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A-M Systems
6
131 Business Park Loop, P.O. Box 850 Carlsborg, Wa 98324
Telophone: 800-426-1306 * 360-683-8300 * FAX: 360-683-3525
E-mail: [email protected] * Website: http://www.a-msystems.com
Operational Modes
Record Mode
Head stage circuitry in Record Mode
In Record Mode, the inputs of the Probe amplifier
are switched by a relay, connecting them
differentially across the two electrodes in order to
amplify with a x10 gain the neural activity
appearing at the electrode-tissue interface. In this
mode the Stimulus relay is off so that the Stimulus
leads do not feed noise
into the circuit. The differential output signal passes through the differential amplifier, the
Low Frequency Cut-Off Filter, and the Notch Filter if activated, in that order. Finally the
signal passes through the High Frequency Cut-Off Filter, whose gain selection circuit is
enabled by the gain switch.
Stimulus Mode
In Stimulus Mode, the differential inputs of the
Head stage circuitry in Stimulus Mode
Probe amplifier are switched so that they are
across a 1 k
Ω resistor that is in series with
PROBE-
,
the indifferent electrode lead. At the same time,
the stimulus source at the
STIMULUS
connector is
connected 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 1 k
Ω resistor. The current creates a voltage
across the resistor which is amplified by the Probe amplifier and passes through the
differential amplifier.
Impedance Mode
In Impedance Mode, the differential inputs of
Head stage circuitry in Impedance Mode
the Probe amplifier are switched across the
two electrode leads. At the same time an internal
current source is connected to the electrode leads.
The current source generates a 0.1 mA, 1 kHz sine
wave that passes through the electrodes, and the
voltage that develops is a measure of the electrode
impedance.