Hey guys,
I posted this question in another thread a while ago, but I guess since this particular thread was already marked as answered, nobody cared about it. So I'll try it with a new post.
Given the amount of (unanswered) posts about the ADS1299 bias drive and lead-off detection, I'm glad that I'm not the only one who has troubles with getting it to work properly.
My first question is, how can I use the AC 7.8Hz lead-off detection (only during startup, not during actual signal acquisition), if I want to use a common reference electrode connected to SRB1 and routed to all negative inputs? According to the datasheet on p. 50 the BIAS_OUT pin must be connected with the positive and negative inputs. To verify the measurement I directly shorted the IN1P to BIAS_OUT and SRB1. IN1P and SRB1 have a 5.1k series resistor, so the measured impedance should be around 10k, right? I don't quite understand the role of the BIAS_OUT pin here.
Also, If I activate LOFF_SENSP and LOFF_SENSN for channel and connect IN1P to SRB1, I should have a closed current path from the current source via IN1P through SRB1 to the current sink. But this doesn't work. Also, connecting BIAS_OUT (with BIAS buffer enabled) doesn't improve the results. I really need help with the correct register settings and wiring for this scenario.
And the second part is, can I use the DC lead-off during normal signal acquisiton while using the patient bias drive? As far as I've seen the Bias drive current saturates the comparators, leading immediately to a wrong electrode-off detection.
I would appreciate your help.
Regards,
Andreas