connecting them would eliminate any DC or low-frequency offset between the two sides, but it does this by allowing currents to pass between the two sections. If you did this you might interfere with the low level signal you want to sample.
Zack, i had open project file but PCB layout doesnt get open. Does it need any system requirements. I have basic altium system recommendations installed on my PC. Any suggestion why i am unable to open it ?
Another brilliant tutorial 🙂Thank you!
Glad you liked it!
Brilliant!
thank you master!
Hi Zack, thank you for these good tutorials! I have a question about the input impedence. Why is the input trace of isolate ADC wider than non-isolate ADC? I am a little confused about when i should control the impedance.
Those lines are the same width in the PCB layout.
The reason the impedance is not controlled in this layout is two reasons: 1) The main reason is that these components do not have an input impedance specification that is controlled to a specific value like 50 Ohms, so you are not matching to a specific impedance. ADCs intended for sub-GHz signals have capacitive input impedance. 2) The frequencies at which this equipment will operate are assumed to be very low based on the sample rate of the ADC (kHz signal frequency range). So therefore the signal source only sees the ADC input as its load because the lines will most likely be electrically short. If these ADCs are only sampling a 10 kHz signal, then the wavelength of that signal will be very long, so the input impedance looking from the signal source to the ADC will be very close to the ADC input impedance. This means we ignore the coax input impedance and the trace impedance.
Thanks for always giving such good tutorials!
Would you please talk about I2S as well for DAC?hardly find information for that layout. Should I2S have impedance control?length matched? Thanks again!
Noted
You don't need to split the ground plane in normal analog measurements. All you need to do proper separation of analog and digital regions. In high-resolution converters, you need to isolate the grounds with a moat. In this case, the ADC is isolated in nature but still, you can join the ground. I can explain the moat concept in the ground plane but it is hard to explain in writing🙂
You're right there is no requirement to split the ground plane in analog measurements, I've said that many times. The point of the isolated ADC is to have complete galvanic isolation between those two sides. Yes you can connect those grounds, but you don't have true galvanic isolation according to the strict definition of the term. Connecting them would eliminate any DC or low-frequency offset between the two sides, but it does this by allowing currents to pass between the two sections. If you did this you might interfere with the low level signal you want to sample.
@@Zachariah-Peterson yes you are right. But using the moat on the ground there won't be any return crurrent issues. I can show that
Zack, i had open project file but PCB layout doesnt get open. Does it need any system requirements. I have basic altium system recommendations installed on my PC. Any suggestion why i am unable to open it ?
I just downloaded from the link and I was able to open it, I am not sure what the problem could be.
I hate the rooms too!