Details of operation
35
The 1902 electrode inputs are inherently differential; they will
reject a signal that is common to both electrodes. This section
describes two or more independent differential inputs. Later
sections will discuss multiple electrode input where there is a
common, shared reference.
Consider the simplest recording using multiple-input: two
independent bipolar channels. Each channel will detect and
amplify the local voltage difference between its +ve and –ve
electrodes. Because
each channel is
independent, any
voltage difference
between the two
electrode pairs will
not be amplified.
Additionally, a sig-
nificant voltage
gradient between
widely-spaced elect-
rode pairs will entail
only insignificant
voltage differences
between the closely-
spaced electrodes of
a single channel.
Because the isolated sides of separate 1902s are isolated from
each other, the Common inputs of all 1902 channels need to be
tied together. The Common input pin is connected to the zero-
volts point of the floating circuitry and serves as a return path
for the very small bias currents of the electrode inputs.
If you are using either the CED1902-10 Active Head Stage or
one of the CED1902-11 Electrode Boxes, note that the
Common inputs of all 1902s are connected together inside the
box and brought to a single input socket.
independent
Dual-channel bipolar configuration
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