Details of operation
37
The table shows the calculated degradation of CMRR with
impedance mismatch. Note how an initial small mismatch
causes the steepest fall-off in performance.
Impedance mismatch (kOhm) CMRR @ 50Hz (dB)
0 >120
0.5 90
1 84
2 78
5 70
10 64
20 58
The diagram below shows the situation when two channels are
used, with a shared reference electrode. The shared electrode
now ‘sees’ a load equal to twice the load seen by each of the
unshared electrodes. Its time-constant may be expected to be
approximately double that of the other two. This is a
configuration to avoid, by one of the methods that follow.
Channels with shared reference electrode
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