A-M Systems 1800 Manual - Page 10

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Operational Modes

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

Probe amplifier are switched so that they are

across a 1 kΩ resistor that is in series with

the indifferent electrode lead. At the same time,

the stimulus source at the

connected to the electrode leads. A stimulus

current from an isolated source passes through the

lead to the active electrode, returning

PROBE+

through the

PROBE-

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

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.

A-M Systems

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

connector is

STIMULUS

lead and the 1 kΩ resistor. The current creates a voltage

Head stage circuitry in Record Mode

Head stage circuitry in Stimulus Mode

PROBE-

Head stage circuitry in Impedance Mode