Part Number: ADS1299
Hello,We have a schematic version that actually works pretty good. Nevertheless, we have some questions to continue with our investigation.1) Input filter. In the datasheet (page 68) says that the filter capacitor in the input stage (Cfilt) should be connected as differential to obtain better common mode rejection. But we have noticed that in the EEG Front-End Performance Demonstration Kit schematic does not have the capacitor in differential mode. It is connected to ground. Why do you have made this choice?2) Bias filter. The bias filter has aproximately 50hz of frequency cut off in the EEG Front-End Performance Demonstration Kit and 150Hz is recommended in the ADS1299 datasheet. Why the change?3) Bias. As example, suppose that we have 1 electrode to take measures and 1 referential electrode. And we are using one more electrode connected to GND. We have a measurement that is fine. But we are not using the Bias electrode. How should be the measurement done correctly? We tryied using the Bias Electrode instead of the GND electrode, but we cant get the signal.We have set CONFIG3 = ECh and BiasSens = 01h. Is there something more that we have to set?4) Active electrodes. We know that in datasheet (page 68) says that the ADS1299 it does not need active electrodes. The questions are, is not recommended? Is not needed to measure some basic signals? Or you dont know or its a matter of further investigation if using an active electrode (buffer or preamplifier) could obtain a better signal.Well, thank you for reading.Regards.Santillan Brian.-
Alex SmithApplications Engineer | Precision Delta-Sigma Converters
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In reply to Alexander Smith:
Hello Mr. Smith, thanks for helping us.1) Differential cap then, perfect!2) Got it, thank you.3) Single ended. But ECh is 1110 1100b. Looking the CONFIG3 register, Bias Buffer power should be 1 (on), using this configuration right? Or I did not understand something? Or do I need to activate this BIAS_LOFF_SENS in CONFIG3 register too?I am writing 01h to the positive node of channel 1 using the register BIAS_SENSP.4) Great.
Your answers were very helpful!Thank you so much!Santillan Brian.-
In reply to Brian Santillan:
Hi!2) Yes, I thought about that and I have already change the cutoff filter to 150Hz aprox., I think it is enough.3) Oh, thats the point. Ok, I will do some other tests.Thank you so much Alexander!Regards,Santillan Brian.-
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