A-M Systems 3000 Manual de instrucciones - Página 13
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Record Mode
In Record Mode, the inputs of the differential
amplifier U11 are switched by relay K2 (in
the off position), connecting them
differentially across the two electrodes in
order to amplify with a x50 gain the neural
activity appearing at the electrode-tissue
interface. In this mode relay K1 is off so that
the Stimulus leads do not feed noise into the circuit. A capacity compensation
circuit provides positive feedback through U7 to minimize the effect of electrode
and cable capacitance on recording and impedance measuring modes. The
differential output signal of U11 passes through the High Pass Filter U1, the
Notch Filter U5 if activated, and the Low Pass filter U3, in that order. Finally the
signal passes through the High Gain amplifier (U2), offering x1, x2, x10, x20,
x100, or x200 additional gain.
Stimulus Mode
In Stimulus Mode, the differential
inputs of the Probe amplifier U11 are
switched by K2 (in the on position) so
that they are across a 100Ω resistor
that is in series with
indifferent electrode lead. At the same
time, relay K1 to connect the stimulus
source at the
STIMULUS INPUT
from an isolated source passes through the
returning through the
voltage across the 100Ω resistor which is amplified by the differential amplifier U11
and passes through the rest of the recording circuit with including the adjustable gain
amplifier U2.
Impedance Mode
When in record Mode and the Impedance switch is
set to ON, the differential amplifier U11 is switched
across the two electrode leads by K2 (in the off
position). At the same time, relay K1 is on such
that the internal current source is connected to the
electrode leads. The current source generates a
2nA, 100 Hz square wave that passes through the electrodes, and the voltage that
develops is a measure of the electrode impedance. The output of is fed through the
recording circuitry including the adjustable gain stage U2.
The current source consists of several parts. A square wave is applied to an active
current source, which converts the square wave voltage to a square wave current of
2nA p-p at 100 Hz. The calibrated current source is connected to the electrode leads.
A-M Systems
, the
PROBE-
connector to the electrode leads. A stimulus current
lead and the 100Ω resistor. The current creates a
PROBE-
131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324
Telephone: 800-426-1306 * 360-683-8300 * FAX: 360-683-3525
E-mail: [email protected] * Website:
Probe +
Probe -
Probe +
Probe -
lead to the active electrode,
PROBE+
Probe +
Probe -
http://www.a-msystems.com
Output
Stim +
Output
Stim -
2 nA square wave
Output
10