| ??? 04/13/06 13:00 Read: times |
#114205 - Looks great, but... Responding to: ???'s previous message |
Ashish said:
To communicate with the micro controller(Digital section) you usually use an i-coupler such as ADUM series from Analog devices. This i-coupler is placed as a bridge between the Analog and Digital sections of the circuit. Input to output stray capacitance per line is 2.2pF. Assume that you must use 8 lines due to a byte wide accessing of converter, then you end up with 8 x 2.2pF = 17.6pF. This looks negligible, but represents an impedance of only 90 Ohm at 100MHz and of only 9 Ohm at 1GHz! So, still very much of the nasty common mode noise is injected into the analog ground! The common mode rejection is much better at much lower frequencies, though. But at thess frequencies the impedance of a solid ground plane presents a very low impedance, not actually needing this galvanic isolation. What counts with such arrangements is the steepness of edges of digital signals and the common mode noise of the digital ground and these both can only be minimized by sophisticated filtering. Kai |
| Topic | Author | Date |
| analog ground of ADC | 01/01/70 00:00 | |
| Re: analog ground of ADC | 01/01/70 00:00 | |
| Its all black magic! | 01/01/70 00:00 | |
| Adding to the confusion | 01/01/70 00:00 | |
| Think about it.... | 01/01/70 00:00 | |
| Article isn't very helpful... | 01/01/70 00:00 | |
| In a nutshell | 01/01/70 00:00 | |
| what about the old "standard" | 01/01/70 00:00 | |
| Re: what about the old "standard" | 01/01/70 00:00 | |
| often the only viable method | 01/01/70 00:00 | |
| Looks great, but... | 01/01/70 00:00 | |
| in a perfect world | 01/01/70 00:00 | |
| what about ... | 01/01/70 00:00 | |
| Re what about... | 01/01/70 00:00 | |
what about ? | 01/01/70 00:00 | |
| Again, it's not helpful | 01/01/70 00:00 |