From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-10 17:14:25
Dear Andreas:
Looks great!
Additions: I would like to see an option to be able to adjust the gain. Probably R22, rather than going to ground, have it go to pin that could be grounded ( normal ) or run to an external resistor or pot with R22 shorted out.
Additions: I would like to see the output of U3B pin 7 available externally to be used for biofeedback. Make C6 much smaller to give a 10 KHz bandwidth.
Additions: It is good practice to put a 100 nf cap right at the op amp power pins to ground. ( You already know this) Also you should put a 10 mf orso tantalum near the 100 nf. And then a 100 mf electrolytic should be on the power bus. Each of these capacitors covers a different part of the frequency spectrum. This is the ideal, and many people do none of these and sometimes get away with it.
Cautions: Not all capacitors are created equal. I must caution you again not to use electrolytic capacitors, especially in the signal path or as an integrator. Try to stay with monolithic ceramics or tantalums. Please look at the LT1167 application note Fig. 10 page 17. Notice that they use 0.3mf for the integrator capacitor. That could be a monolithic. If you cannot do it with a monolithic, the next best is a pair of back to back tantalums. For your design, a 1 meg resistor and a .47 mf monolithic ceramic willgive you the same time constant.
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: sleeper75se
To: buildcheapeeg_at_yahoogroups.com
Sent: Thursday, January 10, 2002 3:16 AM
Subject: [buildcheapeeg] Re: New input stage
Hi Jim, Joerg and all.
I've updated the input stage schematic a bit, so now it is more
flexible. New version is in the files-section.
Changes:
The shield driver is now optional - in a TL061 package on its own.
The biasing circuit is gone - I'm saving it for the ADC/digital board.
In-amp gain is now 112.3, which together with G = 23 forms a total
gain of 2583. That's as close to the optimal 2560 I can get with
standard values and minimal number of resistors. Should improve noise
figures too.
The AC coupling is still there, but you can now disable it by setting
jumpers or throwing a switch.
With both poles enabled, DC and delta amplitudes ranging from +/-30mV
(at 0.1Hz) and up (at lower frequencies) can be handled without
amplifier saturation. The price you pay is lower delta-range (< 1Hz)
amplification.
Power RC filter now sports 220 ohm resistors.
Input capacitors are now 10/100pF, but I'm still using 4.7K carbon
resistors, as recommended by Linear, when there are no FET-diodes.
The filter now has fc = 110Hz => possible to use lower sample rates.
In return the attenuation at higher frequencies (40-60Hz) is greater,
but max 10% (1dB) @ 60Hz.
/Andreas
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST