A-M Systems
131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324
10
Telephone: 800-426-1306 * 360-683-8300 * FAX: 360-683-3525
E-mail: [email protected] * Website:
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 100
Ω
resistor
that is in series with
PROBE-
, the
indifferent electrode lead. At the same
time, relay K1 to connect the stimulus
source at the
STIMULUS INPUT
connector to the electrode leads. A stimulus current
from an isolated source passes through the
PROBE+
lead to the active electrode,
returning through the
PROBE-
lead and the 100
Ω
resistor. The current creates a
voltage across the 100
Ω
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.
Probe +
Probe -
Output
Probe +
Probe -
Output
Stim +
Stim -
Output
2
nA square wave
Probe +
Probe -
Содержание 3000
Страница 1: ......
